91' FJ80 Ignition Coil Heat Soak - Extending Coil Wire

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andersonoverland

andersonoverland

Joined
Nov 18, 2024
Threads
24
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101
Location
Lake Havasu, Arizona
Hey dudes. So I've been chasing this random rough start issue with my truck and I have replaced pretty much everything I can think of including everything per mechanics and chatgpt options and have narrowed it down to either the water temp sensor on the thermo housing (which is brand new) or the ignition coil getting hot and causing spark issues due to heat soak after driving for a period of time.

This happens so randomly and the truck starts perfectly every time. I'm just marking things off my list that it could be and this is my next one.........reposition the ignition coil to a different spot and check grounds. That being said, has anyone ever extended a coil wire and is there any recommended ways to do it? I am thinking of relocating my ignition coil to a cooler spot. Or does anyone know where to buy a longer wire that fits from the distro to the ignition coil since mine has this weird clip connector to the coil? Also going to check all grounds to coil, battery, and intake manifold.

Things I've done so far to attempt to fix this:
New injectors
New fuel filter and complete pump assembly
Fuel regulator
Spark plugs
Distributor
Wrapped EFI relay wires and relocated in the cab
Cold injector replacement
Throttle body cleaned
IAC valve replaced
TPS replaced and re-clocked
New Fusible link
MAF switched out
MAF plug rewired with new clean wiring harness
Throttle cable and trans cable checked and adjusted
Valves adjusted
Timing checked
Vacuum hoses replaced and entire system checked for leaks
Leak down test
Compression test
Combustible gas intrusion test
Head gasket checked for leaks
PCV valve
Rebuilt thermostat housing with all new sensors
New waterpump
New charcoal canister and hoses
O2 sensors replaced

Any ideas would be helpful. The other night she almost didn't start. Had to do the ECU reset with the key on/off method. It finally turned over and then ran great! When its cold, it fires and idles perfectly every time. I just can't track down this heat soak type restart after she gets warmed up randomly. Sometime after hot it starts right up. It's weird, but my girl is losing confidence in the reliability due to this random starting issue.

Thanks so much for you time reading this!

Joey
 
During a no start does the CEL illuminate with the key in the ON/RUN position BEFORE cranking the starter? NO CEL=NO START
Stop using Chat GPT to diagnose things on a 35 year old vehicle. There is no such thing as an ECU reset with key on/off. All that's doing is exercising the ignition tumblers.
Easiest way to reset the ECU is to pull the 15 amp EFI fuse for a few minutes.
 
Last edited:
jonheld said:
Stop using Chat GPT to diagnose things
Click to expand...
100%

@andersonoverland
Might help to know specifically what year we're looking at. My coil on my 96 isn't really in a spot I think of as excessively hot - on the opposite side of the engine from the exhaust.

Also, what do you mean by "rough start"? My first thought for that phrase would be, it cranks fine but sputters and doesn't want to fire. Is that what we're talking about?
 
It fires but it acts like its starving for fuel or something at times when it's hot. And no CEL light at any time.

like it fires and the needles bounces around under 1000 rpms like its trying to start but if just doesn't want to. Wish I had video.

But yeah the ignition coil is on the opposite side of the intake manifold. Its a 1991 3FE.
 
andersonoverland said:
And no CEL light at any time.
Click to expand...
I'll ask again. In a NO-START situation with the key in the ON/RUN position BEFORE CRANKING THE STARTER is the CEL illuminated???
CEL on BEFORE CRANKING THE STARTER is telling you that the ECU is in a "ready state". All systems go.

I'm also questioning where you sourced the parts that you said you replaced. Some of those have been out of production for 15 years.
Additionally, the Toyota FSM has tests for these parts that should have been performed prior to replacement to verify functionality.
 
Last edited:
jonheld said:
I'll ask again. In a NO-START situation with the key in the ON/RUN position BEFORE CRANKING THE STARTER is the CEL illuminated???
CEL on BEFORE CRANKING THE STARTER is telling you that the ECU is in a "ready state". All systems go.

I'm also questioning where you sourced the parts that you said you replaced. Some of those have been out of production for 15 years.
Additionally, the Toyota FSM has tests for these parts that should have been performed prior to replacement to verify functionality.
Click to expand...

I sourced them all OEM from Japan and some here in the USA. Some were like new condition and thoroughly cleaned prior to re-install with the same result. I can't recall the CEL being on as I stated above. I will check that again when it does it again. Like I said, it's very random and does it very rarely, but enough to annoy and worry me.
 
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