ptt

1990 Coupe dies....

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I had the symptoms of a bad crank sensor with the engine starting and when it reached operating temperature it would stall.  I went ahead and checked fuel pressure (41lbs) and it held dropping to 35lbs with engine turned off.  I checked codes and it seems there is a problem with the display that doesn't allow the letters and numbers to display entirely making it difficult to correctly read the codes.  I proceeded by swapping out the Crank Sensor.  Started engine and upon reaching operating temperature it stalled as before.  I had left the Fuel Pressure Gauge attached and it displayed the original (KOEO) 41lbs after the stall. The Coils are new also.  Can I rule out the oil pressure switch killing the fuel pump because of the 41lbs of fuel pressure displayed after the stall????  The faulty code display is making this into a mystery.   

Edited by ptt
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You mentioned the coils are new, what about the ICM below the coils? It can suffer the same temperature related failures as the crank sensor. Check to be certain the plug at the end of the ICM is firmly seated also. The fuel pressure sounds fine, so I doubt that is the issue. If it still stalls when warm, disconnect the MAF sensor and start the engine and see if that helps.

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14 hours ago, ptt said:

Started engine and upon reaching operating temperature it stalled as before.

 

How hot? Without the display working correctly- it's impossible to determine exact temperature when it stalls.

 

14 hours ago, ptt said:

Can I rule out the oil pressure switch killing the fuel pump

 

Yes- with these tests:

 

Install a test light between the fuel pump primer connector and ground. Turn key to RUN. Bulb should light while ECM primes pump. Without turning off first, start engine. Bulb should remain lit, while engine is running. Closely observe light; when engine stalls- does light go out first? (bad fuel pump relay) Engine off, connect light to GREY wire of pressure sensor and ground. Start engine, light should remain lit while running. Closely observe light; when engine stalls- does light go out first? (bad pressure switch)

 

A (mechanical) relay is an electromagnet that operates a switch. Relays get hot in operation; over time, heat kills magnetism, and conductivity of electricity. Relay gets hot, gets weak, shuts off. How old is the fuel pump relay? (stupidly placed above the rear exhaust manifold:blink:)

 

Another test: Disconnect battery, remove the ECM, remove it's PROM cover, and plug in it's 3 plugs, leaving it laying on the floorboard, to get air. Start engine, let it warm up. Does it take longer to stall, if it stalls at all?

 

I say to do this test- because of the poor placement of this module (same as '88-'89 radio) that over time, these units can fail from heat, their circuits that are attached to heat sinks fail. Thermal paste dries out, unit has no sufficient airflow, and dies.

 

When (if) it stalls- lay the back of your hand on the ECM- is it warm? Hot? An overheated ECM could also corrupt the data to the IPC.

 

Just my $0.02

 

(photos will greatly enlarge when clicked twice)

 

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When operating temperature reached on the gauge its right at the middle bar.  The only problem I see with the IPC is the codes not being displayed completely where the mileage odometer is.  Its like the letter and numerical symbols are missing "parts" and are incomplete.  Everything else is fine with the disply.  When in diagnostics it cycles though codes but some arent legible.  I havent tried disconnecting the MAF yet so need to do that and other suggestions.  Thanks.

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I just recalled that I have an old combination OBD-I/OBD-II scan tool somewhere in my archives. I havent used it since I redid some 90s Lebaron Convertibles years ago. Arent the Reattas capable of being OBD-I scanned? Isnt the diagnostic port somewhere in the center console tower?  My scan tool is an AutXray brand.  Hpefully I can scan it so I can get this Coupe ready for winter duty so I can store the Convertible for the winter.

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Yes, it should scan if you have the GM plug for OBD-I. The ALDL port is below and to the left of the steering column. There should be a cover over the port which should be replaced after scanning.

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Can also check by jumpering A to B on the ALDL plug and counting the Check Engine flashes. Not all GM cars have displays.

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