Stroked my 360 to a 408 with lots of fun parts and machine work. I've got just about all the kinks worked out, but ran into what the dealer called a "fuel problem." They synced the distributor for me (why I was there) then told me that the engine wasn't getting enough fuel (still running with no power at all). I had the PCM tuned already, but switched to 36# injectors to see the performance difference. You can smell it runs rich, but for some reason at 3K RPM it dies off and drops to 2500 and shoots right back up only to repeat. It looks like it's hitting a rev limiter at 3K. I checked fuel pressure at the rail, and it shakes consistantly and quickly from 35-45 psi (within specs) even during the RPM drop. Any ideas? I think I'm gonna go crazy over this one!

 

are you running a tune with the new motor ?

 

I thought pressure was supposed to be about 49PSI? The fact that it bounces ten PSI should tell you there is a problem there....

And did the tune you got include the 36lb. injectors?

 

35-45 PSI is not normal for our trucks. I have owned a 1996 5.2 and the PSI was 49. I own a 2001 5.9 and the PSI is 49.


Your fuel pressure is the problem.

Just to be sure, are you running a MSD 6AL without a chip plugged in? Because if you are running a 6AL ignition and take out the external rev limiter ship...the box makes your engine top out at 3000 RPM

 

Working with hemifever for the new (B&G did the first one) tune. Both Chilton and Mitchell have the pressure at 35-45 psi for the rail pressure. The only change to the ignitionis a 70K Accel coil and 7.5 mm wires. I know it runs rich with the changed injectors. I put those in at the reccomendation of a local speed shop (not going back there). First build with MPI, so I'm sure it's related. I think I'll wait for the tune from hemifever before I replace more parts. I guess it's possible it's running so rich now that the PCM is limiting engine speed, or the tune from B&G was bad.

 

post some pics when your done too

 

You need to get a wideband air/fuel gauge. It will never get tuned correctly until you actually know HOW rich you are.

I would also try running it with stock injectors.

ALso, your wires are pretty thin for that coil you have.