Help please.. 5.0L Missing under load, pics inside...

[Mike85000]

Hey Guys,


Car is an 87 5.0L GT. Stock motor other than exhaust.
190kms on it, ran great up till now.

A description of what the car is doing would be missing badly from what sounds like 1 cylinder only ( continuous miss under throttle, rhythmic, not scattered).

Pulled codes, just got the usual emissions codes (thermactor bypassed). Did the cylinder balance test, passed with no codes.

Car does not miss at idle, or if it does, it's very infrequent. I can very lightly cruise just above idle with no missing. As soon as i get on the throttle any amount, it misses.

No backfiring or anything, just shudders and bucks. At WOT the miss is constant. Car still pulls decently hard, but with about 3/4 the power of normal. Car doesn't run any hotter than normal.

Problem came on suddenly.

What i've done, pulled all the plugs (pics below), checked wires, new cap and rotor, new fuel filter. Couple bottles of injector cleaner with 1/4 tank, no difference.

Left to right = front to back


Drivers side #6 looks a little lean.

Pass side, #4 is clean because the plug was changed 3 days ago.

Right now I'm suspecting a fuel delivery issue. I changed the filter, fuel has pressure at the rail, but not sure exactly how much.

I'm suspecting a clogged injector since none of the plugs are fouling i believe it is a fuel issue.

I'm leaning to a partially plugged injector since the miss seems to be in one cylinder only. (#6 is my guess)


Any insight is very much appreciated.

Mike

 

[allballsmustang]

id be suspect to the wires...i see yuo say you have checked them but that doesnt rule them out...ive bought brand new wires that turned out to be bad...if that seems good then i would get a fuel pressure gauge to see how that is, cause you have a few things that could be messin you up on the fuel system...

jim

 

[Mike85000]

Hmm, thanks for the input. I will check the reistsance of the wires one by one tomorrow. They are a decent quality wires though, and worked fine up till now. Also, one reason i don't suspect ignition problems is because none of the plugs are fouled (misfiring due to lack or spark).

I will double check the wires tomorrow though. Working on getting a fuel pressure gauge too.

 

[Ike83]

Well...one way or the other it definitely sounds like an ignition problem.

 

[justagt]

Hmm

Could be plug wires although you look like you are running lean from the look of the plugs.

My guess (just based on your pictures) would be weak fuel pump, clogged injectors or a fuel pressure problem, maybe bad regulator....

 

[Mike85000]

Well I fixed the problem.

I changed the fuel filter, checked fuel pressure. Went to check timing to make sure it was alright, and i noticed the #1 plug arcing. Even though i had all the plugs out at least twice, i never saw it before. Hairline crack.

Anyways, new plug and she was good to go. I just got my Injector rebuild Kit in the mail from Mr. Injector but i'll save that for when i do an intake swap.

Thanks for all the help.

Mike

 

[88mouse]

Well I fixed the problem.

I changed the fuel filter, checked fuel pressure. Went to check timing to make sure it was alright, and i noticed the #1 plug arcing. Even though i had all the plugs out at least twice, i never saw it before. Hairline crack.

Anyways, new plug and she was good to go. I just got my Injector rebuild Kit in the mail from Mr. Injector but i'll save that for when i do an intake swap.

Thanks for all the help.

Mike

I would get a set of motorcraft or autolites to put in there. I had a problem with my car cracking the number six plug for awhile never could figure out why.

 

[Black1987Stang]

Jeez you beat me to it.....I was going to say a wire arcing too