I have a Strange Miss in my car...

[flightlead404]

No, I haven't just been to a drag queen story hour

Background:
'86 with FrankenCIS controlling mixture via eWUR and FV, controlling ignition via toothed flywheel to Toyota/Denso coil packs.

Its been running like a scalded dog! Pulling like a freight train, starting on a turn of the key, idling (13.8:1 AFR) and running beautifully.

Went out a couple months ago to get gas and warm it up prior to oil change, was getting on it pretty hard but not quite hard enough to trigger RPM limiting (I have ignition retard and spark cut enabled for RPM limiting) nor overboost. Suddenly it started to miss and run rough.

Fast forward, here's what I've done:

• complete new tank of fresh gas
• Oil change
• Valve clearances checked/adjusted
• Checked compressions - all 105-110 (I have SC cams)
• Check leakdown - all cylinders are 1-2%
• New set of NKG BKR8EIX plugs
• Checked for air leaks, replaced some suspicious aged caps on throttle body ports
• Cleaned/oiled air filter
• Verified all fuses good, all relays good
• Verified both fuel pumps running
• Verified all injectors delivering identical fuel
• Hooked up Tuner Studio, verified ignition signal perfect
• Via tuner studio all sensors indicating good (except AFR see below), control pressure in target range

wrt AFR, when started for a couple seconds I see around 13.8 AFR which is what I expect than the indication goes off the scale LEAN.

However, I have observed this behavior before when the mixture is excessively RICH. The AFR senses oxygen in the exhaust gas, and excessively rich will often show as excessively lean. Feel free to correct me if you think I'm nuts.

There's a definite miss, which is constant throughout the rpm range when driving, ie it doesn't get worse or better. There's no major bucking or lugging at any point, its just definitely missing and down on power (still enough power to scare my buddy though lol). Some extra backfire on overrun, but of course it does a lot of than anyway lol

I'm stumped. The only two remaining things I can think to do are:

• I purchased an extra coil pack, will try swapping each one in turn
• Put an old-school timing light on an adapter I made to go between coil pack and plug and see if I can observe anything

Other than that, the only other thing I could think of is make an adapter for the ignition harness/coil pack and hook up one of my silly scopes and see if I can observe anything odd.

What have I missed? I would be VERY hard pressed to think there's anything mechanically wrong with the engine itself at this point, my feeling is it is spark related.

[Noah930]

Dizzy/plug wires? Unlikely to be fuel filter, but I didn't see you mention changing it. Coils, but it looks like that's your next item to check.

I actually did go my first drag queen story time last week. I was on vacation in Provincetown and hey, when in Rome, right? Well, to some degree at least.

[flightlead404]

Originally Posted by Noah930

Dizzy/plug wires? Unlikely to be fuel filter, but I didn't see you mention changing it. Coils, but it looks like that's your next item to check.

I actually did go my first drag queen story time last week. I was on vacation in Provincetown and hey, when in Rome, right? Well, to some degree at least.

no dizzy, 60-2 flywheel and electronic pickup

I thought about fuel filter, but its only got a couple thousand miles on it and I'm delivering fuel. Also, I'm pretty sure I'm way rich, not lean. Although the AFR gauge isn't much help as way rich shows as way lean lol

One thing to add to the background, car had set for around 6 months with little fuel in the tank and I was about 1 mile into my trip to the gas station. Maybe its gas related, but I put in a full tank of fresh.

p-town can be fun, used to spend a lot of time in Chatham (and the chatham squire if that's still there).

Went to a good one in Key West over the winter, lots of fun

[flightlead404]

Well looks like it might simply be a bad crimp on the coil plug cylinder #1. I was wiggling plug wires and it just slid out.

Now to fix.

[macronbill]

You didn't mention fuel filter.. might be the problem