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Technical Q&A. HOW TO's, TSB's & Warranty Items Have a Problem? Technical Questions & Answers. HOW TO's & TSB's, Warranty Issues

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Old 07-26-2017, 02:54 PM   #1
Captain Obvious
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Exclamation Need Help with ECU Ground(s)

I've been trying to resolve a spark blowout issue with my rebuilt 2003 Mach1 for longer than I care to admit. Every time I start my car, the dash lights all come on as all of my gauges do a full sweep for 3 to 4 seconds before functioning normally. Given this telltale symptom and my tuner's conclusion that spark blowout is occurring based on my data logs, I'm convinced that my ECU has a very poor ground connection or the ECU itself is damaged.

On a few side notes, I have a brand new Motorcraft battery and can see that my average voltage while driving around is about 13.5. My TR6 plugs are gapped at a tight 0.025", since I'm running a TVS blower with a 2.8" pulley (and stock lower), along with a 9.5:1 CR and stage 3 heads/cams. I've experimented with TR7 iridium plugs and larger gaps along the way, all to no avail. Fuel pressure issues have been ruled out.

While my contributions to this forum are severely lacking, I'd deeply appreciate some definitive answers (or corrections) to a few simple questions:

1. Where does the power supplied to the coil packs ground at? I'm assuming since the coil packs are powered by the coil drivers inside the ECU, the answer is ECU ground.

2. There is a small, short chassis ground wire right next to the ECU box itself. Does this solely constitute ECU ground, if at all? I'm guessing the answer is no.

3. There are two small black ground wires coming out of a pigtail under/near the fuse box, both of which follow along the battery ground cable and ground at the battery. One of these black ground wires also grounds to the chassis along the way. Is this the ECU ground wire I should be concerned with? Or the other? Or both?

Regarding the pigtail referenced in my 3rd question, I did recently find a non-trivial amount of goop and dirt inside which would absolutely compromise conductivity. I'm not sure what got in there, or how. I've yet to get things back together for another test drive after spraying this pigtail to death with electronics cleaner. I do have a replacement ECU on-hand but am still debating whether to throw it in before I hit the road again. Part of me wants to see if this dirty pigtail connection has been the problem all along.

Again, any information or advice offered here will be hugely appreciated.

Here's a picture of my engine, which is probably making less than 100 HP at this point:



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Last edited by Captain Obvious; 07-27-2017 at 12:00 PM.
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Old 08-01-2017, 07:06 PM   #2
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Re: Need Help with ECU Ground(s)

Thanks to DSG2003Mach1, here's the information I'm after, straight from the 2003 Ford Mustang shop manual:



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Old 08-02-2017, 02:25 AM   #3
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Re: Need Help with ECU Ground(s)

Looks like a fun project; motor is clean.... so where's the build log?

Glad you were helped out, folks here are pretty awesome.
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Track Times (bone-stock w/drs):60 ft - 1.90 | 1/8 - 8.67
(100 shot,E85,4:10s,Street tire):60 ft - 1.67 | 1/8 - 7.88
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Old 08-11-2017, 12:34 AM   #4
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Re: Need Help with ECU Ground(s)

I do have a build thread on SVTP, but it hasn't been updated for about 8 months. That's how long I've been trying to solve this WOT problem.

I'm 99.9% sure I finally found the issue: my damned CCRM is plugged in backwards, for sure. So when I go WOT, instead of my A/C clutch power being shut off, the PCM power is. This also explains why my fuel pumps don't timeout under accessory power. I verified all of this by looking at a CCRM wiring diagram, considering it with a backwards connection (i.e. the PCM power relay and A/C clutch power relay are at the far opposite ends, as far as pin connections go).

Once I make more than 20rwhp, which should be very soon, I'll definitely create a thread here to share the build. To understate the matter, it's been quite the journey.
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Old 08-13-2017, 02:17 PM   #5
TKat13
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Re: Need Help with ECU Ground(s)

Is the CCRM not keyed preventing it from being plugged in backwards?
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Darrell
Black '04 Mach 1
Track Times (bone-stock w/drs):60 ft - 1.90 | 1/8 - 8.67
(100 shot,E85,4:10s,Street tire):60 ft - 1.67 | 1/8 - 7.88
New build - 750rwhp; not track tested (yet)
Mods: Build Log
Paint&Body - WickedCustoms in Lewisville, Tx
Tuned by Manny @ HPP
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Old 08-13-2017, 04:54 PM   #6
DSG2003Mach1
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Re: Need Help with ECU Ground(s)

Quote:
Originally Posted by TKat13 View Post
Is the CCRM not keyed preventing it from being plugged in backwards?
That was my thought too but he said the plastic is soft and flexible enough his dad was able to put in backwards. He said he could see it through the hole in the fender well
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Old 08-14-2017, 02:52 PM   #7
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Re: Need Help with ECU Ground(s)

I'm a clown. What I could peek at was misleading. The CCRM pigtail cannot be reversed, as it appeared to be. This was the best, most well-supported, wrong theory I've ever come up with. It would have explained so much. Glad I left the 0.1% open for being unsure.

I did purchase a new CCRM. If my fuel pumps continue to not timeout, I'm going to replace the FPDM.

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Old 08-14-2017, 04:31 PM   #8
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Re: Need Help with ECU Ground(s)

I was completely stunned to think theyd make it possible to do such a thing on something so important. Im sorry to hear that wasnt the issue, it seemed to make a lot of sense.

does the FPDM actual control the timeout on signal to the pump? I have no basis for it but I always just would have thought the FPDM only got a short signal to prime the pump
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