stumble/miss issue with my car

[Jeff88coupe]

Trying to figure out what is causing a strange stumble/miss issue with my car while going down the track.
-It only happens when I'm spraying a 150 or 175 shot...doesn't do it on a N/A or 100 shot pass (going to t&t this week to double check this).
-doesn't do it at the same rpm or gear everytime....usually at the top of 1st...but also did it in 2nd gear this weekend. When it was doing it at the top of first gear...i'd just short shift to 2nd and it would clear up. When it does it it just lays over some...doesn't pop or bang..just doesn't pull like normal...but will usually clear up. It doesn't do it the whole pass or even a whole gear usually.

My combo is in my sig...but it is a 10.8:1 347 that I run on E85 with a NX efi wet plate kit. Run autolight 3923 plugs gapped at .028. I leave on the nitrous off the transbrake at ~4K and shift at 6800. I run a stock A9P computer with a SCT chip for my tune. I pull timing at the distributer for the nitrous.

I have switched the following parts...no fix. Swapped from a 6al to a digial 6, upgraded to a msd 6 series coil, swapped from a msd pro billet distributer back to a good stock tfi distributer, put new msd wires on, swapped plugs many times, rebuilt my NOS solinoid.
I just running out of ideas of things to look at and check. I'm running in a 6.50 index 1/8th mile class at OSM this season for points. I have to spray a 150 to 175 shot to run the number....but with this issue I can't get the car to run the number.

Anyone have any ideas?

[Mongoose]

Fuel pump, regulator or filter?

[chad393na]

Have you tried locking the timing(set it and leave the spout out)? I have had a lot of issues with the computer controlling the timing on my car, even with swapping to another A9L. I started locking the timing(26 deg. with 150 shot), and the problem disappeared. Good luck with it.

[Jeff88coupe]

Fuel pump, regulator or filter?


Fuel pressure is rock solid the whole pass.....I've have a gauge on the cowl that I can look at going down the track. I run a A1000 pump which can supply way more fuel than what my motor can use.

[Jeff88coupe]

Have you tried locking the timing(set it and leave the spout out)? I have had a lot of issues with the computer controlling the timing on my car, even with swapping to another A9L. I started locking the timing(26 deg. with 150 shot), and the problem disappeared. Good luck with it.

Yes...I've tried locking the timing out. Set the total timing at 25....car stumbled the whole pass in all 3 gears. It felt so bad that I lifted at the 1/8th and aborted the pass.

[MFIELD]

Jeff you checked the fuel? Any water?

[89notch]

Jeff is your car tuned to run NA and your just pulling timing from that tune? Or do you have a nitrous tune also?

[mustangboy]

I say just run the 7.50 class:tongue2:

[chad393na]

Yes...I've tried locking the timing out. Set the total timing at 25....car stumbled the whole pass in all 3 gears. It felt so bad that I lifted at the 1/8th and aborted the pass.

That's not right. Have you watched the timing on the balancer while reving it to see if it is steady? I've seen the cam plate wear a groove in it and this will cause timing to go nuts. This usually happens when someone runs a billet t.set with a cast iron plate instead of the steel plate.

[Jeff88coupe]

Jeff you checked the fuel? Any water?

No I haven't....going to go get some fresh fuel before I go to edgewater friday night. Will try testing what I have in the tank for water this week...gotta look up how to do that test.

[Jeff88coupe]

Jeff is your car tuned to run NA and your just pulling timing from that tune? Or do you have a nitrous tune also?


I have a n/a and 100 shot nitrous tune in my SCT chip. Both are the same except that the nitrous tune has 4 degrees less total timing.

[Jeff88coupe]

That's not right. Have you watched the timing on the balancer while reving it to see if it is steady? I've seen the cam plate wear a groove in it and this will cause timing to go nuts. This usually happens when someone runs a billet t.set with a cast iron plate instead of the steel plate.

I haven't checked that...but I will this week. But my issue is that the car doesn't do it when running n/a or on a small shot.
Gonna go to edgewater fri night to double check that.

[Jeff88coupe]

bug is still there....ran 6 passes on a 175 shot tonight...it stumbled every pass. Doesn't do it on a na or 100 shot pass...just 150+.

[kennebellcobra]

You ever thought about doing a tune on regular race gas to eliminate the E-85 as the problem?

[Sharad]

arcing inside the distributor cap?

worn out distributor gear?

electrical interference on the TFI harness on top of the intake manifold? (that one kept me from running NMRA R/S in 2003.



Can you take it to Cincy Speed and check the AFR during a 175 shot AND maybe use a laser thermometer on each header tube to verify the cylinders are firing evenly?


Where is the nitrous nozzle located?

[RACEME]

Is there a way to test the octane rating of your corn fuel? Are you able to switch over to regular race gas for a couple passes?