PCM or wiring harness problem?

[mtenderenda]

During the summer time I drove the Marauder over to the mall. On the way there the car starts going crazy, all the lights on the dash light up, and the car just dies. I found the problem to be a 20amp fuse in the engine compartment that is used for the PCM and the fuel injectors. I replaced the fuse and the problem went away for awhile.
Then the Sunday night right before the Hurricane (Sandy), i drove the car to a wedding reception. The car started to show the same symptoms but it got worse. The fuse would pop every 3 mins. Then at the last mile the fuse kept popping everytime I put the car in drive. I had to get the car towed to my home garage. I'm glad that the tow truck driver understood.

So where should I start first? I hate to work on electrical problems.
How does a PCM go bad? :confused:

[Curless]

I would look into what is going on when it stalls...

1. Will it idle in park?
2. Can you rev it up in park?
3. Can you place it into gear (park or reverse) and have it stay running?

[fastblackmerc]

During the summer time I drove the Marauder over to the mall. On the way there the car starts going crazy, all the lights on the dash light up, and the car just dies. I found the problem to be a 20amp fuse in the engine compartment that is used for the PCM and the fuel injectors. I replaced the fuse and the problem went away for awhile.
Then the Sunday night right before the Hurricane (Sandy), i drove the car to a wedding reception. The car started to show the same symptoms but it got worse. The fuse would pop every 3 mins. Then at the last mile the fuse kept popping everytime I put the car in drive. I had to get the car towed to my home garage. I'm glad that the tow truck driver understood.

So where should I start first? I hate to work on electrical problems.
How does a PCM go bad? :confused:
Check the wiring harness behind the left side, aka: drivers side cam cover. The harness may be rubbing on a long bolt from the cowl.

I moved mine out of the way and installed a rubber cap on the bolt.

[Curless]

Good point Fastblack, that was next in my line of thinking, if it stalls when going into gear, what is moving...engine / trans tilting to one side or another due to broken motor mounts or wiring rubbing...

[mtenderenda]

Car can idle. But when I put it in Drive the fuse pops

[Curless]

Check the wiring that Fastblack was talking about...if you have to, unplug the trans harness from the trans and try again, if the fuse pops its not in the trans.

[Mike M]

Yeah it sounds like a harness rub problem. First check where Fast told you to check, if no joy then do a wiggle test. New fuse, car idling and start wiggling harnesses until it pops, keep doing this until you narrow down the harness and fix it.
When you put it in gear the engine shifts it's orientation by about a inch and that is when the electrical contact with ground is probably happening.

[mtenderenda]

Thanks guys. :beer: Ill try it out soon and let you know what I find.

[mtenderenda]

More details about the car. I supercharged the car bout 4 years ago, from Trilogy Motorsports. As for the long bolt, I replaced the long bolt with the knock sensor during the supercharger build.
I had a retune done to the PCM. Because I couldnt pass inspection with the tune that came with the supercharger kit.

[justbob]

Do you have the original Trilogy chip, or the SCT tuner that they started selling in their kits?


Sent from my iPhone using Tapatalk

[mtenderenda]

I have the SCT tuner that came with the Trilogy kit. Then i added a custom tune to the tuner. Thats how i was able to pass New Jersey DMV inspection

[justbob]

Okay, I have an early kit that came with a chip (long gone now, Handheld replaced) but I was gonna suggest corrosion or loose chip, very common with those, but never mind.


Sent from my iPhone using Tapatalk

[mtenderenda]

Im starting to think its the stupid wiring harness issue. I knew exactly where you was going to say next justbob.

[mtenderenda]

Well I proved myself wrong. Today I was able to take the car out of the garage on its own power. I did the wiggle test on the whole wiring harness, even behind the drivers side cylinder head. I was not able to produce the same symptoms.
I even disconnected the harness from the PCM, to examine the pins. I did not see any rust/corrosion or any of the pins bent.
I was able to drive the car in front of the house.
What the hell can it be now, the PCM is going bad? :mad2:
I must of spent about 3 hours under the hood.

[Vortech347]

Easy way to tell if its the PCM. Datalog it. If you get a bunch of 0's and random ****. Its bad.

[mtenderenda]

I decided that the best way to get thru this problem was to drop the car off at the Ford Dealership. They went thru the whole wiring harness, they could NOT find a problem with it.
I had a chat with the tech, he could not find a problem anywhere on the harness. He said that the only problem that he can see now is the PCM.
I put a order in to replace the PCM.

[JBFTech]

I've seen alot of wiring issues "go away" after doing all of the wiggle test stuff, all too easy to jerk the wire away from the problem area and make the problem go away for a week or more. Also, the only true way to make damn sure there isn't a wiring problem, is to actually disassemble the harnesses in all possible pinch points, chafe areas, bends, etc. anywhere there could potentially be a problem, and physically inspect each wire. Ask me how I know! I have seen PCMs cause alot of flaky issues too though, keep us updated.

[mtenderenda]

I talked to the Tech today about what is going on. He ruled out that the transmission or the harness would be the problem. The harness did not show any signs of wear and the transmission is on a different fuse.

He showed me what components are on this fuse: The PCM of course. The MAF sensor, EGR, DPFE and IAC and the fuel injectors.
What he decided to do is to put fuses on each branch of this harness. The PCM has its own fuse. The fuel injectors have their own fuse. And the EGR DPFE IAC and MAF have their own. So if one of these parts go, that fuse will pop, showing me exactly where the problem is.