The Resurrection: 94 Firebird Formula

[Injuneer]

If the pressure dropped at the sensing point, the regulator would just close down and reduce the return flow to hold the pressure. It's self actuated so response should be instantaneous or close to it. The bubbles are going to form on the pump suction side when there is high temperature, and pressure is lost through the sock and the pump inlet, plus lift when the tank is low. Possibly another cause of the pump heating up, which heats the fuel up - I don’t know if the in tank pump still has the bucket. I have the original pump and it's still in the plastic bucket.

I would also consider relocating the outboard pump. I don't like the way the suction line goes up and over the axle assembly. Pump should be below the level in the tank, and the length of the -10AN suction line should be shortened. It's screwing with net positive suction head. I located the outboard pump where it is now when I installed the NOS kit. It was piped as an inline booster. With the present setup, I hope the outboard pump has a check valve, so fuel doesn’t bypass backwards through it when it’s not running. Also would be good to keep the suction line from draining backwards into the tank, and no suction when the pump is started.

Never had any problems of these sorts. It always “worked”, but I don’t recall the ambient temperatures we are seeing now. I think the cera-metallic coating on the AS&M headers helped keep under hood temperatures lower. The pressure held when the engine was cranking close to 800 flywheel HP on the chassis dyno. But that was 20 years ago.

Maybe consider a fuel cooler. George's car needed one due to the huge amount of fuel that was being pumped.

[SSlowBoat]

"the car is very rich when hot"......
Maybe... check ECT sensor(the one in the water pump), if it's lying to the PCM, it might think the engine is still cold when it's hot and keeping adding fuel.

the temp is accurate, its been logged

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[SSlowBoat]

If the pressure dropped at the sensing point, the regulator would just close down and reduce the return flow to hold the pressure. It's self actuated so response should be instantaneous or close to it. The bubbles are going to form on the pump suction side when there is high temperature, and pressure is lost through the sock and the pump inlet, plus lift when the tank is low. Possibly another cause of the pump heating up, which heats the fuel up - I don’t know if the in tank pump still has the bucket. I have the original pump and it's still in the plastic bucket.

I would also consider relocating the outboard pump. I don't like the way the suction line goes up and over the axle assembly. Pump should be below the level in the tank, and the length of the -10AN suction line should be shortened. It's screwing with net positive suction head. I located the outboard pump where it is now when I installed the NOS kit. It was piped as an inline booster. With the present setup, I hope the outboard pump has a check valve, so fuel doesn’t bypass backwards through it when it’s not running. Also would be good to keep the suction line from draining backwards into the tank, and no suction when the pump is started.

Never had any problems of these sorts. It always “worked”, but I don’t recall the ambient temperatures we are seeing now. I think the cera-metallic coating on the AS&M headers helped keep under hood temperatures lower. The pressure held when the engine was cranking close to 800 flywheel HP on the chassis dyno. But that was 20 years ago.

Maybe consider a fuel cooler. George's car needed one due to the huge amount of fuel that was being pumped.

fred, not sure if you know or not, but did they use the stock relay and wiring for the in-tank pump? im starting to lean to that.

also there is NOT a check valve anywhere in the fuel system. when primed the pressure hits, then when prime stops the pressure drops

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[shownomercy]

I may have missed it but does this issue only present when on Nitrous?

[SSlowBoat]

I may have missed it but does this issue only present when on Nitrous?

nein, basically i threw the parts cannon at it since after the first one nothing fixed the issue.

so before first backfire, car was acting a little funky, would randomly stall when coming to a stop and would also be idling fine and randomly die, like idling then "putt putt putttttt" out. immediately would restart fine, no long crank or anything, key off then crank and fire right off.

suspected opti, changed opti because i found the rotor exploded. then it had a intake pop when revved off idle. changed everything (except fuel pumps/fuel reg/engine harness/ltcc brain).

changed opti to a know good one, still happened, didnt sound right. figured out one of the 60lb injectors was getting wonky (cold cylinder super fat etc), changed to brand new racetronix injectors, while at it made new plug wires, replaced plugs. then the car felt "back" to what it was, felt strong again, no more pop back thru intake when revved.

car was running great. got the blms in line, tuner revised tune, all was well so decided to go to the track. 2 passes no issues, 3rd pass waiting to do burnout (like in the burnout box) idling car does its stall thing again out of nowhere....i was like ok maybe i bumped the key adjusting the wheel, restarted fine, revved it a bunch sounded fine, did burnout fine, go up to line revved it a bunch while purging to try to make sure there wasnt fuel/nitrous leaking in the intake and it was clear. stage and go to leave car was at 2000rpm revved to about 3000rpm and BOOOM again back thru intake

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[Injuneer]

The Bosch pumps don’t have check valves as far as I know. What I was concerned about is the point where the two pump discharges merge in the NOS “Y” fitting, before the fuel filter. If both pumps are running, no problem at the “Y”, the fuel flow merges and heads for the filter.

