Fuel pressure (1965 tri power) - Pontiac GTO Forum
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post #1 of 23 (permalink) Old 06-05-2018, 07:29 AM Thread Starter
 
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Fuel pressure (1965 tri power)

So my car is running fine (for now) but I just installed a FP regulator and inline gauge and my pump appears to be putting out less than 3 psi (regulator maxed) !!! John from Pontiac Tripower suggested that I install a FP regulator and gauge to limit the FP pressure to ~3.5 psi (which he feels is ideal for the tri power setup). I had always thought it was supposed to be more the 6-8 psi. Also, the FP gauge needle is really bouncing (I know the car has a mechanical FP, but all cars I have ever seen with FP gauges are much smoother).

My question is did the factory fuel pump only produce ~3 psi or is there a problem with my pump / setup ? (It appears the new FP are cheap - sub $40 and probably fairly straight forward to replace.) The car runs fine and AFRs are good right now. I am just wondering if it is a matter time.....

Thanks
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1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #2 of 23 (permalink) Old 06-05-2018, 08:35 AM
 
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5-6.5 psi is what's called for. Also check your flow rate as that can be an issue as well.
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post #3 of 23 (permalink) Old 06-05-2018, 08:58 AM Thread Starter
 
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5-6.5 psi is what's called for. Also check your flow rate as that can be an issue as well.
To check flow rate, I am guessing you mean install an inline gauge ? Not sure how I would do that, but I will look into it.

So it sounds like my fuel pump is on the way out ??

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #4 of 23 (permalink) Old 06-05-2018, 09:19 AM
 
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The easy test is take the inlet to the carb off and connect a rubber hose long enough to reach a safe place outside the engine compartment, then put the hose in a coffee can and have someone start the engine. You should have a steady forceful stream into the can (at least a pint) . If it starts out good then falls off in less than 30 sec, then check the sock in the tank for being restricted. These are old cars. Just had a old chev with a plugged sock and it would run but not very well under load, changed the fuel pickup tube and pump and now runs 4-0.

Oh, just to make sure you know, fuel is flammable, be careful when spraying it around a hot engine :-)

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post #5 of 23 (permalink) Old 06-05-2018, 09:53 AM Thread Starter
 
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The easy test is take the inlet to the carb off and connect a rubber hose long enough to reach a safe place outside the engine compartment, then put the hose in a coffee can and have someone start the engine. You should have a steady forceful stream into the can (at least a pint) . If it starts out good then falls off in less than 30 sec, then check the sock in the tank for being restricted. These are old cars. Just had a old chev with a plugged sock and it would run but not very well under load, changed the fuel pickup tube and pump and now runs 4-0.

Oh, just to make sure you know, fuel is flammable, be careful when spraying it around a hot engine :-)
I have a new filter, new sock, and new pickup, so I doubt that is the issue. I know it is flowing good enough to maintain AFRs (logging with a wideband), so if I were to check flow I would do so a tad more accurately ....No idea how this method would work anyways as the FP is mechanical and thus the car needs to be running for the FP to work (unless you are just cranking the car for 10 seconds and measuring output )....

My guess is the pump is on the way out (may be original) and is definitely ancient.

Thanks for your help.

Chris

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #6 of 23 (permalink) Old 06-05-2018, 10:29 AM
 
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Back in the day didn't have a method to do that, only checking plugs for proper color :-)

You can have weak pressure and flow and if a flat lander might be able to get around ok. Living around hills would be a different animal. Trying to make it up a pass like the Siskiyous or Blue mountains you would definitely have an issue!

There should be enough fuel in the bowl to run the car for at least 30 sec at idle. I don't know of a spec back in the day other than the rule of thumb being "at least a pint in 30 sec". I just watch the flow and can tell when it's not enough. Guess almost 50 years of dicking around with carburetors/engines something has to rub off...

If you have already done the work of checking the tank, next would be the pump and I would also replace any rubber lines you have not replaced yet. LOL, 53 years is a lot to ask of rubber :-)

Good luck! Let us know what you find.
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post #7 of 23 (permalink) Old 06-05-2018, 07:29 PM
 
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I would simply replace the pump just for good measure. If original, or even an older replacement, the pump's rubber diaphragm is most likely not compatible with ethanol fuel anyway and is/has deteriorated. For the price, and not too hard to replace, I would opt for an updated fuel pump that is ethanol friendly - and make sure all rubber lines are also ethanol compatible.

Assume that your needle in the carbs are also upgraded to the ethanol compatible type. I also assume that FP might fluctuate somewhat as the bowl fills/empties thus opening the needle and seat as needed- especailly when all three carbs are being used.
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post #8 of 23 (permalink) Old 06-06-2018, 08:06 AM Thread Starter
 
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I would simply replace the pump just for good measure. If original, or even an older replacement, the pump's rubber diaphragm is most likely not compatible with ethanol fuel anyway and is/has deteriorated. For the price, and not too hard to replace, I would opt for an updated fuel pump that is ethanol friendly - and make sure all rubber lines are also ethanol compatible.

Assume that your needle in the carbs are also upgraded to the ethanol compatible type. I also assume that FP might fluctuate somewhat as the bowl fills/empties thus opening the needle and seat as needed- especailly when all three carbs are being used.
Thanks Jim! Would a Carter unit be fine https://www.summitracing.com/parts/c.../submodel/base ?



Chris

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #9 of 23 (permalink) Old 06-06-2018, 07:25 PM
 
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Thanks Jim! Would a Carter unit be fine https://www.summitracing.com/parts/c.../submodel/base ?



Chris
Although the Summit description does not indicate if the rubber diaphragm is compatible with ethanol gas, it seems to be according to this Hot Rod article - so yes, looks like a good one: Pontiac Fuel Pumps - How To Select The Right Fuel Pump - Hot Rod Network
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post #10 of 23 (permalink) Old 06-08-2018, 12:15 PM
 
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Just my 2 cents, but when I rebuilt the 400 I had in my '65 I replaced the fuel pump with a Holley one. Ended up seeping fuel from the tri-power because the Holley was pushing 5-7 psi and the Tri-power floats were being overcome. I installed a Holley fuel regulator before the inlet, which was set at 3.5 psi and never had the float issue again. My tri-power was a '66 version and had been refurbished by PontiacTripower.com, Pete I think.

Joe.
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