Vortech supercharged LT1... Fuel Pressure problem!?!
09-03-2008, 07:02 PM
#1
Vortech supercharged LT1... Fuel Pressure problem!?! I installed a Vortech V1 S-trim supercharger on my 95 formula LT1. I also installed a walbro 255 pump in the tank. I purchased an 8:1 ratio FMU.
My electric fuel pressure gauge is reading just under 40 while the car sits idle and continues to bounce around 38-42 while driving conservatively.
When I hit throttle and the boost pressure gauge goes into positive boost, the fuel pressure doesn't respectively rise. If the FMU is set at 8:1 then the fuel pressure should be rising to about 80 while there is 5lbs of boost. The fuel pressure gauge never reads above 42, so there is a big problem!
I am trying to trouble shoot this... I wanted to test my fmu, so I took the hose off that supplies the boost pressure to the fmu and hooked my air compressor up to it and tried as accurately as possible to blow 5lbs into the fmu to see if the pressure would rise on the fuel pressure gauge which it did rise to above 60... it was hard to tell accurately how many pounds of air were used somewhere between 5-10.
I also used pliars to crimp the gas line to let the pressure build up in the line to see how much pressure my walbro pump would create, and even though it was hard to temporarily crimp the line the fuel pressure still rose to above 70.
I am wondering if anyone else has encountered this problem or has any troubleshooting suggestions? I am wondering if the computer is regulating the fuel pressure or possibly if the boost comming from the manifold to the FMU isn't creating enough force to make the FMU work properly... or it could be something else entirely?
My electric fuel pressure gauge is reading just under 40 while the car sits idle and continues to bounce around 38-42 while driving conservatively.
When I hit throttle and the boost pressure gauge goes into positive boost, the fuel pressure doesn't respectively rise. If the FMU is set at 8:1 then the fuel pressure should be rising to about 80 while there is 5lbs of boost. The fuel pressure gauge never reads above 42, so there is a big problem!
I am trying to trouble shoot this... I wanted to test my fmu, so I took the hose off that supplies the boost pressure to the fmu and hooked my air compressor up to it and tried as accurately as possible to blow 5lbs into the fmu to see if the pressure would rise on the fuel pressure gauge which it did rise to above 60... it was hard to tell accurately how many pounds of air were used somewhere between 5-10.
I also used pliars to crimp the gas line to let the pressure build up in the line to see how much pressure my walbro pump would create, and even though it was hard to temporarily crimp the line the fuel pressure still rose to above 70.
I am wondering if anyone else has encountered this problem or has any troubleshooting suggestions? I am wondering if the computer is regulating the fuel pressure or possibly if the boost comming from the manifold to the FMU isn't creating enough force to make the FMU work properly... or it could be something else entirely?
09-03-2008, 08:59 PM
#3
Def DITCH the FMU get some new 42Lb Injectors and you should be fine. I run 42lb inj with a p-600b procharger NO fmu and the car reads 51-53lbs at WOT 41lbs at idle. Mail order tune. Dyno tune coming this month!!
09-03-2008, 10:23 PM
#5
FMU is a relatively unreliable and unpredictable way to make up for a good tune.
+1 on the injectors and tune by someone that knows their **** on boosted motors with your ECU.
Jim
+1 on the injectors and tune by someone that knows their **** on boosted motors with your ECU.
Jim
09-03-2008, 10:26 PM
#6
Alright fellas, I REALLY believe a tune is the best way to go, but I was going to try to solve this problem and get it running right before I looked into injectors for next season... That being said, next season I would like to get into self tuning... I have done some research and actually ordered a usb cable to connect to my car along with downloading a freescan program to start some research. I am considering tunercat for my 95 lt1. If nothing else I need to switch over my gear ratio from installing new 4:11 gears awhile back so my speedo reads right, so the program will pay for itself... I just wonder how much you can do on your own with that program and how easy the fueling and injectors are to change. I have a lot of learning to do and I am not going to just start changing things at random, I want to learn...
If anyone has any other suggestions on what my problem might be then I am all ears!
If anyone has any other suggestions on what my problem might be then I am all ears!
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03-13-2009, 09:13 AM
#8
B.)
It's not cool to jump in someones thread and try to turn it into your thread. Just do a quick search on the topic you want to know about, and if that doesn't work then start your own topic. Things work out much better that way. 
