Cobra head swap

Thompson452021

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I just bought a 94 gt and from what the last owner stated, it has gt40 heads along with an explorer upper and lower I take manifold as well as a 65mm bbk throttle body. The car does not run right and sputters out after takeoff at around 2.5k and 3.5k rpm, if it makes it past that it runs fine and it does this almost every other time I drive it. It’s also just now throwing codes that there is a short in power to cylinder one and after replacing alternator it ran decently fine no problems until I started it back up again later that day and it started acting up again. Any suggestions on how to fix this? I’ve replaced the IAC and TPS already as well.
 

duh09

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So just trying to get your issue clearly -

The car does not run well below 2500-3500 RPMS, but clears up and runs good after that point?

A GT40 topend shouldn't really cause any major issues. What injectors does the car have?
 

Wood's 5.0

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Sounds electrical. Have you checked your cap and rotor? Mine had a similar problem once. Turned out to be the contacts on the underside of the cap and tip of the rotor button were burned from the Crane HI-6 CD ignition box I was running.
 

302hobronco

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I second the checking of what injectors are on it and the mass air meter.
And while your checking the cap and rotor I would go one step further and make sure your timing is correct.
 
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Thompson452021

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I’ve read some similar posts after posting mine and those two things seem to be the most common possibility, I will be getting to that as soon as I can, thank you all
 

ctandc

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Air, Fuel and Spark.

Personally, I never take for granted the previous owner did anything right. That's just me.

If it were me?

- Replace spark plugs (I'm sure plenty will chime in - but the 5.0 EFI in my opinion always liked cheap Autolites the best - maybe that's just me)
- Wires (you can easily test them)
- Cap and Rotor (check yours - GOOD quality replacement are not expensive)
- Set timing correctly

If the problem still exists

- Fuel pressure checks
- The fuel filter ever been replaced?

These cars are getting old. People may say "parts cannon" - but I've fixed up plenty of 20 year old cars where normal maintenance items have never been replaced. Even if that wasn't causing the problem, it's cheap insurance if you plan on keeping / driving it. I had an intermittent issue with a 5.0 EFI truck...it would run fine for days, then sputter, run like crap only at certain RPMs etc. Did timing check, fuel pressure check, visually looked at the fuel filter (it looked OEM) replaced it. The old filter RATTLED when I shook it. Something had broke loose inside and apparently would randomly partially block fuel flow.

- Aftermarket air intake? Filter clogged? Etc.

HTH
 
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Thompson452021

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Air, Fuel and Spark.

Personally, I never take for granted the previous owner did anything right. That's just me.

If it were me?

- Replace spark plugs (I'm sure plenty will chime in - but the 5.0 EFI in my opinion always liked cheap Autolites the best - maybe that's just me)
- Wires (you can easily test them)
- Cap and Rotor (check yours - GOOD quality replacement are not expensive)
- Set timing correctly

If the problem still exists

- Fuel pressure checks
- The fuel filter ever been replaced?

These cars are getting old. People may say "parts cannon" - but I've fixed up plenty of 20 year old cars where normal maintenance items have never been replaced. Even if that wasn't causing the problem, it's cheap insurance if you plan on keeping / driving it. I had an intermittent issue with a 5.0 EFI truck...it would run fine for days, then sputter, run like crap only at certain RPMs etc. Did timing check, fuel pressure check, visually looked at the fuel filter (it looked OEM) replaced it. The old filter RATTLED when I shook it. Something had broke loose inside and apparently would randomly partially block fuel flow.

- Aftermarket air intake? Filter clogged? Etc.

HTH
Adjusted the timing a bit and it seemed to help so after taking a quick test drive it seemed to run pretty decent just at a bit higher of an idle but that’s also because I had the tp a little tighter. Coming near the end of the drive it would act up but not nearly as bad, when I parked and let idle, it was running around 35psi of fuel pressure, but before the drive it was sitting comfortably at 38-40. I’ve noticed on days that it’s running decent, after having to sit at a light or parked in a spot it’ll begin to act up again. I think next I’ll try the filter and if that’s not it then either pump or injectors, recommendations on what to get for either?
 

96blak54

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Be sure to check the injectors, in your hand. Look them over good to be sure they are not Chinese like(copy) bosch injectors. Ford parts were copied throughout the 2000's and sold during the Ebay boom. For the most part the copy injectors did ok untill any fuel psi was higher than stock causing the injectors to lock and not function.
 

95opal

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Adjusted the timing a bit and it seemed to help so after taking a quick test drive it seemed to run pretty decent just at a bit higher of an idle but that’s also because I had the tp a little tighter. Coming near the end of the drive it would act up but not nearly as bad, when I parked and let idle, it was running around 35psi of fuel pressure, but before the drive it was sitting comfortably at 38-40. I’ve noticed on days that it’s running decent, after having to sit at a light or parked in a spot it’ll begin to act up again. I think next I’ll try the filter and if that’s not it then either pump or injectors, recommendations on what to get for either?

So it seams as though your issue is heat related.
Pump failing
Coil on its way out
PIP failing
What do the plugs look like?
Was that fuel pressure with vacuum off or on?
 
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Thompson452021

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Be sure to check the injectors, in your hand. Look them over good to be sure they are not Chinese like(copy) bosch injectors. Ford parts were copied throughout the 2000's and sold during the Ebay boom. For the most part the copy injectors did ok untill any fuel psi was higher than stock causing the injectors to lock and not function.
That’s good to know, who should I get injectors through if it is those? After messing with the car, it does seem like a fuel cut
 

r3dn3ck

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That’s good to know, who should I get injectors through if it is those? After messing with the car, it does seem like a fuel cut
The ford parts counter is normally a solid option for knowing what you're getting even if you'll probably pay a premium for the privilege. Might be able to just have the injectors cleaned. They might just have some buildup. They'll likely need new o-rings anyway if they're stock or even just old. If they're very old the original o-rings gotta be pretty hard by now. I'd buy new o-rings before you pull the injectors.
 

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