Hard cold starting

[dadsgreentruck]

Need some help here...

I have a '96 S10 4x4 with the 4.3L. Over the past year, it has slowly become harder to start in the morning. It now takes 6-8 twists of the key when it's cold. After it's warmed up, it starts up first crank, no problem. I have changed the cap, rotor, fuel filter. Spark plug wires are fairly new MSD. No change.

I'm thinking it might be the fuel pump and/or FPR. I picked up a fuel pressure gauge and hooked it up to the valve at the back of the engine. Here's what I got:

COLD
Turn key, pump primes and in about 3 seconds reaches 53-54 PSI.
It bleeds down to about 11 PSI after about 15 minutes.
Running at cold idle, I have about 51-52 PSI.
If you shut it off before it's warmed up and try to start it again, the pressure primes to only about 51PSI and it takes about 10 key-twists to start.

WARMED UP
Turn key, pump primes to 54 PSI. Bleeds down to about 30PSI after about 1/2 hour. Starts right up. Running pressure is about 51-52 PSI.

The return line appears to be steel all the way back to the tank, so I can't crimp it to test the bleed down.

Does this sound more like the pump going bad or the regulator ?

[tubbedII]

Hey dads...did you ever get a fix to this issue? It's been a while since the OP.

Well, I'm not 100% sure on the difference between a '96 and a '01 (which is what I have for a DD), but there's a spider injection set up under the top half of the intake manifold on my '01. There's little plastic tubes that fail over time and usually is where the bleed down comes from. It's either that or the fuel pressure regulator which is also connected to this whole injection set up. When mine failed, it acted just as you are saying.

The "easiest" way to tell if this is the case was to pull the throttle body off and see if you have wash down on the back side the lower intake manifold. It should be pretty black, but if there's been gas leaking from these tubes, it usually washes to the back and leaves a nice looking aluminum.

If this is the problem, GM makes a newer part that's around 150 or so that replaces all the injectors with a better design as well as the regulator.

[dadsgreentruck]

I haven't had a chance to get to it yet. I was going to pick up a regulator and try replacing that. I hadn't thought of the injector spider leaking though. I thought that was only on pre '96 CPI systems. I guess I'll tear it apart and inspect it first.

[tubbedII]

I think it's the other way around on when the spiders came into play where it's the newer models that have the spider set up, but not sure on the year change. Mine's an '01 and I have the spider set up. Good luck though!!!

[68C15]

95 and older have the single injector with the plastic supply tubes between the plenums that leak. Dorman (Motormite HELP line) calls them fuel fittings.

a 96-up needs at least 58psi to start.

open throttle and look for clean aluminum at rear of lower plenum (regulator leaking).

you could have a bad check valve in the pump letting pressure bleed off and/or not build on key-up.

I start diagnosis by installing a pressure/flow tester and a lab scope to watch for commutator damage and pump speed.

do you have any drive-ability issues or warning lights?

[dadsgreentruck]

OK... It's been getting worse. It took about 20 tries to get the thing fired up after work the other night... Finally got the plenum taken off. It was really stuck to the injector module too! By the clean look of the rear of the intake manifold, I'm thinking I have a leaking regulator. Second opinion, anyone?
I'll probably replace it anyway just to do the MPFI upgrade. Those poppets can't be in that great a shape after 135k miles.

[gchemist]

You'll like the new spider!! I upgraded a few years ago,.



If you need info on it, let me know. I'll link you to helpful info.

[68C15]

with plenum off hook up fuel lines and have someone turn key on (or jumper pins 30 and 87 on fuel pump relay with key on). look for leaks. from that pic it seems you do have a bad regulator.

[dadsgreentruck]

Fixed. Replaced the spider with the MPFI upgrade. It starts up on the first crank again. On another note, does anyone know the thread size of the 10mm bolt that holds down the fuel line bracket? It slipped out of my fingers while I was trying to thread it in and it's dropped somewhere that I can't see or feel...

I hate when that happens!

[gchemist]

That bolt is a PIA!! I almost dropped it too. You may to get a replacement from the dealer or find it. Use a mechanics mirror and magnet to probe around. It's there somewhere.

[68C15]

8x1.25mm about 1/2" long (whatever that converts to in length)
any hardware store will have it. it doesn't have to be a 10mm hex. 13mm hex will work.