Tommybe1

New here haven’t seen this issue discussed before, , hoping someone can advise me on this problem I’m having a with a. 88 chevy silverado, stock 350. Idles extemely rough with white/gray exhaust smoke and a very rich gas smell. until warm and will occasionaly spudder on idle even when warm. On the road it runs fine and has good power. I just did a fuel pressure check (between filter and tbi) and have 12 psi with key on, it jumps to 20psi when started. From what I have read it should stay at 12 psi. I pulled the return line off at tbi and line to carbon canister with no change. The man I talked to at the company that sold me the regulator said I needed to check pressure on the return line which I don’t think is correct but I had 0 pressure on the return line and only a couple of drops of gas coming out when disconnected at the tbi. Could bad or wrong injectors cause this? I replaced the regulator and filter with no change. The spray pattern at the injectors is like their open all the time, no pulse. TBI was replaced a year ago. Distributor at same time, along with most sensors. Others tested ok. Wires, plugs, vaccum lines replaced, Grounds cleaned and reconnected. I did attempt min air idle adjustment, several times, could this be causing my problem? seems unlikely, but open to any ideas.

Any advise would be greatly appreciatd as I’ve run out of things to replace or test

PS. I made up a cable and got winaldl to work. All sensors appear to be working within parameters, not sure how to interpert the data.. Receiving frequent code 45 , turn off key and back on clears Service Soon light.

stew'86MCSS396

The spring in the fuel pressure regulator is suppose to collapse at the set pressure sending fuel back to the fuel tank through the return line but to me it seems that it's too high for your situation since there's nothing coming out of the return line. Typically a TBI fuel pump will not generate enough pressure to go over 20 psi. At a higher 20 psi fuel pressure your 61 pph fuel injector will put out closer to 78 pph which will create a rich condition hence the code 45. It seems that the fpr that you were sold was assembled with the wrong spring.

Edit: Forgot to mention that there also could be an obstruction preventing the fuel to "bleed" off back to the return line.

Tommybe1

Thanks Stew thats what I figured was going on but wasn't sure as I was getting the same problem from 2 regualtors. Do you know if all tbi's required the same 11 - 13 psi,, maybe I got the wrong one?

stew'86MCSS396

That psi would be correct for a stock 350. I'm not quite following who sold you the regulator. Typically you purchase a rebuild kit that comes with a new diaphragm and spring. The fpr would get disassembled and the parts changed out. Perhaps you're sourcing your parts from an aftermarket TBI specialty company? If that's the case, it's possible that you're being sold a spring that will net you >11-13 psi. There's also another possibility that the spring is for another application like later model TBI BBC trucks came with a 28-30 psi spring. I'm not sure if there's an easy way to apply higher pressure to see if the spring would collapse at a higher pressure. Perhaps some compressed air would work but I would turn the air pressure down to about 40 psi as anything more than that you could rupture the diaphragm on the fpr...and of course as mentioned before, there could be and obstruction but that would have to be inside of the injector/fpr pod assembly.

Tommybe1

Well to follow up, I borrowed a regulator and now have flow thru the return side, I know this because I somehow stripped the threads on the tbi return port (it never ends) and had a good leak. Before I shut it off I noticed that the spray was still solid , no pulse. I was told this is due to the injectors being stuck open. I have another pod and regulator on the way. My plan moving forward is to make sure the ecm is pulsing the injectors, if so, see if there is a way to unstick them or replace them ( I can hear the wife already) It was very kind of you to take your time to help a stranger. Thankyou!

Schurkey

Key on, 12 psi for about two seconds...rapidly dropping to zero after that. Right?

Engine running, alternator brings the voltage up, pump runs faster. But the regulator is screwed-up, because the pressure should not increase beyond 13 psi. GM spec is 9--13 psi.

I don't know why the carbon canister would have any effect.

WHAT regulator? Photo? Link? Part number? Is this an OEM-replacement, or some aftermarket add-on clusterfook?

Checking pressure on the return line is nuts.

No fuel coming out of the return fitting on the TBI seems like a problem.

Yeah, that's a problem.

"Attempt" min idle? Do it according to the service manual.

Pretty much everyone who dicks with the minimum idle speed screw, lives to regret it.

Not if there's zero pressure in the return plumbing.

Again...are these OEM-style regulators, or are they some aftermarket add-on disaster?

Some 454 TBIs had higher pressure. Most if not all small-block and V-6 TBIs ran 9--13 psi.