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1978 SEVILLE MISFIRES (FLOODS) PLEASE HELP!

Started by corporate53, January 30, 2020, 06:28:45 PM

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corporate53

Hello Cadillac lovers and thank you for the add. I'm the proud second owner of a 1978 Seville with only 38,000 original miles on it in mint condition. Since I purchased the car 10 years ago, I've maintained it well and re-did the exhaust, the A/C and the brake system to name a few. Recently however, the car started shaking, losing power and getting me stuck and my mechanic can't figure it out until recently when the car wasn't driveable anymore. Here is what happens exactly: I start the car in the morning, the RPM is high and it runs fine. As the car warms up (2-4) minutes, too much gasoline floods the engine and one or more cylinders start to cut out. The engine shakes almost violently, strong un-burnt gasoline smell comes out of the exhaust, thick black smoke leaves a mark on the ground under the tailpipe and the car slowly loses most of it's power until it eventually dies and won't come on any more until the next morning. This is a 5.7L fuel injection engine. PLEASE be kind and help, I need to fix this beauty. Thank you! 

bcroe

You might unplug the 2 temp sensors in case they are shorted, or measure
a lot less than the nominal 1000 ohms cold.  However this would be very
unusual.  Check your fuel pressure, which should be 39psi at key on, drop
to around 30 with high manifold vacuum.  A test, just turn on the ignition,
the pumps should run a second before turning off, but pressure should hold
for some seconds.  If not you may have a badly leaking injector. 

Also check for a vacuum leak in the hose from the throttle body to the ECU. 
I would use a hand pump to pull a vacuum from the throttle body end. 

HOWEVER, the very frequent cause, is a fault in the ECU.  If an IC in the
cold enrichment circuit fails, it can flood the engine.  I can replace these
with cheap generic ICs after a run on my ECU test set. 

Bruce Roe  CLC # 14630     bcroe@juno.com   

corporate53

Hi Bruce, I really appreciate the info, I will share that with my mechanic and will update you. He's going to start working on this again on Tuesday. Really appreciate your time.

bcroe

Quote from: corporate53
Hi Bruce, I really appreciate the info, I will share that with my mechanic and will update you. He's going to start working on this again on Tuesday. Really appreciate your time. 

Sounds good.  If he agrees, my advice is do not trade yours in, many
have regretted doing that, just get it fixed for under $100.  Some will
sell you one for a small fortune, but probably they have no way of
even knowing if this early 70s design is any good.  good luck, Bruce

corporate53

Thank you, I really appreciate you and I'll let you know how it goes. Fingers crossed!

corporate53

Hi Bruce,
So, my mechanic just called me today and mentioned that he has tried everything on your list and there's still no luck! He can't find the issue! If I'm sending you the ECU, where should I send it to, how much would this test cost and also, where is it located? I'd have to take it out myself to send it in. Thank you kindly, please let me know.

bcroe

Quote from: corporate53Hi Bruce,
So, my mechanic just called me today and mentioned that he has tried everything on your list and there's still no luck! He can't find the issue! If I'm sending you the ECU, where should I send it to, how much would this test cost and also, where is it located? I'd have to take it out myself to send it in. Thank you kindly, please let me know. 

F.  Robi,
OK, it will be impossible to fix the car, with a bad ECU.  You could send it here
with $30, which will cover return postage in USA, replacement of the bad IC,
and parts to avoid the common failures of the fuel pump circuit.  Email me
your return address and the tracking number, I will advise you of the fix and
the return tracking number. 

You can read about 70s Cad EFI on the first album of my PHOTOBUCKET,
the internal wiring of your 78 ECU is a few albums down.  Satellite view my
place and see over 100 solar panels running it. 

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

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

BRUCE ROE
5719 EAST SKINNER ROAD,
STILLMAN VLY, IL    61084-9215

Phone  815 234-8039           bcroe@juno.com
GPS 42 deg  08.403 min N
         89 deg  13.561 min W

corporate53

That all sound great and I will do that. Spoke with my mechanic and he said he would help me take the old ECU out of the car, I just have to be patient with his very busy schedule. I will send you the unit as soon as he gets to it. Thanks again.

bcroe

Quote from: corporate53 on February 06, 2020, 05:52:56 PM
That all sound great and I will do that. Spoke with my mechanic and he said he would help me take the old ECU out of the car, I just have to be patient with his very busy schedule. I will send you the unit as soon as he gets to it. Thanks again.

