My stock TPI L98 is not running well. The car seems to have lost the ability to pull past 4000 rpm, however the motor runs fine below that point.

Timing and fuel pressure are good and all injector ohms are right on. I do not suspect the catalytic converter and my car is not MAF. I really think it must be something quite simple for how well the car runs through the rest of the power band.

What should I check out next? What vacuum leaks could cause this? Maybe just the ignition coil?

I had a new mustang GT provoking me on the road yesterday and it was very frustrating that my car was not running well enough to “fight back”. Thanks for any help.

 

Or maybe it could be a faulty knock sensor?

 

hard to say without a scan tool to watch the timing the motor is seeing and if there is any knock counts or spark retard from knock.

TPI doesnt pull well above 4000 rpms to begin with but if its cutting out bad, then definately check out ignition and fuel related items

start with checking the distributor cap and plugs. replace your ignition coil and check the ignition module to see if its corroded or not.

make sure there are no vacuum leaks either but i dont think thats it.

How old is the fuel pump and fuel filter?

 

Well when my foot is down my car usually shifts at like 5500rpm. When I say the car doesn’t “pull” I mean power drops, the engine just lingers around 4000rpm and doesn’t move towards redline.

The fuel filter is brand new. The fuel pump is stock but that is not something I want to replace on a guess. I will check the ignition parts and maybe buy a new coil.

Thanks for the suggestions and I would appreciate any others.

 

Sounds a lot like a fuel pump going out. I put my bird in the shop due to the same symptoms you stated but instead of 4000 it was more like 3500 ran great until then and it just wouldn't go past it. After $500 and about 4 days the mechanic figured out it was a fuel pump going. To bad it took 500 just to figure that out.

 

when my car did the 4000 rpm and not pulling anymore it was 2 bad stock injectors
Ohm them again once they are hot and at operating temps

 

The manuals describe a way to test the flow of the fuel pump but it does not sound very precise. Is there an easy way to test the fuel pump?

I checked the injectors cold so I will recheck them at operating temp.

Thanks

 

Tape a fuel pressure gauge to the windshield and see if the pressure drops at 4000 rpm.

 

I had the same problem except around 4400, i did everything then finally got it compression tested and found it was leaking in the top and bottom end, so that was my problem. The engine threw a rod a few months later. hopefully that isnt your problem.