Testing the PCM (computer)
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I own a 1992 Ford Explorer with the 4.0 push rod engine. One day after driving the truck I pulled into the driveway, shut it off and then came back about 5 hours later only to find that it wouldn't start. It , when turned over, sounded as if the firing was out of wack, like the timing was wrong. Never having this problem with the truck, I was surprised. So far I have checked the coil pack with that of one which works, no change. I have replaced the spark plugs ( gapped 52 - 56 thousands) and wires (in the correct order). Of course this was done as regular maintenance. I checked the ignition module with that of one which works, no change. I replaced the crankshaft position sensor, no change. There is plenty of fuel. The plugs are soaked. Every few cranks it starts but runs as if the timing is wrong and quickly shuts down. I never touched the timing. What would you suggest is the problem?
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From: UT
First step in determining if the computer is bad would be to run the self-tests. On a '92, this can be accomplished with nothing more than a paper clip. A good description of the KOEO test is under "retrieving codes" (or something to that effect) at www.fordfuelinjection.com A more complete description of the KOEO and KOER tests is at www.dalidesign.com/hbook/eectest.html.
If you get all pass codes, then I would expect the computer is good and that your problem lies outside of the EEC-IV system. If you don't get any codes, then the computer may be bad, but you'll need to do further diagnostics to determine that. If you get other codes, then you'll need to resolve them one at a time, starting with the KOEO hard faults.
Another thought: you say the plugs are getting "plenty of fuel." Any possibility it's way too much fuel from a bad fuel pressure regulator diaphragm, insanely high fuel pressure, or stuck open injectors? Seems like a long shot, but it wouldn't hurt to put a fuel pressure gauge on it and see what the fuel pressure is.
You say it acts like the timing is off, will it run if you disable the timing advance by disconnecting the SPOUT connector?
If you get all pass codes, then I would expect the computer is good and that your problem lies outside of the EEC-IV system. If you don't get any codes, then the computer may be bad, but you'll need to do further diagnostics to determine that. If you get other codes, then you'll need to resolve them one at a time, starting with the KOEO hard faults.
Another thought: you say the plugs are getting "plenty of fuel." Any possibility it's way too much fuel from a bad fuel pressure regulator diaphragm, insanely high fuel pressure, or stuck open injectors? Seems like a long shot, but it wouldn't hurt to put a fuel pressure gauge on it and see what the fuel pressure is.
You say it acts like the timing is off, will it run if you disable the timing advance by disconnecting the SPOUT connector?
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From: ut
(I've read these threads with interest because I have a 92 Exp also,) but I have a friend who had a similar problem with his Ranger. He never had any codes and he'd gotten to the point where he was "shotgunning" the problem with parts. The fuel press. regulator was the culprit in the end. This should be an easy check if you can obtain a pressure tester. His problem was that the regulator failed OPEN. He was getting too much fuel. Good luck.
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Thanks, I'll check the KOEO tests via the web site you suggested. Actually, I have a test kit I bought from Autozone. I got the "everything ok" 111 code..nothiong else.
Where is the fuel pressure regulator diapharm ? Also, What is considered "normal" fuel pressure?
Where is the SPOUT and how can I disconnect it?
Thanks again for your help this far.
Where is the fuel pressure regulator diapharm ? Also, What is considered "normal" fuel pressure?
Where is the SPOUT and how can I disconnect it?
Thanks again for your help this far.
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to sjwoody,
mrshorty suggested the fuel pressure regulator diaphram. I am going to check it once he points me in the direction to find it. Thanks for your input, greatly appreciated !!
mrshorty suggested the fuel pressure regulator diaphram. I am going to check it once he points me in the direction to find it. Thanks for your input, greatly appreciated !!
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From: UT
Fuel pressure regulator (FPR) is at the front end of the fuel rail, just underneath the throttle body. There's a Schrader valve (lookes like a tire stem) in about the middle of the fuel rail on the passenger side where you can hook up a fuel pressure gauge. Normal fuel pressure with no vacuum to the FPR is 35-45 psig. One of the FPR's failure modes is for the diaphragm to leak, allowing fuel into the intake via the vacuum line. Quick test for this is to remove the vacuum line and see if there's any fuel there. In addition, with a pressure gauge attached, see if the fuel rail will hold pressure after the fuel pump turns off.
SPOUT is a wire with either a shorting bar or a single connector. On my '92 I think it was a pink wire coming off of the coil pack connector, but I don't remember for sure. A good wiring diagram should help you find it.
SPOUT is a wire with either a shorting bar or a single connector. On my '92 I think it was a pink wire coming off of the coil pack connector, but I don't remember for sure. A good wiring diagram should help you find it.
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Thank you once again for your help. Prior to getting this reply from you, as mentioned above, the fuel pressure regulator was suggested as a possible cause. Acting on this chance, I found the fpr, disassembled it and from what I remember there was fuel in the vacum line. It was an easy part to take off. I've decided to reassemble it, check the fuel pressure as you suggest before making the conclusion that the fpr is in fact the problem. I will keep the forum informed as to my progress. Thanks again. Enjoy your weekend.
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The vacum line appears to have fuel in it. My intent is to replace the fuel pressure regulator and the vacum line. I will also, at the Schrader valve, check the fuel pressure before and after. Thanks for your input. Once I've got the truck back on the road I will post the entire "chapter" in this forum.