Car misses/holds back under WOT

[ttypewhite]

Just throughing this out there to give me more avenues to check for on my beater. Under WOT the car feels like its holding back and kinda stumbling, then goes after 3 sec. I have changed this to remedy the problem with no luck.

-another ignition module and coil pack off of my T that I know works great
-tired another set of wires off my dad's car which works well.
-changed the plugs gapped at .32 Delco 42TS
-changed the 3 bar map sensor with the one on my T
-buttoned up all exhaust leeks at the downpipe and headers
-pulled out the intercooler and flushed it out
-put a new o2 on the car
-changed the fuel filter
-re adjusted the T&D's
-added new ground straps to the motor

This car has the SFI acell unit on it so I have no mass air to change. There are no vaccum leaks. It stumbles under wide open throttle only, drives and revs really good and smooth. My air fuel ratio is at 11.4 WOT and when it stumbles it goes to 11.8 then back to 11.4 when it clears up. Boost is pretty steady at 17 psi. The issue is probably staring me right in the face, but I have yet to touch on it. Any ideas?

 

[norbs]

If it has a voltbooster on it take it off and retry the car.

 

[ttypewhite]

no voltbooster on the car.

 

[ttypewhite]

I have also ran it on the street at 17psi with no exhaust after the downpipe to rule out the exhaust as a restriction.

 

[norbs]

try the stock ecm and see if its the dfi?

 

[bison]

What happens to the a/f ratio for the 3 seconds of breakup?

 

[ttypewhite]

What happens to the a/f ratio for the 3 seconds of breakup?

The air fuel goes to 11.8 then when it clears up it goes back to 11.4.

Norbs- i no longer have a stock computer with drivers in it or a mass air for that matter. Everything else with the car is great. Just a stumble for a bit under WOT.

I check out the cam sensor last night for a loose top or the screw inside the cap and both are good. I have my gap set at .032, I am going to try a tighter gap at .028 just to see how it responds.

 

[cabech984]

could it be possible that the TPS or Fuel pump is going out? Just a thought.

 

[Underboost]

Yeah maybe a flat spot in the TPS sweep?

 

[bison]

could it be possible that the TPS or Fuel pump is going out? Just a thought.

Maybe TPS but not fuel pump. It goes to 11.8:1 which would not cause a misfire. It would go a lot leaner if it was the pump. Maybe a sudden voltage drop?

 

[Bird of Prey]

how to check for a bad tps?

 

[ttypewhite]

I checked the TPS and at .42 v off the gas peddle I get 4.08 at WOT. When I adjust it to 4.6 the best I can get off the gass is .98 is this ok or do I need a new TPS?

 

[cabech984]

I checked the TPS and at .42 v off the gas peddle I get 4.08 at WOT. When I adjust it to 4.6 the best I can get off the gass is .98 is this ok or do I need a new TPS?

I wanna know too. I was wondering how you can adjust the idle number vs. WOT. It doesnt seem possible? Not w/ idle screw??

 

[bison]

I checked the TPS and at .42 v off the gas peddle I get 4.08 at WOT. When I adjust it to 4.6 the best I can get off the gass is .98 is this ok or do I need a new TPS?

You can remove the TPS and carefully grind off the raised plastic stop that only allows you to turn the tps in a circular motion. After grinding carefully and NOT letting the swing arm snap backward you will be able to pull the TPS sensor forward and up as much as you want to hit 4.8 at WOT and then push it down to get it at .42 idle. It is very important to not let the arm snap back after grinding off the stop or it could break the TPS. I usually hold the arm while grinding and dont release it till its bolted tot he TB. You will see why this allows for so much more adjustment after you re-install it. Be sure you are achieving WOT from inside the car when mashing the pedal after you set the sensor.