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? Under load the car struggles to climb above 2500 rpm with lots of backfiring through the CAI as the rpm's climb. With no load it revs easier but you can still detect difficulty climbing through the rpm band.

Thanks.

 

Chilton's shows the fuel pressure requirements as being the same for both the V6 and V8 engines (95). Check the fuel pressure with the engien running. At idle, remove the vacuum compensation line from the fuel pressure regulator (hold your finger over the line to avoid a vacuum leak). The fuel pressure should be in the range of 41-47psi. Reconnect the vacuum line. The fuel pressure should drop proportional to intake manifold vacuum. 36-37psi would be acceptable with full vacuum.

Tape the pressure gauge to the windshield and take it out on the road. With the engine at max load/max RPM and at WOT, the fuel pressure should be the same as you measured at idle without the vacuum line. In no case should the fuel pressure be less than 41psi at WOT.

 

Injuneer,

Thanks for the suggestion. I will do this tomorrow and post back here with the results. I suspect the pressure will sit around 36 psi like it did when I just ran the car at idle and with no load. I look forward to getting more feedback from ya

Thanks again....

 

Ok here is a rundown of what I did today and what the results were.

Hooked up the tester and began taking measurements:

41 PSI ignition on but engine off
37 PSI car idling
41 PSI car idling vacuum line unhooked from the regulator and plugged
37 PSI car idling vacuum line reconnected
35 PSI engine at 2000 rpm car stationary
41 PSI engine at 5000 rpm car stationary
39 PSI under light load
40 PSI under moderate load
41 PSI under heavy load WOT 2000-5000 RPM

Pulled back into the driveway and tried to measure pressure with the vacuum line unplugged again. Could not do it as the car would die immediately after unhooking line.

Waited 15 minutes and went for round 2:

41 PSI ignition on but engine off
36 PSI car idling
41 PSI car idling vacuum line unhooked from the regulator and plugged
32 PSI between 2000 and 5000 rpm sitting in the driveway with no load
38 PSI under light load
40 PSI under moderate load
42 PSI under heavy load WOT 2000-5000 RPM

Not sure how to decipher this information but hopefully it means something to you.

 

Injuneer,.....anyone else any ideas on where to go with this? Regulator, injectors? Fuel pump would appear ok to me.

 

Pressure meets minimum specs. Have you changed the filter?

 

First thing I did. Cheap and easy. Original was remarkably soiled. Literally looked like pasty mud when I I cut it open and ran my fingers against the element. Wonder if the sock/ element on the pump itself is in similar condition. May get me 1-2 more psi but I don't think that is the main problem since the pressure is still technically within spec.

 

Thought I would post an update.

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?

 

Bueller? Bueller.....?

Injuneer?

Any help out there?

 

Low system voltage will affect both the fuel and the ignition. The injectors slow down and the spark weakens.

Have you looks for problems with the 3 coil-packs?

 

I've checked out the Alternator and it's fine but I have not checked the coil packs. Is there a way to measure output?