My LT4 is lacking performance... What do you sugg.
Thread Starter
Racer
Joined: Jan 2000
Posts: 268
Likes: 0
From: Gilroy CA
My LT4 is lacking performance... What do you sugg.
Seems since I replaced the fuel pressure regulator (because it was leaking) with a TPIS adjustible regulator that I'm always adjusting it to keep it running strong. First after the install it ran great. Then a month or so I notice it doesn't pull as strong as it should. Found the pressure was high, adjusted it down to 47psi and it ran great again. A month or so goes by and it seems lacking power in the upper RPM range again. I adjust the pressure and it is good again.
Well the last time I had to adjust it I went by the instructions exactly by adjusting it to 47psi then driving it and increase it .5psi until I feel performance drop off. I've got it around 48psi right now and put a drop of thread lock on the screw thinking it was moving causing me to re-adjust it.
It now still isn't running as strong as it should be in the upper RPM (3k to redline). I changed the plugs, cleaned the K&N and pintle valve in the throtle body. Still no inprovment. It starts perfectly, idles perfectly and smooth, just doesn't pull to redline as it should.
Should I replace the pressure regulator with a stock one ? Should I replace the fuel filter ? Should I reset the ECM ?
Any suggestions would be greatly appreciated !
Well the last time I had to adjust it I went by the instructions exactly by adjusting it to 47psi then driving it and increase it .5psi until I feel performance drop off. I've got it around 48psi right now and put a drop of thread lock on the screw thinking it was moving causing me to re-adjust it.
It now still isn't running as strong as it should be in the upper RPM (3k to redline). I changed the plugs, cleaned the K&N and pintle valve in the throtle body. Still no inprovment. It starts perfectly, idles perfectly and smooth, just doesn't pull to redline as it should.
Should I replace the pressure regulator with a stock one ? Should I replace the fuel filter ? Should I reset the ECM ?
Any suggestions would be greatly appreciated !
Burning Brakes
Joined: Feb 2001
Posts: 882
Likes: 0
From: Chicago, IL
Cruise-In II Veteran
Re: My LT4 is lacking performance... What do you sugg. (GenoLT4)
You shouldn't need a AFPR on a relatively stock car, I'd go back to stock. I've never seen these really help at all on a stock car. I have seen them hurt performance though.
Fuel filter can't hurt either.
Fuel filter can't hurt either.
Safety Car
Joined: Mar 2000
Posts: 4,847
Likes: 10
From: Bartlett, IL
Cruise-In XI Veteran
St. Jude Donor '06-'07-'08-'09-'10-'11-'12
Re: My LT4 is lacking performance... What do you sugg. (C4 4Me)
47-48 PSI seems to be quite high for a stock car, I would suggest setting it to 42-44 PSI. It should not make a huge performance differece, try replacing your fuel filter.
Mike
Mike
Thread Starter
Racer
Joined: Jan 2000
Posts: 268
Likes: 0
From: Gilroy CA
Re: My LT4 is lacking performance... What do you sugg. (MVR 155)
The instructions with the regulator said "start at 47 psi, then go up .5 at a time until performance drops off ".
I'll change the fuel filter and try dropping the pressure. What about the air temp sensor ? It feels stronger when it is cold (under 170 deg.).
I'll change the fuel filter and try dropping the pressure. What about the air temp sensor ? It feels stronger when it is cold (under 170 deg.).
Safety Car
Joined: Jun 1999
Posts: 3,570
Likes: 3
From: Austin, Singapore, Kuala Lumpur, Houston, Dallas, Hong Kong, Elgin, etc.. Texas
Re: My LT4 is lacking performance... What do you sugg. (GenoLT4)
Seat of the pants testing is not reliable. Best to take it to chassis dyno and do the tuning.
Burning Brakes
Joined: Jan 2001
Posts: 964
Likes: 0
From: Cedar Park Texas
Re: My LT4 is lacking performance... What do you sugg. (GenoLT4)
I agree with C4 4ME. I would go back to stock on the AFPR. You don't need it for your setup. You can see my minor mods; and my car runs super strong,
and it is super fast.
and it is super fast.
Burning Brakes
Joined: Feb 1999
Posts: 1,157
Likes: 3
From: Encino CA
Re: My LT4 is lacking performance... What do you sugg. (Ed Ut)
My impression is that merely replacing the stock fuel pressure regulator with an adjustable one should never have a negative effect--if you set it to the same pressure as the stock one was running then you essentially have the "stock" regulator. The instructions that came with my TPIS for my LT-1 said to start with the pressure at 39psi (stock was 46psi)! I have tried all sorts of adjustments--some higher than stock and some lower (I am currently running about 48psi). My understanding is that no matter where you set it, the computer eventually compensates--increasing the pressure will cause the computer to shorten the pulse while decreasing the pressure will cause the computer to lengthen the pulse. My impression is that a higher pressure/shorter pulse combination is preferable as the fuel is more atomized.
Any others have better or more accurate info compared with my crude understanding of how this works?
Any others have better or more accurate info compared with my crude understanding of how this works?
Burning Brakes
Joined: Feb 2001
Posts: 882
Likes: 0
From: Chicago, IL
Cruise-In II Veteran
Re: My LT4 is lacking performance... What do you sugg. (DougSilver)
I wasn't sure so I didn't say initially but I do believe I have also heard the computer will eventually compensate anyways so you gain nothing by playing around.
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Drifting
Joined: Mar 1999
Posts: 1,250
Likes: 1
From: Greensboro NC
Re: My LT4 is lacking performance... What do you sugg. (SteveElliott)
I agree...I would get a new regualtor....however, if you change your fuel pressure, you PCM will change the injector cycle i.e. more pressure = shorter injector opening to achieve the correct fuel/air ratio as determined by the oxigen sensors...I really think adjusteable FP regulators are a waste of money on a stock car, especially an OBD II car (96 and later).