Fuel pressure test schrader valve location.

[yorxs]

I'm starting to suspect the fuel pump is going out on my 93 GP 3.4. I replaced the fuel filter this weekend and while I was under the car I didn't see a schrader valve on the fuel rail. Am I missing the location or do I need some type of t-connector to do this test?

[94 olds vert]

It's located near the plenum fuel line. It should have a black cap on it.

[yorxs]

Plenum? Would this be in the engine bay then?

 

Also I don't see fuel pressure specs for an LQ1 with MPFI only PFI and SFI at 40 to 47 psi, would MPFI be the same?

[55trucker]

You need to pull up the engine cover, under it you can see the fuel rail that supplies the front bank, at the far right side where the rail makes a 90 degree to go around the front side of the engine you'll find the schrader valve there.

The fuel thru the rail when the engine is running can be from 40 to approx 48 lbs.

[yorxs]

Testing fuel pressure now but getting 0psi at key on but the car runs. Is 0psi even possible or am I just way off the mark?

[19Cutlass94]

0psi is no possible to obtain and still have car run. With the key on, pump will prime, but then pressure will bleed off. Best to test with motor running.

Edited April 7, 2013 by 19Cutlass94

[yorxs]

Should've clarified in the last post, 0psi at key on and while ruinng. If I depress schrader valve on the fitting to the guage it will squirt gas at key on, just not sure its 40+ psi or not, just can't get the guage to read anything.

 

Also how does one determine if the pump or the fuel pressure regulaor is the cause of low pressure?

[55trucker]

What are you using as a gauge to test the rail's pressure?

[yorxs]

Alright, tested before the pressure regulator, I'm getting 45 to 46 psi at key on and about 39 to 40 with engine is running. These numbers look good, but still 0psi after regulator so I replaced it and the Plugs, PCV and O2 sencsor since the is plenum off.

 

I still get an idle with lots of vibration, but a steady needle on the Tach. Car is slow to accelerate but seems to surge up to speed at about 35mph+. The engine has never stalled on me and the car starts right up.

 

Anyone had sucess with similar symptoms?

[Garrett Powered]

sounds like good fuel pressure. sounds like something else is going on though.

[55trucker]

Hmmmm........next step,

 

at idle, when this situation occurs, shut down the engine, pull the plugs out, and look for any plugs that are wet or discolored (not tan).

You said you replaced the plugs?....what about the plug wires?

 

If you find that they are all as they should be, put them back in, fire the engine, when this situation occurs (at idle), one by one pull off the plug leads and note any LACK of change in the engines idle.

 

start there, report back.

[yorxs]

Cylnders 1 and 4 seemed to have the least effect on the idle when removed. Tracing the plug wires back to the coils, they just so happen to be fed from the same coil pack. Looks like I finally found the culprit!

 

I'd like to remove each pack individually so I have an easier time marking which wire goes where. But its looking like the assembly they bolt to has to come out thus I need to remove all six wires at once. Kind of a pain to mark everything when you can't see shit down there. Advice anyone?

[jman093]

You can remove an individual coil. Remove the 2 small bolts going through the coil. They're like 4mm or something. It will then pull off of the ignition module.

[55trucker]

Cylnders 1 and 4 seemed to have the least effect on the idle when removed. Tracing the plug wires back to the coils, they just so happen to be fed from the same coil pack. Looks like I finally found the culprit!

 

I'd like to remove each pack individually so I have an easier time marking which wire goes where. But its looking like the assembly they bolt to has to come out thus I need to remove all six wires at once. Kind of a pain to mark everything when you can't see shit down there. Advice anyone?

 

 

The replacement of the coils is easier done with the rad fan assembly removed. It's up to you whether you want to tackle the coils with it in, personally I don't mind taking the time to make the job easier,

as Jesse said the coils can be removed individually.

 

 

[yorxs]

So trying a 5mm, 6mm and 1/4" and nothing seems to really fit. If this is a 5.5mm any ideas where to get a socket? Harbor Freight appears to be a bust.

[yorxs]

Nevermind I found a set there, cheap too!

[yorxs]

Car is fixed, coil 1/4 was the problem. Talk about making an easy fix a tough one. Between the metal hose blocking the way and the starter power blocking the way one can only wonder if the engineers at GM are assholes or stupid.