Been trying to troubleshoot a problem with the 3.4 in my Firebird see this thread if interested: https://www.camaroz28.com/forums/sho...d.php?t=627327 and today I hooked up a fuel pressure tester. Fuel pressure with the pump on and the engine off was around 36-37 psi. With the engine idling pressure was the same 36-37. I ran the rpm's up to 5k with no load and the pressure sat around 35-36 psi. Anyone know if this suggests I have a bad fuel pump or fuel regulator or both?

Thanks.

 

41-47 is listed as normal key on engine not running.

Engine running at idle it can drop by 3 -10psi

 

Didn't really drop at idle except for maybe 1 psi. Sat right around 36 psi from idle through 5k rpm. What do you Fuel pump or regulator or both? The car has 150k so I'm tempted to say screw and throw in a new pump, regulator/ fuel rail and injectors and call it a day. Should fix whatever fuel problem there is if there is one and I should be good to go for another 150k.

 

Thats fine if bucks are unlimited, but it may not solve your problem.

I just read the other thread and it does sound like a clogged cat, but you said you don't have one.I highly doubt its a bent cam,but stranger things have happened.

Even if the timing chain jumped a tooth or two it wouldn't behave like that.

It could also be an EGR valve problem or your Map sensor.

Do you see where I am going with this?

Do not throw a bunch of parts at it,you need to get to the heart of the problem.

You need to get a scanner on it to see what your engine is doing in real time,it could be the Map as the 3.4 is SD and that controls load

What is your altitude?

I have a chart with proper voltages for different altitudes

 

I hear you on throwing parts at the problem. I'm just frustrated at this point.

Certainly have no cat and I can't comment on the timing chain although this sounds as unlikely to me as the bent camshaft.

My altitude is probably around 300-400 feet.

I updated the other thread with more readings from the pressure tester if you are interested.

 

Below 1000 feet your voltage range on your MAP sensor should be 3.8v-5.5v

Low Altitude = High Pressure= High voltage

To test Black is ground - and gray is positive +

 

Here's an update. Also posted in the other thread.

I have now replaced all 6 injectors and the map sensor. The car runs even better up to 2000 rpm (feels stronger) but begins to sputter and backfire through the CAI the same way it did before. Anyone have any more ideas as to what else may be causing this problem? I'm considering taking the car to a dealership at this point to have the problem pinned down so I can finally get it fixed.

Could a bad alternator result in poor spark creating the same type of problems that poor fuel delivery would cause?