Pro60modman
New Member
- Joined
- Jan 5, 2017
- Messages
- 5
Alright so I have a 2008 GT500 that is giving me fits.
JLT big carbon fiber intake, Kooks LTH, and 2.6" Metco pulley and idler kit.
First thing it did was drop fuel pressure at WOT down to about 10psi by 4800rpm. Replaced the pumps with Deatschwerks 300M, fuel filter(old one was recently replaced and in good shape) and deleted the PPRV and that fixed my fuel pressure issue. After the fueling issue was fixed I found it would misfire above 5000rpm and after a lot of testing I concluded that the alternator was dropping from 14v to 12v at WOT then spiking back and forth from 12v to 15v which I figured was tripping up the coils due to the dwell times bouncing all over the place. I replaced the alternator and added two grounds from the block side of the engine mount to the sway bar brackets. This fixed my voltage problem and it now stays rock solid at the PCM commanded 13.75v at WOT. The car no longer misfires above 5000rpm.
Now however the car drops fuel pressure at WOT like stone around 4000-4500 rpm. Not like before either with the worn out stock pumps. Before when it had the fuel pressure issue it would gradually fall from 39psi to 10psi at WOT over the course of 2000-3000rpm. Now it drops instantly from 55psi(I changed WOT fuel pressure to 55psi after I did the pumps) to 10psi when doing a pull. When I replaced the pumps initially it held 55psi to 6000rpm without issue so I don't know what the hell happened. I checked the fuses and they aren't blown. I removed the fuel pump hanger and confirmed both pumps work with no abnormal noises. Everything is hooked up properly, no damaged hoses or wiring. The filter socks are good as well. When this happens the car triggers a P0148 and that's it. I suspect an FPCM is dropping out at high load but I'm not sure how to test that on the street. Any pointers? You can't log the 2 FPCM individually on HPtuners and I'm not confident enough to stuff myself in the trunk and have a buddy go WOT while I probe each one lol.
JLT big carbon fiber intake, Kooks LTH, and 2.6" Metco pulley and idler kit.
First thing it did was drop fuel pressure at WOT down to about 10psi by 4800rpm. Replaced the pumps with Deatschwerks 300M, fuel filter(old one was recently replaced and in good shape) and deleted the PPRV and that fixed my fuel pressure issue. After the fueling issue was fixed I found it would misfire above 5000rpm and after a lot of testing I concluded that the alternator was dropping from 14v to 12v at WOT then spiking back and forth from 12v to 15v which I figured was tripping up the coils due to the dwell times bouncing all over the place. I replaced the alternator and added two grounds from the block side of the engine mount to the sway bar brackets. This fixed my voltage problem and it now stays rock solid at the PCM commanded 13.75v at WOT. The car no longer misfires above 5000rpm.
Now however the car drops fuel pressure at WOT like stone around 4000-4500 rpm. Not like before either with the worn out stock pumps. Before when it had the fuel pressure issue it would gradually fall from 39psi to 10psi at WOT over the course of 2000-3000rpm. Now it drops instantly from 55psi(I changed WOT fuel pressure to 55psi after I did the pumps) to 10psi when doing a pull. When I replaced the pumps initially it held 55psi to 6000rpm without issue so I don't know what the hell happened. I checked the fuses and they aren't blown. I removed the fuel pump hanger and confirmed both pumps work with no abnormal noises. Everything is hooked up properly, no damaged hoses or wiring. The filter socks are good as well. When this happens the car triggers a P0148 and that's it. I suspect an FPCM is dropping out at high load but I'm not sure how to test that on the street. Any pointers? You can't log the 2 FPCM individually on HPtuners and I'm not confident enough to stuff myself in the trunk and have a buddy go WOT while I probe each one lol.
