high rpm miss fire.

[Bruce W.]

hey Guys,
could use some help. My 58 fuelie fouls plugs after 2 to 3 runs up to red line. I am running ac46's. have put in new kb spark plug wires' a new coil. Have ti ignition. timing is correct. I run racing fuel. plugs have soot on them. like I said runs great for a couple of runs then the plugs foul. Any help would be appreciated I am at a loss?
Bruce

[Jim L.]

Re: high rpm miss fire.

My 58 fuelie fouls plugs after 2 to 3 runs up to red line.

Plug fouling suggests that the wide-open-throttle air/fuel mixture provided by the FI unit is too rich. Significantly so.

I'm curious: By what method was the air/fuel ratio (WOT and cruise) of your FI unit calibrated? Manometer? Chassis dyno? Seat of the pants? Other?

Jim

[Bruce W.]

Re: high rpm miss fire.

Jim, Jerry Bramlett set up the unit. As you know he is excellent. I think he used a chassis dyno. Is this something that I can adjust?
Bruce

[Frank D.]

Re: high rpm miss fire.

All the plugs are fouled or just a few ?

[Michael W.]

Re: high rpm miss fire.

What type of TI ignition is it?

[Bruce W.]

Re: high rpm miss fire.

Frank, all the plugs look the same to me. Black soot, electrodes are white.
Bruce

[Jim L.]

Re: high rpm miss fire.

Jim, Jerry Bramlett set up the unit. As you know he is excellent. I think he used a chassis dyno. Is this something that I can adjust?
Bruce

Yep, Jerry uses a chassis dyno and modern instrumentation to get the two stop screws correctly set. Don't touch them..... ever!

I still think, however, that your plug fouling is due to an overly rich mixture at WOT and here's how it could happen: Your '58 unit has a device called a Cranking Signal Valve located on the front, upper, passenger side of the plenum. It's supposed to be open during cranking and closed when the engine is running.

However, if manifold vacuum dips below the set point of the CSV it will open and apply manifold vacuum to the very sensitive main diaphragm which regulates nozzle fuel flow. If this happens, the air/fuel mixture will go extremely rich. And guess what..... during WOT, manifold vacuum takes a significant drop. If the engine vacuum during WOT is less than the set point of the CSV, well you can guess the rest.

That's my theory and I'm stickin' to it. (And I've seen this behavior on a couple of FI units which had defective CSVs.)

In any event, you ought to give Jerry a call. He'll have some good ideas for you.

Jim

[Joe R.]

Re: high rpm miss fire.

Probably 90% of misfires are caused by ignition problems but yours sounds like you have a heat soak problem after several runs.
Jerry Bramlets work is perfect as he actually runs the unit and produces a tape sent with the unit. I would call Jerry and look to his experience in dealing with the heat soak problem.
He has more experience with FI than this entire board combined.
JR

[Michael W.]

Re: high rpm miss fire.

electrodes are white.
Bruce

That doesn't sound like fouling to me.

Got a pic?

[Rick A.]

Re: high rpm miss fire.

agree with Mr Lockwood

[Frank D.]

Re: high rpm miss fire.

Yeah -- I'm thinking the same thing. May not be a fouling issue at all.

In fact, depending on color, you may want to back down a heat range on those plugs.
And, yes, pics would help a diagnosis.

[John D.]

Re: high rpm miss fire.

For anyone here with a fuel car that has the pesky cranking signal valve. That would be '58 to early 64.
If your suspect your are having cranking signal valve problems and don't have a spare try this easy trick.
Put a longer piece of 1/4" ID rubber hose between the cranking signal valve and the steel vacuum line. Then clamp the hose shut.
This will take the CSV out of the system and get you home without a flat bed truck. You could actually drive across the county like this although starting may be difficult.
To put a longer piece of rubber hose on you will have to loosent the vacuum line fitting up and swing it up in the air for more clearance.
So always car a short piece of rubber hose and vise grips or a professional hose clamp tool like the appliance repair men carry.
Or of course carry a CSV and spare drive cable all the time. Tip of the day.
As far as the problem Bruce consult Jerry and not the forums. Better than way. Thanks, John

[Bruce W.]

Re: high rpm miss fire.

John, Jerry is away for 9 days on vacation and not available. thanks for your suggestions.
Bruce

[Bruce W.]

Re: high rpm miss fire.

Jim, thanks for the help. It is not the CSV. Guess I will have to send the unit to Jerry. BTW what does WOT stand for?
Bruce

[Jim L.]

Re: high rpm miss fire.

Jim, thanks for the help. It is not the CSV. Guess I will have to send the unit to Jerry. BTW what does WOT stand for?
Bruce

Sending the unit to Jerry is a good plan.

WOT == Wide Open Throttle

Good luck,
Jim