North American Turbocoupe Organization



Help! Electrical issues threatening my Chumpcar Race
BigKeyserSoze Offline
Member
#1
First, this car is supposed to run a 24 hour race with Chumpcar this Saturday. It has to be in the trailer Friday, hence my urgency.

I have some threads elsewhere on this board but an old problem just resurfaced today. In essence, its running on what seems to be 2.5 cylinders.

First, the car has new spark plug wires, new spark plugs (gapped .034) and a new fuel injector wiring harness. It has a new fuel pump and a new fuel filter. I have a fuel pressure gauge on the rail that shows 39psi with the vaccumn line disconnected and plugged.

It idled fine tonight. I took it out for a short boosted run and it dropped a cylinder or two. It did this at my last race as well.

I pulled the intercooler and put my shop-vac hose from the turbo to the throttle body so I could shoot temperatures on the exhaust manifold. When idling, cylinders 1 and 2 were around 400 degrees. cylinder 3 was around 300 degrees, and cylinder 2 was around 200 degrees. The spark plugs looked good but I put new ones in anyhow, same issue.

I have proper plug wire routing. 1-3-4-2

The funny part is, the car will be sitting there idling terrible, then for a split second it runs fine, then it goes back to dropping cylinders.

Cylinder 1 and 2 seem to be fine. Cylinder 4 seems to be dead. I can't figure out why cylinder 3 seems to be half-live.

I have ordered in a new distributor and TFI module, since the problem does seem to be electrical. Any thoughts on whether this will solve the problem. I still can't rationalize out why the distributor would fire cylinder 1 and 2 but not 4, and maybe half of 3. You can't fire half a cylinder, so I'm thinking that maybe 3 is being fired terribly out of timing.

The car has an old cap and rotor on it. I have ordered in a new one, but the car will shock you senseless if you try to pull a wire off when running which makes me think it isn't that. Which reminds me, if you pull the spark plug wire off any of the cylinders, insert an old spark plug and start the car and ground the old plug, you do get spark out of all the cylinders, which would seem to negate it being a bad distributor or TFI, unless those, when they go bad, would make the car run, but badly out of timing.

I didn't check the TPS voltage, because it seems to me that if the TPS was off, all 4 cylinders would be off. If I'm wrong, let me know.

I'm out of time and ideas and need help fast. Any thoughts?
1987 Turbo Coupe
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Joe F Offline
Posting Freak
#2
Just a hunch - check your EEC grounds. They run from the battery negative terminal to the wiring harness on the driver side via a two-prong plug.

Up until a few years ago, ever since my TC was new, I had an intermittent "hiccup" that would come and go for no reason. The engine would drop down in idle RPM and nearly die, then hiccup and recover.

Then a few years ago I replaced the old grungy ground leads, including the main battery ground to the engine block. I also totally removed the plug and hard wired the EEC grounds to the harness. The hiccup disappeared and has not returned since.

Like I said, just a hunch, I have no real data with which to back it up. I do know, though, that if the grounds were flaky, the EEC would very likely be very susceptible to RFI and EMI.
JR's Place - My '87 Turbocoupe
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BigKeyserSoze Offline
Member
#3
Joe:

We gutted all of the car's wiring and rewired everything a while ago. I will check the EEC grounds, which I ground directly out of the EEC to something nice and close. My grounds do not go to where the stock battery is. The battery now rides shotgun in a battery box.
1987 Turbo Coupe
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natmac3 Offline
Administrator
#4
Possible culprits?

Knock sensor acting up? Unplug and try to duplicate...

Eec injector grounds? Try swapping banks (1/3 & 2/4)...

EGR issue? Cyls 3 & 4 are closer to the egr port and would read lower temps if egr was hung open...

Definitely sounds like a frustrating issue.
Intermittent faults are the worst.
1987tc
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BigKeyserSoze Offline
Member
#5
Natmac3: We have no knock sensor. Its disconnected. I will check the EEC injector grounds. I'm assuming the EEC grounds are the pulsing circuitson pin 58 and 59.

Would an EGR cause a miss like this?
1987 Turbo Coupe
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Pete D Offline
Administrator
#6
What brand of plug wires?
Pete Dunham


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Jeff K Offline
Administrator
#7
EEC ground should be a heavy gauge wire (I would use 10 ga) DIRECTLY from pins 40,60 to the batt negative terminal. Grounding 40 and 60 to the chassis near the EEC is a BAD IDEA!!
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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BigKeyserSoze Offline
Member
#8
It was a bad computer. We had to put an old SVO computer in then change the wiring to get the Thunderbird vane air meter to work. It idles and pulls now. Does the 1986 SVO and the 1987 Thunderbird Turbo use the same fuel injectors?
1987 Turbo Coupe
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Pete D Offline
Administrator
#9
Yes, both use brown top injectors
Pete Dunham


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BigKeyserSoze Offline
Member
#10
Thanks everyone. With a little luck we should be ok. Anything I'm forgetting using an SVO computer with a TC engine and TC sensors? As I said, we worked the harness to get the SVO computer to see the TB VAF.
1987 Turbo Coupe
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