Lizard928

I doubt it. Dirty injectors will be more linear and will have more issues at lower rpm vs higher rpm like these.

terry gt

Fuel filter ? With that low milage is could be full of water . If not , tell him the car is done , and he should sell it cheep

dprantl

When the problem is happening, what is the readout for TempII on the SharkTuner on both the fuel monitoring and ignition monitoring tabs?

Dan
'91 928GT S/C 475hp/460lb.ft

canuck0199@hotmail.com

I hope these videos work.
Here is the hesitation problem. Sorry about the one under load, I was driving and filming.
It feels a lot like hitting the rev limiter at various rpm's while driving.

Any more suggestions?????

Thanks!!

Steve

the flyin' scotsman

what are the ST II readings when the hesitation occurs?

from the vid it does seem rpm related.

killav

I would inspect the injector harness/wires very carfully. Check for kinks/cracks. Bad spots in general. The resistance will go up at a bad spot as you demand more fuel from the injectors and the voltage is applied over a longer period of time.

Then I would at least have the injectors tested (as Andy mentioned). After reading, you pretty much have done everything else. It's worth a shot.

Lizard928

I inspected the new harness before installing, it was in mint shape.
Problem was there before and after.

I doubt that injectors could cause this.

The car now has new spark leads as well.

canuck0199@hotmail.com

The car revved and pulled perfect when I went out to film the problem.
Then after 15 mins of warm up and driving it started.
It seems to take a bit of time for the interference to build up. I'm assuming it is time related and not engine temp related?

When the hesitation turns from intermittent to fairly steady - popping the car in neutral, turning the ignition off and re-starting the car seems to clear the fault for awhile.

Thanks again!

John Speake

The quick cut/recover suggests either ignition of fuel injector pulses are cutting out, certainly. From the video is sounds as though all cylinders are cutting, rather than 4. Is that how is feels ?

I wouldn't rule out a break in a wire harness, the harness will become more pliable when warmed, more flex more curtting out ?

Is the cutting out any different now with numerous parts changed to how it was originally ? Or just more frequent, or less ?

canuck0199@hotmail.com

[QUOTE=John Speake;9584894]The quick cut/recover suggests either ignition of fuel injector pulses are cutting out, certainly.

I think this is correct.
The wiring harness is new. The cutting out is basically the same, it has maybe improved a bit in the 3000rpm range, it seems the hesitation doesn't start until a little higher in the rpm range. Could be all in my head though.

borland

Have you monitored the fuel regulation? Could be pressure surges. Try Replacing the fuel diaphragm dampers.

John Speake

I see the cut outs are very quick, but do you get the impression that all cylinders are cutting out, or just a few ?

A SharkTuner setup to data log what happens during the cutouts could be very helpful.

canuck0199@hotmail.com

It feels like all cylinders. Very similar feel to the rev limiter.

jcorenman

I assume this is still showing up with higher RPM's in neutral? If so, that makes troubleshooting much simpler.

You've thrown a lot of parts at it, what I would suggest is going back to some basic diagnostics. All the engine needs is air, fuel and spark-- it has to be one of those three (and air is unlikely).

Have you fit a fuel-pressure gauge and watched pressure when it cuts out?

What about a fuel-volume test, has that been done?

(Disconnect the return-line at the top of the tank, connect a hose to extend it to a jug and then jumper the fuel pump for 30 seconds... volume should be 1.25 liters, per factory tech specs. That's a pretty good test, because you are measuring the volume of fuel after it gets pumped up to rail pressure (55 psi), run all the way around the engine and through the regulator, and back to the tank).

And as John mentioned, getting a Sharktuner hooked up and watching that while the engine is cutting out might be very enlightening.

Do you have access to a 'scope? That might be the next step. It would be useful to have a look at injector pulses and ignition waveforms, and also CPS signal waveform-- there is some good info in the WSM on this.

Lizard928

Unfortunately, I couldn't bring all my tools with me.

All cylinders or ign are cutting off. It's not one or two or 4.

My next step I want to do is put it on the dyno w/ sharktuner. As well as an ign moniter to verify as to if it's fuel or ign.