TBI 1992 Caprice Classic LTZ 5.0L Intermittant stall & no-start condition. experienced techs only please.?

Question

92 Caprice will occasionally stall with no warning & will not restart immediately.
-Has new fuel pump with more than enough pressure past the filter.
-Within the past year has had ignition coil, TPS, IAC valve, plugs, wires, cap, rotor, distributor with ignition module & pick-up coil all replaced.
-Engine will run for over an hour sometimes & five minutes others before stalling. Then the engine will crank but not fire & has good spark to the plugwires but no injector pulse. However if you spray carb cleaner below the throttle plates, engine will start & injectors will begin firing again for a few minutes & will stop firing again causing another stall. Are there any GM techs who can explain to me what besides the ECM & pick-up coil controls injector pulsing? And has anyone ever encountered this before? Should I replace the ECM and if so will I need to have a GM dealer program it? or can I just swap the chip from the old one to the new ECM?

I guess I need to repeat myself. I have good fuel pressure coming from the fuel pump THROUGH the filter which has been changed twice this year. The tank was dropped and flushed (plastic tank so no rust in case that is the next suggestion) There is no debris and all maintance items and THEN some have already been replaced. Again I ask please only experienced techs with technical information about the GM TBI fuel injection system control or who have encounter this problem before and solved it need reply. Thanks so much. I appreciate any help you can offer. This has been a frustrating case. And I am sure I have enemies somewhere yes but this isn't my car. But thanks for the suggestion because it is something that one wouldn't normally consider. But I am afraid it doesn't apply here. Anyone else wanna try your hand at it? 10 points to the person who provides information that leads to the elimination of this stalling problem... where are all my ASE master certified GM super techs?

Answer 1

Yes, these are very frustrating and enraging to find problems like this. I have read your notes and also the suggested fixes. The really long one has a point. Here's what I used to do with this type of a situation. As far as I can recall, this motor uses a TBI type of injection with two big injectors sitting on top of the intake. What you have to do is eliminate issues. It sounds like you already have eliminated most of the usual problems like plug wires, distributors, and modules, but even new parts sometimes have problems or you might have a loose connection. When this motor stalls out and will not restart is when you have to perform the diagnosis. I realize this is time consuming, but it is the only way to be sure so start your diagnosis when the motor quits and won't restart. If it restarts while checking, all of what follows will not find the intermittent. When it stalls, you have to quickly check for coil outputs at the plug wire spark plug end. From what I've read it sounds like you have spark when this happens, but be sure as if there is no spark there will usually be no injection. Assuming you have spark that will mean you have a fuel system fault or an RPM input fault to the PCM. You say fuel pressure is good, are you sure. This injection system runs on about 12-15 psi. The only way to be sure it is getting this pressure is to have a guage installed in the pressure line leading to the TBI unit and running the motor until it stalls. If unsure, leave the guage in the line while continuing your diagnosis. Obviously if you still have the correct amount of pressure, the pump and lines are okay as well as the electrical circuit for it. Be sure about this as I have seen people think the pump is okay because it is new, but they do not always work properly or there can be a connection problem to the pump especially on the fuel sender unit or the ground that leads away to the body for the pump. Let's assume the pump is okay and the spark is okay. That only leaves the injectors or the circuits that runs them. This is a pretty simple circuit and I have not seen one of these have this trouble, but there is always a first. When the motor stalls and there is no spray of fuel from the injectors but spark is strong and consistent, pull the connectors off of the injectors and test the connections. This system uses a 12V supply and the PCM grounds the circuit. Make sure that first there is a full 12V at each of the connectors by sticking a test light connected to a known good ground and the light should be on with the ignition on. Test the injectors internal coils for continuity to be sure the injectors are not open, which they probably won't be, with an ohmmeter. If that is for sure then the thing to do is bare the ground side of the wires that lead to the PCM, do this where it can be easily re-insulated after. Install your test light onto the ground side of the injector connector with the connectors back on the injectors. Now crank the motor over and watch the test light while it is connected onto the PCM side of the injector connector. It should flash very quickly as the PCM grounds the injector. If the test light does not flash, you either have a broken or internally corroded wire, poor connection somewhere from the injector to the PCM, or a faulty PCM. There is also a likelyhood that the wire lead from the distributor to the PCM that is an input for RPM could have connection or continuity problems. Be sure of an RPM input while cranking by using a scanner and watch engine RPM while cranking. If the test light is blinking while cranking but still has no fuel spray, you have 12-15 psi fuel pressure, and strong and consistent spark, your injectors are inop. and need to be replaced. I have never seen two injectors fail at the same time in this type of a configuration. I cannot over emphasize the need of constant rechecking of problems like this as you can see replacing parts because you suspect them is quite costly and you usually cannot return parts after trying them out. I have never seen a PCM in this type of a unit burn out an injector driver, but there is always a first. Good luck and post another question if you need to chat again or let me know that you fixed it and how.

