Misfire above 4000 RPMs.

A

Ares67Coupe

New Member

Jun 16, 2004

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Nor Cal

Oct 27, 2004

#1

• Oct 27, 2004

• #1

I have a stock dist with the Pertronix points replacement deal, fresh plugs, and 2 year old wires. With the modifications I have done to my car should I upgrade the ignition? Or should I replace with stock parts? For aftermarket systems I have been looking at MSD and Davis Unified Ignition systems. Any ideas or suggestions?

 

mdjay

Premium Sponsor

Dec 9, 2003

896

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16

Las Vegas, NV

Oct 27, 2004

#2

• Oct 27, 2004

• #2

It might be valve float! I would get it looked at before you do some real damage!

 

A

Ares67Coupe

New Member

Jun 16, 2004

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Nor Cal

Oct 27, 2004

#3

• Oct 27, 2004

• #3

Valve float? The engine is pretty damn fresh, only has 4500 miles on it, and it runs strong up to 4000rpms and starts to misfire. That is the main reason I mentioned the ignition. Well I guess if it is the valves floating, give me reason to get that 427 stroker motor.

Also why would you say valve float?

 

mdjay

Premium Sponsor

Dec 9, 2003

896

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Las Vegas, NV

Oct 27, 2004

#4

• Oct 27, 2004

• #4

I read your sig and saw the 40k orig miles thing. I didn't realize your rebuilt it.

The ignition is a viable consideration by all means. I have never been a fan of the pertronix, but some people swear by them.

Check to make sure the distributor doesn't have any slop in it. The distributor itself could be going! Pull the rotor cap off and see if you can move the center shaft.

I have the MSD pro billet dist. and the MSD-6al box. It's good stuff...

 

A

Ares67Coupe

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Jun 16, 2004

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Nor Cal

Oct 27, 2004

#5

• Oct 27, 2004

• #5

I'll check for slop in the dist. If there is, it is another reason to spend some money this Christmas.

 

mfp4073

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Mar 14, 2001

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Hells Ditch, FL

Oct 27, 2004

#6

• Oct 27, 2004

• #6

Other things to check. Temp (is it running warm), fuel (try the really high octane stuff and see if it improves...could be silent preignition), carb tuning.

I had a high rpm power loss. Felt like it was kinda partially missing or only half hitting. Finally determined it was silent preignition. Turned out somehow I had ended up with a 190 degree thermostate. Car was NOT overheating. By replacing the theremostate and going with a higher octane the problem was solved. Almost like you said though...right around 5000 rpms at like 80mphs.

 

A

Ares67Coupe

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Jun 16, 2004

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Nor Cal

Oct 27, 2004

#7

• Oct 27, 2004

• #7

I am running 87 octane right now, I'll try 91, I really hate to pay that nasty price for CA gas right now. It is at $2.75 average in the Bay Area, it is friggin insane. However this is the fun car, I have a motorcycle to get around town. Temp is good, running fairly cool all day long. Even with the temp up, the only time it rises is on long distance trips, but not that much. New toys

 

one2gamble

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Feb 27, 2001

902

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Monterey

Oct 27, 2004

#8

• Oct 27, 2004

• #8

check your timing

 

latamud

Founding Member

Oct 22, 2002

791

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19

Tampa, FL

Oct 27, 2004

#9

• Oct 27, 2004

• #9

You might have bad plug wires. I had an old set on my car and they were arching onto eachother at the cap. Try running the engine at night and watch for sparks. Rev it up to 4000 if that's where its been missfiring. This happened to a buddy's car too. The wires were bad so I took a look, just happened to be dark. Saw the spark jump to his intake mounted coil strap. I put a piece of cardboard between the cap and coil so he could make it home.

 

mfp4073

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Mar 14, 2001

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Hells Ditch, FL

Oct 27, 2004

#10

• Oct 27, 2004

• #10

About gas prices...look at it like this. If you run your tank down fairly low and put 10 gallons in, the total cost of the test is less than $5 to test. Sound better that way?

 

A

Ares67Coupe

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Jun 16, 2004

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Nor Cal

Oct 27, 2004

#11

• Oct 27, 2004

• #11

LoL

I use this car on the weekend for weekend fun, so not tooooo worried about the gas prices, just I enjoyed the 87 octane usage, so much for that.

 

HistoricMustang

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Apr 11, 2003

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Confederate States of America

Oct 27, 2004

#12

• Oct 27, 2004

• #12

If it is happening at the same RPM each and every time replace the plug wires, expecially if the skip stops after going through that particular RPM.

HistoricMustang
www.historicmustang.com

 

BBRacer

Founding Member

Nov 8, 2001

99

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8

Calgary

Oct 27, 2004

#13

• Oct 27, 2004

• #13

I'm suddenly having the same problem!!

HistoricMustang said:

If it is happening at the same RPM each and every time replace the plug wires, expecially if the skip stops after going through that particular RPM.

HistoricMustang
www.historicmustang.com

Click to expand...

I suspected the plug wires - my question - would this go away at different rpms??

i.e. ok at idle and top speed - but hits (or misses in this case) at about the same rpm (I havew no tach).

 

HistoricMustang

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Apr 11, 2003

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Confederate States of America

Oct 27, 2004

#14

• Oct 27, 2004

• #14

My statement is based on an actual experience that happened to me in rhe 5000 rpm range at the track. Wires may or may not be the problem but they are a relatively cheap replacement item.

Heck, if you do not have one laying around borrow one from a friend (or someone here will be glad to loan you one) and then make eight different "runs" to see if a bad wire is the problem.

HistoricMustang
www.historicmustang.com

 

A

Ares67Coupe

New Member

Jun 16, 2004

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Nor Cal

Oct 27, 2004

#15

• Oct 27, 2004

• #15

Well as soon as I get payed I am gonna purchase some plug wires, and new spark plugs and check both my timing and see if there is any play in the dist.

 

V

VictorII

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Jun 19, 2004

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Cotati, CA

Oct 28, 2004

#16

• Oct 28, 2004

• #16

Ares67Coupe said:

Well as soon as I get payed I am gonna purchase some plug wires, and new spark plugs and check both my timing and see if there is any play in the dist.

Click to expand...

If that doesn't work, try putting the points/condenser back in the distributor (I assume you have a new cap?) and try that. Pertronix is usually pretty good, but sometimes fails. Also check all ignition connections. Maybe you have a bad connector that only bounces around that RPM.