Its a 5 minute job after you find 7/16 wrenches and a screw driver. 
Pull the hose off and pinch the 3 connectors.  Bruce

corporate53

Hi Bruce, I've been standing by to hear from my mechanic and he keeps putting this project off (pulling out the ECU) and I'm having a feeling I need to get the unit out myself in order to send it to you. Where is it located on my 78 Seville and is there a video out there on YouTube that I can watch and figure this out myself? Please let me know, I've been ready for the past couple of weeks to send you the unit and I can't. Thank you as always.

79 Eldorado

#10
If it's in the same place as the 1979 Eldorado it will be above the passenger's foot well. You should be able to look up in that area and obviously see a bare metal colored box. Bruce will likely confirm but it's easy to see if it's in the same area. They are not difficult to remove.

You may also want to add one of Bruce's external fuel pump relays while you are doing the job. I posted how I approached the wiring according to Bruce's diagram in a thread with pictures for my 79 Eldorado. Yours may not be exactly the same but it will be close.

http://forums.cadillaclasalleclub.org/index.php?topic=153100.msg414525;topicseen#msg414525

Good luck,
Scott

bcroe

The Seville ECU is located on top of the trans hump, up under the
dash.  It should be obvious how to get it out, think there is a plastic
cover over it held by a screw on each side.  Squeeze the 3 plugs to
wiggle them out (can only be put back one way) and twist the little
hose off.  Easier than my Eldo or any other. 

Your mechanic will be embarrassed when he sees how easy it is. 
Bruce Roe

corporate53

Hi Scott and Bruce, thank you so much for taking the time to write back, I really appreciate it.... So, the problem isn't the ECU!!!! I'm really frustrated with this. Long story short, I took the ECU out with the help of a friend and he knew a really cool old gentleman with the same exact car down in Orange County and he was awesome enough to let us swap ECUs to see if that's the real issue with my car. Drove all the way there, we had a good chat, he let us take the ECU out of his car and drove all the way back to my town and sure enough, the car is doing the same thing with his ECU! I'm returning and re-installing his tonight, but what should I do now?!!

79 Eldorado

Your issue sounds exactly like what happens when a carbureted car has a leaking needle and seat. Bruce really knows these systems very well and it would be worth waiting to have him weigh-in again. I didn't reply originally after reading his reply because I suspected two of the items he had already mentioned: leaking injector(s) or bad sensor(s). I think you had your mechanic check both of those. The sensors are an easy resistance check if you tell us the resistance and temperature we can tell you if they are good. I also suspect that it would be strange if the sensors caused the car to run so rich that it would act as you described. Did your mechanic also check the injectors for leaking?

One other thing which could be happening is that there's an issue with the ECU plugs or wiring to the ECU (still unique to your car even when you change the ECU). I know I've read that if the sensors are good but the symptoms point to the sensors you should check their resistance at the ECU plugs. In other words you can unplug the plugs at the ECU and check the resistance of the wire pairs going to the sensors.

When you removed yours did you also check the vacuum line going to the ECU? If your fast idle is operating when the car is warming up maybe it could mask other issues which could cause a stall once the fast idle valve closes. Maybe other vacuum leaks? There are a fair number of vacuum lines in these cars.

Scott

bcroe

#14
I do not have an answer for this information.  I still suspect the
ECU, they sometimes have multiple issues.  If you have no other
options, you might want to get it tested here anyway. 

So back to basics, do you have an engine?  Air, spark, fuel.  Are
all cylinders good, spark is good and not sloppy (timing chain)? 
The car has an ESS system tied to the ign, could be a problem. 
If it is really flooding, why?  I think the possibilities have been
listed, are you so sure the mechanic who could not be bothered
to pull the ECU, really checked out all that stuff?  You could just
unplug the temp sensors if the engine is warm, they do nothing
after warm up. 

I also have a special, adjustable test ECU which has traveled a
lot to help to help with some situations.  Bruce Roe