Modern (after market) ECU in 70's EFI cars

[78Elegante]

I want to start this topic as a followup on some discussion from http://forums.cadillaclasalleclub.org/index.php?topic=159785.0

I wrote:
"Another thing is the ECU. What I wonder is if it isn't a better idea to use a modern replacement ECU like a MegaSquirt or equivalent.
To keep two ECU's sounds a bit silly to me and what when there is nobody around anymore to repair them?
I saw that TJ Hopland has an aftermarket ECU in his Eldorado."

And I was triggered by Bruce Roe's answer:
"The problem with a later EFI is the Seville is the last and best of the analog technology systems, everything starting in 1980 uses the then introduced digital microprocessor technology.  So just about nothing can be carried over, you would really be adding a new system from scratch.  I actually managed to do it, my car with all new wiring and many other parts added, can run an OEM or newer ECU.  Even the peak and hold injectors are not compatible with newer saturated injector drivers, even though some claim they are."

And use this topic to collect information needed to do a conversion to a modern ECU without destroying the cars originality.

Based on my information until now, the 70's EFI system was built around the following components.

The ECU:
In http://forums.cadillaclasalleclub.org/index.php?topic=149351.0 Bruce Roe gives a list of P/N for the different ECU's used over the years in the different models.

The ECU can be seen as 'the EFI computer'. Based on different inputs, it controls the injectors and the ignition (?).

In the Seville the ECU is located under the dash, under the radio. Most likely also in other models the ECU can be found there.
Please find a picture of an ECU attached for your reference.

Manifold Pressure Sensor:
The first input, or sensor, for the ECU is the Manifold Pressure (or MAP) sensor.
This is measured by the ECU itself through a vacuum line (a tube) connecting the manifold with the back of the ECU.
The sensor is part of the ECU and cannot be replaced easily. In principal this means that a broken MAP sensor means a broken ECU.
In a replacement ECU it should be possible to use a separate, after market MAP sensor, that can be replaced when broken.

Speed Sensor
The second input is the RPM. The ECU gets this information from the speed sensor in the distributor.
The question is if this information is used by an after market ECU as an after market ECU will get timing information from a different source and it can calculate the RPM from that.

Temperature Sensors
The third and fourth inputs are temperatures. The coolant temperature and the intake air temperature.
These are the infamous sensors that are unavailable as OEM. The original part numbers are 1605641, 1606011 and 1609968.
I know Scott sells a modern replacement for this sensor, but in my opinion we shouldn't have to rely on one source.
An after market ECU handle a lot of temperature sensors.

Throttle Position Switch
The last input is the Throttle Position Switch (TPS). It tells the ECU how far the throttle is open.
The part number is 1606785.
From what I understand it is difficult to adjust and lock this switch in the correct position. With an after market ECU, the ECU can be callibrated on any every position.

In addition to above mentioned sensors, an after market ECU needs al least two other sensors:
- It needs to know the position of the crankshaft; when is cylinder 1 at TDC? (from this info, it can also calculate the RPM).
- An O2 needs to be added so the ECU has information about the amount unburned fuel in the exhaust gases. With this information the ECU can increase or decrease the amount of fuel injected in the engine to keep an optimal fuel to air ratio.

So, there are three reasons to investigate and document this:
- Our cars have an old ECU that is preset to fixed values. This means that we depend on sensors that produce correct values otherwise the car will not run correctly, where an after market ECU can be calibrated to use a number of different sensors and interpret their values correctly. So, adapt the ECU to the sensor and not the sensor to the ECU.
- Less than a handful of people have the ability and tools to repair ECU's or know to source the sensors we need. I hope these people will be with us for a very long period, but the simple fact of life tells us there will be a moment that we can no longer rely on their knowledge......
- As number one. Because our old ECU's are preset to fixed values, we cannot adjust them after we made changes to the car (different air filter, different exhaust, different fuel, etc.) like we can with carburetors. So in order to keep our engines running optimal, we should be able to program the ECU.

