I didn't want to risk taking the fiero for a drive before taking care of this problem. We hooked it up to a scanner and read some data... it put up "Intake air temperature sensor intermittent high voltage"... which doesnt make much sense to me.
Scrolling through streaming data, the IAT was reading -38F the entire time, while it was 80F outside and the engine warmed to 180F.

So questions... where is the IAT located? 3800SC series 3 motor converted with a 98 throttle body/fuel rails/pcm. There is one connection on my harness that I dont have hooked up (2 pin but cant remember wire colors), and one sensor in the side of the supercharger that isnt plugged in (oposite the bypass valve, near the TB), but they dont fit together (i tried).

The engine wants to stumble and return to idle if I rev it passed 3k... I'm guessing the IAT could cause this?

On the plus side, no KR haha

IAT does little to nothing fueling wise, it basically will give you or subtract timing...

The iat is a 2 wire sensor, should be RIGHT next to the throttle body wiring. Most people wire in a resistor to emulate 50F weather as it may effect some advanced forms of tuning (VE tuning).

The 3800 IAT is in the rubber intake tube and pops right out, this sensor does not fail often and can usually be checked visually for damage once removed. I would also make sure the sensor was wired in properly during the swap. The black wire from the IAT does not go to chassis ground it goes to a sensor ground fed by the PCM. Dan

Dark, may I ask what size resister?

Thanks Dan... that explains everything. I don't have the sensor at all...

try something around 2800ohms, would put you in the 75 degree F area.

5500 would be colder like 50.

[This message has been edited by darkhorizon (edited 07-20-2008).]

found out it wasn't the air intake sensor causing my stumble around 3k
now the car wont even run. No fuel pressure.

I dropped the tank to inspect the fuel pump and it had separated where the pump presses into the piece above it. Reinstalled it... now the pump makes a funny noise, squeaking like, and still no fuel pressure

time to drop again? I'm getting real sick of this

Make sure you use tank safe hose.... It will fall apart in days if you dont.

I dont know your issue with the funny noise other than maybe it is out of gas? You will need roughly 3 gallons in there to make it kick up every time.. I noitce whenever I install the high flow pumps you lose effective fuel tank capacity.

I hope you didnt put a resistor in for the IAT. in open loop it is a crucial sensor and in closed loop it is still used to help compensate for temp changes. dont just put a resistor in, if you want a properly running engine that is a dumb thing to do.

if it will not let you rev past 3k it sounds like a torque mannagement issue. my olds 98 3800sc wouldnt allow me to rev past 3k in neutral either. if its just a stumble then it could be a few different things.

as for how much gas you need, my fuel gauge is very innacturate and I have put 9.5 gallons in the thing and had no problems with my fuel pump not giving enough fuel. thats just my experience though. if you did run the pump dry for an extended period of time it might be cooked.

I just went to advance auto and got the IAT sensor for $13. That's no longer an issue.

I've dropped the tank 3 times so far... 3rd time to replace the coupler between the pump and output line with a hose and clamps. I used the same hose I'm running to the fuel rails, so I hope that's considered tank safe

The noise is gone... idk what it was all about. Perhaps I didn't have enough fuel in the tank after all. The pump seems to function so i don't think it's cooked.

Since I know it's not a leak in the tank anymore I started checking other things. It would always fill the fuel rails but less than 1psi... the engine would start and die immediately. So I blocked off the return line to the fuel tank and turned the key 'on'. Amazing! Pressure! The pump spun and changed tone as pressure built... I shut the key off quickly and checked the fuel rail... it's holding pressure.

So I guess that means bad fuel pressure regulator? I called advance and had them order me one... have to wait another day and I'm out another $70. Think this will get me on the road?

Unless your current pump is relatively new, I would have replaced it as a precautionary measure. As for aftermarket pumps causing reduced effective fuel usage from the tank, that probably has most to do with the install, if you're not careful it is easy to install any replacement pump higher than what it should be in the tank so that it is not as close as it should be to the bottom of the tank resulting in fuel starvation eventhough there is sufficient fuel in the tank. You have to make sure the lower ring stop at the bottom of the assembly is not bent upward displacing the pump to a higher position.

It's a walbro 255 pump. I ordered it brand new around christmas and haven't even driven the car yet... just had it idle for a while in the garage. That's why I didn't believe it could be the pump. Do you think replacing the fuel pressure regulator will fix it, based on what I wrote above? Blocking off the return line, I've got pressure. Otherwise, the pump can run all it wants but I build no fuel pressure, it all runs back into the tank.

Got a new fuel pressure regulator. I'm at work now so I havent installed it.

What range of fuel pressure should I see once it's installed? A manual for an NA 3800 said no more than 60psi. Is there a difference for the 3800SC?

i have my pressure base at 50psi, i believe the stock pressure is 45lbs with the vaccum line disconnected.

Base is 50 with no boost, then mid 40's at idle, and low 60's at full boost.

So basically, you will want a 1psi fuel pressure ramp per PSI.of boost pressure, with a base of 50.

I'm getting REALLY frustrated trying to get this thing going.

Could my pump be bad? I changed the fuel pressure regulator and still build little to no pressure.... I need suggestions. Any ideas at all... I need this car running because I move in two and a half weeks