In reply to Pete Gossett :
No, and honestly it would be REALLY rough to do- the turbo and header are right where I need to be to get the tester in there. I can use a welding blanket or something I guess. You thinking valvetrain? It still seems unlikely that it would jump around to different cylinders. For what it's worth, the previous engine had less of a misfire when one of the cam lobes was completely flattened after racing with nearly zero oil pressure.
Distributor looks good, and this failure profile doesn't look like what it does when the gear or bushings are taking a dump- that misfire doesn't go away until you replace the thing, hot or cold.
Are you using low impedance injectors?
In reply to ¯\_(ツ)_/¯ :
I’m just thinking of what could be heat-related problems, since you said it cleared up after it cooled down. Like a head gasket failure that only presents its self at extreme limits, or maybe a valve/seat/lifter issue?
Is the ECU underhood? Could turbo/exhaust heat be causing vapor-lock? Do you have/have you tried water/meth-injection and/or an intercooler sprayer?
In reply to Pete Gossett :
ECU is in the passenger area and doesn't get hot. Head gasket I wouldn't expect to be a roving issue, or a dead miss on that cylinder. Valvetrain stuff is a possibility, although the top end noise doesn't seem to change.
If vapor lock is a possibility, how do I test? Would it clear up in a hurry if I could cool the injectors faster? That I can test.
remove 2.3t replace with 302. that should fix your issues
In reply to ¯\_(ツ)_/¯ :
If you can test that easily I’d do it just to see if it makes a difference. Typically it would be due to too much heat in the fuel lines though. Maybe the next time it occurs check the injectors & fuel lines with an IR thermometer & see how hot they are?
¯\_(ツ)_/¯ said:
In reply to Pete Gossett :
If vapor lock is a possibility, how do I test? Would it clear up in a hurry if I could cool the injectors faster? That I can test.
Test that by making holes in the hood? 
Honestly I never knew vapor lock was a possibility in a FI system.
My '88 Impulse Turbo had a tiny little injector cooling fan and associated ducting for (presumably) this reason so I'm willing to entertain the idea that another turbo E36 M3pile from the same era could have a similar issue.
Looks like 6.4 powerstroke ford use fuel coolers as do r35 gtr's. seems like it could be an option for you.
Here's another thought- as far as I can tell, this issue only occurs after lots of swings from full vacuum to full boost. Is this when the injectors are working the hardest? It's certainly the biggest spike in fuel pressure.
Swings from full vacuum to full boost are when the fuel pump is working the hardest which would cause a fuel temperature spike. Fuel coolers are cheap (since they're the same as auto trans/PS coolers) and easy to add on the return line.
Also I have to see this Impulse Turbo injector air cooling system 
In reply to GameboyRMH :
The snorkus and duct running from the fender to the firewall in this picture, blowing in between the intake manifold and the head to reach the injectors:
GPz11
Reader
5/14/19 9:23 a.m.
Not sure if I missed it or not but do you have another wiring harness for the injectors to try out?
In reply to GPz11 :
Yes, that is one of the things I've changed. I may also replace the connector on the main harness, or at least the pins.
GPz11
Reader
5/14/19 9:31 a.m.
How about tossing the Megasquirt back on the car?
That would say if it was a ECU issue or something else.
In reply to GPz11 :
It's running a different ECU now than when all of this started! The MS was sold a while ago otherwise I'd be giving it a shot.
¯\_(ツ)_/¯ said:
In reply to bentwrench :
Yes.
Pretty sure low impedance injectors need resistors.
In reply to bentwrench :
If that's the case either Ford didn't know that, or I can't figure out where they put them.
I have had injector resistor failure on my X1/9. The resistors are somewhere within the harness, I.E. a piece of resistor wire. I never did find the actual resistor, but made a new harness with my own resistors at the processor end. Fixed the car. Make up a duplicate harness and install it parallel to the original. Remove the original when you are confident of the repair.
¯\_(ツ)_/¯ said:
In reply to bentwrench :
If that's the case either Ford didn't know that, or I can't figure out where they put them.
Ford didn't berk around with resistors, they pulsewidth modulated the injectors, like should be done. That is why they are called Peak and Hold injectors. Computer runs the full 4a current to slam the injector open, then steps it down to 1.5a current to keep it open. It's not just a clever name
I'd want a scope and an amp clamp to make sure the computer is actually dropping current and not slamming 4a through them all the time.
That's the only thing I can think of that would spoil an injector electrically.
Most OEMs that used low impedance injectors, used resistors.
Look up the year and model of your ECU, and then cross reference the injector used with that ECU, then look up the data on that injector number.
Your back of the napkin drawing showed the injectors grounded. Not so. X19 also mentioned it. The injectors get a constant 12v or so, and the ECU switches the ground side of the circuit, so I would definitely check the ECU ground wires. I don't think an injector would heat up and saturate with a bad ground, just the opposite. Maybe it isn't quite getting peak voltage to trigger due to a bad ground, so it just buzzes and cooks?
Maybe a failing fuel pressure regulator not holding enough pressure on the rail causing the starved injector to overheat? Far-fetched. Are you measuring the fuel pressure in real time or just doing a test from cold? I'd be curious to know fuel pressure on the rail when it starts to run poorly.
In reply to BrianC72gt :
The hand-drawn sketch was mine, and is not correct. I was trying to get my head around the batch fire operation in order to understand what was happening electrically.
Drove again, failed much faster this time. Cat is glowing, do we think symptom or cause of the misfire? Car still made boost.