I hope to collect info here about possible replacement parts, experiences etc. and hear your opinions.

[TJ Hopland]

I remember reading about a guy that did a Megasquirt swap with his but was able to go back to stock.   I think he may have even used an original ECU to get the connectors for his new one.    I really don't remember details but seems like he did have to replace / duplicate some of the sensors because even something as configurable as Megasquirt has issues with some of the sensors because they were so different than what was used with digital stuff.   I have had my current EFI system for 4 years now.  I had the Megasquirt for at least 4 years too.  I also had an analog Holley system for a bit and then spent a few years researching before I did anything so it could have easily been 10 years ago I read about that one guy's system and I don't think it was exactly new at the time. 

Thinking about it now I would guess the sensors would be the biggest issue.   I'm not saying it can't be done.  Im sure if current Megasquirt could not do it that you could take something like an Adruino or Raspberry Pi and put it in the middle to convert the funky analog sensor signals to something the digital system could understand.  It would take a Cadillac analog EFI enthusiast that already had a background in that sort of programming and that had a lot of free time.   May get 2 out of those 3 but I bet there are not many out there that check all 3 boxes.

Its a neat idea but in the end I would think all you would really gain is being able to day you did it. 

[78Elegante]

In fact that was my first thought as well. Try to get a broken ECU for the housing and if possible the three connectors as well.

'The sensors' 
The temp sensors should be OK. They are just NTC resistors. The MegaSquirt (and all other after market ECU's) can 'learn' the resistance vs temp line of the particular temp sensor that you use. So the original temp sensors should be OK.

The MAP is part of our original ECU, so a new one will be needed to connect to the new ECU. No problem, many are available.

An O2 sensor is also no problem. Can just be added to the exhaust.

I expect problems with the TPS. Ours is a funny switched thing where modern ones are just variable resistors. To find a modern replacement that fits on our original throttle body may be a difficult task.

And the last input you need is a kind of timing. This can be done by picking op a signal from the distributor. Or adding a pick up wheel to the crankshaft pulley. I would have to investigate if the 'speed sensor' can be used for this purpose.

I gave three reasons why I think this has to be investigated (and tried). I think there is more than just being able to say that you did it.

[Phil Weber]

 Antoon

Haltech would be able to help you .https://www.haltech.com/. The Haltech 950 looks good.
They also have an agent in Sweden.

The TPS on the Cadillac is a bosch unit , # 0280120047 , made in Germany . By part number it is unique to Cadillac but that could be because of the mounting or something . A trip to your local bosch dealer with the sample might solve that hassle.
A Haltech will come with a wiring harness so all you have to do is change the terminals on your sensor wires .
I don't know about the Seville but on the 500 eng the EFI harness is a separate harness and can easily be removed.
I live not far from Haltech head office so if they ever ask to see a sample of anything I'd be happy to call in . I have spare ecu, injectors ,tps etc

Phil

[78Elegante]

Phil,
Thank you for thinking with me!

Over here in the Netherlands we have our own manufacturer of ECU's:
https://translate.googleusercontent.com/translate_c?depth=1&pto=aue&rurl=translate.google.com&sl=nl&sp=nmt4&tl=en&u=https://www.efignition.nl
I understand  they all are based on the MegaSquirt design and they all use TunerStudio (http://tunerstudio.com/) to program the ECU.

My neighbor is also a petrol head and he has done several of his cars with this Dutch ECU.

My main concern against this ECU (and that from Haltech) is that it comes pre-packed in a plastic housing. What I like about the MegaSquirt is that it comes as a PCB which I hope to build in an original ECU case so it will keep the looks of the car original. My first idea is to leave the wiring as much original as possible.
Maybe, later in the project, this turns out to be a silly idea. But my initial goal is to change as less as possible.

