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Knock Light Causes


eightpilot said:
Easily.... AFR's go way lean and boom....Knock light city Had it happen a few years back.
Click to expand...
Interesting. I would get knock on good fuel even with additive 2 years ago. Last year I didn't get knock once. One thing I did change was the fuel pump. It was just as a safety precaution since I was running the 300 tune a lot more, but maybe it was the reason my knock went away. Hard to say. I changed clutching as well so not a great baseline, but now you have me wondering.
 
Get an AFR gauge on that sled. It’s the only way to see what’s going on. I run an AEM setup and it’s well worth the $120. Especially if you're running the adjustable regulator.
 
DooZ said:
Didn't you put a new one in last year?
Click to expand...
New one going in today or tomorrow. I did relocate the GAS return line last year. That did not solve my issue last year. I had a new pump last year and was trying to eliminate one thing at a time to see what worked.
 
snowdust said:
Interesting. I would get knock on good fuel even with additive 2 years ago. Last year I didn't get knock once. One thing I did change was the fuel pump. It was just as a safety precaution since I was running the 300 tune a lot more, but maybe it was the reason my knock went away. Hard to say. I changed clutching as well so not a great baseline, but now you have me wondering.
Click to expand...
300 tune on stock fuel pump is suspect for sure IMO.
 
Agree. I know that with a PEFI 300 tune, you need a higher volume fuel pump.
 
I believe TD says 290. I believe the stock is fine with a stock machine. ANY TUNE is pushing the limits. IMO. At least in my experience with mine. Plenty out with miles on and TUNES WITH no issues. Hell mine was always good with half a tank or more. Until 9k then symptoms really started even at half tank at the end of last year.
 
I am going to find out. Upgraded to the 240/270/300 tune with trail muffler this year. There was no suggestion of a fuel pump upgrade........
 
STAIN said:
I am going to find out. Upgraded to the 240/270/300 tune with trail muffler this year. There was no suggestion of a fuel pump upgrade........
Click to expand...
I was told 300 is the max for the stock pump. Since I was running the 300 tune as well I didn't want to be close so I just upgraded the pump. I got mine through Tommcat Performance. It wasn't a requirement though. Opinions vary of course.
 
How many of you w 290 tune or more tune are able to record or data log fuel pressure at WOT?
PEFI told me their 280 tune maxes out the fuel system at ambient temps at -10 degF or below. In other words, with their 280 tune, if you're running WOT below -10 degF, you're gonna lean it out on long pulls. Fuel pump/injectors will not be able to keep up with demand.
 
Will the new closed
Turboflash said:
How many of you w 290 tune or more tune are able to record or data log fuel pressure at WOT?
PEFI told me their 280 tune maxes out the fuel system at ambient temps at -10 degF or below. In other words, with their 280 tune, if you're running WOT below -10 degF, you're gonna lean it out on long pulls. Fuel pump/injectors will not be able to keep up with demand.
Click to expand...
Will the new closed loop tunes help with this or am I way off base?
 
eightpilot said:
Get an AFR gauge on that sled. It’s the only way to see what’s going on. I run an AEM setup and it’s well worth the $120. Especially if you're running the adjustable regulator.
Click to expand...
Where do you get a AEM setup for $120 ?
 
Turboflash said:
How many of you w 290 tune or more tune are able to record or data log fuel pressure at WOT?
PEFI told me their 280 tune maxes out the fuel system at ambient temps at -10 degF or below. In other words, with their 280 tune, if you're running WOT below -10 degF, you're gonna lean it out on long pulls. Fuel pump/injectors will not be able to keep up with demand.
Click to expand...
I've logged lots of tunes and 19- 20 psi seems to be the threshold where things can go lean but needs to be cold and a long pull.
 
This fall while doing maintenance on my sled i drained down my fuel tank due to it being full and wanted it lighter for moving around the garage.
I removed the fuel line and installed a clear hose from pump to gas can and hooked up wires to the battery with an inline switch to drain it using the pump.
When pumping the fuel out below half tank I was getting air bubbles in my fuel. I would stop for a bit then go again. After about 4 seconds it would show air bubbles again in the fuel.

I am going to pull the pump and lines out to inspect. Will a bad pump cause this?
 
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