HELP Intermittent miss

[collector]

My car runs flawlessly at idle (in gear) and then it had a slight blip, as if the ignition has cut off. The RPM's drop by 20 and in millisecond it recovers. Then, might it run for 5 minutes without a single variance of the RPM's. Then the slight stumble which can go on for a while then stop and it will be fine.  What could it be? The car is an EFI 1979 Eldorado Biarritz with 16K miles. The CTS and ACT shows the resistance of 9.8. I have tested a few and have found some that have 0 resistance (meaning they are dead). I'm at a total loss. The car at times has no odor coming out the exhaust and at other times has a strong odor. I'm going to pull my hair out by the roots If I can't figure out the issue. Anyone had this happen to them on any car? I've checked the Ohms resistance on the wires and they all are at or around 15. The plugs are gaped perfectly and are New NOS originals. There are no vacuum leaks. I replaced the ignition module with a new NOS GM one but still the problem persists. When cold it seems to be fine but the minute it starts to warm just slightly, the stumble at idle starts up but not always. ideas?

[TJ Hopland]

I'm sure Bruce will be along soon with some other ideas.   My only idea is assuming this doesn't have the electronic spark control thing and still has a regular looking vacuum advance is check the pickup coil wires.   Idle usually isn't a problem but who knows at this age.  As the vacuum operates the wires flex and eventually crack so they loose contact in certain positions.

Any idea on the timing chain condition?  Just like Cadillac these had the plastic cam sprockets too.

[collector]

With only 16k miles I'm positive the timing sprocket is perfect. I have NO variations on timing and yes it does have an Electinice box to control spark.

[TJ Hopland]

Age can be harder on plastic than mileage and we are coming up 40 years now.

So does this have a 5 or 7 pin module?   Bruce will have to let you know if there is any special places to look at that timing thing.  I think he has messed with them.   I have only seen one car with it and it wasn't something I was asked to work on so I don't have any first hand experience with it. 

[collector]

Again, timing is not an issue. As for 5 or 7 pin module I have no clue as to what your referring. If your talking about the ignition module, it's a 5 pin style. That is also, NOS GM. I Changed the plug wires and that didn't make any difference, so I put the originals back on. It's possibly the distributor weight springs or the ESS box. I can't get a E Fed box, so I'm going to replace the entire emissions system to a CA known working system. Also, you can buy CA boxes but there aren't any Federal boxes to be had.

[bcroe]

Age can be harder on plastic than mileage and we are coming up 40 years now.

So does this have a 5 or 7 pin module?   Bruce will have to let you know if there is any special places to look at that timing thing. 

Mine is a 79 Eldo too.  Intermittents can be the worst to identify, swapping
parts (you DO have a complete set of spares?) to get rid of it may work.  Do
check the timing chain for slack, and better plan to change it to an all steel
set soon.  Don't tell me what a miserable job that is on a front driver, I've
done 3 79 Es and many others. 

The car has an Electronic Spark Selector, with the HEI cabled to a special
module, an ESS DECODER on the firewall.   These can fail and there is no
replacement that I know of; the special module in the HEI seems to have
a better record.  I have one fix for that failure.  Drop in a 76-77 Seville
HEI, which will run your EFI, but doesn't use the ESS.  Others had done
this; haven't changed mine YET.  If you do, beware that fully HALF of the
rebuilt HEIs I have checked have those SPEED SENSOR magnets below
reversed, which hurts the idle.  You can check a rebuilt against your
original HEI, turn the magnets around before installing if needed. 

I AM NOT saying this IS the problem; do the usual complete ignition
checkout.  If your mixture doesn't seem to be consistent, better check
out the Engine Control Unit.  There is a vacuum hose going down to it,
and it had better have no leak (I always replace the original hose
inside the ECU).  If fuel pressure is good, you could have MAP circuit
issue in the ECU throwing the mixture off.  Swapping ECUs is one check,
a 78-79 Seville ECU also works but has wrong mounting brackets. 

Lately I have been running both a Wide Band OX sensor and an electric
fuel pressure gauge on my 79; I have seen many EFI problems that
these would help pin down.  Your mixture is greatly enriched cold by
the engine temp sensors which should measure around 1000 ohms cold. 
They fail open a lot, leaving you with no enrichment. 

Read some about 70s Cad EFI on my PHOTOBUCKET, first album.  Note
the fuel pump power fix you might need to avoid trouble someday. 

     http://s93.photobucket.com/albums/L71/bcroe/

  click on an Album
  click on a picture to enlarge + description

If you later decide it should be faster, yank my chain. 
good luck, Bruce Roe

[collector]

Ok, just installed an original distributor as the idiot before me changed that to an A-1 Cardone. It didn't work and the weights were 139 instead of 130. The original springs feel a bit loose and I'm going tomorrow to part a running 79 Cal Eldo. I'm going to get all the wiring and the TB and the TVS switch and the EGR switch and the decoder and the distributor. I'm going to change my car over to a CAL emissions car. You can find CAL boxes and the one on the car is working perfectly. I have the smog print out and it was like they didn't even put the sniffer in the tail pipe. So, I know that is an excellent running car. Its my last chance. Now, I can change out the decoder from the other car as they are the exact same part number with the E stamped on the side. That is my last ditch effort before changing over to the CAL emissions. The ECU seems to be good after I replaced the MAP sensor inside. The car runs flawless once warm but after restart. It stumbles at idle, that is until it's totally hot. I've just put in an NOS heater and that makes the world of difference and I have good working ACT and CTS sensors. They both have good ohm's resistance. So, there is nothing more I can do until I change out the decoder. The only way to change an ECU from a Seville is if it is an open loop unit ( doesn't have an 02 sensor). I know these run flawlessly as mine that I wish I hadn't sold did.

[collector]

Also, I know the timing chain is perfect as it NEVER varies from 10 TDC. If it wondered I would consider changing the sprocket but I'm not going through that. I even have two NOS nylon ones in case I needed to change it.

[V63]

I would try adding marvel mystery oil to the fuel,  2oz per 5 gallon. Those early Bosch pumps do NOT like alcohol blended fuel.

[collector]

bcroe, I just did a fuel pressure test and the fuel is pressurized at about 25 pounds and when I disconnect the vacuum fuel pressure regulator, the pressure is at 38 pounds. The last owner put in both pumps. I'm now thinking the fuel pressure is to low and I need to replace which pump? both? Aftermarket parts are always a risk. Which one controls the pressure?

[bcroe]

bcroe, I just did a fuel pressure test and the fuel is pressurized at about 25 pounds and when I disconnect the vacuum fuel pressure regulator, the pressure is at 38 pounds. The last owner put in both pumps. I'm now thinking the fuel pressure is to low and I need to replace which pump? both? Aftermarket parts are always a risk. Which one controls the pressure?

Port injection fires fuel into manifold vacuum, or lack of it.  The fuel pressure
tracks the manifold (absolute pressure) so the injectors have a constant
differential in to out.  Throttle body injection fires fuel into atmosphere
(above the throttle plates) so pressure is pretty constant.  Bruce Roe

[The Tassie Devil(le)]

No wonder I love Carbies.

Bruce.

[35-709]

   Me too!

[walt chomosh #23510]

collector,
  Timing chains and sprockets can be checked by pulling the distributor cap and moving the crankshaft in one direction to tension,then reverse direction and viewing degrees that the crank moves before the rotor moves. (hope that makes sense) I believe that as long as your have less then 7degrees the chain and sprockets are serviceable.(don't quote me on that degree figure, I have performed this check but generally never allow any motor of mine to become questionable)....hope this may helps....walt...tulsa,ok