[TJ Hopland]

Let me make sure I understand the goal.   You would like a similar or even identical looking ECU that would just interchange with the original stock one?   But the new one would interface with tuning software on a remote device like a phone or laptop?   At any time you could plug the stock one back in?  Or are you willing to change some components?   If you did change would you want to use the original harness and connectors?  Temp sensors may not be too bad because they had a pigtail so you just need a donor sensor to make an adapter.   What sort of connectors did these use?  Its been too long since I worked on one.   It was something between the packards and weather packs?     


Maybe Bruce Roe can jump in here and refresh my memory on what was unique about the temp sensors.   Seems like there was a thread talking about why you could not replace them with more modern ones.  I remember thinking about that problem and it was a real problem but then we were trying to make it work the other way so maybe this would not be that big of a deal.

I do remember reading about some people that had just gone straight Megasquirt with the Cad systems and I think they found a TPS that almost directly fit as well as doing a few mods to make a more modern IAC fit the Cad throttle body.  I do remember Jeep but don't remember if that was what the parts fit or perhaps maybe the guy just put the engine in a Jeep.  If you had a modern sensor I don't think it would be a big deal to have a modern sensor connected to something like an Arduino you could write a simple program to turn that linear signal into what the original was looking for. 

If you had a working original IAC that would not be a problem for a new system to operate you just need the ability to program an output based on temp which MS has.

MAP sensor was on the MS2 boards, not sure if they changed that for the 3 if they did go to a remote sensor I would think you could still mount it within the case so that really should not be a problem.

I never did sequential injection with MS but I'm pretty sure it required a combination of a crank trigger and some sort of cam sensor.  I'm pretty sure with the current generation of aftermarket systems that some of them do offer a special distributor that offers the type of signals and resolution to emulate a crank trigger. They may offer that in an Oldsmobile and a machinist can modify a Chev one to fit a Cad.   If you just want to batch fire you should be able to do that off the regular tach signal.   

The other little nugget I remember is that the Cadillac used low impedance injectors and almost all other multiport injectors are high impedance.  Megasquirt supported low because that is what most of the OE throttle body injectors were.   I would have to go back and read the manual but I think you actually had to change components on the circuit board to go between the two types.   Or did I get that backwards?  Did Cad use High and others low?

[78Elegante]

Once the new ECU is in, the original will stay out. So it is no problem changing (or adding) necessary components. It does not have to interchange with the original. When it 'looks' like the original through the untrained eye, I'm happy.

What I think is unique about the original temp sensor is that it is a PTC (resistance increases with increasing temp).
According my "EFI Diagnosis Guide", the original sensor is about 700 Ohm at 0F and 1600 Ohm at 240F
Where a modern replacement is a NTC (resistance decreases with increasing temp). They are about 6k Ohm at 0F and <100 Ohm at 240F.

About the TPS I will make some phone calls next week. A modern TPS has 3 wires (and not 5 like our TPS).
If you recall the p/n of that (almost) direct fit replacement TPS that would be great!

IAC = Intake Air ?? If you mean the intake air temp sensor, I'm pretty sure a MS will work with the original and also with a modern replacement.

MAP I don't see a problem. They sell the MS2 and the MS3 with MAP onboard, but also with external. Whichever you prefer, both will work as they will both tell the CPU about the measured vacuum.

A crank sensor (or other timing sensor) is always needed, So I will have to find a solution there.

In principal I will stay with batch fire (and not sequential). My injectors measured <3 Ohm. That is considered low-Z (around 16 Ohm would be high-Z).
The MS supports software based Peak and Hold (PWM). An other option would be to add series resistors, but that would influence the behavior of the injectors. Another option would be to add P&H driver boards.
So, our low-Z injectors should not be a problem

[TJ Hopland]

Not needing to be able to interchange with the original makes it a lot easier.

IAC is idle air control.  Cadillac called it something different and the term is slipping my mind at the moment.  I think the mod was to take apart an original to get the mounting then sticking the new one on the old mount.

