here's the deal....so the other day I was driving my 91z28 on the freeway when I got on my throttle I noticed a bog or lose of power in every gear but only at high rpms. so I thought it was my clutch slipping? Or my rear end? a couple of my mechanic buddy just told me that would not be the problem. so then I resorted to maybe it was just bad gas. so I drain the tank and changed the fuel filter and still getting the same problem. so then I started to talk to a couple more guys now I'm getting it's either a fuel pump, a vacuum advance on my distributor, or possibly I'm getting bad igntion spark at high rpm?? Any thoughts

 

Im just throwing this out there because i want to make sure, im not trying to insult you or anything. Was the bog at around 4000-5000 rpms? Because the TPI engines (stock) are notorious for "running out of breath" at about 4500rpms. I just want to make sure you arent looking for problems that arent really there, instead its a normality for the engine.

If you dont think / know thats not it, id start with the "basics". If it needs a tune-up (plugs, wires, cap & rotor, ect.) start with that. If not, it doesnt hurt to inspect them for any problems.

You can look for vac leaks by spraying carb cleaner on all the vac lines and intake gaskets, if theres a leak where you spray you will notice the rpms surge a little. Usually you feel/notice the vac leaks at lower rpms though, and its not usually something that "kicks in" at a certain rpm, its a constant problem at any rpm, growing worse with the higher rpms of course. As cheap as vac lines are, any soft lines that are in even somewhat questionable shape, replace. If you dont now, youll still have too soon!

After that, id check fuel pressure & ohm injectors.

Hope this helps, good luck!

 

black88z you stold what i was gonna say. Check all those things and if you have an actual issue you will find it

 

Thanks guys....well I just did the coil, plugs,cap, rotor,and wires less than a year ago. Its reall not at that high of RPMs. Its more like at 2800-3500RPMs. (to touch on what you said on running out of breathe is that fixable with a new set of performance runners?) I spoke to a guy I know at a muffler shop before I had this issue. I had him look at my exhaust from a leak I was having by the y pipe and he told me I have to many bends and my pipes were not.all the same size. He asked me then if I was feeling any kind of power lose? Could that be what it is too? he explained to me if the pipes are not bent correctly or have to many unnecessary bends and the sizes are not the same it can reduce the flow of the exhaust(explained to me the hour glass theory) and at high rpm's almost feel like a power loss

 

Put a fuel pressure gauge on the fuel rail you can get them at Oreillys..long hose attached to them. Tape it to your winshield then see what happens under load.

How old are your catalytic converters?

Your muffler guy was trying to sell you a new system you dont need.

 

Well I work at a part store so I know.everyone pretty well no one trying to sell me anything...my exhaust was put on poorly and it shows....my hooker y pipe was all bent to sh#t by the person who put it on before the guy who did it can't bend 3inch pipe so he took a piece from my old y pipe (21/2") And tac welded it into my hooker y pipe that's 2 3/4 to my tail pipe which its 3 its all fed up lol.....any way I don't have cats on the car they been gone for years now.fuel gauge idk because of its driven nice and smooth out don't do it only when I get on it is where the problems are coming from

 

If you hadn't said you had no cats, I would definitely be looking for clogged cats. What muffler are you running? Is it possible that the muffler is broken down internally and restricted.

 

well I'm running flow masters 80 series

 

Flowmasters aren't likely to breakdown. A couple of things that I would be checking: Fuel pressure as this happens. Cuisinartvette already detailed that test. Fuel injectors. If you don't know how old yours are or where they came from, they are suspect in a power loss problem. Of course check your air filter and air inlet for any restriction.

As far as TPI "running out of breath". I will agree that TPI is not the ideal intake for a high revving engine. Many FI intakes will outperform TPI at high revs. Having said that, look at my sig, at the details of my build. Research the ZZX cam from TPIS. The twisted wedge heads that are perfect for this setup aren't available anymore but AFR195s should give similar results. This long tube TPI motor hits it's rev limiter at 6,900 in a heart beat. On a full throttle pull through 2nd gear it does not drop off at all until 6,500 where there is a barely noticeable plateau before I shift at 6,800. Even with the plateau it pulls hard enough that it's well worth shifting at 6,800 instead of 6,500. So, yes, high flow intake parts will help you raise the rpm shelf of TPI. To get the results I got required a very carefully designed system including heads and cam and everything ported for maximum flow. Along with a little luck that it works as well as it does.

 

Glad i found this thread! I'm having the same problem with my 87 trans am. Im running a 383 with all new parts (2 years old). Mine seems to sputter whenever I give about 3/4 to full throttle... otherwise it runs great. My question is what should the fuel pressure be at?