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1994 deville 4.9 starts nice. Then wont. Sometimes chugs


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Hello new here.

My GF bought a 1994 deville 4.9 from her brother, who bought it from Mom, who bought it new.  GF doesn't have the best history for doing maintenance and hasn't been using premium fuel.  I was told a week ago the car started to run rough with barely enough power to get off the road and then died.  She tried to restart it but ended up having it towed to a mechanic.  The mechanic had no idea why it stranded her because it started and ran well for him. 

The other day I was doing errands with it and it began running rough after a warm startup and then died.  I tried to restart it, but in would fire a second but not continue to run.  I checked for anything apparent and didn't smell fuel from the exhaust.  After about 15 minutes it started right up and drove well.

Has anyone experienced these symptoms and then figured out what was wrong? I wish I could give you more details but I'm not the owner and I don't know much about this model. Its super clean and worth trouble shooting IMO though.

Thanks!

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Does it show any diagnostic trouble codes in history?   When it is not running you want to check for causes -- either no fuel, no spark, or no air.

Bruce

2016 Cadillac ATS-V gray/black

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Sounds like the sensor on the distributor shaft has a thermal open - that would explain why letting it cool down for 15 minutes allows it to restart.  The codes will confirm this.

With the key on, simultaneously press and hold the OFF and WARMER buttons on the climate control panel.  The codes will be displayed on the information center.  Write them down and post back here.  Note which are current and which are history codes as well.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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I022 = Panel dimming potentiometer switch circuit

A012 - Low side temperature sensor circuit

Neither of those codes point to the problem you're having.  I would have expected a PCM code.  You might try checking the fuel pressure when it acts up.  Other than that, I'm at a loss.  Intermittent problems are the most difficult to troubleshoot.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Ok....1994....2017s are being built now....so 23 year old car.

Could be a bad ECM....you can try dropping it down and tap test it. Any stalling or glitches while running and tapping indicates a failing ECM. 

Pretty much any thing in the distributor...GM HEI units can have green pickup coils....rotted control module wires...cracked cap....burnt rotor...etc.

It could be a bad engine ground. It is mounted to the engine block very near the starter. Can look ok...but does need to be taken apart and cleaned.

 

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The symptoms remind me of a 92 4.9 that we had here a few years ago.  It ended up being the PCM, do a tap test as Logan states above.  Also, check the fuses and relays for green/white corrosion, especially the pcm/ecm, fuel pump and coil/ignition and injectors. Put a fuel pressure gage on the Schrader valve on the fuel rail, a bad pump or relay may show up.  

Do you hear rattling under the car when the engine runs?, bang the cat converter with a rubber mallet and see if you hear noise like marbles.  These cats can fall apart and clog the exhaust.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Since you don't know the history of the vehicle pull the ECM as Logan suggested and tap test it, only with your hand though please

I've had a LOT of ignition modules fail and show symptoms very much like you're experiencing. It especially becomes an issue if someone replaced the ignition module and did not put silicone grease under the module. The silicone grease acts as an insulator to help keep the module cooler. OR, the same thing can happen if they used a cheap after-market unit.

The ECM was my first thought as well, they are easy to pull down and tap test, the ignition module is a bit more challenging... Do the easy stuff first :)

BTW, don't worry about her not using premium fuel - the ECM will adjust.

Edited by OldCadTech

THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!!

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Image result for 1994 cadillac 4.9 ignition module   Ignition Module lower left in picture, just above the '33' of the time stamp

                           graphic 

Remove the glove box to access the PCM/ECM, tap test with the PCM removed from the holder and the engine running. As a personal preference I pull the passenger side hush panel to provide a little more room.

Edited by OldCadTech

THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!!

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Possible fuel pump issue or check the main ground by the starter. Its a heavy gauge cable that tends to loosen up over time. 

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Total guess (and just relaying similar symptoms but with my '00 Intrigue); crankshaft position sensor.  I know it is just a shot in the dark (but that's what happened to me).

Edited by cdgrinci

Chuck

'17 XT5, '04 Bravada........but still lusting for that '69 Z-28

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Thanks guys.   If it was my car, I'd be on it.

Id agree with her to abandon it..  But that would mean she needs a cosigner or down payment for another "problem car".

Edited by rebar
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My bet is the issue is in the distributor somewhere - either rotted/corroded wires like Logan stated, a bad ignition module or a bad pickup coil.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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