Batch fire is what I did with by 2bbl TBI setup and I did that with a regular HEI.   To get a clean tach signal I did have to parallel another ignition module to create the signal for the computer.  Taking it direct always had random blips that really confused the system.   I tried some filters but they didn't solve the issue and I had an extra module laying around.  I just ran a couple wires in and paralleled off the pickup coil terminals.  Worked great, no glitches after that.  I do remember having to add a loading resistor on the module output.     

I will do some digging to see if I can find any of that old info.  I know the computer I was using back then had the SSD fail but I still have the one that came after so maybe I saved some screen shots or bookmarks on that one that will yield some clues. 

[TJ Hopland]

I found some of my own posts from 2007 where I was talking about that system I saw so we are looking for some pretty old information.     

[78Elegante]

We are also talking about some pretty old cars here, so pretty old information can still be very helpful 

Ah, now I understand IAC. I think back then it was called 'Fast Idle Valve'. Personally I doubt if you need to use that. I think you can use that, but it is not necessary to make the car run good.

I understand what you say about the two systems next to each other. Maybe especially in the 'development phase'.
But you will need to change the TPS.
In that case I should try to get a EFI wiring harness from a donor car so I can read all original sensors and control the injectors independent from the original ECU. I don't think such harness will be easy to find over here.
I tried to find a source for the injector connectors, but nu luck yet. The same for the funny round connectors for the temp sensors.

[Phil Weber]

I've tried to find the original style injector connectors with no luck . The only ones I've found are the Standard Products # SK21 or # Hk9314 . You can get these from Rock Auto or in your part of the world at https://finjector.com . I would love to find some originals. Find an old Bosch D-Jetronic dealer and you might have some luck.

The round sensor plugs are available ok . Google these numbers and you'll probably find someone local.
Female plug is # 1208551000 and the male plug is # 1208552000 .
One of the guys on the forum here sells these with wires attached .
I think the metal connector numbers are # 3308672000 for the pin and 0318703000 for the socket but double check that.

Phil

[bcroe]

Several decades ago I did hands on with half a dozen different brands
of engine management systems.  More recently I have not pushed the
idea of custom modifications to the 70s Cad EFI systems, because then
the owner has a vehicle for which OEM parts are not compatible and
only the designer is able to fix.  That is OK for a few DIYers who want
to experiment, but the average owner just wants the car to run right.  All
the Cad mods I have proposed still allow OEM parts to be plugged in. 

Changing to a different ECM does not relieve the need for a spare,
which could be more difficult to locate.  A replacement would need to
be loaded with the proper software, quite a difficult problem on the road. 

Another note, I typically set up an EFI system on the bench, where it
is easily exercised to any limit of operation, and the actual performance
can be carefully monitored on lab type equipment.  My research found
that many add on EFI systems have quite a few shortcomings and bugs
compared to the claimed performance.  These would simply remain
confusing mysteries in a vehicle.  Have not checked the latest generation. 

After getting familiar with my 79 Eldo EFI, I had the idea of keeping all
the original fuel system, but changing to sequential port injection using a
well known aftermarket ECM.  The idea here was to be able to plug it in,
or go back to the original 79 ECU.  It actually did work, here are some of
the compatibility challenges.  Some pictures are on my PHOTOBUCKET. 

The new ECM would not plug into the original Eldo harness, so an
ADAPTER BOX was built to go between. 

The fuel injectors were wired to a common ground, but all newer
systems use a common 12V ign rail.  A NEW HARNESS was made
plugging into each injector and bringing the 16 wires into the car. 
This could be plugged into a new connector on the original harness
to restore the original HIGH SIDE injector drive, or into the adapter
box to supply the 12V common and the 8 injector LOW SIDE drives
from the ECM. 

