94 Explorer VIN X V6 runs for a minute and dies

[MrShorty]

In most cases, there isn't a test for a bad PCM. You determine a bad PCM by process of elimination. If every other possible cause is eliminated, then the PCM must be bad.

Aside from that, the other "test" for a bad PCM is "guess and check" In other words, replace with a known good PCM and see if it fixes the problem. This isn't bad if you can return the replacement if it doesn't fix the problem. Not as desirable if it costs a bunch to test. Especially because, as you say, the PCM doesn't fail that frequently.

 

[jadams]

In most cases, there isn't a test for a bad PCM. You determine a bad PCM by process of elimination. If every other possible cause is eliminated, then the PCM must be bad.

Aside from that, the other "test" for a bad PCM is "guess and check" In other words, replace with a known good PCM and see if it fixes the problem. This isn't bad if you can return the replacement if it doesn't fix the problem. Not as desirable if it costs a bunch to test. Especially because, as you say, the PCM doesn't fail that frequently.

I pulled the PCM and removed the cover and did see anything obvious, as in something burnt or slightly burnt or smells that would also indicate something burnt. It is beginning to more and more like a shorted wire in the CKP circuit. If that fails, then the only thing left is the PCM (by process of elimination) as the injector light test indicated. My local Ford dealer wants $825.00 for a new PCM. That being the case I will go to the junkyard as doubledflooring suggested and pull the eprom from mine and swap it, except where is it and what does it look like? Mine has the part number F47F-12A650-DBA, the -DBA is the part that is specific to mine which seems to mean AT plus California and New York. Emissions stuff and automatic transmission I assume. The F47F-12A650 is common to to the Explorer/Ranger from 91-94 from what I have read as there seems to be a bunch with that prefix.

Thanks for your input

 

[jadams]

CKP circuit

I just disconnected the CKP sensor to test the circuit. I inserted my test light (jumped) in one end, CKP, and tested with a DVOM and the reading at the ICM was identical with the reading of just reading Ohms on the test light, does this mean anything? Should I still start removing the auto loom to inspect the wiring? The reason I bring this up is the 'stuff' I have to remove to get to entire length of the harness, such as alternator, drain coolant, etc.

Appreciate any input.

Jim

 

[MrShorty]

Personally, I would work from connector to connector until I saw a reason to tear into a specific section of the wiring harness. From what you describe, that section looks good (at least right now). One of the difficult parts with something that sometimes works and sometimes doesn't is you don't always know if you are looking when the problem occurs.

With the same setup, try reaching around things (with a stick, long screwdriver, or whatever) and "wiggle" sections of the harness in question while watching the ohmmeter. See if you can see any changes/breaks.

This also may not be a good test of the connector at the CKP, because you've replaced the CKP with the test light. You might try measuring the resistance of the CKP, and then connecting the CKP to the harness and measuring resistance through the harness to see if they are the same. Also, another wiggle test to make sure the connector isn't momentarily losing contact at the CKP connector.

 

[jadams]

Personally, I would work from connector to connector until I saw a reason to tear into a specific section of the wiring harness. From what you describe, that section looks good (at least right now). One of the difficult parts with something that sometimes works and sometimes doesn't is you don't always know if you are looking when the problem occurs.

With the same setup, try reaching around things (with a stick, long screwdriver, or whatever) and "wiggle" sections of the harness in question while watching the ohmmeter. See if you can see any changes/breaks.

This also may not be a good test of the connector at the CKP, because you've replaced the CKP with the test light. You might try measuring the resistance of the CKP, and then connecting the CKP to the harness and measuring resistance through the harness to see if they are the same. Also, another wiggle test to make sure the connector isn't momentarily losing contact at the CKP connector.

I just completed connector to connector testing and found no problems in continuity for the CKP circuit and the circuits where the PCM and the ICM communicate (PIP signal, Tan/Ylw wire)and found nothing wrong for any of the three circuits. Well I did get a .1 Ohms variation but you can get that so easy I consider it insignificant. I did the tap/wiggle test on the harness and connectors and nothing out of the ordinary popped up. Can't really do the test with CKP connected because because I need a backprobe, plus I have no idea what one is. Just had the ICM retested, 25 cycles, and it came back OK. Am I down to the PCM?

I'm ready to start at the beginning, but at this point I have no idea what that might mean. I could probably follow a specific sequence if I knew what it would be.

Thanks

Jim

 

[jadams]

Personally, I would work from connector to connector until I saw a reason to tear into a specific section of the wiring harness. From what you describe, that section looks good (at least right now). One of the difficult parts with something that sometimes works and sometimes doesn't is you don't always know if you are looking when the problem occurs.

One thing is consistent it always dies after running for a short period of time, by that I mean less than two minutes and the RPMs don't matter. Prior to dying it always starts missing and this coincides with the injector test lamp not displaying a steady pulsing light, as in it is missing also.

