sparks

Hello to all. Have not been here for tooooo long. I have an '81 L-jet that uses too much fuel. Was getting 8-9 mpg, down from about 14-15 mpg. Went thru complete tune-up and new air meter and got to 11 mpg. Plugs read very rich. Replaced FPGs and had psi checked. Was running at 55 psi. Found out I was sent regulaters for '85 or '86. Replaced with correct ones and now running at 36 psi. Still running too rich. I pursched 1 new injector, put in new plugs and drove about 3000 miles and checked plugs again. Cylinder with new injector was way leaner than other 7. Question is could the injectors be damaged from too much pressure? Every part in fuel system is new except the 7 original injectors. Had a local shop that knows L-jet systems check out fuel system and he tells me fuel psi should be 29. Also found the "timing retard" function of vacuum advance unit does not work. Thanks in advance if anyone has any ideas/solutions.

hacker-pschorr

Doubt it - I was running well over 100psi through stock 81 inejectors for many years (supercharged).

Temp II sensor on the coolant bridge is what I would check next. The resistance of that sensor directly controls the pulse width of the injectors. Too much resistance = rich running.

O2 sensor too, when was that last changed?

123quattro

The extra pressure would not adversely affect the injectors.

Kiln_Red

The FPR at the front of the engine is the same between L-jet 928s and S3s.

36psi is too high at idle on L-jet. This should be closer to your WOT fuel pressure. The regulator and dampeners rely on engine vacuum to work correctly. Based on the information you have provided, I would check vacuum. It sounds like the regulator you replaced was stuck.

NordicSaab

Forgive me if i'm being dumb, but wouldn't improper atomization of the fuel by old injectors cause all of these problems? It just seems strange that you replace one fuel injector and immediately have a better burn on that cylinder.

Kiln_Red

It wouldn't explain the fuel pressure being too high at the same time that spark plugs were sooty.

sparks

O2 senser is new. Replaced tempII sensor and it checked with correct omh reading. I cannnot think of anything else to check. Have also tried another "brain" and had same results. Have installed aftermarket temp gauge and engine is running aroung the 185 degree range when fully warmed up.

sparks

Also I have vacuum at the regulators.

Kiln_Red

Any black smoke exiting the tail pipe?

Kiln_Red

Check the whole system over from the ECU..

sparks

Thanks for the info Red. I have been all through the wiring and found nothing wrong. No black smoke from exhaust, but tail pipe shows it is running too rich. This problem happened suddenly. I assumed it was something with wiring or electrical. The engine has been re-gasketed, and runs smoothed since. But fuel consumption is still high. It is an '81 with original wire harness. I will probably continue to look there. Can't think of anywhere else to look. Any with a guess why fuel psi is always at 36? I do have vacuum at them.

danglerb

Any chance somebody is stealing your gas?

joejoe

My '81 had same mpg when I got it years ago 10-11 no matter how driven. What was found was the retard on distributor had come loose (still worked just not hooked to anything) and a previous owner had pulled distributor, moved dist a tooth and reinstalled. Dist was then turned full advance. It was very 'peppy' and ran like a raped ape.

The fix on mine was to pull distributor, reattach vacuum (the screws holding it were missing and I never found them) install, re time, and mpg doubled.

Ducman82

^^^ sounds like timing to me

Lizard928

Make sure the damper on front of engine holds vacuum and doesn't leak fuel!