Okay, I have replaced the MAP sensor, TPS, Alternator (was overcharging), Battery, the Idle Air Control Valve, fuel pump, external fuel filter, and fuel level sensor assembly. There are no flash codes and the CEL is not illuminated. When you start the engine from a dead-cold condition it runs perfectly smooth at a fast idle (1100 rpm) and as it comes to temp over about 5 minutes -- the idle speed drops slowly as expected. Then -- the Tach needle will start to "flicker" and jump when the idle comes to about 950-1000 rpm and the engine will just quit. If you try and re-start it, it just cranks with no life. If you wait about 15-30 minutes and hold the throttle partially open it will re-start, but repeat the same deal -- UNLESS you manually hold the engine speed above 1500 rpm with the gas pedal. Then -- you could sit there for 15-20 minutes and it would run fine with no misses or stumble at all. Again-- let the engine come down to normal idle, the tach needle jumps about and it quits again. Sounds like a classic crank position sensor failing when it warms up, but I didn't think the 1993 RM 5.7 liter V-8 engine had a crank or camshaft sensor. Could it be the Coil -- getting a little temp in it, and then dropping out? It seems to be a sensor issue related to the idle circuit. Maybe the main ecu with an internal fault? The tach needle jumping should be a clue-- but I know not where to look at this point. I'm stuck -- and out of idea's. Anyone out there seen this?
You may be correct guessing the coil, but look at the Ignition Control Module (ICM) under the dist. cap as well. Can you check your fuel pressure while all this is happening? A noid light on the injectors will tell you if the computer is firing the injectors properly. Those will help eliminate a fuel issue. TBIs do not have a crank or cam position sensor so to speak, the cpu gets that info from the distributor. Mike
It's fixed !! I pulled the old ignition module, and noticed two things. First -- there was a kinda "copper colored dust" on the base plate in one area. I cleaned that off, and scraped what was left of the heat-transfer paste off of the plate where the module bolts to it. The second thing was that the paste was only on a dime-size area on the underside of the module. I read on the instruction sheet with the new one -- that the paste must be smeared on the entire metal underside surface or pre-mature failure of the module may occur. So -- back together and it fired right up and idles fine for the hour I let it run. No more tach needle jumping. Thanks for your tips and info!
Yeah it does. Actually -- I don't let anyone else work on my cars. I was a mechanic, service writer, service manager over many years in a past life <grin>. It's just that this one stumped me, as I usually work on foreign cars. Thanks again!
I would still check the condition of the ground connection to the module with a multitester. I've had my Trans Sport van do this many times. It turned out it was only grounding through the base plate of the module, because the ground wire was only good enough to pass 10 volts instead of 12. So when conditions got iffy it would lose ground and die on the side of the road. I just ended up splicing and soldering in a new wire to the ground lead and ran it to a bolt in the frame with all the other grounds. No more problems.
Cleaning those 2 bolts that hold the EST/ICM module in is imperitive as it is the ground for that module. As you noted the heat sink grease needs to cover the entire bottom of module or they overhear and prematurly die... If your distributor was that gren dusty crap you may want to go further and pull distributor, take off gear, pukll shaft and replace the pickup coil. They are only about $10. but known to fail after years of the corrosion. This corrosion can be stopped if you vent the distributor cap like on the LT1 1994 to 1997 LT1 Optispark distributor that uses a vent system.