Jim

 

[doubledflooring]

Shot in the dark:

Pull both battery and altenator and have tested also check cables and all connections at both and clean.

While you're doing this I'm still researching other possiblities

 

[doubledflooring]

also have you tried starting it with slight pressure on the gas pedal.

And check the TPS

Also pull the MAF and have it tested.

have we verified if there is spark at all cylinders? After the stall

 

[doubledflooring]

Also are you positive you set the timing correct?

And have you recently checked it?

 

[Weatherman]

Look at it from this angle: why does it run for a minute - not why does it stop. In the first minute you're bypassing some components and running off a preset mode. It appears you're dying in the transition (actually a minute is a little late for that). Also, several types of component failures would send you to limp home mode, which you're not making it to.

For the basic components:

IAC can be bypassed by holding throttle open

All fuel delivery problems would appear in the first minute when you're feeding more fuel than later when you're feeding less fuel.

TPS is easily checked with voltmeter, and from experience the engine will still run if the TPS is bad and you hold throttle wide open.

Do the following and see where it takes you:

1. Plug the vacuum lines you don't really need. Definitely plug vacuum line to EGR (this is a Ford suggestion).
2. Pull plugs - how do they look.
3. Make sure you're getting spark at each place while cranking.
4. Do compression test just for the hell of it.
5. Watch it run with vacuum gauge and fuel pressure gauge hooked up. See other threads or manuals for what you should be seeing.
6. Check your air temp and engine temp sensors - they won't kill my '91 but maybe by '94 they cause a shut down - like the engine thinks it's overheating.
7. Start looking for things that might get hot and shut down - I've had this happen before with other vehicles.

I'm assuming with the upper end work you didn't touch anything that could affect timing, right?

Ben

 

[Weatherman]

BTW - watch a volt meter while you're playing with this thing.

And another one of those for the hell of its - leave your gas cap off and make sure it's not vapor locking somehow - I had a vehicle do that many years ago and act exactly as you described because it took one hour do naturally relieve the vacuum the fuel pump was holding on the intake. Also, I once had a brand new fuel pump that would put out standard pressure until there was a heavy load on the engine. I had to floor it with the brakes applied in order to find a pressure drop.

Some things to think about...

 

[MrShorty]

I'm ready to start at the beginning, but at this point I have no idea what that might mean. I could probably follow a specific sequence if I knew what it would be.

As I mentioned before, a good repair manual can be invaluable. A quick check of the Pima county public library shows that they carry Motor and Chiltons (apparently professional editions as well as the DIY versions you're used to seeing). My next step would be a trip to the library, find the 1994 light truck engine performance and troubleshooting volume (or whatever Motor calls it). Then find the circuit pinpoint test that applies to a CM 211. Take some change, becaue libraries usually put these in the reference section where they can't be checked out, so you'll want to make photocopies of the appropriate pages.

 

[jadams]

New test results including engine running.

I made some new test connectors and this improved the sensitivity. Retested all circuits pertaining to CKP/CMP/ICM/PCM for shorts/open circuit and nothing was out of tolerance or obvious.

The car has also sat for 2 days while I traced circuits and had the ICM tested. I also pulled the PCM and it sat for the same period disconnected. Removed the cover of the PCM looking for obvious burns or loose connections and also found nothing.

Today I reconnected all components with the exception of spark plug wire #2 and injector #2. Attached spark tester to #2 wire and test light to #2 injector connector and placed both where I could see both easily and clearly without moving my eyes from the drivers seat.

Started the engine and took it up to 2000 RPMs and held it steady for 4 minutes (a new record), at 4 minutes there were a couple of small misses then they became more pronounced and longer. The spark tester stayed steady and the injector test light would fluctuate in conjunction with the misses, but I had to be paying very close attention to see the differences. When the stalling started the spark tester was steady and the fluctuation in became more obvious, then the car died.

Ran the KOEO and DTC came back 111, 10, 111. System pass.

Restarted car within a couple minutes of dying and it started right up. Took the RPMs up to 2000 and ran that way for 4 minutes again before the missing started, but this time the misses were a little longer and the injector test light was noticeably fluctuating with each miss, but the spark tester was steady. Then it died at 4 minutes 30 seconds, same as before.

Ran the KOEO and DTC came back 111, 10, 111. System pass.

Tried to restart and no luck, BUT.... this time observing the spark tester and injector test light the difference was great. The spark tester was steady and the injector test light only lit intermittently and each it came the engine would catch briefly and no start.

Ran the KOEO and DTC came back 111, 10, 111. System pass.

Fuel pressure was good and engine temp sensor is new. Timing wasn't tinkered with at any time. Next step is the library and get relevant info. Then try the suggestions each of you contributed to my trouble shooting. In light of my new testing procedure does any of this yield new insights. Even though the 211 Profile Ignition Pick-up code hasn't reappeared it still is very relevant as it has to do the communication between the CKP/ICM/CMP/PCM and the PCM controls the injector activation. The CEL has not come on either.

