Help diagnose this possible misfire?

86 Fox

86 Fox

Forum Member
My dad has been having some trouble with his 99 Mustang GT, its a stock 4.6L and it seems like it has a misfire of some kind. He pulled the plugs, cleaned and regapped them, took it to a shop and hooked it up to a scope and took it for a drive and nothing came up out of place, the fuel rails were at 40psi, everything seemed in place. Can't seem to locate the issue, what happens is it shutters when you get on the throttle, like its not all there when it should be. It doesn't really bog down but it feels like its struggling to fire at full force but we can't seem to figure out why.

Just wondered if anyones had an issue like this before with their own car, i know a bunch of people here have the 4.6 didn't know if its a common thing or not. If anyone knows a good place to have it tuned or looked at then please let me know, he's willing to try just about anything at this point, just wants to enjoy his car now that its nice haha

Thanks in advance for any input
 
Check all vacuume lines including PCV hoses.

Clean MAF sensor (only with MAF Cleaner and not brake clean or carb cleaner)

How many miles?
 
smooth said:
I've heard of cracked intakes causing his problem
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That's what he's afraid of..

OMG ITS BEAN said:
If you put a scanner on it, it should tell you what cylinder is misfiring. Coils can go bad if they get wet.
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The scanner he used didn't show that, maybe we need to find a different one?

that could be the case also with the coils, one of the o-rings was leaking and gas was shootin all over the place, we cleaned it by usin an air compresser to blow it dry but I'll let him know that

glh_turbo22 said:
Check all vacuume lines including PCV hoses.

Clean MAF sensor (only with MAF Cleaner and not brake clean or carb cleaner)

How many miles?
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just over 100k miles, he did clean the MAF with carb cleaner a few weeks ago, only to read a few days ago that its coated with a chemical that your not supposed to use carb cleaner on.. it idles a little funny now, fluxuates between 500-1200 rpms but not iradically, its a smooth flow up and down so that could be why.
 
I'd bet a considerable amount of money it has a bad DPFE sensor or burned out DPFE hose. Either that or a small vaccum leak.
 
My misfire was caused by a bad coil pack, but it's a '97 GT. I think your car should have better coil pack(s).
 
thanks for the help, were gunna give all the vacuum lines and hoses a good running through. What's the best way to test the coils?
 
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