Answer 2

I own a shop, and have seen this problem many times. I know you don't want to hear this, but the ignition module is bad. If you have it tested it may check good, and it may check bad. This is the classic symptom of a bad ignition module overheating and shuting down. This may be caused by not enough heat sink lube being put under the module when it was installed. The computer is the sole control of the injector firing, but it fires the injectors based on information it receives from other components, and/or sensors. I have seen this problem at least 50 times in the past several years, and 99% of the time the problem went away upon replacing the ignition module. I would pull the codes from the computer, unhook the battery cable, change the module, and hook it all back up & start the engine. I don't think there is anything wrong with the computer unless you are getting a bunch of random type codes that make no sense. This is the normal sign of a bad computer, many off the wall codes that don't corrospond with each other. If you had to replace the computer, you can get a rebuilt one from Auto Zone pretty cheap now, but you have to trade them your old one, and be careful to not kill the new one with static electricity. Use a can of electronic cleaner on all connections to insure no problems with corrosion. I can contribute 75% of all computer related problems to a bad battery, a bad engine ground, or just dirty corroded terminals. A computer is designed to operate on 12 volts, not 11.3 or 4. A missing ground strap that goes from the engine to the body is another culprit of computer problems. As you know an intermittant problem is the worst kind, and a pain to run down. Most shops won't even work on one like that, and I don't blame them, because there is no money in working (all day) to find something the customer is not going to want to pay for you finding, no matter how long it took to find it. I could go on and on about this, but I will spare you. You will just have to trust me on this one, as I have seen it many times, and even had a vehicle towed 400 miles to my shop, that the dealer couldn't fix. If I had not seen it before, then they would still be looking I guess.
Glad to help out, Good luck!!!

Answer 3

1992 Caprice Classic

Answer 4

1992 Caprice

Answer 5

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RE:
TBI 1992 Caprice Classic LTZ 5.0L Intermittant stall & no-start condition. experienced techs only please.?
92 Caprice will occasionally stall with no warning & will not restart immediately.
-Has new fuel pump with more than enough pressure past the filter.
-Within the past year has had ignition coil, TPS, IAC valve, plugs, wires, cap, rotor, distributor with ignition module & pick-up coil all...

Answer 6

I'm not an experieced tech, as you requested, however, this came to mind. Do you have enemies? What your describing is definitely difficult to diagnose. My suggestion, check your fuel tank for floating debris. Anyone can drop things into your tank, which will float allowing you to use your vehicle, once the object gets sucked into the fuel pump, you loose fuel, hence, stall.
You'd be amazed how many things will not dissolve in gas.

Best of luck

Answer 7

Keep looking out and make sure nothing else comes sliding under the stall.......

Answer 8

I have the same car and I also have a extra working ECM If you want one cheep contact me! you dont reprogram the PROM chip you just pop it out of the old one and insert it into the replacement one

Answer 9

change your fuel filter..........check your old filter for debris.

Answer 10

What the hell was the solution?