3.8 fuel issue

[jeffcoslacker]

OK, I'm trying to help someone online with a '98 LeSabre 3.8 236,000 miles

Problem is it starts hard, runs like it's only got 3-4 good holes, straightens up as it warms up but not completely, with lingering random misfire and has a hard time taking the throttle unless feathered carefully.

He says it shows codes for random misfire and lean, Bank 1 .

Says the ECM is saying it's trying to run fuel trim as rich as it can.

He had the fuel pump, filter, and FPR replaced, no change. Also did some ignition stuff, plugs, wires etc, no change.

He says the rail only shows 10 psi w/key on, goes to 13 psi running. I can't believe it even runs like that, it shouldn't be able to open the injectors. He also says the rail does not hold static pressure after shut-off, bleeds down to zero.

It seems to point to a bad fuel pump, which wouldn't totally surprise me, but I can't understand how it could act exactly like the one taken out of it? As far as I'm aware, there is no external check valve or something like that in there that would not be a part of the pump assembly, correct? That sure would explain a lot.

Really scratching my head here. Oh, car also shows a strong 19.8 Hg vac reading when it idles, despite the misfire, so we can reasonably conclude the engine is sound enough.

I'd take any ideas at this point.

I'm asking him to test the gauge on another vehicle too, just to be sure about those readings. I smell something fishy there.

[inafogg]

yeah i agree 13 psi & it runs!! can he pinch off the return line & see if pressure comes up pull the plugs see what they look like. what brand pump? no external valve that i no of
could have 1 - 2 injectors stuck open

[jeffcoslacker]

Originally Posted by inafogg

yeah i agree 13 psi & it runs!! can he pinch off the return line & see if pressure comes up pull the plugs see what they look like. what brand pump? no external valve that i no of
could have 1 - 2 injectors stuck open

I agree...I was thinking if several injectors were stuck open, that could explain how it's running on pressure that low, as well as why it won't hold static pressure when shut off...but it should also have a few wet plugs, sooty exhaust, and codes for rich, not lean.

It was an Airtex pump, should be OK, we sold them and had good luck and they are OEM supplier for GM too...

He said with the return pinched it only goes to 13 psi at best, same with the vac line off the FPR and running. It sure sounds like the rail is depressurizing massively.

Maybe I'll have him leave the key on for a while and then pull the plugs, just see if we can get a flood going. I'm outta ideas at this point...

[inafogg]

i never use anything besides delco/delphi pumps. i heard the airtex are suspect so you may be right thinking its a bad pump

[Jrs3800]

After the things you have done, this sounds like a bad pump to me... In reality the car shouldn't even run... 48-55 Psi is required...

[jeffcoslacker]

Well, as we all suspected, owner dropped in a new Delco pump and it runs fine now.

Man, talk about your Occam's Razor type problem solving...it just seemed it couldn't be anything else.

Screw Airtex, far as I'm concerned...we used to install them and never had problems like this, but maybe something's changed. I talked to a GM master tech on this and he also said he's seen this exact problem several times before with Airtex pumps on GM stuff....

Well at least the next guy will know, if they find this thread on a search...

[Tech II]

Sounds like it was the WRONG PUMP....13 psi sounds like a pump for a TBI unit....