Occasional Miss

[Voyager]

Took my new Cobra for a spin today. Need to address a couple things. The car is occasionally missing. The ignition box that came with the Superformance is a Motorcraft 5U2J-10316AA, N4CMB. Any ideas? I assume a loose wire somewhere?

[Tommy]

Circumstances? Steady cruise, accelerating, hot, cold, when? Just started, has always been this way, what?

[timsullivan]

What brand of distributor are you running? MSD?

[vector1]

plug wire loose? bad spark plug?

[Blas]

Seeing that its new...
I have heard of fuel related problems due to dirt in the fuel filter...
Just part of the debugging process...

[mr0077]

Lots of guys have an occasional miss, in addition to their regular girl...they're often cheaper and more fun.

(Sorry, I just couldn't resist. Hope you find the culprit.)

[madmaxx]

Ford Duraspark ignition box is located in passenger foot well. $20.00 at autozone. Plug and play. Good to have a spare but probably not your problem in this instance.

Ensure all plug wire are on tight. Ensure rotor tab is TOUCHING dist cap button if msd. bend tab way up.

Run some known good gas through it.

[Voyager]

Thanks for the replies. Understand debugging a new car/motor is part of the process. I’m actually enjoying it.

The dealer noticed the miss fire when they test drove the car (8 miles). They were in the process of swapping in an MSD box when they noticed a loose wire, put the Ford box back in and declared it fixed.

Driven it 3 times since it arrived yesterday. Still missing/stuttering under steady & light throttle at 1800-3500 (did not go above 3500 yet). Good news it that it seems to get better as I rack up the miles (up to 50 miles now). It’s also shuttering/bucking on deceleration (maybe characteristic of motor?). I’ll inspect the MSD distributor.

Bob

[timsullivan]

I'm currently running the Duraspark module with an MSD distributor.

For lower rpm problems I'd also recheck the ignition timing and carb mixture screws. My guess is that the problem may be the former. I'd also check the plug wire and coil wiring connections.

I had problems with rotor phasing in my MSD distributor that required me to get an adjustable rotor with a movable rotor pin, from MSD but my problem was higher RPM operation, above 3,000 so I suspect that isn't the issue with your car.

[Voyager]

Up to 80 miles now. Missing seems to be lessening. Only an occasional stumble at steady throttle. Have my fingers crossed that it was just junk somewhere in the system.

I do need to tune the carb a little. Float bowls too high. Also not real clean at low RPM transitions (throttling out of a corner). And bucking on off throttle applications. Maybe it’s the nature of the beast. Don’t know. I’m loving it either way.

[xlr8or]

It may just be the timing advance is sticky. Pull the cap and see if it snaps back when you advance it by hand.

[Tommy]

Originally Posted by Voyager

And bucking on off throttle applications. Maybe it’s the nature of the beast. Don’t know. I’m loving it either way.

Don't accept that as "the nature of the beast." Keep posting and folks here will help you get it right. .. As for bucking when opening the throttle, I need to ask. Are you running a carburetor with mechanical secondaries? If so, there is some driver technique required to get a smooth opening. Think of it as rolling in to full throttle rather than stomping on the gas pedal.

[madmaxx]

I could not agree more with the quote below, dont get used to it or take it for normal, fix it once and be done with it. What is your timing at idle and at 4K rpm's? Did you use a vacum gauge to adjust your mixture screws? These things are to simple not to get them perfect.

Originally Posted by Tommy

Don't accept that as "the nature of the beast." Keep posting and folks here will help you get it right. .. As for bucking when opening the throttle, I need to ask. Are you running a carburetor with mechanical secondaries? If so, there is some driver technique required to get a smooth opening. Think of it as rolling in to full throttle rather than stomping on the gas pedal.

[Blas]

Do the things that cost nothing first. I would do a resistance text on the plug wires and check the end connections on all of them. Dielectric grease on all the boots and connectors. Connections and crimps on the coil wires, Power and ground to the MSD box itself. Igniton switch wire to MSD box, temporarly relocate to new hot tie-in. Then start looking for $$$ items. Have you pulled and inspected your spark plugs?

[Voyager]

Guys,

Thanks for the feedback. Since the car is only 2 days old and has 10 miles on the odometer, I had the dealer truck it back to their shop to work off the gigs they considered their responsibly. I reassess it’s status when they return it back to me today. Most critical is to fix the temp gauge and confirm or deny the existence of a coolant overheating problem.

Bob

[209]

Yup, dealer/installer problem not yours. Mine's just over a year and I think it's finally sorted after 6k miles, I hope. 209

[JBCOBRA]

Maybe a burned plug wire by the headers? Been there done that.
Maybe you need to Blow that sucker out! Fowled plug(s)

[67JET]

I agree with JBCOBRA.
And even if blowing it out didn't work --- It's always FUN!!!!
That car is just begging for some hard miles and then when you get back home it will be easier to tell where the problems are.

[Voyager]

Not blowing it out yet!

Only 200 miles on the Keith Craft engine and still battling an overheating issue (addressed in another thread). Longest I’ve driven it is about 10 minutes at an easy pace.

It will need a good clearing out, but the minor miss is about 6th or 7th on the punch list. Sending it back to Superformance for the 2nd time in as many weeks to work the cooling system.

Thanks for all the feedback.

Bob