Check valve in fuel pump stays open, does this hurt performance?

evil666

Active Member
This is concerning my brother's 87 GN. When he shuts off his car the fuel pressure drops to zero and when he cranks to start it, it takes a little longer for it to fire up because the fuel lines are empty. I was wondering if the check valve stays opened on the fuel pump , does this hurt performance? The fuel pressure at idle is 42 (vacuum on) and when the car is floored the fuel pressure goes past 70 psi. His car most of the time always gets KR off take off, something like this ( 38-19-6-0) on the otc 4000e, but after take off it drops back to zero for the rest of h 1/4 of a mile. The same thing happens off a roll on take off, except the car feels worse, as if something is holding back and as soon as it shifts in 3rd it takes off like a bullet.

Any replies will be appreciated, thanks Marco.

My brother’s 87 Grand National t-top (92 000 km)
Stock block with trw pistons and 30 over, stock heads, 210-205 lunati cam, PT61 Turbo, 65 mm kenne bell TB and plenum, 9 inch 3000-3200 stall art carr convertor, 22 ½ boost, 94 octane with 100% methanol with smc alk injection, thdp, hooker 2 ½ exhaust, 42 ½ lbs injectors, Armstrong 100 chip, ESP front mount IC, 26 BY 10 M/T ET STREEET TIRES, 3800 LBS race weight.
BEST ET= 1.60 60FT- 7.47 1/8- 11.80 ET-113 MPH
BEST MPH= 1.72 60FT – 11.87 ET AT 114,74 MPH

My 86 Grand National t-top (59900km)
stock long block,stock suspension, red stripe convertor, te44, smc alk injection, 24lbs boost, 94 octane, hooker cat back with dyno max ultra flow muffers, tomco 30lbs injectors, dynotech stage 4 street chip, thdp, mease 24 row IC, Ron Custom max boost brake module, MT drag radials (275/50/15) 3800lbs race weight with driver.
BEST E/T
60FT=1.52
1/8= 7.38
I/4= 11.74
MPH=113 BEST MPH=114
 
sluggish

Hi Marco,
Is the thdp a 3" job? Even if a 2.5, I suspect false knock.Check the exhaust system for contact.If that's OK,then check the accessory drive for funny noises,etc. Beyond that, possibly you have a hypersesitive knock sensor, though I have never heard of this. I don't think they cost much, though. Torque converter problems are a possibility. Does your brother hear the knock when the scanner shows it? If not, then start looking for false knock. Even with open exhaust, it should be noticeable. Good luck with your trouble.
Dale
 
First,
I would fix the fuel pump issue. This could be a faulty regulator, pump or line. Even though it says 70 PSI this does not mean the flow is there. I would really recommend replacing the pump and go to a 340 pump.

For your knock issue. Fix the pump first. I would back my boost down to 16 to 17PSI. Test with 94 and alchy. If that is OK then add 1 pound of boost and test. Ease up on the boost so not to pop a head gasket. If with 16 or 17 pounds of boost you still get that crazy knock, then I would look at what ever is causing false knock. DP hitting, loose brackets, serpentine belt and so on. Once you hav determined this not to be an ssues you may want to look at the cam. I had a reed 210/205 that for some reason set off the knock sensor.
 
Hi Dale
My brother has a 3 inch thdp and it is not touching anywhere. The only noise that we hear is the exhaust manifold leaks which I don't know if this could activate the knock sencor. When he takes off from a dead stop he doesn't hear noises or doesn't feel anything weird. When he floors the car from a roll on he doesn't hear any noises but the car feels as if it doesn' want to take off (as if it is forcing he says) but when it shifts to third it takes off. By the way what is a hypersesitive knock sencor?

Hi Machinegun
My brother recieved his brand new walbro 340 fuelpump but he hasn't installed it yet. I never thought if the check valve in the fuel pump would stay opened would affect the flow of fuel since the fuel psi is still above 70 psi. We will have to wait and see what happens with the fuelpump next year since the car is stored for winter. I don't think the 210-205 lunati cam is the problem because he has had this cam for a while and he didn't have any KR with this cam in the past.

Thanks for your help guys.
Marco

My brother’s 87 Grand National t-top (92 000 km)
Stock block with trw pistons and 30 over, stock heads, 210-205 lunati cam, PT61 Turbo, 65 mm kenne bell TB and plenum, 9 inch 3000-3200 stall art carr convertor, 22 ½ boost, 94 octane with 100% methanol with smc alk injection, thdp, hooker 2 ½ exhaust, 42 ½ lbs injectors, Armstrong 100 chip, ESP front mount IC, 26 BY 10 M/T ET STREEET TIRES, 3800 LBS race weight.
BEST ET= 1.60 60FT- 7.47 1/8- 11.80 ET-113 MPH
BEST MPH= 1.72 60FT – 11.87 ET AT 114,74 MPH

My 86 Grand National t-top (59900km)
stock long block,stock suspension, red stripe convertor, te44, smc alk injection, 24lbs boost, 94 octane, hooker cat back with dyno max ultra flow muffers, tomco 30lbs injectors, dynotech stage 4 street chip, thdp, mease 24 row IC, Ron Custom max boost brake module, MT drag radials (275/50/15) 3800lbs race weight with driver.
BEST E/T
60FT=1.52
1/8= 7.38
I/4= 11.74
MPH=113 BEST MPH=114
 
it could be the check valve in the pump, or a torn hose from the pump to hanger.
i have seen it, not alway is the valve bad-
Neither are horrible, but the hose should be checked to see if its perfect.

I know a guy that went 11.0 at 122 with a hole in the hose from the pump to a hanger... he drove it like that for quite awhile.
BW
 
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