The mfr claimed his ECM was capable of driving either saturated
(high impedance) or peak-and-hold (low impedance) injectors.  The
bench test revealed that the drive was entirely UNSATISFACTORY
for the Cad peak-and-hold injectors of my Cad.  An 8 channel adapter
box is available to solve this problem, or they could be built into my own
adapter box.  This overhead ultimately hindered the project completion. 
Changing injectors would mean ANOTHER part of the original system
could not be used.  And, would not allow my original ECU to work. 
Please do not tell me to use such kluges like resistors that draw 4
times as much current (risking overheating) and work improperly. 

If injectors do get changed, some work will probably be needed on
the fuel rails and intake manifold.  The likely change to high impedance
injectors will require a new fuel pump and fuel pressure regulator. 
Going backward to throttle body injection will simplify this, with a
carb type intake manifold. 

The ECM had a different fuel pump control, which was translated
in the adapter box.  One of the speed sensors was rewired as the
cam sensor required for a sequential system, with the proper time
offset programmed to phase it in. 

The Throttle Position Switch on the throttle body cannot tell the
throttle position, it only can initiate extra enrichment pulses as
the throttle is opened.  So I left it and mounted a later TPS on
the other side, which was wired to the new harness and through
the adapter box to the new ECM.  Similarly the 79 PTC linear
temp sensors were not compatible with the needed NTC log
temp sensors the ECM was set up for.  I mounted 2 more temp
sensors and connected them to the new harness. 

Newer ECMs expect to use a stepping motor air valve to control
idle speed.  But there is no place for it on the original throttle body,
so either the throttle body must be swapped, or the original open
loop cold idle air valve retained, which I did. 

One advantage of the ECM is that many functions can be programed
with the right equipment, and a second passenger.  I have already
demonstrated that mixture adjustments can be made on the original
ECU by adding a simple knob (circuit on PHOTOBUCKET), results
observed on the Wide Band OX sensor that is a mandatory device
on any experimental EFI system. 

The original ECUs ran completely open loop (like a carb), not
depending on sensors to make fuel corrections.  The sensors
were only active before warmup, still open loop.  A very few ECUs
in the last applications (79-80 California cars) did have an OX
sensor, but that circuitry almost always has failed by now. 

Some effort can program an ECM to control spark advance, but first
the original HEI must be replaced with an 81 Cad or Olds type. 
That would remove my speed sensors used with both the original
EFI and my sequential injection, so it was not done.  The crank
timing was taken from the original HEI, again fed from the new
harness to the ECM.  An aftermarket HEI could supply the 2 ECM
signals. 

So by the time this conversion worked, practically all the original
79 EFI components were swapped out.  There are probably a
few more items forgotten since then.  No problem if you want
to try your own EFI system, but forget about any originality in
the car, or anyone else fixing it on the road.  Bruce Roe

[TJ Hopland]

I wonder if Bruce was one of the systems I read about?   Some of what he wrote seems familiar but that could just be from when the subject comes up here.  Quite the list.

Being reminded of his tuning mods to the original I wonder if just for the fun of it you could add a digital component to emulate and vary the analog components and actually build it into a self tuning open loop system?  How many people can say they can tune their 70's efi from their phones? 

Its finally nice weather again so I am about to go out and enjoy the EFI system on my 73.   Fires up like any modern car no matter how long its been sitting.  You barely hear it crank which can lead to issues because you don't realize your battery has lost most of its capacity till you leave the glove box open for a couple hours.     

[78Elegante]

Phil, Bruce and TJ, Thanks again for the added information.

