miss fire at high RPM

[Bruce W.]

hey guys,
could use a little help. 1958 290 hp fuelie. breaks up after 5,000 rpm in second gear not first. I am thinking maybe the plugs or power stop is to lean. has electronic ignition no points. running cam two. running ac 45 plugs. Any suggestions??
Bruce

[Mark E.]

Re: miss fire at high RPM

How long since last tune up?

And maybe don't wind up the old girl past 5,000. Especially if your 290hp is original.

[Bruce W.]

Re: miss fire at high RPM

Hey, Mark, tune up last summer. this engine was rebuilt. Probably has a few hundred miles on it. has far as winding it up , isn't that the whole joy of owning these cars. do you think it sounds like plugs? thanks for your help
Bruce

[Terry D.]

Re: miss fire at high RPM

How about third gear? Does it do it if you take it up and over 5000 slowly? Could it be a fuel problem?

[Dan D.]

Re: miss fire at high RPM

Bruce, thinking about this - you say it breaks up in second - not first. Could be it is running out of fuel, seeing how it would wind out faster in first than in second. Look at engine fuel pump and fuel filter, and the sock on the gas gauge sender in the fuel tank. Don't know how old any of this stuff is, but I have had similar problems with the fuel filter before.

And it sure is fun to wind these old engines out. But you don't want to hole the block either, assuming it is original to the car. This sounds like a real nice car. I hope you have the anti-siphoning valve. A lot of 58 FI engines met their maker because of this.

-Dan-

[Mark E.]

Re: miss fire at high RPM

A miss can be caused by a myriad of things.

I usually start by asking: What's changed? Did the problem begin after I changed something?

Did the miss develop suddenly, or get worse gradually over time? This can help narrow the possibilities. For example, I once had a miss develop suddenly, and knew it unlikely it was due to fouled plugs (turned out a spark plug boot popped off).

Does it seem like an ignition miss, or fuel issues? You might decide to use a vacuum gauge and read the plugs for clues.

Is one cylinder the culprit, or are multiple/all cylinders misfiring? I have a basic "engine analyzer" by MAC that can disable one cylinder at a time to measure RPM drop. Or just disconnect one spark plug cable at a time.

I learned that high-performance engines are sensitive to even slightly worn/fouled plugs. Replacing used plugs that look ok with a fresh set has eliminated high speed/high load misses several times for me.

Search through this forum. There's a lot of stories and wisdom regarding engine misses, including examples of obscure causes.

If it is the fuel system, you have a more unique problem since you have fuel injection. If you isolate the problem to FI, this Forum has some experienced folks who can help.

Let us know how you progress.

[Harry S.]

Re: miss fire at high RPM

Swap the easy components first. I'm fighting a similiar issue but it happens when the engine is hot. I think I have it down to my coil.

[Bruce W.]

Re: miss fire at high RPM

Dan, yes I have a anti-siphoning valve. i am thinking it is a fouled plug? the accelerator linkage stuck twice recently while only for a moment it reved to probably 8000. I had the valve covers off and the ground wire was hitting the linkage. do you find that if there is a plug problem it usually starts with cylinder #8? By the way this car duntov'd with 99.5 score. I will look at the fuel situation you mentioned. thanks for your help.
Bruce

[Bruce W.]

Re: miss fire at high RPM

Harry, i had the same problem. Car ran fine for a couple of runs then started to miss fire. It was a brand new GM replacement coil that would break down as soon as it got hot. Here is an easy check. when the engine is hot pull the coil wire from the distributor. hold it about an inch away from the cap. Have some one crank it over. You should have a clean blue spark. if the spark is yellow the coil is bad.
Bruce

[Bruce W.]

Re: miss fire at high RPM

Thanks Mark, I am thinking it is probably a fouled plug. But here is the question why would it run fine in first and only notice it in second at above 5000 rpm? could it be there is more load in second. i have found cylinder # 8 to be the first to show a problem. Is that your experience? thanks for your input.
Bruce

[Dan H.]

Re: miss fire at high RPM

Bruce, cylinder number eight will foul due to gas running back into engine after shut off. Only cure is to put electric shut off valve in the feed line to prevent this. It also will wash oil off rings in number eight resulting in extra clearances etc. Sounds like several little things causing bigger problems.
Dan

[Bruce W.]

Re: miss fire at high RPM

Hey Mark,
Thanks for your help. as it turns out it was the plugs!! Funny thing is that the plugs looked fine?Just goes to show you looks can be deceiving
Bruce

[Dick W.]

Re: miss fire at high RPM

Oh for the days of the Sun 1120 and the scope

[Dan P.]

Re: miss fire at high RPM

Spark plugs . Drive it on the highway fro a few miles and see if it clears up0 Next is point bounce. Chevrolet found out this was a problem and drop the dual points.

[Gene M.]

Re: miss fire at high RPM

Dan, yes I have a anti-siphoning valve. i am thinking it is a fouled plug? the accelerator linkage stuck twice recently while only for a moment it reved to probably 8000. I had the valve covers off and the ground wire was hitting the linkage. do you find that if there is a plug problem it usually starts with cylinder #8? By the way this car duntov'd with 99.5 score. I will look at the fuel situation you mentioned. thanks for your help.
Bruce