My 89 Trans Am 350 came bored .060 over with a BBK adjustable fuel pressure regulator. I have no idea what the pressure was set at when I got it. When you floor it, it accelerates hard up until about 4500 rpms, when it loses almost all power. It takes forever for the engine to accelerate from 4500 to 5000 if you keep your foot down. I realize that this is out of the powerband of this engine but this is an abrupt loss of power. The problem was worse before (stuttering at 4500), and I got a new fuel pump, which helped the problem some, but it still feels extremely weak. What do you guys think I should do? Do I need a high volume fuel pump or should I just try increasing the fuel pressure?

 

What is the pressure at now?? My first step would be verifying pressure and making sure that it is holding under load. Then I might double check the ignition timing as well as inspecting the ignition components, make sure thats all okay. Then it might be informative to hook it up to a scantool and see where the o2 is going under WOT (see if it is leaning out)..

 

I have no idea what the pressure is now....I don't have a guage or anything and I haven't adjusted it since I got the car

 

If your running TPI its prolly the intake thats holding you back. TPI is notorious for after 4500 RPM power loss because of the long runner design. Fuel flow could effect it, But if your TPI I'd almost bet its because of your intake. Well I don't really know about a sudden loss of power, I know TPI doesn't drop off like rev limiter. I would check the pressure

Tyler

 

It shouldn't drop off drastically like that.. This situation sounds more like its ignition related then fuel and/or intake design.

I still have the stock runners/plenum/throttle body on my e-tec motor (with stock manifolds as well at the moment), and you can tell that its not making any extra power past around 5000 rpm, but nothing strange happens.

 

Our intakes were designed with the 305 motor in mind and the 4500rpm drop off doesn't sound too uncharacteristic.

 

I have to agree..

They will fall on their face past 4750...welcome to the wonderful world of TPI...these intakes should have came stock on 1/2 tons...

Later,

Erik

 

If it's missing/stuttering, has nothing to do with the intake...my guess would be ignition failing or possibly valve float frmo weakazz factory springs.

 

There is a difference between drop off of horsepower increase (and even drop off of horsepower) and drop off of engine-running.

 

The first thing to do in these situations is to check the fuel pressure at idle and at WOT, as stated above by thirdgen88.
Do yourself a favor and buy a good fuel pressure gauge.

 

Huh..I did not read int oit enough...no that is not normal. If oyu look at a TPI dyno sheet, the torque curve will platue at 4750 ish depending on CID, BUT it should not miss...it should run to 5-6k but you effectivly just reving the motor at this RPM.

I would check a few things like are you getting injector pulse at these RPM's, and does your firing voltage drop off drasticaly at these high RPM's?

 

I will definitely get a gauge and try to check the pressure. The thing that makes me thing it is a fuel flow problem is that when I put a new fuel pump in, it made a big difference. I know TPI is limited to low end, but I have driven TPI cars before and the power has never just dropped off like this.

 

How hard is it to install a fuel pressure gauge? By the way the TPI car that I've driven is an iroc with a 305 and although its weak up top, it doesn't feel anything like this