Need some help diagnosing a misfire. Went to test n tune today. The car has a skip that develops at the top of 1st and 2nd gear (powerslide). It runs fine during the burnout (6500 rpm). I leave the line and it leaves sorta lukewarm, but not missing. 60 ft fell off .05-.06 from normal. Then at about 6300 or so it starts to skip. Shifted at 6700 (still missing), ran ok until it hits 62-6300 in 2nd, where it started to skip again then I shut it off.
It idles and drives around the pits/return road fine.

I don't think it is fuel related. No changes to the fuel system since last year and it has always been enough. It's just 1/8 mile so I don't need a huge amount of volume. It has a Holley black pump and -08 line front to rear.

I went to a tnt a few weeks ago and it did the same thing. Only got to make one pass then. Starter went bad. I thought then maybe it was jetted too lean. That day it was low 50's. Jetted 84/85 no pv's Holley 950HP Today was 75�� I still jetted up 1 size over the 50's temp. It ran fine last fall with the 84/85's in 70��weather. Even after jetting up a little and much warmer weather it still had the skip, so I think it's not too lean.

I'm thinking ignition. Setup is an MSD7AL2, MSD dist with locked timing (have tried 36��and 38�� MSD 8.8 Super Cond wires (4yrs old), MSD Blaster 3 coil, and Autolite AR135 racing plugs. The plugs were left from last year. Have 75 or so passes on them.

The only engine related change that has been made to the car over the winter was locking the timing out. It used to have 18��initial and 39��total. I locked the timing in the dist, but made no other changes. It does idle better and has a little better throttle response off idle (that doesn't matter as I leave off a two step/trans brake.

Today I checked the plugs and they looked all the same, also replaced the MSD chips to make sure I didn't have a bad one. Only made two passes, didn't want to hurt it. Valve lash is also ok.

For those who don't know my combo: 383W stroker, Windsor Sr iron heads, solid roller cam, 13:1 comp, all the usual bolt ons. In my 69 Mustang @3025 lbs with a powerglide/5400 stall converter/5.43 gear/ 32" tall tires it normally runs 6.8x's @ 100 in the 1/8 mile.

Any input would be appreciated. Going to start with new plugs and wires this week.

Thanks,

David Cole

[This message has been edited by Dave_C (edited 03-24-2002).]

My money, although maybe wrongfully, would be that it is fuel related. Does it keep good fuel pressure as it is missing? Maybe the pump is getting bad and just cant do its job properly now.

See Ya!

------------------
James
67 Coupe
393W, AFR 185, 4 Speed, 4.11 9 inch
7.09 @ 97MPH 1/8
1.55 60'

Are you sure you just don't notice it during the burn out? After all the burnout is momentary and the car is shaking etc...

The needle and seat on the secondary bowl doesn't seem to move as smoothly as the one on the front. I think it may be sticking and not allowing full fuel flow at wide open. I'll pick some new needle/seats up this week. For good measure I'm still going to be replacing the plugs and wires. Next test n tune is Fri. night.

Thanks for the help, I'll repost after I test it and see it if helps.

Later,

quote:

---

Originally posted by mvierow:
If it isn't happening when you remove the chip then how could it be fuel related?
btw, do you run a mechanical or electric fuel pump?

---

Huuhh..

I never said it wasn't happening with the chips removed. I said I swapped them out to make sure that wasn't the problem. Even with known good chips it still had the skip. I'm hoping the new needles and seats do the trick.

The fuel pump is an electric Holley Black pump. Almost new. I ran the same Holley Blue for almost 7 years with no problems or lack of volume. Last year the Blue pump started leaking from the pump to motor seal. No replacement seal is available. You have to buy the whole lower housing. Since that was more than half the price of a new pump I upgraded to the Black pump.

I'm also going to pull each plug wire and check them with an ohm meter. I'll be sure and line them up with plenty of space between them when I put them back on.

Later,

David Cole

BS

quote:

---

Originally posted by Dave_C:
I think I might have found it. The shiny nickel goes to kv. Possible fuel related

David Cole

---

Since it was happening at the end of each gear, that would have been the first thing I questioned; fuel system. You have to start somewhere. I hope that is it, it sure would make the "fix" pretty simple.

quote:

---

Originally posted by Mark T 7724:
Try looking at your Rotor Phasing ,Since you locked-Out your distributor the rotor is no longer advancing

---

Hmmm, that's a new one. Great idea, I'll take a look at it!

Later,

David Cole

http://www.rehermorrison.com/techTalk/13.htm

Some of the other articles are very interesting too, even if they are chebbie guys.

Don't want to talk about my reaction times though.

On the 4th pass I tossed the alt belt, so I decided to put it on the trailer while my battery was still good.

Later,