Should fuel press. rise 1psi per 1 lb boost at part throttle? Knock problem

[Boston GN]

Had my car out for about a month now since the winter hibernation. Car seems to be running perfect, but at part throttle and at ~5lbs boost I got 4* of knock. This has happened a few times now at part throttle, I don't dare go full throttle. Checked plugs and they're white. New FP regulator was put in last year.
I am going to test it again with the fuel gauge attached to the windshield, but wanted to make sure at part throttle that the fp should rise 1-1 with boost and not only at WOT. I've been meaning to swap out my double pumper as I definitely don't need that much fuel anyway, but I want to diagnose the issue first before I go that route.
Scanmaster numbers seems dead on. I definitely need to get a powerlogger though.

 

[TurboTom72]

Fuel should rise 1:1 when making boost always, not just at WOT. I am definitely an advocate of the Powerlogger. I had mine for several years now. Very useful tool. Logging helps a lot with troubleshooting and tuning. Your scanmaster will be a lot quicker with the data and be able to display a lot more stuff.

 

[Boston GN]

Excellent, Thanks! Just wanted to double-check

 

[87GN_70GS]

It should be 1 psi : 1 psi but below 0 it should be 2" Hg vac : 1 psi fuel (same as 1:1, just units conversion since most gauges read inches Hg vac)

 

[TR Custom Parts]

Why would you want to take out your double pumper?

 

[Ttype6]

I've been meaning to swap out my double pumper as I definitely don't need that much fuel anyway.

This wouldn't be wise. The two pumps don't hurt the car in any way. They'll be there for possible future needs.

 

[krom]

I would check pressure with both pumps running to see what baseline is, on my car it is 60. When does the 2nd pump activate? Your numbers may not be 1-1 depending on your pressure levels.

 

[Boston GN]

This wouldn't be wise. The two pumps don't hurt the car in any way. They'll be there for possible future needs.

Car's been retired from racing. I use it for shows and just cruising around. Would make no difference in my application

 

[Boston GN]

I would check pressure with both pumps running to see what baseline is, on my car it is 60. When does the 2nd pump activate? Your numbers may not be 1-1 depending on your pressure levels.

2nd pump comes on at 10psi

Problem is I'm getting knock at part throttle way under 10psi. I wouldn't want to take the chance of getting it up to 10psi and popping something.

 

[Boston GN]

Why would you want to take out your double pumper?

The only reason I'd be taking it out is if the pumps aren't running as they should. I need to test the first one and go from there. Although, I guess I could just always replace that first pump if that's the case and keep the entire set up

 

[TurboTom72]

Or just swap pumps and see if the issue goes away.

Tom

 

[Ttype6]

Car's been retired from racing. I use it for shows and just cruising around. Would make no difference in my application

It would make no difference if you left it as is,if the pump and or pumps are good. Have you checked to see if fuel pressure rises?

 

[Boston GN]

It would make no difference if you left it as is,if the pump and or pumps are good. Have you checked to see if fuel pressure rises?

If the pumps are fine, it will stay as is. No reason to replace good parts.
Haven't checked if the FP rises correctly yet, hence my original post. That's my first step. Once I do that, then I can move on from there to further diagnose what my issue may or may not be.

 

[Amelio]

try jumping the power to the second pump so it is always on.....go for a spin and monitor for kr.....if it goes away then your primary pump is weak....then you can just swap the power from your second pump to run as the primary......quick easy test with a quick easy fix.

 

[TurboTom72]

Amelio, well put. That's what I meant, but you explained it a heck of a lot better than I did.

 

[Boston GN]

try jumping the power to the second pump so it is always on.....go for a spin and monitor for kr.....if it goes away then your primary pump is weak....then you can just swap the power from your second pump to run as the primary......quick easy test with a quick easy fix.

Great idea! Thanks

 

[Amelio]

Amelio, well put. That's what I meant, but you explained it a heck of a lot better than I did.

yeah no prob....I did the same thing years ago when chasing kr issues it ruled that out real fast.....

Hey Boston GN have you always had your second pump coming on at 10psi even when the car was running right? The reason I ask is because I think when I first went to a double pumper the pressure switch it came with was set around the 10psi range. Back then not knowing much about tuning these cars thats the way I left it.....years later after learning how to tune I have found that my car will run up to 19psi on my primary pump. I currently have the second pump coming on at 15psi I think because I have since gone to a bigger turbo but the car was just too rich when both pump were on below 15psi.

 

[Boston GN]

yeah no prob....I did the same thing years ago when chasing kr issues it ruled that out real fast.....

Hey Boston GN have you always had your second pump coming on at 10psi even when the car was running right? The reason I ask is because I think when I first went to a double pumper the pressure switch it came with was set around the 10psi range. Back then not knowing much about tuning these cars thats the way I left it.....years later after learning how to tune I have found that my car will run up to 19psi on my primary pump. I currently have the second pump coming on at 15psi I think because I have since gone to a bigger turbo but the car was just too rich when both pump were on below 15psi.

Its always come on at ten. Mainly because thats the way it came. I've always thought about changing it because of what you indicated. Once I sort through this, I may go through with that depending on how it's running.