drdd

1997 Jimmy. Something is still leaking down inside the plenum. Fuel pump and filter is new. Fuel pressure gauge hits 64 and then bleeds back to 40 in about 1 minute. Then it goes to 0 in about 4 minutes.

Does anyone have a diagram of the fuel pressure regulator and how it seats into the metering body? I replaced the fuel pressure regulator but I may have messed up the o-rings or the screen.

Also, do the metal fuel lines going into the metering body need o-rings? Mine had one metal washer on the pressure line going in ...

Also, do the metal fuel lines (the ones bracketed together) need o-rings where they connect to the lines running to the back of the truck?

Here's a picture of the inside of the plenum. You can see washing by the 6, 5, and 3 port. I replaced the #3 injector because the plastic looked bad. The other injectors/tubing/poppet looked fine and seated fine.

When I pressurize the system with the plenum off, I don't see or hear any visible leaks.

Should I just do a new o-ring kit, put a new o-rings on each injector, and see what happens ($25)? Should I try another fuel pressure regulator ($65)?

maybe the poppets are leaking when under engine load ??

MT-2500

Best to prime up fuel pressure with intake off and look for the area it is leaking.
Also.
But also make sure it is not leaking back threw the fuel pump and fuel pump lines and check valve.

__________________
Remember proper testing gives us the answer to many problems.
MT

drdd

Yes, I've looked for leaks when primed. I can't see or hear anything.

Fuel pump and filter are new, installed at the dealership, but I'll check again for any leaks.

MT-2500

Block off or plug the return line and see if it still has fast leak down.

3 places pressure can leak off.
Threw fuel pressure regulator outside or bypass inside.
Back threw fuel pump.
Or a injector or injector body leaking off.

__________________
Remember proper testing gives us the answer to many problems.
MT

drdd

Okay, I plugged the return line. When primed, the gauge at the schraeder read 75 quickly and then held at 63 for a long time.

What does that mean? I'm still not understanding what plugging the return line does. Bad regulator? or, something inside the spider metering body?

another question ... I don't NEED engine vacuum for the fuel pressure regulator to work correctly, do I? When working properly, I should be able to prime the system and have it hold good pressure for several minutes -- without cranking the engine and creating vacuum --- right?

The fuel pump and filter are new - installed at the dealership -- but just to double check, I used the ball valve tool that Old Master recommends to separate plenum from fuel pump. With the ball valve closed, there was still fairly quick leakdown (telling me it's something under the plenum).

any thoughts would be appreciated. thanks guys!

MT-2500

If it holds pressure and no leak down with return line pluged then it is leaking of threw the regulator.
But 75 is low for full fuel pump pressure with return line pluged.
Should be 95-105 full pressure.

Replace the fuel pressure regulator and put it back together and run fuel pressure test.
Are you having any other problems with it besides the fast leak down?

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

__________________
Remember proper testing gives us the answer to many problems.
MT

drdd

Thanks for all your help. I got things figured out tonite.

I did like you said, and put the regulator back on. No go, still leaking down. I went out and bought another regulator (which is actually the third one I tried). Still no go and leaking down.

I remembered what you said: three places to leak from 1) back thru pump (check valve) 2) injectors/poppets 3) regulator external or internal bypass

With the fuel pump and filter eliminated, and visible injector/poppet leaks eliminated, and leaking fuel lines onto the floor eliminated, and regulator eliminated, the only thing left was an internal leak within the spider bypass. Sure enough, that was the case.

I did the CSEFI to MFI swap. Routing the lines wasn't too tricky -- follow the instructions carefully. I didn't need to replace the fuel meter bracket. Woohoo - $30 bucks back! Pressure built up and held great. I took a test drive with the fuel gauge on and all was within specs.

MT-2500

You are welcome and thanks for posting back how it went and the fix.
Glad you found it.
The change over should make it run better.
Good luck
MT

__________________
Remember proper testing gives us the answer to many problems.
MT