Problem with hesitation

[Aaron]

I'm not sure where to start looking for this problem, so I'm sure somebody here will know. I own an 87 GT which is fairly stock. The only upgrades are BBK headers, H-Pipe, Flomasters, K&N Filter, and underdrive Pullies. The problem is when the car is warmed up it does some major hesitating when in 4th (and sometimes 3rd) gear when I'm just crusing (2000 - 2500 RPM). The problem seems to get worse when my gas guage goes below 1/2 full. If the car is cold, everything is 100% fine. I need to upshift when the car starts doing this so that I can get it to stop. The car idles great so I don't think it's strictly related to RPM. Any ideas?

 

[50Dreamer]

I dont think your getting enough fuel pressure. Make sure the vacuum line is on the regulator. This could also be a fuel pump problem. If you can get a fuel pressure gauge for the shrader valve and check that out. Thats where i would start.

 

[jrichker]

Since you have a K&N filter, the MAF element may be dirty. Clean the MAF element with non-flammable brake cleaner or electrical parts cleaner. Spray it down and let it dry before re-installing it into the MAF housing.

 

[Aaron]

Since you have a K&N filter, the MAF element may be dirty. Clean the MAF element with non-flammable brake cleaner or electrical parts cleaner. Spray it down and let it dry before re-installing it into the MAF housing.

I don't have a MAF sensor - my car is an unconverted 87 GT (Speed Density - not mass air). I'll check out the fuel pump though.

 

[hi_po_heads]

have you checked for a melted plug wire or fouled plugs. my problem like that was caused from the wires.

 

[PRO50SC]

Does this problem occur at light throttle pressure(meaning pedal pressure is just past idle, to maintain your cruise speed) if so you could have a glitch in your TPS.

 

[plastic_cow]

It could also be that it hasn't been converted - my car hasn't gone over to MAF yet, althought I have everything all ready to be hooked up, I just haven't done it yet, and the car hesitates and bucks, we did a MAF conversion on my friends 87 and it fixed the problem for him...

 

[Aaron]

Does this problem occur at light throttle pressure(meaning pedal pressure is just past idle, to maintain your cruise speed) if so you could have a glitch in your TPS.

Well it does it then, but it also does it when I push the gas pedal down a lot more too. The only times it will stop is if I upshift. If I get the RPM's up close to 3000, it's fine again. And it only seems to do it once the car is warmed up, and especially when it's warm and the gas tank is below 1/2 full.

 

[Aaron]

have you checked for a melted plug wire or fouled plugs. my problem like that was caused from the wires.

My plugs and wires are actually fairly new (Within 2 years and I only drive the car 4-5K miles per year.) That is all in good shape. I physically looked at the wires and I didn't see anything bad. I haven't pulled the plugs though...I'll check to make sure the tips are in good shape.

 

[The Shape]

Have you pulled your codes to see if anything pops up? Not saying it is your problem, but as a poster above said it could be TPS related. Mine would do the same type of thing and it would clear up if I gave it a more gas I just had a bad spot in the sensor and it would hesitate at a certaing RPM. It is worth checking out you can probe it with an analog volt meter and see if the needle sweeps up smoothly as you push the throttle open. Mine actually threw a code for TPS sensor voltage below minimum or something like that. You are in the same boat I am with the 87' year model no check engine light to tip you off.