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Discussion Starter · #1 ·
Looks I will need new fuel pump internals! I have experienced the worst knock that I have ever had with this car. Anywhere from 2.1~5.25 at wot. I have experienced knock in 3rd and 5th gear. I have logged for the last two days to figure the problem out and here it is.

Mods:
Stage1 +SF 93 v103, Cobb SF Short Ram Intake, Synapse Synchronic BOV(100% recirc.), RPMC Motorsports Turbo Inlet, StreetUnit Silicone Boost Tubes, Redline MT-90 Gear Oil, Royal Purple 5w30, Denso Iridium Spark Plugs(ITV22).

Problem:
The stock fuel pump can not supply the proper fueling on the “fly” that the map requires. Every single instance where I had hardcore knock, I lifted of the throttle, then shifted, then went back wot.

Hypothesis:
Stock fuel pump is fine when it is flowing at its max, continuously, during wot. No lifting of the throttle when shifting keeps the fuel pump running max flow. I have several logs showing little to no knock when I do not lift off the throttle to shift. I have other logs showing that when I lift off the throttle to shift, the fuel pressure drops and stock fuel pump struggles to deliver the required fuel when going back up to wot.

Evidence:

No lift, 3rd & 4th gear pull, kr=0



No lift, 3rd & 4th gear, kr<1.05, lift/shift 5th gear pull, kr>4.9



Cruising-WOT, 3rd gear pull, kr>2.1



I will not be going wot until I get my fuel pump internals from pg. Normally I do lift off the gas to shift when I am going wot. It was a just a fluke that it happen on one of these nights, that revealed a huge problem. So, until I get my internals, I will be babying the car and watching for any more hardcore knock.

Anyone else seeing this problem? Please post your concerns and opinions.
 

· Registered
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595 Posts
Discussion Starter · #3 ·
[quote author=pwrful4 link=topic=137644.msg2967540#msg2967540 date=1235862647]
The lift/no-lift has nothing to do with, but you are right you do need new fp internals, your last graph shows fuel pressure around 1100, well below the allowable specs Cobb put out.
[/quote]

The problem only occurs when I lift. Lifting off the throttle, even for a second, cause the fuel pump to reduce its flow. Then, in an instance, getting back on the throttle cause the fuel pump to sputter due to it can handle the dramatic change in fuel demand that the map requires. So it sputters untill it can keep up with the fuel demand causing knock. Or am I thinking to hard about this and just need new internals? :)
 
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