I have a 96 Explorer, v6 4.0, in fact not long ago we had to replace the engine-so it has 106k on this one versus 267k on the old one--of course everything but the engine has 267k on it. It has new plugs, wires, oil change, fuel filter, fuel pump relay, pcm relay, the 02 sensors and cat were done 60k ago. Even before we swapped the engines, once in awhile for no reason she'd just die--maybe 3 times in 3 years--we chalked that up to the 02 sensors and replaced them. Our last trip to Oregon, I would be in cruise control doing 50-60mph and she would stall--not die just stall until I floored the gas and she would pick back up and be normal for 100 miles or so. That's when we replaced the fuel filter, and then the engine crapped out so we replaced that too. Now that last few weeks at low idle and only occasionally she'll die, but will restart right away, even if she dies again immediately after a few restarts she'll stay running just great for 100 mile or so and then out of the blue, drop the idle and die within seconds. Today she died and will not restart, just crank and crank til the battery dies too. I came here and searched and ruled out the PCM Relay, Fuel Pump Relay (replaced it) and Fuel Pump Shut-off Switch. I hear a very quiet buzz when the key is turned to on and I am by the fuel tank. I looked back through all my reciepts on repairs and 35k ago we had the same problem--now at the time the shop said it was the fuel module inside the tank that went bad $600 later she was fine--but in my parts list on that reciept it says "fuel module", and in the Labor decription it states "remove and replace fuel pump and in tank filter"---Is a fuel module just another way of saying fuel pump or are they different? Anything else I should be checking--and pardon this dumb question--but if she's cranking, thats proof of spark isn't it? or is that just proof the battery isn't dead? All help is welcome and appreciated, I reallt tried to search and rule out everything possible before posting, but I am still at a dead end. Thanks!

 

Fuel module, fuel pump assembly, whatever is a generality for the complete in-tank assembly that consists of the fuel pump, pick-up tube and strainer, along with the float and sending unit for the gague. Now for some of the others.

Cranking is NOT proof of spark. To prove that, you need to verify spark at the plugs thru the wires.
How did you manage to rule out the PCM relay? Did you change it out or swap it with one of the others?
Your symptoms of random cut offs would be very consistant with a weak PCM relay, contact problems at wire connectors on one or several of the engine sensors, or even a flakey sensor itself.

At this point, since the spark function is integrated into the PCM, I would inspect/suspect (assuming you really do NOT have a fuel related problems)
1. no PCM power thru relay
2 Bad coil pack / wire connectors
3. Bad PCM
4. Other sensors on engine

 

Hi there, I ruled out the PCM by swapping it with the new Fuel Pump Relay, since it didn't start after replacing the FPR I figured the old one is probably fine, and it still didn't start. I'll check for spark in the morning and get back here on that one, you know the longer I thought about that question (crank equals spark ) I realized how lame my question was lol. Thanks for the guidance.

After pondering these other options awhile, I remembered that before the engine swap we were getting a p0420 code coming up at Autozone--catylist inefficiency or something like that, but it was just replaced along with the 02's 60k ago. After the engine swap the check engine light stayed off for about a week even if she died--but of course it came back on about 4 days ago and I hadn't had time to get the codes pulled again---could the p0420 cause any of this?

 

AHHAAA! No spark from plugs, I tested one on each side, woohoo! it's not the pump!.....Now I guess I check the coil right? I'm headed to autozone website to find a picture of it, can you give a bit of direction where it is located? Originally I thought--follow the seventh plug wire off the distributor (like my old truck) and it'll lead me right to it, but there is only 6 plug wires and of course all those go to plugs. We're narrowing it down.

 

Not sure about your location of the coil pack, but on my 91 it was mounted on the top of the engine, passenger side towards the rear of the engine. It is a rectangular "brick" that has a 6 spark plug wires comming out the top at a right angle. It had an oval shaped 4 wire connector harness that controled it.
These 4 wires are
1. 12 Volts DC to power the module
2. 3 leads pulsed to ground by the PCM (or ICM in my case) that fire the coil segments. One thing to keep in mind, is that 2 mating cylinders are fired together. One is on the power stroke and it's mate is on the exhaust stroke. This is called a wasted spark system.
With the key on, verify standing 12 volts on the coil pack connector first. On my 91, this same 12 volts also fed many of the engine sensors that used 12 VDC and also the injectors. If it is missing, a whole host of stuff won't work.
Dialtone

 

LOL I have everywhere under the hood today and it was right there staring at me Alright, I'm not great with testers but the battery is at full charge, and when I put the needle right in along side each one of those 4 wires (1 red and 3 yellow) with the key on they each read exactly the same as the battery does with the key off. I was really hoping it would be the coil but only because it looks fairly easy to fix lol. What would you suggest next?


