Fuel 89 GT low fuel pressure

[FetusLasVegas]

Hi all! At koeo, when the pump primes I get zero reading at my fuel pressure test gauge. Once running, at idle it sits at 20psi, under throttle sits at 20psi, vac line removed from fpr, 20psi, etc.

Along with this I have all the symptoms of low fuel pressure/running lean. Hard starts, difficult to keep running when first started. Misfiring/backfiring, bucking in low rpm, power falls off at high rpm, cel and codes 41/91. I have just replaced the fuel filter and fpr, and the problem persists. Before ordering a new fuel pump I’d like to be sure that’s the issue. I feel like it’s the last piece of the puzzle, but I want to be sure.

 

[General karthief]

Yea,go ahead and replace that fuel pump. Just don't jump on the 'go big or go home' bandwagon. A 155 gives you lots of room to grow. Check the filler neck grommet and the seal at the top of the filler neck too, they get hard and torn with age.

 

[FetusLasVegas]

Is there a specific reason not to ‘go big’? With a negligible price difference and a return fuel system like ours why wouldn’t I go with larger knowing that outside of pump failure, I’ll never have to do this install again, regardless of the directon my build takes.

 

[General karthief]

Just because you can does not mean you should. The more fuel you move the more heat transfer the fuel is subjected to, also airiating the fuel is not a good idea. A 155 will support a bunch of hp, I think most here will agree no bigger than 190.

 

[FetusLasVegas]

Just because you can does not mean you should. The more fuel you move the more heat transfer the fuel is subjected to, also airiating the fuel is not a good idea. A 155 will support a bunch of hp, I think most here will agree no bigger than 190.

Damnit!!! I had to get my order in before 3pm and ended up going with the 255lph. The 155 and 190 were both out of stock anyway. I hope it's not too big of an issue.

 

[General karthief]

Doubtful, just do this alot.
you may need an aftermarket regulator, check you pressure to be sure.

 

[a91what]

255 is not a problem thats what i run but i have alot of mods that make it necessary. now i would also replace the fuel pressure regulator, nothing fancy is needed just a stock replacement will work. If you want you can step up to a kirban fpr and set it to the stock pressure.

 

[Dan02gt]

There is a short S hose that goes between the fuel pump and hangar connection. It has a tendency to split and might be your problem. I upgraded my fuel pump about a month ago and found this hose was about to let go on my car.

 

[FetusLasVegas]

255 is not a problem thats what i run but i have alot of mods that make it necessary. now i would also replace the fuel pressure regulator, nothing fancy is needed just a stock replacement will work. If you want you can step up to a kirban fpr and set it to the stock pressure.

From what I've read I didn't think it would be a big deal. I did just replace my fpr with a factory replacement so I should be all good on that end.

There is a short S hose that goes between the fuel pump and hangar connection. It has a tendency to split and might be your problem. I upgraded my fuel pump about a month ago and found this hose was about to let go on my car.

If that's the case I will find out on wednesday and update if so. I prob should have checked that before getting the new pump, but with a half tank currently I'd prefer to only drop the tank once...

 

[Blown88GT]

Damnit!!! I had to get my order in before 3pm and ended up going with the 255lph. The 155 and 190 were both out of stock anyway. I hope it's not too big of an issue.

255 is the max for another reason. Vacuum compensation at idle will be minimal; the factory return line is just too small. I have a 255 with a Kirban AFPR & it won't go below 40psi. Normal idle with vacuum line attached is 34-35 psi.

The Megasquirt can be tuned no matter what the idle pressure is.

You can use the existing pump to empty the tank before you drop it. You don't need pressure, only flow. Remove the schrader valve innards, attached a hose to it with a hose clamp. put the hose in a 5 gal fuel can. Jumper the test port to ground, turn the ignition on & the pump will run continuously.

 

[FetusLasVegas]

255 is the max for another reason. Vacuum compensation at idle will be minimal; the factory return line is just too small. I have a 255 with a Kirban AFPR & it won't go below 40psi. Normal idle with vacuum line attached is 34-35 psi.

The Megasquirt can be tuned no matter what the idle pressure is.

You can use the existing pump to empty the tank before you drop it. You don't need pressure, only flow. Remove the schrader valve innards, attached a hose to it with a hose clamp. put the hose in a 5 gal fuel can. Jumper the test port to ground, turn the ignition on & the pump will run continuously.

Is it a big deal to be running that rich at idle? Is there something I can do other than ordering a different pump?

 

[Blown88GT]

Is it a big deal to be running that rich at idle? Is there something I can do other than ordering a different pump?

If you don't mind a surging idle.

 

[FetusLasVegas]

If you don't mind a surging idle.

So an adjustable fpr wont amend this situation? I either need a lower volume pump or deal with surging idle? How bad of surging are we talking about? Is there a different option? No one has anything less than a walbro 255 in stock.

 

[Blown88GT]

1. So an adjustable fpr wont amend this situation?
2. I either need a lower volume pump or deal with surging idle?
3. How bad of surging are we talking about? Is there a different option?
4. No one has anything less than a walbro 255 in stock.

1. Nope. I even drilled out the return port as far as I dared to, maybe a few 1000th's
2. Or larger fuel rails & return line back to the tank. The restriction causes the pressure to be higher.
3. Can't say for sure. There are many options, but none may be desirable for you.
4. Did you look at getting a 155 or 190 locally? The factory one was an 88 which may be all you need with your current build.

In my case it was a defective pump sock that killed the pump.

 

[a91what]

I ran the 255 with the stock ECU no issue. I still get my 34psi at idle now with the gss255lph hp pump in tank. maybe I got lucky or I have it mixed up in my mind with the 225hp version.

 

[Blown88GT]

I ran the 255 with the stock ECU no issue. I still get my 34psi at idle now with the gss255lph hp pump in tank. maybe I got lucky or I have it mixed up in my mind with the 225hp version.

It could be because there are now many different 255''s, mine maintains pressure at high flow, I think it's the GSS342.
https://walbrofuelpumps.com/walbro-gss-fuel-pumps

4 different 255's shown here.

 

[JD1964]

There is a short S hose that goes between the fuel pump and hangar connection. It has a tendency to split and might be your problem. I upgraded my fuel pump about a month ago and found this hose was about to let go on my car.

Yeah, mine split!

 

[Steel1]

I've been running a TRE 255lph pump (not high pressure) on multiple different engine combos (supercharged stock ecu w/fmu and ecu w/chip)
Always ran a stock fpr and never had any high pressure issues.
Now currently running with my 393w PimpXS set-up.