LT1 will not Rev past 4500 RPM
06-24-2013, 01:58 PM
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LT1 will not Rev past 4500 RPM Ok, Here is my first cry for help….
I currently run a ’94 Trans Am with the following setup. Short block pulled from ’94 Corvette all stock, not an LT4 either. 1.6:1 roller rockers, 42lb. Bosch injectors, Walbro 255LPH in-tank pump, Aeromotive Adjustable fuel pressure regulator, Hooker shorty headers with Edelbrock Cat-back less the cat, Jet MAF sensor, MSD 6BTM ignition, Pro Charger P1SC 7lb. boost with single cooler, Snow Stage 2 Methanol injection system, Moser 12 bolt with 3.73:1 rear end and a T56 6Spd transmission.
I have reprogrammed the ECU with various different tunes including one custom built for the above description by a reputable source. The issue I am having that I cannot seem to resolve is this. At full throttle or at least more than 85% throttle, the car will just fall on its face a 4500 RPM. There is no missing, no sputtering, no weird noises at all. It just goes from 4500 RPM down to 2000+ RPM and loses power. Both the boost gauge and fuel pressure gauge drop from about 7 PSI boost back to vacuum and fuel goes from about 50 PSI to below 30 PSI. I have replaced all of the following parts as a test and varied the fuel pressure from 43 PSI to 50 PSI to try and compensate. MAF sensor, MAP sensor and the ignition module.
I can run the RPM up past the 4500 RPM mark into the 5000+ area if I do not exceed the 85% throttle mark. If I put a 5000 RPM pill in the BTM it will bounce the limiter and pull the ignition as expected giving me the indication that the coil and ignition components are working properly.
If I prime the pump with the ignition in the ON position, I have the regulator set to 48 PSI the pressure will drop almost immediately. I read that is because the Walbro pump does not have a check valve in it. Is there a way I can test the fuel system to see if it is unable to feed the motor at full throttle conditions, or is there something else I am missing?
Any help would be greatly appreciated.
I currently run a ’94 Trans Am with the following setup. Short block pulled from ’94 Corvette all stock, not an LT4 either. 1.6:1 roller rockers, 42lb. Bosch injectors, Walbro 255LPH in-tank pump, Aeromotive Adjustable fuel pressure regulator, Hooker shorty headers with Edelbrock Cat-back less the cat, Jet MAF sensor, MSD 6BTM ignition, Pro Charger P1SC 7lb. boost with single cooler, Snow Stage 2 Methanol injection system, Moser 12 bolt with 3.73:1 rear end and a T56 6Spd transmission.
I have reprogrammed the ECU with various different tunes including one custom built for the above description by a reputable source. The issue I am having that I cannot seem to resolve is this. At full throttle or at least more than 85% throttle, the car will just fall on its face a 4500 RPM. There is no missing, no sputtering, no weird noises at all. It just goes from 4500 RPM down to 2000+ RPM and loses power. Both the boost gauge and fuel pressure gauge drop from about 7 PSI boost back to vacuum and fuel goes from about 50 PSI to below 30 PSI. I have replaced all of the following parts as a test and varied the fuel pressure from 43 PSI to 50 PSI to try and compensate. MAF sensor, MAP sensor and the ignition module.
I can run the RPM up past the 4500 RPM mark into the 5000+ area if I do not exceed the 85% throttle mark. If I put a 5000 RPM pill in the BTM it will bounce the limiter and pull the ignition as expected giving me the indication that the coil and ignition components are working properly.
If I prime the pump with the ignition in the ON position, I have the regulator set to 48 PSI the pressure will drop almost immediately. I read that is because the Walbro pump does not have a check valve in it. Is there a way I can test the fuel system to see if it is unable to feed the motor at full throttle conditions, or is there something else I am missing?
Any help would be greatly appreciated.
