2008 Mercury Mountaineer, 4.0 SOHC, AWD

I am almost at the end of my troubleshooting. Still have a random misfire #2 cylinder at or below 1200 rpm's due to the PCM not sending a pulse signal to the injector. Currently, the last thing I can think of doing is to do a voltage drop test on the injectors ground wires/circuit. I have ordered a book, "2008 Explorer, Mountaineer Wiring Diagrams". I hope this shows the individual pins for the PCM harnesses.

If the ground checks out then I'm stuck! My next course would be a PCM replacement. I have read good and bad about this. Have you done the swap and was there any issues? Is it best to take it to FORD and let them do the swap. They charge $1300 for the PCM compared to other reputable places $300 - $400. BIG price difference and I read on the FoMoCo parts site theirs are remanufactured. It's not like I'm getting a new from factory computer.

Any advice/comments are appreciated!

 

If you had the proper Shop Manual, it would give you a diagnostic sequence to follow to arrive at the problem, unless there is a TSB issued.

The PCM has injector drives which can malfunction. You need to verify the injector first.(ask me how I know).

Save you an awful lot of money and frustration.

Check parts prices @ the online FORD Dealers or if MOTORCRAFT, AMAZON.

 

If you replace the computer, get a junkyard one. I found one on eBay for $18 with free shipping. They rarely go bad, so any used computer most likely works fine. But you'll have to have a Ford dealer reprogram the PATS system. The engine won't start with the new computer until you do that. I would definitely check the wiring integrity before replacing anything though.

 

KULTULZ: I purchased the Ford (08 Explorer/Mountaineer) 2 volume shop manual with the wiring diagram. Just waiting for delivery. This will be a big help!

You say "verify the injectors", do you mean test them? I did, it was one of the fist things I eliminated but will test again to be certain.

If the Injector was bad, COULD/WOULD THIS CAUSE THE PCM TO NOT SEND THE PULSE???


exranger06: This is my first time messing with the PCM so I have asked many questions. My SUV is the "Premier" version and has many electrical gadgets. I've been advised, more than once to get PCM matching or compatible to my OEM part. If I could find part specific in the salvage yard it's worth a try for that price but I will probably go with a unit thats been tested.

Thanx

 

I was having problems and bought another PCM from an ebay site, I provided the VIN number and a couple other things. I received it and it went in without issue. It turned out my other PCM is OK, now I have a spare unit already programmed for my truck.
I'm OK with that.

 

No. The injector being bad would not allow it - ECM - to not operate. The ECM would still send the signal but that particular injector would not open (or close in some instances). Now the ECM/PCM would do the same thing if defective, either not send a signal through the injector drive feature or possibly a continuous signal, holding the injector open and causing smoking.

GOOGLE injector noid light and you really need a EFI pressure gauge (to verify correct rail pressure and volume delivery and leak-down tests).

 

IMO
I do have noid lights. That was my first clue as to what was happening. Problem was, the first time I checked it was one of the random times that it was sending a pulse. I then checked and replaced several things. All seemed to help but not cure the problem. I then started from beginning and this time caught it while it was not sending pulse. I tested it at the connector and at the PCM to eliminate wire problems.

I also have fuel gauge but for some ignorant reason Ford/Mercury did not put a schraidder valve on this SUV. So you have to have special adapter and I decided to skip that test. Thinking if there is no pulse signal it doesn't really matter how much fuel pressure there is.

I have since determined that the PCM gets very hot (too hot to rest my hand on) It's mounted in the engine compartment but the hood was open while the engine was running so a lot hotter than I would expect it to be!

 

...hmmph...

When you get your manuals, can you post a copy of that attachment adapter?

Maybe before replacing the PCM, wait for the manual and follow the diagnostic routine?

 

Wow! My spelling. I meant schrader valve.

A wise, helpful member (shorod) explained, due to no schrader valve I would have to have a "T" splice to connect my gauge to the fuel line. I assume there is a "T" connector that has Ford fittings on it so it could be connected at a splice point instead of having to cut and patch the OEM line. I hope Ford Techs do not cut & splice. I do not know if Ford makes a special connector for fuel pressure testing.

KULTULZ, do you know of any situation that lack of fuel pressure would cause one injector not to pulse? I have not found any info leading me to believe that. I do understand if I skip steps in the testing routine I may miss something.

I believe I did my last diagnostic test. I did a voltage drop test on #1 and #2 injector pulse wires and grounds (wires from PCM to ground, black with yellow tracer) under load. From ground to PCM, from PCM to injector connector (pulse wire) and from ground (blk/ylw) to the injector connector (pulse wire) so the ground goes thru the PCM. It only showed a voltage drop above .6 when it went thru the PCM. Fluctuated but average drop of 1.3 on #2 cylinder.

For now I'm at my knowledge limit! I called Ford dealer and explained situation. I asked if they could test my PCM to determine if the pulse drivers were bad. After putting me on hold to ask the Tech, he replied YES, the Tech could test for that. Tomorrow at 1 he will test my PCM. $100 and hopefully some specific information to help me make a decision about the PCM replacement.

 

There are spring lock quick connectors on the fuel line, similar to what Ford used for fuel filters and the A/C fittings. There is an adapter that more modern "master" fuel injection pressure test kits have that will enable pressure measurements to be made. I think even the Harbor Freight master kit has the correct adapter.

-Rod

 

Thank You!

I will never come across one but just like to keep up.

 

Did you buy the actual SHOP MANUAL for the car or just a Wiring and Vacuum Schematic book? There may also be a TSB on this problem. Ask the tech to check and print if possible. He may also have to update the PCM.

Anyways, the fuel pressure tester is OTC 7293A I believe. Can't find a photo.

Take all of your notes with you and let us know what you find.

 

What is the correct noid light to use on a Ford injector harness?

 

part #310-180 per Ford/Rotunda "fuel injection pressure test adapter" This is the part number Rotunda said would fit. It does not! I believe this is 1/2" line and the line that feeds the injector rail is 3/16" (I believe).

 

My visit with the Ford Tech didn't goes as expected!

As I have replaced a part or potentially eliminated a possible cause of the misfire, I have cleared the DTC codes. Then I drive it until the light comes on and reread the codes. This way I can compare codes to determine if there are any changes. Each of the 8 times (or more) I have done this the scanner comes up with the same thing, misfire #2 cylinder and twice it also said lean bank 1.

Yesterday, I started the SUV and it was stumbling at the start and all the way to the shop. I thought, awesome he will have a good opportunity to diagnose the problem. Keep in mind I specifically wanted him to test the PCM to determine if the pulse drivers are bad. His diagnosis is, Pulse drivers are not bad, it was not misfiring at the time he tested it and his scanner said #1 injector circuit open and lean bank 1. We talked for several minutes about my diagnosis and he didn't really have one and the fact that I had never gotten any code for #1 cylinder and that it had misfired all the way here and now he's not getting one. I walked out dismayed and confused! I started the SUV and MISFIRE!!!! Probably should have walked back in but I was disgusted.