Tach/ignition issues

[Christ]

The ignition module inside the distributor sends the tach signal, right?

I have this issue while driving that the engine will cut out, not a random misfire but actually shut right off, and the tach starts jumping around.

My best guess so far is that it's the wires between the distributor and ECU, but it also seems to be affected moreso by application of the brake pedal.

At times, this happens until the engine will not start, but it still had spark the whole time. When the wires had been shaken around enough, it finally started and ran fine for awhile, but has started this issue again.

[nitrofarm]

Demon possessed tach

For the sake of troubleshooting rule out CPS,Ignition & Coil. You've got spark when it "Hard Failed" correct???
When you said you shook the wires. You should make a note of what wires.That will help us figure it out. Anytime you can wiggle wires and fix an intermittent problem.Thats much better than wigglin wires & NOT getting any results.Your half way home. Next try the one wire wiggle.Seriously.While its running start wiggling single wires.You might get lucky & it'll shut off.
From the outside looking in,sounds like NO FUEL.But I don't know why the tach would jump (thinking out loud) ?

[FestYboy]

you sure of the constant spark? may want to monitor the fuel pressure AND spark via a gauge and spark bulb respectively and report back. if you're having a tach issue i would suspect the ICM. but you describe an issue present with application of the brakes, i would want to verify the fuel pressure.

[nitrofarm]

Festyboy I just saw this....

you sure of the constant spark? may want to monitor the fuel pressure AND spark via a gauge and spark bulb respectively and report back. if you're having a tach issue i would suspect the ICM. but you describe an issue present with application of the brakes, i would want to verify the fuel pressure.

Really? It's just a pair of switches in that big, obnoxious housing?

I was messing about, figured that since there were so many random little issues with my car, I should check this... The last time it wouldn't start, rapidly depressing the throttle would make the tach jump when the key was on. There appears to be no wires affected by the movement of any part of the pedal or linkage/cable, so I piped the cover off the TPS and found that...

How to properly set the adjustment of the tps?

Whata make of this?

[WmWatt]

The brake booster works off engine vacuum. I would check vacuum lines.

Also you can take the ignition control module (ICM) out and get it tested for free at some auto parts stores. Transient stalling is a symptom of a failing ICM. Letting the engine cool down can fix the problem. Playing with stuff while the engine cools may just be misleading. Been there.

[FestYboy]

DO NOT TOUCH the TPS adjustment. if you have a bad one, replace it, but don't adjust it.

[Christ]

The issue was shorting wires in a section of the main harness that the po routed between the (loose) battery and the radiator fan shroud.

When I touched the brakes, the battery would shift into the harness, causing the short.

I'm still trying to figure out why it doesn't DFCO right when you close the throttle all the time, but I haven't actually fixed the bad section of wiring yet, either.

[Christ]

DO NOT TOUCH the TPS adjustment. if you have a bad one, replace it, but don't adjust it.

Why? I've adjusted TPS units on load of cars bc theyre not perfect from the factory, or after doing parts/engine swaps. If anything, the one on the festy should be even easier than any of the others.

[FestYboy]

do you have the factory manual that specificaly says NOT to touch the adjustment? i do... (but then again, it also goes on to give you the feeler gauge measuerment to set the TPMS). you have to remember that the festy TPS is a 3 position switch, not a constant sweep style like most other types.

[Damkid]

I've tweaked with a stock TPS before and it didn't hurt anything..... You don't always have to strictly follow the service manual, if we all did that then no one would do engine swaps and we'd all drive un-modified cars

[FestYboy]

i think at this point, touching the TPS isn't going to do anything but complicate the issue since the TPS has nothing to do with the intermitant issue at hand. that and i have no doubt your were up to something else when tweeking the TPS, Damkid. i'm wodering if this sudden intermitant stall (with spark) is a fuel issue and should be diaged from that perspective. no matter what position the TPS is in, fuel is always available and the car should continue to run provided there is sufficient fuel pressure and spark AND injector control.

[Damkid]

Maybe fuel pump relay acting up? Connecting as it wants to?

[FestYboy]

thinking along those lines, the VAF could be doing the same thing (intermitant actuation of the FP relay).
this is why i suggested that a fuel pressure gauge be installed to monitor the pressure or lack there of when running.

[Damkid]

Probably not a bad idea

[Christ]

None of those things explain the stall under braking, tach fluctuation, or stall under hard left (didn't mention before).

However, moving the wiring harness has mostly fixed the issue. Just need to break the loom and find the shorts.