Did a Fuel Pressure Test=results

[Angry7M]

Ok so lately when i got WOT in the upper RPM's it feels like the engine is holding up or like Rpm's are going up slower than usual, this is usually in the 4,000-5,600 rpms range ( I shift at 5,500 or so) its like at those RPM's the engine is not making any power. But when i accelerate normally without going WOT it accelerates just fine. I was getting a code 25 running Lean, so I had the injectores cleaned at a shop (Injectors were installed while being cleaned). So after that the code didnt come back, but i did the fuel pressure test anyways just to make sure everything was ok. Although im still feeling the same problem described at the beggining.

Fuel Pressure Test results:
Fp and +B bridged (vehicle off of course)= 38 psi

(idle)Vacuum Hose disconnected from the FPR= 36-37 psi

(idle)Vacumm Hose Connected on the FPR= 28 psi

All the reading on the gauge seem to be with in spec according to the TSRM and my HAYNESS manual.

But the last thing to check is what got me. After the vehicle is tuned off, fuel pressure should remain at 21 psi. But on my gauge the Fuel pressure drops quickly after i turn the engine off. As soon as a shut off the engine the Fuel Pressure just drops all the way to 0 psi.

Okay so now where do i go from here? Or what else do i check? Thanks


Stock fuel pump im guessing.

Mods on 1989 Turbo 7mgte:

Stock CT at 10 PSI
Intake
2.5 Hard Piping
Spearco style intercooler
3" dowpipe and exhaust
5 speed swap
And im also throwing no codes

 

[IJ.]

Can you get FP under boost?

How do the AFR's look while boosting?

 

[Angry7M]

Can you get FP under boost?

How do the AFR's look while boosting?

Well the gauge im using is just a tester, its not an actual gauge in the car. And nope unfortunately i dont have a wide band. :nono:

 

[suprabad]

Can you get FP under boost?

How do the AFR's look while boosting?

I bet ya he's going lean at higher boost levels...dangerous.

 

[IJ.]

Personally I'd either get it on the dyno to check the pressure under boost or buy a gauge I can see and test it.

If it's laying down enough for you to feel the engine is living on borrowed time.

 

[Angry7M]

But as long as I dont go WOT anymore it should be fine shouldnt it?

Well im going to extend the Fuel pressure gauge to the cockpit, and see what kind of FP i get. What should the FP read?


BTW where i live we have no Dyno, which sucks.

 

[IJ.]

Is it a mechanical guage?

If so DON'T take it inside the car.....

Just tape or cable tie it to a wiper.

Keep it out of boost totally not just WoT.

 

[jetjock]

Do a snap throttle test with the diag block jumpered and the FPR hose off. See if pressure drops more than 2 psi.

The loss of rest pressure could be anything from a bad FPR to a leaky injector. I'd be fixing that if I were you...

 

[Angry7M]

Do a snap throttle test with the diag block jumpered and the FPR hose off. See if pressure drops more than 2 psi.

The loss of rest pressure could be anything from a bad FPR to a leaky injector. I'd be fixing that if I were you...

Okay exactly how do i do this snap throttle test? Also is the engine on or off for this test?

Yeah i wanna fix this as soon as possible.

Edit: do i jump FP and B+?

 

[jetjock]

Disconnect the hose and, while monitoring fuel pressure, quickly snap the throttle wide open from idle several times. Fuel pressure should not drop more than 2 psi. The test works best when the engine is running

edit: no can read?

 

[lagged]

its not a bad idea to just replace the fuel pump.

and do not boost on it until you fix the problem.

these pumps in my experience dont last much longer than 10 years.

in my 86.5 with a GTE i blew a head gasket due to a failing fuel pump.

in my 91 1jz i have not detonated, but the car has been hard to start recently and sure enough, the check valve in the fuel pump is no good. the fuel pressure drops right to zero when you shut the car off, just as you have described.

you should replace it with a walbro or a mkiv twin turbo denso fuel pump.

 

[Angry7M]

its not a bad idea to just replace the fuel pump.

and do not boost on it until you fix the problem.

these pumps in my experience dont last much longer than 10 years.

in my 86.5 with a GTE i blew a head gasket due to a failing fuel pump.

in my 91 1jz i have not detonated, but the car has been hard to start recently and sure enough, the check valve in the fuel pump is no good. the fuel pressure drops right to zero when you shut the car off, just as you have described.

you should replace it with a walbro or a mkiv twin turbo denso fuel pump.