Basically I have the following roadmap in my head:
- Getting a license for my Seville in it's original state (but the Dutch DMV doesn't work because of the Corona situation, so who knows when this will be).
- Have a simple LPG-system installed. This will give me LPG registered as primary fuel on my license. The good thing about that is that after that I can do whatever I want with the car, it will not have to be inspected anymore by the Dutch DMV. Only a yearly emission-test, running LPG. Emissions on gas are no longer important as LPG is the primary fuel which counts for the emissions test (so maybe the cat can be removed without failing the emissions test).
- Play around and test with the aftermarket ECU. The car will always be able to run on the independent LPG system, so when I screw up on the gas ECU, I will not be stuck on the side of the road.
- When the aftermarket ECU is running good, I will convert the LPG system to LPG injection.
- If all above works, be proud 

I have a feeling that my definition of originality gives me more play room than yours
As long as all new parts are invisible at first sight (a lot of them will be hidden under the air filter housing), in my opinion, the car maintains it's originality.

This car will be a driver, not a show car where judges are searching for Cadillac logo's on every bolt and nut.
Next to that I plan to keep this car as long as possible. The '78 or '79 Seville Elegante is my dream car (next to my '73 Corvette), it is an old-timer, so no road tax anymore which means that I don't have a problem spending a little bit money to make and keep it running good.
Antoon

[TJ Hopland]

Do you have to get it to pass a regular inspection before you can get the license switched basic LPG?   

Does your area have regular safety inspections or does that only happen when the car is first brought into the country?

[78Elegante]

In principal not but now the car doesn't have a license now which means that I would have to transport it on a trailer to a LPG shop and back.
Without a license you are only allowed to drive directly to the closest Dutch DMV inspection station (and they are closed for an unknown period).

Yes, we also have a yearly safety inspection (for this car every two years because it's over 40 years old) and during that inspection they will test the emissions (running the primary fuel).

[79 Eldorado]

Antoon,
I think there’s more to what is being referred to as originality. Your concern for the general population is that there are a handful of people who know these systems well enough to keep them going. The big issue for me is we’ve seen during the financial crisis of 2008 that just about any company can go under. So if the system you are proposing is modified to the point that it is a mix of old and new, which essentially will not interchange, now there are even fewer people who will be able to fix them. It would be one thing to make it so you could swap the ECU and possibly add maybe add something like a different TPS but when you start mixing everything you end up with a mess.

I have a car with Global West suspension but even when they use off-the-shelf parts they don’t make it obvious as to what they are. It’s a Chevelle but I’ll mention it here because it has Cadillac “D” Car front spindles. That meant that the outer tie rods needed to be different (not D Car and not Chevelle but a hybrid). So if/when those fail I don’t know what I need to replace them. Yes I can likely figure it out but what happens when the next person gets the car? My point is I think the goal needs to be to keep the replacements as plug-and-play compatible as possible. Either plug and play or change the entire system over to a modern EFI kit which the “big guys” are making as universal kits. I agree with what I think Bruce alluded to though in those systems go to a single point TBI system so it’s a little like going backwards. These systems at least had 8 injectors. And now we're in the Covid-19 crisis so will companies like FITech exist long term? I hope so but there is always a risk a company will decide to eliminate support for older systems.

Regarding the physical plugs for the ECU I wouldn’t let that be the reason why something couldn’t interchange. The case you make for needing to tune for special circumstance is a good one but if long after we’re gone and someone gets these cars and they have a “mystery” mix of OEM and unidentifiable aftermarket parts which are not compatible then it seems you’ve just caused a bigger issue with the very thing which you were hoping to avoid in the first place…. An issue or what if in the future the expertise is reduced.

Going back to the ECU connectors. I already found the ECU plug terminals after you asked me earlier. As for the plastic plugs/connectors I could easily make something which looked like the original and worked for a prototype given the dimensions. If you needed a true production part then it could be a small family mold. I wouldn’t expect that it would even be that costly. Even a 3D printed proto in the proper material should be ok for the connectors.

Scott

[TJ Hopland]

Is a company like FiTech going to be around long term is a very good thing to question.  It was started by people that came from other big names in the industry that thought they had a good idea and a way to pull it off which they did.   It was the $1000 mostly self contained system.  That was a game changer because previous systems tended to be closer to $3k and had a lot more wiring which scares people and some people didn't like the look of.   