As far pulling the CMP and having it tested I will have remove a bunch of stuff, as in all the way down to the lower intake manifold. I'm prepared to do that and will probably have to next if nothing improves.

Hi Ho Hi Ho it's of to the library I go.

 

[MrShorty]

One thing that often gets neglected is the computer's grounds. The computer acts like a ground side switch for the injectors, but, if the computer doesn't have a good connection to ground, it won't complete the circuit. I've heard of several who find those grounds, especially those that run directly off of the negative battery cable, to be corroded.

Also, don't forget to verify that there isn't a bad connection between the EEC relay and the fuel injectors.

 

[jadams]

One thing that often gets neglected is the computer's grounds. The computer acts like a ground side switch for the injectors, but, if the computer doesn't have a good connection to ground, it won't complete the circuit. I've heard of several who find those grounds, especially those that run directly off of the negative battery cable, to be corroded.

Also, don't forget to verify that there isn't a bad connection between the EEC relay and the fuel injectors.

I've been going over the engine wiring diagram and have a question regarding this part. Where do each of the grounds go to? In tracing the circuits, the PCM relay in particular, the Yellow wire goes from the PCM relay to a 30A fuse and then goes to pin #1 on the PCM and 2 red wires one to the fuel pump relay and then the other branches to the MAF sensor and each of the injectors. Actually that red wire is shown common to almost everything, but the ground is Blk/Wht and the PCM ground is also Blk/Wht and terminates someplace else. I scanned it from my Haynes book and turned it into a JPG so I could enlarge it for easier tracing of wires. By the time I got to the library it was closed, closes early on Friday.

Can we post images here? It's 2 1/2 MB in size.

 

[BrooklynBay]

You will need to either become elite or post the images on a site like photobucket.

 

[jadams]

Also, don't forget to verify that there isn't a bad connection between the EEC relay and the fuel injectors.

I don't see where I would do this.

I can test the CMP and PCM, but the testing procedures require a backprobe. Any idea how the tests can be run without one?

Just gained access to Mitchell on Demand and found the section you mentioned on engine performance. Very detailed! Especially the testing procedures. Also, much better wiring diagrams than my Haynes book and includes location where grounds are terminated. I did a quick check of grounds for corrosion and didn't find any, now on to the circuits. It's California car that has been in Arizona for the last five years.

 

[MrShorty]

I just use a straight pin soldered to an old DVOM lead for backprobing.

 

[jadams]

I just use a straight pin soldered to an old DVOM lead for backprobing.

I'm not clear on this. I mean I don't understand how to use it and what it looks like. Are these pins that pierce the wire? If that is correct, then I take a pin, nail or something similar and grind it to a point that can pierce the insulation of a circuit to measure voltage or voltage drop.

Can you identify the positive in one of the injectors and measure the voltage against ground when the car dies? Is the 12V present all the time when the ignition switch is on? Remember, the injectors have the +12 on all the time, and the PCM switches the ground on and off as required.

Does this mean identify the positive lead which would be Tan or some color and the ground would be the Red, since Red is common to all the injectors. and measure across them or attach one lead to the Tan wire and the other lead to the engine. In testing the CMP and PCM would I follow this same procedure? I have the test procedures from Mitchell (and there are a lot) and it looks I can identify whether it is a fault in the circuit or defective PCM or the CMP is defective. Is that logic correct?

Thanks
Jim

 

[budwich]

His "pin probe" is made by taking a "straight pin"... sewing pin used to hold cloth together while you sew... ask your wife... basically its got a small sharp pin end and is strong enough to "pick" a small hole thru leads to test for voltage without really "disturbing" the insulation too much.

Interesting. It would appear that you are "almost there"... but maybe not. Lots of testing.

Anyways, if I follow some of the testing and "conjectures", its appears that the system starts to failing in terms of timing / pulsing. However, from "conjectures", supposedly if it loses pulse from the ckp, it should go into limp mode with a X% timing (sorry I didn't go back... but the actual value does matter... only the "conjecture"). My suggestion would be for you to put it into limp specifically.... that is when you get it started, have someone pulled the connector on the ckp... it should go quickly into limp (and you should also get a code). The system should still run... right???? at least for your "new record" of 4 minutes. My guess is your ckp is "dynamically bad" (which can't be tested statically) and / or the "missing tooth" on the sprocket has a problem.

One other thing that was mentioned is TPS.... there have been posts about a bad TPS causing a total shut down.... maybe after the system has "warmed up" for a few minutes, it starts to come off "system choke" and "reads" the TPS as being "fully closed" and starts shutting down fuel which starts shutting down the engine until it fails.

added:
I see from further truck cd reading that base timing is 10 BTDC.... I would expect the system to "fail" to this limp mode which should be OK for an "idle plus gas pedal run". My "expectation" is that your system will dies quickly / immediately up pulling your ckp connector which means that your ckp isn't the start of your problem.... but hopefully your testing will / has confirmed this. Good luck