I've been trying to get my 1991 Firebird running, and it's been fighting every step of the way. It was running fine earlier today, but now it's running rough. It's bucking and has a very poor idle. I ran codes and got codes 33 & 34, both are related to the MAP sensor.

I bought the car without it running. Huge mistake. The distributor, cap, and rotor were replaced before I bought the car. I've personally replaced the timing chain, head gaskets, spark plugs, and probably more stuff I'm forgetting. The fuel injectors all tested within spec. 5 were above 12 ohms, one was 11.6 ohms. I don't have a fuel pressure gauge, so I wasn't able to test that.

The spark plugs are black, not fouled, but black. The exhaust does smell a bit rich. There might be an exhaust leak, it's kinda hard to tell. The oxygen sensors "look" new, but who knows. The exhaust from the cats back is completely new.

I just wanted to get your opinion before I swap out the MAP sensor, they aren't exactly cheap. Maybe there's some more trouble shooting I should do.

 

Go to a junkyard and grab 3-4 MAP sensors. I believe I gave the guy about $5 for 3 of them. They're all over the place on FWD cars, and pretty much everything past 90... The ECM is telling you there is a MAP fault. You need to reset the ECM to find out which code is current. You can't do anything else before you find put which code is current.

 

one is MAP high and one is MAP low, if both codes come back again then it might just be trashed. Check the vacuum line to it though.

 

Plus you can bench test the MAP sensor. You need a 5v supply, volt meter and vacuum pump. You can see how to wire it up from the manual. When vac is applied you should see a steady change in the output voltage. It's a bit to learn but being able to test your components can save you time and money in the long run.

 

Well, I replaced the MAP sensor. Didn't help. The car has no power, and it stalled twice when I tried to drive it around the block. The vacuum line going to it is in good shape. I really want to just give up and swap in a 350.

 

Use a multimeter and check the harness pins, one should be 5 volts, one should be ground and the other is the signal.