They were delivering systems almost a year before anyone else.  Holley either had one in the works or got one developed pretty quick and theirs has a few bugs but they seemed to stand behind them and make em right.  They also have quite the production, distribution, and support network already in place which was a huge problem for FiTech.  I think they were way more successful than they thought initially and had some serious production and support issues.   

Am I going to take the FiTech off my car as long as its working?  No.   If I do another one or someone asks me what I recommend I think it would be the Holley Sniper.  FiTech doesn't list any repair or refresh parts on their site.   Holley I can still get some parts for their original Projection systems which are over 20 years old now and they are not a special order direct from them, they are often in stock at the popular online vendors.   Sure Holley could go bankrupt (again) but their name is big enough and there are enough of their products out in the world that need support someone will buy what is left and continue to make products and parts.     

[79 Eldorado]

TJ,
Good points. To be clear I was not picking on FITech specifically. They just happened to be relatively new (compared to Holley /MSD etc) and as well they are selling a system with an obvious parallel to the topic. I can say though that if buying a new EFI system was in my future I would certain put heavy weight on believing future support will be available.

I believe to keep these cars functional over a long time any new parts need to be as compatible with the old stuff as possible so if someone has an issue it's not like throwing a 1000 pc puzzle in someones lap and telling them to fix it. Bruce always recommends carrying a spare ECU. The issue is if anyone with any car of any make breaks down, especially away from home, we need to reasonable get our car back to home. That might mean taking it to a shop on the road. Taking away any cross reference to the original always complicates things.

I had a starter issue on a car which I replaced a diesel for the Olds 350. I wasn't at home and I needed to take it to a garage which I had never done business with. It sounds unreal to me even now but it was really difficult to figure out what application the starter should come from even with my help. We got the one we thought it was and when it arrived it was different and enough where it wouldn't work. That swap was relatively simple meaning a lot of the parts interchange. I couldn't recall if I stayed with the diesel starter or if I ordered one for the same car but for the gasoline version. I was even the one who did the engine swap and I was the one who ordered and installed the starter... over 15years before the issue though. That garage was also very good at finding the precise problem internal to the starter.

One other comment. I went through a curve, or maybe a roller coaster, on these systems. When I initially learned exactly what I had I was really scared. Thanks to Bruce and others I became more comfortable that there is still support. I still get concerned when I think about the questions Antoon is asking and even prior to him raising the concern. I would say thank God for this site and the helpful people. I would also say we need to organize the forum a little better to make very informative topics which are frequently needed very easy to find. There should be a "sticky" section in the Technical part of the forum. I do try to place helpful links in my threads to hard to find related information. My point is what we document here will be "forever" on the internet so as long as it's documented and we can find it people with talent will eventually figure it out even with cryptic notes.

Scott

[bcroe]

Scott,

As you know the 5.7L diesel used a different (massive) starter and
a different ring gear.  My recollection is the diesel ring gear will not
bolt to a gas engine.  The 79-85 TH325 FWD trans used a slightly
smaller ring gear, 2 more types.  All the small and big block Olds
starters are basically the same except for a couple things.  The big
block heavy starter used a longer magnetics inside, I always use
these on my 403s.  And the aluminum nose mount is different for
TH400 (RWD) trans, TH425 FWD, and TH325 FWD.  I have been
able to swap these nose pieces to fit the situation.  The TH425 has
the same dia ring gear as the TH400, but they made the teeth about
1/16 inch deeper to reduce wear caused by the extra stuff (they said). 

Since my primary 403 source was 77-78 Toronado, I have been able
to get enough of these heavy duty ring gears for every car.  That
includes the 79 Eldo, which now carries a 78 Toro trans (converted
to switch pitch).  For many parts searches I just say 78 Toro, which
eliminates 350 brand C parts and gives me the heaviest version. 
Bruce Roe