Wait I'm confused, how can I have no spark at the plugs, but plenty at the coil?

 

Oh my, I am so sorry, I have got to be the having the dumbest day of ....well of atleast this week. I got it all backwards when I tested for spark on the plugs this morning--see I pulled the boot, put screwdriver at the end of the plug and said "start it"! Totally backwards on my reasoning as to where the power comes from.

Now that I've learned all day long how to test everything electrical and everything tests fine lol. I guess it is a fuel problem--only test on fuel today was key on and press the schrader valve on top (looks like tire valve) and gas squirted out about 1 1/2 inches and then quit. Like I said originally the pump was replaced about 35k ago, I replaced the fuel pump relay last night, swapped the pcm relay with a working relay and nothing changed. Now that I'm back at square one......what do I look at next? Once again really sorry for being a complete ignoramous this morning.

 

Well, you certainly have me confused with your terminology. What was the reading on the coil pack wire harness? Did you get 12 volts or not.
If so, then proceed to check the 3 yellow leads while cranking the engine over. You should see them drop to 0 volts momentarily if the PCM is pulsing the coil pack to fire the plugs. If not, then the PCM is not working correctly and I would VERIFY power to the PCM thru the PCM power relay. Just because you swapped it does not mean it is working and sending power to the PCM.
If you do not have one, I suggest getting a Haynes manual to consult the wiring charts for wire colors to test. Looks like you definately have an electrical problem as you stated you do have fuel under pressure at the fuel rail check valve.
Dialtone

 

OK, yes I got 12 volts from from the coil with the key in on position. I tested each yellow wire while cranking the engine and my tester did exactly what you said it would--drop to zero briefly and then back up. I really appreciate you taking the time to walk me through all these steps, I really want to be able to track down the problem and fix it, there's a certain sense of accomplishment that goes with it, plus I can stop driving the "borrowed car".

 

OK...now we are getting somewhere. With what you described, the coil "should" be firing to the spark plugs. Re-test again for fire at the end of the spark plug leads with a screwdriver stuck into the lead end to ground on the block jumping about 1/8 inch, with a bright blue spark. If no then the coil pak is bad. Replace and re-test for spark.
Dialtone

 

Small step forward today. I retested for spark like you said, and I got spark but no blue spark, so I replaced the ignition coil and retested for spark, now I get blue spark but she isn't starting --just cranking. What's next?

 

At this point, all that is needed is spark, fuel and air.
You need to re-verify you have pressurized fuel at the fuel rails. Really need a fuel pressure tester to see if pressure is around 40-45 PSI when cranking.
If so, then with your meter, verify the injectors all have 1 lead standing at +12 volts dc and the other lead is pulsed to ground by the PCM while cranking, just like the coil pack leads did.
If this all works OK, only other things that may keep it from firing off are the crank position sensor and/or cam position sensor, but I think it would at least cough once in a while anyway.
Crank and cam sensors are used to synchronize the injector pulses, so one of them may well be at fault if you get no injector pulses.

Dialtone

 

I can come up with a fuel pressure tester tomorrow, but as for verifying 12v on each injector lead--I'm not sure I understand what you mean by "injector lead"--I imagine I am making this term seem more difficult by over thinking it, but if you could explain it'd be handy

 

Each injector has a 2 wire connector pluged into it. 1 of the wires has 12 volts standing there with the key on. The other also reads 12 volts thru the injector coil, but is pulsed to ground by the PCM to open the injector when the engine is cranked or running.
Check for the standing voltage on 1 lead and the ground pulse on the other while cranking the engine.
Dialtone

 

oh oh oh! I got it, I saw those lol In fact I tested 3 of them today (just messing around)with just the key on (my seven year old couldn't crank it for me) I couldn't get a read off any of those three. I also tried testing the wires going into my alternator just for the heck of it, and the green one pulses with the key on, but the others showed nothing. Like I said i'll track down a fuel pressure tester tomorrow and check that too.