[ejw]

New prob w/ car. Have had this happen before a few weeks ago, but know happens every pass. While pulling out of burnout car stumbles and dies and then i have to refire (starts right up). Car runs 1/8th mile okay (though i have been trying to figure an ongoing loss of power issue which i figure is part of burnout/top end probs - loss of 3-5 mph and 2 tenths in 1/8). Today i was in a 1/4 mile race and on top end pass 1000ft car began to stumble/pop (almost likeon rev limiter, though i was only around 5500 rpm). Does not happen 1-2/2-3 shifts which happen around 5800.
I have been fighting ongoing issues past month(tach causing 2 step/electronic shifter to act up and yesterday while loading up car it would die after a few minutes swapped out coil and fixed prob
I only have fuel presure gauge in engine compartment set 8psi and in pits, car revs fine and gauge remains steady, though i know that has nothing to do w/ car under load.
I also just put new plugs/wires/cap and installed MSD RFI filter

any help. i am at my limit after 2 weeks of probs -nice way to end year at track

[Chupa]

Sounds like fuel pressure.

Get a gauge on it during a pass

[RAIV55]

Is that 8 lbs at the needle and seat??? First thing I'd adjust that, check the float level and go from there.

I'm thinking fuel problem.

[ejw]

i have a small fuel pressure gauge at regulator

[ejw]

checked bowl levels good. figured 8lbs at idle about as much as i want to set it at. whether 7 or 8 psi no change. I did have a fuel pressure variation i noticed when revved (about 1 month ago) and i changed out BG fuel fillter w/ paper element before pump to an inline jegs filter w/ stainless filter (before pump) and pressure drop when rev engine disappeared

[67cruiser]

CHOKE PULL-OFF???

[lugnutt]

Mine used to do that, it was lack of fuel. I installed a mechanical gauge on the hood temporarily. It was dropping on the top end. Increased fuel hose diameter, and changed filter.
Another idea. What about the float bowl vent? Make sure nothing is plugging it up!

[ejw]

i just flushed system, checked filter and ran pump w/ fuel line into gas can for 2 gals. twice and timed it, both times pump sounded fine and pumped a gal in less than 20 sec. i have used same fuel line diameter for yrs w combo (10an to pump, 8 an to reg and 6 an to each bowl) and gone 10.70s w/ combo.
I have a fuel pump switch on dash that is up for on w/ ignition, middle off and down momentary on. I tested pump in momentary position. I am wondering if something off in switch or i also have it run through an oil pressure switch to shutoff if pressure goes low. wondering if either of those is failing. I use a relay mounted in trunk and don't notice pump hesitating.
Has only happened under load.
heading to track fri w/ fuel press gauge. i was hoping running pump at house today would show something

[67cruiser]

Tell us about your fuel tank set up??? After i sumped my stock tank(Thanks to Cliff) car runs like a animal. Maybe your not getting fuel on full acceleration.???

[wrench]

I had the same thing happen. Ended up being a junk fuel pressure gauge I had mounted on the regulator. I used my Snap-on gauge and tested fuel pressure during actual driving conditions to figure it out . I think that should be your starting point.

[Brian Baker]

Gonna' need a mechanical pressure gauge to monitor what is going on when the problem rises...but...keep in mind that 7-psi of nothing is still nothing.

Pumping a gallon in 20 seconds while remaining static is one thing...doing it under the G-forces associated with lateral acceleration is another. Given everything else you have gone through, it would not surprise me if the electric pump is starting to "go away" and can't keep up with the demand under load and lateral G's from acceleration.

[fasteddy]

Tell us about your carburetor. Is this a Holley? Do you have jet extensions? Did one of them fall off?

[Blued and Painted]

Originally Posted by ejw

and on top end pass 1000ft car began to stumble/pop

A pop is almost always a super lean condition--------------or late Ig timing.

[ejw]

carb is 975cfm race demon, i took off bowls to check and everything looks where its supposed tor be w/ jet extensions. i was hoping to hear pump stumble, but i tied pump 2 gal twice and ran strong both times. I did find a loose connection at oil pressure switch (tied in to fuel pump to kill it if pressure goes) wire was not loose, but terminal at switch was loose so i am bypassing it and just using fuel pump dash switch (if nothing found w/ gauge at track fri, i'm going to bypass pump switch and let it run off ignition to see if painless switch could be bad. It just doesn't seem electrical/ignition/timing to me as it should appear idling/reving and at top of 1/2, 2/3 shifts around 5800 rpm.

[67cruiser]

Again you may be uncovering your pick-up in the tank, whats your set up, only happening after a burn-out, fuel towards rear of tank not front. Where,s your pick-up located??

[ejw]

was talking to a buddy about prob and he suggested it could be a carb issue. poss power valve or clogged air port. wouldn't a blown pv make it run rich and wouldn't a carb issue show up more than just prior to areas. i would think it would pop/hesitate at shift points also not just burnout/top end

[grandville455]

Make sure u don't have a bad head gasket possibly? Have u done a leak down, or cranking test? relashed valves? Get rid of power valve and square jet it anyway least for now.

[turbo69bird]

Im assuming your not a boosted car, the reason I ask is because a turbo car will occasionally blow out the spark and it acts very much like this, heat range on the plug and position in the cylinder can cause it. Have you used different plugs?


Also Ive seen a similar problem with radio frequency issues that show up under load. I think its usually at 4000 rpm points if I remember correctly. It's caused when the wires for a 2 step or something else runs parallel to the MSD wires going through the fire wall/under dash. They should be crossed at as close to 90s as you can get or a shielded wire might help.

I chased a popping banging loss of spark situation for a whole season due to RF signal interference. Drove me crazy.

[ejw]

i added msd rfi filter and shielded wire few weeks ago w/ no change

[turbo69bird]

Originally Posted by ejw

i added msd rfi filter and shielded wire few weeks ago w/ no change

Well look at it this way that's one thing you know it's not.

Just keep checking them off the list you'll find it.

Try a different plug maybe? Mine liked colder plugs believe it or not.