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1985 Cadillac stalls at idle
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CadillacGirl1985
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Feb 8, 2009, 1:47 PM
Post #1 of 8
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1985 Cadillac stalls at idle
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Hi,
I have a 1985 Cadillac Eldorado (4.1 engine) (only 66,000 original miles) and I've been having a lot of trouble with my idle. The car used to periodically have trouble idling at stop lights, rev forward, and stall. This only happened after driving relatively long distances when the car was warm. It was a very rare problem, but now the car stalls nearly every time it idles for more than a few minutes (even cold).
It became really bad when I was driving it, heard a couple of choking sounds like the fuel wasn’t flowing right, and the car gradually lost power. Since the "big" issue came to be I've had the distributor cap and rotor (also the wiring for the cap), spark plugs, ISC motor, and coolant temperature sensor changed to no avail. Diagnostics test throws a code (18) for crank signal circuit but the mechanic is unsure if that is the actual problem. When the car idles at a stop light it'll run for a few minutes and stall out. It also struggles quite a bit in motion and when it is parked with the engine running it idles high, low, and stalls out within minutes. However, if you keep your foot on the gas pedal the car will idle well until it’s removed. I have a "service now" light that comes on right before the problem really kicks up. The MAT sensor is a suspect, as is a potential electrical short.
Any help would be greatly appreciated,
Kasey
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Loren Champlain Sr
Veteran
/ Moderator
Feb 8, 2009, 2:04 PM
Post #2 of 8
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Re: 1985 Cadillac stalls at idle
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CadillacGirl; If it is coming up with a CKP code, that is definitely worth a look, but generally when they go bad, the engine will die (or be unable to start) because you will lose injector pulse. Keeping the idle up wouldn't normally help. But it is definitely worth checking. The MAT sensor can cause an idle issue, but I'm not convinced that it, either, would cause the symptoms you are experiencing. The problem with the older Cads, you can't get live data from the ECM, just the hokey heater controls. There are a couple things I'd like to check; 1) MAP sensor, and 2) Fuel filter and pressure. (mainly because this is happening at various temps). Might also have him check the O2 sensor. Unfortunately, most of these are going to have to be checked manually, so you are probably looking at some diagnostic charges.
Loren
SW Washington
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CadillacGirl1985
New User
Feb 8, 2009, 2:18 PM
Post #3 of 8
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Re: 1985 Cadillac stalls at idle
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Loren,
Thank you for the suggestions. We do need to replace the fuel filter, but do you think that could be the sole issue causing this? It seems like more than that. I've also experienced the air conditioning turning itself on at one point which makes me feel like there might be a short. The electrical has been acting a bit strange since we changed the coolant temperature sensor. Any chance that one of those wires shorted out and is causing this? Also, my ECM shouldn't be bad if it's only throwing the crank code right? I'm fearing the worst right now. We've been fighting this issue for a week now. Been through two mechanics and both are stumped. I was told something is messed up in the communication with the ECM. Not quite sure what that comes down to.
Kasey
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Double J
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/ Moderator
Feb 8, 2009, 2:29 PM
Post #4 of 8
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Re: 1985 Cadillac stalls at idle
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Agree with Loren...Checking the fuel pressure ,replacing fuel filter....
Also ,these had intermittent faults with the Pick-up coils.
Does the vehicle start right back after the stall?
May want to take it to Cadillac for diagnosis....
Here is the possible causes of a code 18...
During engine cranking, a 12 volt signal is present in the cranking circuit between the ignition switch and ECM.
Code 18 indicates that the ECM is not receiving the 12 volt signal while the engine is being cranked. Possible causes of this condition are:
- Defective ignition switch
- Defective wiring harness or electrical connectors.
- ECM not processing signal.
- Blown 3 amp ``Crank'' fuse.
To diagnose a Code 18, proceed as follows:
- Check condition of 3 amp ``Crank'' fuse. If fuse is blown, check circuit 6 (1985, 806) for a short circuit to ground between the fuse and ECM. If circuit is satisfactory, replace fuse. If fuse blows again, check for faulty ECM or ECM connector and repair or replace as necessary.
- Crank engine while checking for voltage at crank fuse using voltmeter J-29125 or equivalent connected between fuse and ground. If reading of zero volts is obtained, check for open in circuit 6 (1985, 806) and repair as necessary.
- If reading of 12 volts is obtained at fuse, connect voltmeter lead to pin No. 1 at blue electrical connector. If voltmeter indicates 12 volts while cranking, check terminal for open condition. If terminal is in satisfactory condition, check for faulty ECMor ECM connector and repair or replace as necessary.
- If voltage reading is zero, check for open in circuit 6 (1985, 806) and repair as necessary.
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Loren Champlain Sr
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Feb 8, 2009, 2:31 PM
Post #5 of 8
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Re: 1985 Cadillac stalls at idle
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Kasey; The communication problem with the ECM is, unfortunately, uh, normal? I dread it when one of the older Caddys comes in. They are a diagnostitions nightmare.  The CTS is very important; It tells the ECM engine temperature, and controls fuel delivery accordingly. If shorted to ground, I'm pretty sure the system would go full rich, which would cause an overfueling problem. Same with the MAP sensor. If it is 'falsely' seeing a drop in manifold vacuum, it will go full rich. If this were a normal OBDI system, you could hook up a scanner and see what the ECM is seeing. There is a spec chart that your mechanic can check CTS values at given temps. The A/C is climate control, correct? It will do 'it's' thing by itself, heating and cooling. There is an inside sensor to detect cabin temp, which could be causing that issue? Your Caddy is a low fuel pressure system. It only needs around 15psi, but if too low, could be definitely causing your grief. Have the fuel filter replaced, regardless, then have the fuel pressure tested if still having problems. Yes, it's possible it could be something very simple. Or not.
Loren
SW Washington
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CadillacGirl1985
New User
Feb 8, 2009, 2:34 PM
Post #6 of 8
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Re: 1985 Cadillac stalls at idle
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Jim,
The car does start right back up after stalling. For a while it runs fine and acts like nothing happened, then the "service now" light starts flashing, and it struggles a bit. At a stop light when this is happening, the car stalls out at idle. It almost seems like it resets itself for a while and then the problem hits again. I did take it for diagnosic and the ISC was bad. They fixed that, however, and the code for that is now gone. The only code showing was for the crank now.
Hope this extra info helps. Thanks for everything.
Kasey
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Double J
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Feb 8, 2009, 2:35 PM
Post #7 of 8
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Re: 1985 Cadillac stalls at idle
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The starts right back is indicative of the intermittent failure with the pick up coil...
Let us know
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CadillacGirl1985
New User
Feb 8, 2009, 2:41 PM
Post #8 of 8
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Re: 1985 Cadillac stalls at idle
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The plug on the MAT sensor is coated with gunk, which can't be good. Tonight the fuel filter and MAT sensor will be replaced. If those don't work, I'll definitely be checking the pick-up coil next. I sometimes hear a strange clicking noise when the car is idling. It's like a little tapping sound of metal. Any theories for that?
Kasey
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