Ohh thats something else I forgot to mention, the car wont start right away, it take a lil longer but not much.

 

[Angry7M]

Disconnect the hose and, while monitoring fuel pressure, quickly snap the throttle wide open from idle several times. Fuel pressure should not drop more than 2 psi. The test works best when the engine is running

edit: no can read?

LOL its cuz i got confused when you said to jump the diagnostic box.

Okay ill try that ina min. Thanks

 

[Angry7M]

Disconnect the hose and, while monitoring fuel pressure, quickly snap the throttle wide open from idle several times. Fuel pressure should not drop more than 2 psi. The test works best when the engine is running

edit: no can read?

Okay I just performed the test.

Okay I snapped the throttle three times repedetly real fast. The FP at idle is 36 37 with the vacumm hose disconected

The first and second Throttle snap it went down to 29 psi and the third snap it went down to 35 psi

 

[lagged]

replace your fuel pump.

hopefully you didnt rattle your motor too bad.

 

[Angry7M]

Lagged so your telling me to replace the fuel pump based on the throttle snap results?

Okay so if its not holding pressure, the check valve in the fuel pump would be at fault correct?

If so would someone explain to me how this can cause my car to run lean? Wouldnt a bad check valve in the fuel pump cause stariting problems only? Im just curious lol.

Also with the throttle test i did, what did i check for?

Thanks guys

 

[Angry7M]

any help>???

 

[annoyingrob]

If your pump is getting old, and not flowing what it should, as boost pressure increases, the pump will have a harder and harder time maintaining pressure.

You should really find a way to check your fuel pressure at high boost. If it's not putting out 38+boost psi, then it's having flow problems.

 

[jetjock]

The loss of rest pressure (which will cause starting problems, usually when hot) should be treated as a separate issue although it's possible to have it related to the other symptom depending on where it's "leaking". That's why I said you ought to fix it. The fuel pump check valve could be at fault but it could also be lots of other things.

Assuming no leaks excessive pressure drop during a snap throttle test indicates a restriction in the supply side of the fuel system. Kinked line, poorly flowing filter, plugged sock, anything that could starve the engine of fuel during demand for it. The drop could be from a dying fuel pump but there are ways of testing for that. Measuring pump current, rpm, deadhead pressure, flowing the supply side of the fuel system into a container (minimum is 1 liter/30 seconds), etc. Point is pressure should not drop more than a couple of psi with the regulator hose disconnected.

Fwiw my fuel pump is over 21 years old and works fine. Then again the car has less than 150K miles on it. That doesn't mean it won't die tomorrow just as I'm putting my foot down. Based on that alone lagged's advice has merit....

 

[Angry7M]

The loss of rest pressure (which will cause starting problems, usually when hot) should be treated as a separate issue although it's possible to have it related to the other symptom depending on where it's "leaking". That's why I said you ought to fix it. The fuel pump check valve could be at fault but it could also be lots of other things.

Assuming no leaks excessive pressure drop during a snap throttle test indicates a restriction in the supply side of the fuel system. Kinked line, poorly flowing filter, plugged sock, anything that could starve the engine of fuel during demand for it. The drop could be from a dying fuel pump but there are ways of testing for that. Measuring pump current, rpm, deadhead pressure, flowing the supply side of the fuel system into a container (minimum is 1 liter/30 seconds), etc. Point is pressure should not drop more than a couple of psi with the regulator hose disconnected.

Fwiw my fuel pump is over 21 years old and works fine. Then again the car has less than 150K miles on it. That doesn't mean it won't die tomorrow just as I'm putting my foot down. Based on that alone lagged's advice has merit....

Well the last time i changed my fuel filter was about a year ago(If i remember right). But ill probably just replace it anyways. Yeah im probably going to replace my fuel pump anyways but that will be in a few weeks when i get money to do it.

And ill also try to get some reading of FP when im boosting. Although i didnt really want to keep boosting it since of the mentioned problems of boosting and running lean.

Thanks for the info guys!