We have a 1995 Pontiac Transport and we have a lean fuel problem. You cannot believe what we've done to find this out. We've had engine computer rebuilt..lot's of parts put in etc. etc. everyone thinks it's something different. Mechanic ran diagnostics 2 days ago and found the lean fuel problem...how do we fix this without spending 100's more in $$...HELP!

 

What were the symptoms that led you to do all this?

 

And what were those parts put in? They must be on the receipt. Like o2 sensors, temp sensor, map or maf sensor, fuel pressure regulator,etc.

 

Symptoms were at idle that went "up & down" for lack of better words and then it would sometimes die and be very difficult to start again. The car also was backfiring on the intake valves..I learned that from a post on here.

 

symptoms were at idle a "surge and back off" for lack of better words. Sort of like a reving up and then reving down..again for lack of better words. An O2 sensor was put in and also a vaccuum part & hose. We thought the fuel regulator should be next because this other stuff didn't work.

 

The surging or "hunting" can be cause by the idle air control valve. That isn't a secret to a mechanic, though, and probably considered.

Vacuum leaks cause that sort of thing also. They can be around the intake gasket or any of the vac lines, including the brake booster line or diaphragm itself.

I don't know what your mechanical skills are, but a vacuum gauge is easy to use and interpret. If you have a valve/valve timing problem a vac gauge would show it. They come with instructions for use.

Fuel regulators and fuel pumps are normally tested with a pressure gauge before installing new parts. That gauge is in most mechanics tool kit. You can rent/buy them yourself and test the pressure at a test port on the fuel rail. If you want to do that, post back accordingly.

Regular backfiring through the intake on a fuel injected can be the engine computer, which you indicate you have replaced. Or it can be in the valve train. The vac gauge would show that.

 

is to use a spray can of penetrating fluid, with the spray tube attached you can direct the spray at individual hoses. The stuff is flammable and engine RPM's will increase if drawn in through a vacuum hose.

 

I have a list now of the parts we've put in so far:
fuel filters, 2 times... PVC valve,...O2 sensor,..idle air control valve,...tps sensor..thanks for your time!

 

I don't know if I'm using this forum correctly..so at risk of repeating myself, here's a list of the parts we've put in so far: As stated before engine computer, fule filters (2 times), PVC valve, O2 sensor, idle air control valve & tps sensor. We did a complete tune-up recently.

 

That's quite a lot. Were those parts put in based on a computer diagnosis and fault codes or more on a hit and miss?

I would suggest hooking a pressure gauge to the Schrader valve on the fuel rail (looks like a little tire valve stem) and see if the pressure is low or fluctuates while the rpms are dizzy.

If not, I would rule out fuel pressure as the cause.

 

The lean mixture gas came from a diagnostic machine. He said that he was "pretty sure" it was the O2 sensor. But it wasn't obviously. So we've talked to other people and mechanics and they sugggested this and that, so yes it's NOW a hit and miss. Do you think it could be the fuel pressure regulator? We've been trying to get someone to tell us what the fuel pressure should be and the closest we've come was from a mechanic several months ago that said we had 10 lbs.

 

If you had 10 lbs of pressure with the key on and or the engine running, that could be a problem with the fuel pressure. That would point to the pump or the regulator.

Some of those have TBI and others sequential = different pressure specs. To give you an idea, a typical sequential spec would be 40lbs upwards to 65 lbs, depending on the make and model of the engine. What engine do you have - I'll see if I can get a spec for you.

But to put all this in perspective for you: a low fuel pressure problem is easily diagnosed and the symptoms for that problem are pretty obvious to a mechanic.