But, what if only the in-tank is running? There is potential for the pressure at the “Y” to cause some of the fuel to bleed into the outboard pump discharge line. With no check valve in the pump, you're losing some fuel capacity, with back flow thru the pump, into the tank. The correct thing to do would be to add a check valve to the outboard pump discharge. I don’t think you would want to place a valve in the pump suction line and cause pressure loss (valve open, but still a restriction of some sort compared to an open line). On the other hand, putting a full diameter, low delta P check valve in the outboard suction line near the tank would also keep the suction line full where it goes up and over the rear axle. Having the outboard suction line drain back to the tank could make it difficult for the outboard pump to prime when it turns on. I never observed any pressure issues that indicated this was a problem.

Even with the check valve in the outboard pump circuit, the pressure would still drop to “0” when the pumps shut off, because there would be no obstruction in the in-tank flow path.

I guess I get obsessive on the fuel system. After I graduated with my BSME I went to work for “Esso (now Exxon) Research & Engineering” doing conceptual design for refineries and chemical plants all over the world. We were constantly in graduate level classes learning more about fluid flow, hydraulics, thermodynamics, heat transfer, oil, gasoline, etc.. Sure, it’s a major scale down to an automotive fuel system, but the principles still apply. I just wish I was not 5.000 miles away in Italy when Second Street was putting the car together. There are some things I would have done differently.

[SSlowBoat]

The Bosch pumps don’t have check valves as far as I know. What I was concerned about is the point where the two pump discharges merge in the NOS “Y” fitting, before the fuel filter. If both pumps are running, no problem at the “Y”, the fuel flow merges and heads for the filter.

But, what if only the in-tank is running? There is potential for the pressure at the “Y” to cause some of the fuel to bleed into the outboard pump discharge line. With no check valve in the pump, you're losing some fuel capacity, with back flow thru the pump, into the tank. The correct thing to do would be to add a check valve to the outboard pump discharge. I don’t think you would want to place a valve in the pump suction line and cause pressure loss (valve open, but still a restriction of some sort compared to an open line). On the other hand, putting a full diameter, low delta P check valve in the outboard suction line near the tank would also keep the suction line full where it goes up and over the rear axle. Having the outboard suction line drain back to the tank could make it difficult for the outboard pump to prime when it turns on. I never observed any pressure issues that indicated this was a problem.

Even with the check valve in the outboard pump circuit, the pressure would still drop to “0” when the pumps shut off, because there would be no obstruction in the in-tank flow path.

I guess I get obsessive on the fuel system. After I graduated with my BSME I went to work for “Esso (now Exxon) Research & Engineering” doing conceptual design for refineries and chemical plants all over the world. We were constantly in graduate level classes learning more about fluid flow, hydraulics, thermodynamics, heat transfer, oil, gasoline, etc.. Sure, it’s a major scale down to an automotive fuel system, but the principles still apply. I just wish I was not 5.000 miles away in Italy when Second Street was putting the car together. There are some things I would have done differently.

im actually looking at check valves now. also gonna investigate the wiring back there. may try something, switch the external and internal pumps triggers so external is primary, just to see.

also found an interesting one on the nitrous side. the 12v trigger wire from the wot switch leading to the relay has resistance to ground when off and disconnected from the relay. this wire was an existing wire from the nitrous enable switch in the door that ran under dash, i just spliced a wot switch into it lol. guess there is a slight short in it. could explain my window switch issues

final thing is i thiiiiink i am gonna try 1 more time for spray and change the fuel solenoid. i have a nib Zex fuel solenoid i got from a buddy. one of the NJFBOA guys with a beautiful third gen is talking about a early october rental at our local track, and ive wanted to run him all year.
@shownomercy if dave does that you coming? thinking of bringing both cars, so yeah @Ltconvert

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[Injuneer]

Look at Kinsler for hard to find fuel system parts. Old school but a lot of good info in their huge online “Handbook”.

https://kinsler.com/Kinsler-Handbook/HTML/

See page 194 for some check valves.

The window switch and nitrous activation was all in the MoTeC. When it was set up originally with 2 stages, stage 1 was activated by the arming switch in the door, and stage 2 was activated by a button on the shifter (was still T56 at that point).

[JOATMON]

When I replaced the pump on my Camaro with a high LPH Quantum pump, the built in pump check wouldn't seat. I cut the line close to the fuel filter and added this;
https://www.summitracing.com/parts/u...83Bwx8HX3Tg8nw

Then on the LT1 powered '57 PU the same thing happened with the in-tank pump I used. I added one like this on the truck;
https://www.summitracing.com/parts/r...SABEgKfdfD_BwE

[SSlowBoat]

Look at Kinsler for hard to find fuel system parts. Old school but a lot of good info in their huge online “Handbook”.

https://kinsler.com/Kinsler-Handbook/HTML/

See page 194 for some check valves.

The window switch and nitrous activation was all in the MoTeC. When it was set up originally with 2 stages, stage 1 was activated by the arming switch in the door, and stage 2 was activated by a button on the shifter (was still T56 at that point).

yeah that wire for stage 1 12v hot when turned on has 3000 ohms resistance to ground. thats no good.

lookin like a vibrant high flow check is on order

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