Electrical issues, need help...

[SoundGuyDave]

Okay guys, I’ve got problems; electrical issues that I’m just not able to track down.

Setup: After my wreck last year, I’ve slowly been fixing the car up as time and funding allow, and am now down to trying to fix the electrical issues, without much more to do before putting it back on track.

The car is a 2006 tub, with stock dash, SJB, PDB and front light harnesses, but with an FR500S chassis harness, 2008 MT engine harness (I think), and a 2008 PCM. The car starts, runs, idles decently, and is a monster at WOT, but is an absolute mess in between. Tune is custom from Modular Depot, and is most likely NOT the issue. At idle and at part throttle, the A/F ratio wanders cyclically from around 11.0 to 15.7, but datalogging reveals that the computer is NOT commanding the mixture change. Under load, the engine loads up and stumbles badly, and some test tunes with locked (huge) amounts of extra fuel do nothing to alleviate the symptoms.
Doing some double-checking for verification purposes, I was checking the pinout on the engine harness, and connector C175E (bottom on the PCM) looks like a 2008 harness, but has no Ford part number on it, just a tag/bar code that reads “K05”, back near the IMRC motor control plug.
Issue two: The one time I had it out on track post-wreck, I had a cooling issue, which may or may not be relevant. Under high load, I was able to get two hard laps at Road America prior to having to pit in to cool the car down. This was with the radiator completely unboxed (no side or top deflectors), so that may be the main cause, but if I shifted at 6K up into fifth (GOD that ratio sucks!), I could keep the temps manageable.
I’m about at my wit’s end with this, and I’m hoping that somebody might be able to come up with an idea or two of what’s going on. Honestly, it sounds like a bad ground in one of the sensor loops, but I went over all the ground connections and they all appear to be clean, tight, and low-resistance.

HELP!!!

 

[kevinatfms]

Dave,
you say it cycles the a/f through the mid range? if so, check to make sure you have full contact at the VCT solenoids. check the terminals for fretting and if need be tighten the connections up and use electrical grease. you could also have MD lock the timing in the tune and see how it acts, it may be low on power but if it does not stumble you may see that something is wrong with your VCT system(sprocket, solenoid, harness)

i dont have the books in front of me so i cant say for sure, but ill check tonight on the connector.

what are the datalogs saying about timing and o2 readings? short term and long term? full advance/retard on both banks? also crank position and TP voltages during the trouble time?

about the cooling issue, new fan? check the fan motor to make sure it isnt dragging. when i totalled my car a few years ago i had issues with the original wreck fan, it would kick on low fine but when the high speed would kick on the fan would drag really bad and cause the car to heat up very quickly. you can take the fan out and power it with a 12v source and see if both high and low speeds function correctly.

also i remember it was a pretty bad wreck, engine wise did you replace the thermostat? sometimes you can knock it around and get the pintle/spring assembly stuck if you jar it enough during an off track excursion.

 

[Sky Render]

Check all ground connections. Disconnect them, clean the connections, and re-torque them. Pay special attention to signal-reference grounds, to include the ground straps on the block, fuel rails, etc.

If you're good with a multimeter, disconnect the battery and EMS and check the continuity and resistance of all ground connections, as well. With the EMS and battery disconnected and removed, check the continuity and resistance of all sensor wires. Verify continuity between the sensor's plug and the pin on the EMS connector.

 

[SoundGuyDave]

Awesome, Kevin, thank you!! I'm heading down to work on the car some more today (cage prep: decontenting the dash harness, scraping noise control and seam sealer, etc.), so I'll check on the connections to the VCT solenoids and test the fan. I'm also going to pull the engine harness next week and do a continuity check on every single flippin' pin, just to verify that it is a 2008 harness.

I don't have a copy of the datalogs, MD's tuner had the car on the dyno at the track, and that's when we found that the car wasn't commanding the A/F changes, but IIRC, it was happening any time the car was in closed loop. As soon as it went open-loop (WOT on the rollers) everything worked fine, and the A/F was bang on target. To me that smells like a sensor feedback issue of some sort.

I think at first, I'll just jump the relays for the fan to test both speeds... that will also test the in-car wiring and the relays themselves as well. I will also order up a new thermostat. Cheap insurance, eh? Yeah, it was a pretty decent wreck, but it's surprising how little real damage was done. Frame was off, but not badly (pulled 6mm out, and 4mm down). After I get it running right again, I'll put it on the rack and check the K-member, but I suspect that I'll be replacing it.

Thanks again, man, and if any other ideas (or things to check) come to mind, don't hesitate to shout out!

 

[SoundGuyDave]

Dusty: posted above while your post was going in! I'm pretty handy with a multimeter, so yes, I have verified the grounds are at or under 0.1 ohms in situ (measured from the ground tab to the battery terminal). I'm still going to pull the engine harness and beep out all the lines (roughly a hundred of them!), but you have a great idea also measuring the resistance of all the ground lines in the harness as well. Thanks, and keep 'em coming!!

My background is as a former ASE Master, as well as currently being an audio engineer... Wiring doesn't scare me, and I'm actually pretty handy with a soldering iron and a meter. My ASE certs are about 20 years out of date, so these "new fangled" electrical systems are kind of a new experience.

 

[Sky Render]

Dusty: posted above while your post was going in! I'm pretty handy with a multimeter, so yes, I have verified the grounds are at or under 0.1 ohms in situ (measured from the ground tab to the battery terminal). I'm still going to pull the engine harness and beep out all the lines (roughly a hundred of them!), but you have a great idea also measuring the resistance of all the ground lines in the harness as well. Thanks, and keep 'em coming!!

My background is as a former ASE Master, as well as currently being an audio engineer... Wiring doesn't scare me, and I'm actually pretty handy with a soldering iron and a meter. My ASE certs are about 20 years out of date, so these "new fangled" electrical systems are kind of a new experience.

I'm an EE; I'm way better at electrical systems than mechanical ones. Make sure you completely REMOVE the battery and EMS before testing signal wires, however. I think you might have a bad sensor connection or wire...

 

[SoundGuyDave]

Oh, no doubt, don't want the DC from the continuity tester hitting the PCM in the wrong spot... For the harness, I was actually planning on pulling it completely off the motor and sitting down at the bench with it. Thanks for the reminder, though!

 

[kevinatfms]

the fact that the car acts up during closed loop would def shoot me to a timing/trigger sensor. if the a/f was in check you can rule out a pinched o2 harness or MAF.
if you need the pin outs i still have a few of the workshop service manuals/evtm manuals and i am pretty sure i have misplaced most of the fr500s stripped harness evtm/wiring diagrams....Fail on my part.

dave you can pm me and we can work out if you need the books in hand, i would be glad to send them to you for however long you need them for. just let me know.

 

[SoundGuyDave]

MUCH appreciated... I bought the 2006 and 2008 wiring manuals, so I have hard copy on all the schematics and connector pinouts. I will admit, though, that I would KILL for a copy of the FR500S harness, though. If there's any way that you could help me find a copy, or point me toward someone that would have it, I would gladly enroll you in the "beer of the month club!" Seriously.

 

[kevinatfms]

haha, ill take you up on the beer of the month offer. let me call a few people and see what i can do.

 

[zquez]

As far as the stumbling problem, are you sure its even electrical at all? My car was stumbling pretty badly a couple weeks ago. Would start, idle, and even drive if you were careful, but give it a little juice and it would fall on its face. Turned out the fuel line from the pump to the top of the hat ruptured. Just a thought.