engine misses at WOT

[AzStang98]

Recently I changed my plugs, cap, rotor, and plug wires. I installed frpp 9mm wires, bosch platinum plugs gapped to .054, and an msd cap and rotor. I took the car for a drive and it seemed fine to me. It has been about 4 weeks now maybe slightly more since I did the above maintenance, and I noticed in the last two weeks that when I stomp on the gas and hit WOT the engine misses as the rpm's climb. I usually only notice this in 2nd and 3rd gear.


My 02 sensors from my stock h pipe arent plugged in but dunno if that might have anything to do with it. What should I do? Or what could the problem be? Today I went out and took the cap off the distributor and it was nice and dry and clean, the rotor looked fine. I checked all the wire to cap connections and they were in the correct order and snug. I checked all the wire to plug connections and they were all tight and the wires were going to the correct plug.

 

[AzStang98]

help

 

[Hunter26]

I'm no expert by any means, but I've never heard anything good about the platinum plugs and 5.0's. Everyone I talked to says just stick with the good ol' copper Autolites. You might try swapping the plugs, the Autolites aren't all that expensive. What plugs did you have before you switched the platinums? Hope that helps you some.

 

[AzStang98]

I'm no expert by any means, but I've never heard anything good about the platinum plugs and 5.0's. Everyone I talked to says just stick with the good ol' copper Autolites. You might try swapping the plugs, the Autolites aren't all that expensive. What plugs did you have before you switched the platinums? Hope that helps you some.

I was using the same kind of plugs. bosch platinums and never had any problems then

 

[Hunter26]

I was using the same kind of plugs. bosch platinums and never had any problems then

Shucks, I'm not exactly sure. Maybe some trash is in the intake (filter, etc)? Have you checked to make sure your getting a good spark? Or maybe something is going bad, like a part that has do with the throttle etc?

 

[CPB00GT]

Don't know for sure. But maybe the fuel filter or TFI module located on the side of the distributor. I have a similar problem with mine and somebody posted about the TFI module. I have not tried to replace it yet though. I did a tune up and replaced my fuel filter though.

 

[Schlodes]

I'll bet you it is the plugs.

I had an 1989 GT Cobra 5 speed in 1996 that LOVED the bosch platinums. Car screamed with them. I even used them with a 75 shot of nitrous and gapped small NO misses or problems.

However in my current car and my friend Rodneys identical 89 LX Notch....

First got our cars did the complete wires, cap, rotor, etc etc etc... and used the Bosch Plantinums like b4 cause they seemed to work years ago in my 89.

We troubleshot for DAYS on end a miss in both our cars that would only occur in the upper 4000 and beyond RPMs... sorta like a very faint "bubububububub" type of miss under upper RPM WOT. Changed diff wires, caps, coils, on and on.

Went to the Ford dealership, bought some brand new stock ford Motorcraft plugs, gapped em, installed em problem gone on BOTH cars.

Swap the plugs out for some Ford ones!!!!!!!!!!!!!!!!!!

 

[StreetStang37]

I had a miss too above 4000 with platinum plugs, put in cheap autolites and car ran perfect.

Another time I had a miss at 4000+, I guess I had a bad cap. It was brand new (only drove a few hours on it) but it was missing pretty bad up top so I put the old one back on and it went away. could be that too.

 

[AzStang98]

thanks for the replies guys. guess I will be pulling the plugs and putting some different ones in. might as well buy a new cap too, even though its not cracked.

 

[QUICK91LX]

when i did my last tune up on my 89 LX, i used autolite platinums and it ran good until i ran it hard one day haha...after that it didnt run so hot...decent, but far from perfect. i never got a chance to try changing the plugs because a week later an old man decided he was gonna drive right out of a gas station without stopping, RIGHT in front of me then say he never saw me. arghhh...but im willing to bet the plugs might be a problem

 

[wildstang347]

its prob. the plugs. swap them out for the heck of it with some normal plugs or even splitfires. same thing happened to me with my bosch +4's in upper RPM's but not in lower RPM's. dont know why, but it pissed me off that i payed so much for them and to have them do that.
i'm lucky enough to have access to exspensive diagnostic equipment were it showed up on the analyzer 2 cyl. were dropping off above 4200 RPM intermitently.
needless to say i got a refund.