RMC

For my '94Z..
When I reach full throttle it stumbles horribly. It's not at any particular rpm. I don't think it's opti related because i had a bad opti not too long ago and it's not feeling the same, plus it's only when I hit completely full throttle... I just replaced the opti recently with a brand new GM unit too a few months ago.

It is definately related to reaching that full throttle position because it's only as soon as I hit all the way. It also seemed to work great earlier today at full throttle.. I broke very loose in second gear. Anyway now, this evening it was terrible at full throttle but otherwise up to that point it runs very very smoothly.

The stumble feel a lot like hitting an MSD rev limiter where half the cylinders cut.

Now I'm wondering are my injectors possibly cutting out at full throttle? Would that cause a similar problem?

I'll scan tomorrow to see if that clears anything up but I'm wondering now what to look for or if anyone has ideas.

I can't figure what it might be, if anyone might know I'll have a run or two tomorrow on datamaster than you can verify with.

My motor has 1.6rr's, headers,cold air intake, exhaust, 3.10's, electric water pump, underdrive pulley.. that's about it for engine enhancements.

Thanks for any help,
Ross

Fastbird93

Have you checked your TPS or your thorttle blades to ensure they are opening all the way??? That's just the first couple of things that popped into my mind.

RMC

Yeah I was wondering if it might be the TPS sensor.

Anyway this morning it was fine again??

But I'm going to keep scanning it and try to get it while it's acting up.

Anyone know the correct voltage for the TPS at full throttle?

Other ideas welcomed.

Thanks,
Ross

Fastbird93

Should be at about 4.50.

My service manual says to look for .3 to .9 at idle, and up to 4.5 at WOT.

Brandon94Z28

clogged up fuel filters can make a car stumble during wot.
Brandon

RMC

I've replaced that fairly recently as well.

It really seems like some sort of fuel delivery problem... so far my best guess is either injectors cutting out under too much load, failing TPS or pump. Also, it seems too random to be fuel filter

95z28 -quicksilver

MIne did the same thing with an arching spark plug wire on the header once......


Chris

RMC

Update:

Just looking at my in-car air fuel gauge as soon as it hits the weird stumble the whole entire range from stoich to lean lights up all at the same time???

So there's definately something weird going on.

I would think just being too lean it would register lean not everything at once...I'm now leaning towards misfire..

Maybe a misfire from arching? What are the symptoms...

when it starts doing this it does feel like an extra cylinder is going off though.

I swear I hope it's not the opti. I just swapped that thing out a few months ago.

This is really annoying.

keep the ideas coming.

Thanks,
Ross

Camaro_Guru16NY

Could it possibly be a bad fuel pump, and is just not delivering enough.



Good Luck.
-JOhn

RMC

Well I think I found the source.

I finally got a decent scan on it.

At 100% throttle I'm only getting 3.8-3.9 volts.

What I didn't know was that I am also getting an intermittent ESC SES.


Would this just require a replacement of both parts and be done!

Ross

speed76demon

my stumble at wot was fuel pump and opti man thats an expensive hesitation for a 94 z28