motor stumbles after it warms up

[fixkick]

88 1/2 Samurai that has been converted to EFI with a 89/90 ECU and wiring harness.
but what was the donor car?
Is it TBI EFI?


Starts perfect and idles great.
Idles down after a few minutes fine.
Runs and drives great until it gets hot.
Then it starts to stutter sporadically at highway speeds and sometimes (rarely) will backfire when you let off of the accelerator.
what is compression, WOT, at wide open throttle.?

It has died several times when pulling up to a stop sign and when taking off easy.
To restart it takes several seconds of turning it over and when it finally starts it acts flooded. Does WOT cranking clear the flood,? all EFI does that, its feature to cut fuel, cranked.

It never dies if I rev it up a bit on take off. My wife commented on the smell of fuel when we were tooling around in it with the top off.
Ok sounds like rich misfire. is the CEL lamp glowing key on, it must then go out running? i guess spark tips are black.?


My first thought was either fuel pump or regulator.
Put a fuel pressure gauge on the banjo fitting come off of the fuel filter and started the motor.
Pressure stayed a constant 40 psi. (good for sealevel, spec)
Pinched off the return line for just a few seconds and the pump fluttered between 75-80 psi.
No fuel leak from the regulator vacuum nipple.
Allowed the motor to get hot and start to miss sporadically while setting in the driveway.
Watched the fuel pressure while it was stuttering and it didn't fluctuate the needle even a little bit.
So I'm confident in the fuel pump. New plugs, cap, rotor, coil. (2 wire or 3 wire low voltage connector ?on distributor., wish new donor car)
I'm I right in assuming since the problem occurs after it is up to temperature that it isn't likely anything to do with IAC, dash pot, etc?
the ECU uses a map , so air leaks all cause racing with perfect mix. Jeep like. same.


I'm almost positive that the TPS is not calibrated correctly since it has been moved. I marked it before I moved it but I only marked one side and it moves on both sides. ECU was rebuilt a few weeks ago by Speedometer Repair Guy in Winona, MN.
Connected and disconnected the vacuum advance and it doesn't make a difference that I can detect.
I'm 80% fabricator and 20% mechanic so any help would be appreciated.
Also, FIXKICK refers to adjusting "duty cycle" but for the life of me I can't figure out what he is referring to.
yes that is me, the suzuki uses those exact words, as do all PWM modulation schemes..
The ECU controls idle speeds at all times, (using electric solenoid ISC) and modulates it PWM way, and 50% duty, is perfect.
50% means it can speedup 50 and slow 50, and not run out of air. at ISC. it modulates 200 times a second to do that,
my jeep uses stepper motors and are different.
So whats missing now. after the swap, EGR? CAT, other things?

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Forgot to mention that the fuel pressure immediately drops to zero after the motor is shut off. Does not hold any residual pressure in the lines.
That is 1 of 3 things.,
1; injector leaks.
2: FPR leaks.
3: tank check ball leaks.

if you pinch return get 60psi, as most do yours is healthy, and then cut engine, and keep it pinched if it still leaks down , its not the FPR leaking , cuz line pinched, so is injector , or the tank check ball.
to prove ball ok, then just lift off TBI air horn, cut key (2nd person) if injector leaks, key off, bingo, bad injector. and not tank ball.
the key must cut injector at speed of light, well near there. 3/1000th of a second.

cheers to you and welcome!!