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Author Topic:   High rpm misfire? Long......
Dave_C
Gearhead

Posts: 1069
From: Gadsden, Al
Registered: Aug 99

posted 03-24-2002 08:01 PM     Click Here to See the Profile for Dave_C   Click Here to Email Dave_C     Edit/Delete Message   Reply w/Quote
Hi all,

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).]

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

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kid vishus
Gearhead

Posts: 6590
From: middle of NC
Registered: Oct 2000

posted 03-24-2002 08:10 PM     Click Here to See the Profile for kid vishus   Click Here to Email kid vishus     Edit/Delete Message   Reply w/Quote
I also would go with new plugs and wires, and I would check the rotor and the cap and make sure they look ok. I would think if it's the ignition it would be more constant.

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.

Could be the coil, or a ground wire that isnt "tight" anymore.

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67Coupster
Gearhead

Posts: 189
From: Fortson, GA, USA
Registered: Oct 2001

posted 03-24-2002 08:21 PM     Click Here to See the Profile for 67Coupster   Click Here to Email 67Coupster     Edit/Delete Message   Reply w/Quote
My MSD 6AL does that at the same rpm as yours when I have any chip in it. Runs fine with no chip installed. First pass today a friend gave me a 7400 chip to try out and it still started missing about 62 to 6300 rpm, I shift at 6500. Just something else to try out. I've been meaning to send it in for repair just been having too much fun.

See Ya!

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

[This message has been edited by 67Coupster (edited 03-24-2002).]

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64FalconF-16
Gearhead

Posts: 233
From: Republic Of Texas!! Temporarily living in KY
Registered: Feb 2002

posted 03-25-2002 02:37 PM     Click Here to See the Profile for 64FalconF-16   Click Here to Email 64FalconF-16     Edit/Delete Message   Reply w/Quote
I had a bad chip in my MSD on my Cuda last year. Was a 6500 chip and it was doing it's job at 5600. Unfortuately I shift at 6000. Replaced it with another and problem went away.

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...

------------------
64 Pro-Street Falcon
351C 4V 8.1s in 1/8
79 Ford Bronco 4 X 4 Lifted 6"
400 9.9s in 1/8 :)
70 Plymouth Cuda'
440 Magnum. 2600#
Race Car 6.90 in 1/8

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Dave_C
Gearhead

Posts: 1069
From: Gadsden, Al
Registered: Aug 99

posted 03-25-2002 03:37 PM     Click Here to See the Profile for Dave_C   Click Here to Email Dave_C     Edit/Delete Message   Reply w/Quote
I think I might have found it. The shiny nickel goes to kv. Possible fuel related

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,

David Cole

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mvierow
Gearhead

Posts: 209
From: Bay Area, Ca
Registered: Apr 2001

posted 03-25-2002 07:29 PM     Click Here to See the Profile for mvierow   Click Here to Email mvierow     Edit/Delete Message   Reply w/Quote
If it isn't happening when you remove the chip then how could it be fuel related? I'd check the high amp power lines that go to the MSD. If you run them any further than stock length the MSD manual advises using a lower gauge to compensate for distance. I also remember some other high-rpm related topics in the manual so if you still have it, give it a look over and see what you can find. I'd also make sure your spark plug wires are not all tangled together or even close together as they can cause misses if to close.

btw, do you run a mechanical or electric fuel pump?

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Dave_C
Gearhead

Posts: 1069
From: Gadsden, Al
Registered: Aug 99

posted 03-25-2002 08:29 PM     Click Here to See the Profile for Dave_C   Click Here to Email Dave_C     Edit/Delete Message   Reply w/Quote
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

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bluestreek
Gearhead

Posts: 1724
From: Athens,GA
Registered: Jul 2001

posted 03-25-2002 10:24 PM     Click Here to See the Profile for bluestreek   Click Here to Email bluestreek     Edit/Delete Message   Reply w/Quote
Don't forget to check the simple problems like valve springs, spark plugs too hot (preignition), spark advance.

BS

[This message has been edited by bluestreek (edited 03-27-2002).]

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kid vishus
Gearhead

Posts: 6590
From: middle of NC
Registered: Oct 2000

posted 03-25-2002 10:31 PM     Click Here to See the Profile for kid vishus   Click Here to Email kid vishus     Edit/Delete Message   Reply w/Quote
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.

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Mark T 7724
Gearhead

Posts: 262
From: Palmdale, CA
Registered: Nov 2000

posted 03-26-2002 03:20 PM     Click Here to See the Profile for Mark T 7724   Click Here to Email Mark T 7724     Edit/Delete Message   Reply w/Quote
Try looking at your Rotor Phasing ,Since you locked-Out your distributor the rotor is no longer advancing

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Dave_C
Gearhead

Posts: 1069
From: Gadsden, Al
Registered: Aug 99

posted 03-26-2002 11:44 PM     Click Here to See the Profile for Dave_C   Click Here to Email Dave_C     Edit/Delete Message   Reply w/Quote
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

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Just Strokin
Gearhead

Posts: 754
From: Tuscaloosa, Alabama
Registered: Dec 2001

posted 03-27-2002 07:24 AM     Click Here to See the Profile for Just Strokin   Click Here to Email Just Strokin     Edit/Delete Message   Reply w/Quote
Dave, here is a link to an article written by David Reher or Reher-Morrison for National Dragster about spring cleaning (of the race car after sitting all winter).

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

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

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

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Dave_C
Gearhead

Posts: 1069
From: Gadsden, Al
Registered: Aug 99

posted 04-07-2002 08:56 PM     Click Here to See the Profile for Dave_C   Click Here to Email Dave_C     Edit/Delete Message   Reply w/Quote
Update.....
Went to test n tune today. It turns out the problem was the needle/seat in the secondary. Put the new one in and the high rpm skip was gone. The jetting wasn't exactly right, it's got more in it, but it ran pretty consistent for an ol bracket car with the Powerslide trans. Hate they were not running for money today.

Made 4 passes, all 1/8 mile
1st, 1.480 60ft, 6.870 @ 97.98 (timing @ 40)
2nd, 1.483 60 ft, 6.852 @ 99.71 (backed timing down to 38 and got more mph)
3rd, 1.481 60ft, [email protected] 99.71
4th, 1.484 60ft, [email protected] 99.72

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,

David Cole

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