Help me solve this bucking in low boost problem.

275hptbirdsc

Registered User
So my car bucks when brought around 5 psi but the threshold is lower for some reason in different gears but I doubt that has anything to do with it(5psi in 1st,4psi in 2nd,3psi in 3rd etc). The car runs perfect when not brought up that high. Car has brand new plugs and wires as of last year. This problem didnt start until after my maf was dirty and I thought it was my dis and coil pack. So im thinking it may have somthing to do with either the coil pack or dis but I bought both brand new. Could it be the cam or crank sensor? Any help/troubleshooting would be great.
 
Could be??

What gap are the plugs at?

Did you reseal all the intercooler plumbing if you took any of it off, if so with what teflon gaskets or RTV.

Any other connections you may have taken loose to do the plugs needs to be checked for tightness and sealing properly.

Could have cracked a plug like I did recently and it would miss and stumble with any type of boost. Just a few thoughts.

Smitty
 
When i went to pick my car up it ran fine til low boost. The previous owner couldnt get the plug wires on, a heads up woulda been nice. anyway, it bucked. Not sayin you didn't but thats how my car reacted to it. Vacuum leaks usually idle like crap but smooth out with higher rpms. Ic piping not being sealed does a number on them. Clogged fuel filter could be an issue like this. Has it gotten progressively worse? Any codes?
 
If all of the above checks out OK, then I would suspect a bad intake gasket....

I've seen this identical problem on 2 SC that I've bought...

Get a 3' long piece of vacuum hose....

Put one end in your ear and probe around the intake / head area with the other....

You will hear a definite hissing sound if there is a leak....
 
It's 99% certian to be a spark plug or plug wire issue. The lower boost threshold in the higher gears is normal because the load increases. I think you're going to find a loose or damaged plug wire.

David
 
What gap are the plugs at?

Did you reseal all the intercooler plumbing if you took any of it off, if so with what teflon gaskets or RTV.

Any other connections you may have taken loose to do the plugs needs to be checked for tightness and sealing properly.

Could have cracked a plug like I did recently and it would miss and stumble with any type of boost. Just a few thoughts.

Smitty

The plugs were done before I got the car last summer but im pretty sure they are just regular gap. Did Ford seal the pipes with anything? If not then the upper pipe looks like it make have been sealed with some sort of gasket-maker type substance.

When i went to pick my car up it ran fine til low boost. The previous owner couldnt get the plug wires on, a heads up woulda been nice. anyway, it bucked. Not sayin you didn't but thats how my car reacted to it. Vacuum leaks usually idle like crap but smooth out with higher rpms. Ic piping not being sealed does a number on them. Clogged fuel filter could be an issue like this. Has it gotten progressively worse? Any codes?

No codes and as far as it getting worse no. It just happened one day. When I bought the car it ran like a top but then about 2 or 3 months after I bought it it started doing this and like I said the only thing I did to it in that period of time was replace the DIS and Coil pack.

It's 99% certian to be a spark plug or plug wire issue. The lower boost threshold in the higher gears is normal because the load increases. I think you're going to find a loose or damaged plug wire.

David

Thats kinda what I was thinking when it first started happening because with my last tbird I had a really bad bucking at wot and that turned out to be a wire issue. Ill go and double check to see if each wire is seated perfectly. It has the livewire plugs are those known to go bad?
 
The plugs were done before I got the car last summer but im pretty sure they are just regular gap. Did Ford seal the pipes with anything? If not then the upper pipe looks like it make have been sealed with some sort of gasket-maker type substance.



No codes and as far as it getting worse no. It just happened one day. When I bought the car it ran like a top but then about 2 or 3 months after I bought it it started doing this and like I said the only thing I did to it in that period of time was replace the DIS and Coil pack.



Thats kinda what I was thinking when it first started happening because with my last tbird I had a really bad bucking at wot and that turned out to be a wire issue. Ill go and double check to see if each wire is seated perfectly. It has the livewire plugs are those known to go bad?

Since you mentioned replacing the coil pack, please tell me it's not a Screamin Demon. If it is, that's most likely your problem.

David
 
Since you mentioned replacing the coil pack, please tell me it's not a Screamin Demon. If it is, that's most likely your problem.

David

Nope it was bought brand new at Advance auto parts. It turned out I didnt need the new DIS or Coil pack but I left them on anyway. Maybe if I put the old coil pack on it might fix the problem?
 
Nope it was bought brand new at Advance auto parts. It turned out I didnt need the new DIS or Coil pack but I left them on anyway. Maybe if I put the old coil pack on it might fix the problem?

The only coil packs that SCs seem to have trouble with are the Screamin Demon, so that's not likely to be the problem. Pretty sure it's going to be a plug wire issue.

David
 
The only coil packs that SCs seem to have trouble with are the Screamin Demon, so that's not likely to be the problem. Pretty sure it's going to be a plug wire issue.

David

Other than replacing all the wires at once is the a way to troubleshoot the wires and find out which one is the faulty one.
 
Other than replacing all the wires at once is the a way to troubleshoot the wires and find out which one is the faulty one.

You can try looking at the motor running with the lights off to see if a wire is arking from the wire/boot to something else. If it is arking you can usually hear it too, because it makes a clicking sound.

If it were me, I'd just buy a set of Taylor Spiro core wires from Summit and a set of Autolite 103 plugs from the local auto parts store and change them both. I'm not sure what the standard gap on the 103 plugs are, but I'd re-gap them to .045.

If you want the part number for the wires, search "Taylor" and you should find a Summit link.

David

David
 
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