no start: "I have fuel, spark, and compression"; or, "how I set myself on fire"

[knightpitt]

Well, I'm throwing my post up here because I finally got back to the Ex again. It's been a busy summer, and there's hardly been a week when I haven't wished my Ex was up and running again.

So, I tossed in a new computer and that didn't work.

The red wire at the injectors is reading 12V to chassis ground with key on engine off. And through my digital multimeter, when my wife cranks the truck, I get 6-7V, from pin to pin on the injector harness, which I have no idea what that means. Whatever it does, it wasn't enough to flash my test light.

So, that's where I'm at. I'm going to try to get a CPS and ICM from the wrecker where I got my PCM. Perhaps one of those will help? Beats me!

I'm just hoping to get my truck back on the raod again... it's been a long summer without it!

 

[budwich]

in terms of injectors, power is always there as you determined in your test. The PCM module switches (pulses) the grounds on the injectors. As you found out, the voltage drop across the two leading is something less than 12v. The reason for this of course is that with the lack of ground (nothing switched in), the voltage is basically "floating". It is unlikely that you will be able to see the voltage "happening" as expected (ie. 12v) with a volt meter as the response of the meter is probably too slow. As for your test light, potentially you should see something (pulse of light) but it depends on the filament in the bulb and duty cycle of the pulse but I would have expected you to see something. Not sure if you have access to other vehicles but you should be able to test out your "test setup" (ie. with your test light) to see what happens on a working vehicle... that will give you a "benchmark" and probably help you out a lot.

Added: Check all your grounds going into the PCM... and powers for that matter.

 

[EMG7895]

Check your fuse box under the hood, mine was dieing on bumps in the road, shutting the hood etc. I had a friend man the starter while i moved things around and tracked it to the box, then I took the cover off the bottom and moved the wires one by one. It ended up being some corrosion on the pcm diode.

 

[Josh]

Yep I had the same problem. as far as the motor dying when hitting bumps anyway. Mine was a nasty fuse. I could kill my truck by wiggling the fuses. I used some 2000 grit paper to clean the contacts and no more problems.

 

[knightpitt]

Alright, so I "went to it" this weekend... meaning that I went kind of crazy with trying things out on the truck.

budwich, I liked your idea of trying a different vehicle, but I face the issue that none of my other vehicles are Fords and will thus have different duty cycles, etc... so I'm not sure if it would validate my test setup or not. Instead, I went to the approach of using my "mechanic's stethoscope" on my working vehicle (a VW). I could _definitely_ hear the injectors clicking on the VW and I could _definitely not_ hear the injectors clicking on the Explorer. Hmm.

Anyhow, I went to AutoZone, where they have a tester apparently, and they tested my ICM "OK". They even ran the test about a half dozen times for me and it tested "good" every time. I have to wonder if that tests everything, though?

After talking to the guy there, he said that the "only" thing that could be causing the issue is crank position sensor. So, I bought one of those ($36). It didn't help anything.

So, I started testing wires. All of the wires going to the ICM are good. All of the wires that go the the PCM that I tested (about half of them) are good. (I'm sure that it's getting power and ground -- there are several of each that all checked out) I checked the wires that go to the injectors as well, and they're good. All of the wires that go to the test connectors are also good.

So, I'm at a complete loss. I don't even know what to check or replace anymore!

I'm sure that the PCM is getting power... but I also know that it won't spit out codes to me. However, I have 2 PCMs that are behaving in the same exact way, so I don't think that it's an issue with the PCM itself. I'm really at my wits' end here.

So, here's the issue: PCM not spitting out codes, injectors probably not firing but getting power.

 

[Turdle]

Does that year have a CAMSHAFT position sensor?

It triggers-times the injectors y'know.

 

[knightpitt]

Does that year have a CAMSHAFT position sensor?

It triggers-times the injectors y'know.

Good point. I believe that it does and I'll have to investigate what I can find out about it.... hopefully it is easy to check/replace! I'll let you know the results (hopefully tomorrow!)

 

[Turdle]

Good point. I believe that it does and I'll have to investigate what I can find out about it.... hopefully it is easy to check/replace! I'll let you know the results (hopefully tomorrow!)

You might take the sensor off the shaft, see if the shaft is even rotating.

 

[budwich]

with all the stuff you tried, something is funny. I didn't see a response to people's query on fuses. Make sure you check (that's check with a meter not your eyes) ALL your fuses. I suspect one of them is gone that feeds something critical... cps or a "leg" of you computer which has lots of feeds.

 

[knightpitt]

You might take the sensor off the shaft, see if the shaft is even rotating.

Well, I checked the Camshaft Position Sensor last night and it was reading strong pulses every time that the engine rotated.... something like 5-7V. It took me a little while to find -- all the way on the back of the engine and everything!

Interestingly, though, seeing that working made me want to double-check my Crankshaft Position Sensor -- the new one that I put in. It's about ~760 Ohms across the pins (Haynes says that it should be 2-3kOhms?) and when I back-probed it, I didn't get any voltage pulsing with the cranking... like nothing at all... all that it got was the 1.5V to ground from the computer/ICM (as expected). It seems that possibly the new CPS that I got is bad, so I'm going to return it and see if a new one gives me any pulsing -- I can hope!!

with all the stuff you tried, something is funny. I didn't see a response to people's query on fuses. Make sure you check (that's check with a meter not your eyes) ALL your fuses. I suspect one of them is gone that feeds something critical... cps or a "leg" of you computer which has lots of feeds.

I have checked continuity across all of the fuses in the power distribution box (they have those neat spots on top that make it easy) and they're all good. As for under the dash, those are all supposed to be accessory fuses, so I think I can rule those out... maybe?

 

[EMG7895]

Checking continuity on the top of the fuses doesnt matter in this case for 2 reasons. 1 is that you are only checking if the fuse is good internally, not the holders, wirng etc. that you need to check. And 2 you need to check the relays and the 2 diodes in there also. The fuse box can be removed and disasembled easily to check it out.

 

[knightpitt]

cool, thanks for the advice on that. I'll pull it out if my new CPS doesn't work out (picture me holding my breath).

 

[bulldoser50]

did you ever figure it out my 94 explorer is doing the same thing

 

[Ismael18]

strong cranking but won't start

 

[Sedition]

Don't tell me your still holding your breath? I got the same problem with another car of mine, did you ever figure it out?