Questions and Answers

GMC S-15 Running Very Lean Q. Hello, I have a 1986 GMC S-15 4X4 pickup VIN "E". 2.5 liter, automatic transmission, 71,000 miles. I just got this pickup from my Grandpa, who wasn't able to take care of it anymore due to age. My dad and I just rebuilt the engine, and were on our way to having a great little pickup when it crapped out.

I gave her the first start and the Check Engine Light came on and gave me code 13 and 35. (13 O2 sensor; 35 Air Idle Control Valve) I replaced both of those parts and things were going well. She needed to warm up a little bit, but drove okay.

About 4 miles into breaking in the new engine around town, I pulled up to a stop light. When the light turned Green, I hit the gas a bit and she just died and wouldn't restart. Finally when she did restart, she stumbled badly and required WAY too much pumping on the gas.

We towed it home, and did the air, spark, fuel check and decided we weren't getting any fuel. I ran a hot wire to the fuel pump and got quite a bit of volume. 2 gallons inside 1 minute. I replaced the fuel filter. I replaced the injector and she finally started but needed ether or propane to start. She gave me a Code 44. (O2 sensor rich/lean vary).

She runs terrible, like she's running on 3 cylinders. I plugged the Code Reader in while she was running and she tells me she's running lean. Only with propane added does she run normal or rich. Without the propane, she idles terrible at 1,000 rpm and bounces back and forth erratically. Around 3,000 to 4000 rpm without propane she runs great, but anything less than that it's bad.

We used the propane to search for a vacuum leak, but didn't find anything significant, but replaced tubes and gaskets where it did anything. I even emptied the old gas and put mid-grade in.

I'm not sure what to check now. But it seems that the more fuel it has the better it runs, but getting fuel the way it's supposed to seems to be the issue. It's either that or a vacuum leak I can't think of. I'm at a loss. If you can think of anything to check, I'd be grateful.

Thanks,
Jeremiah

A. Make sure the vacuum line at the brake booster is not off. This would be a large vacuum leak, as would the PCV system. Make sure the PCV is there and plug it off to see if idle is better. How's the cam timing? Does this have a distributor? Is the timing okay? The EGR valve can also be stuck wide open or have the wrong gasket causing a vacuum leak. Clean the IAC valve so it moves freely back to idle as it could be stuck open, but that should give you a high idle speed. Try these items and let us know.

Added 12/01/2005

Hey, Just thought I would update you on my problem:

I finally ran out of things to evaluate when I decided to start double checking everything. SO I went ahead and got the pressure gauge out for the fuel, something I had just done a volume test on before. I expected to get 9-13 psi, but I got 3 psi instead!

I took the bed off instead of draining and dropping the tank. When I pulled the fuel pump bracket out, I was displeased to discover that the thick rubber hose that connects that fuel pump to the bracket was so soft it felt like gum.

It had split out the side in so many places that it must have leaked off any pressure that the pump had tried to build. When I had done the volume test, of course I got a lot because there was no resistance!

Had I checked the pressure with a gauge in the beginning when I suspected the pump, two weeks of random checking could have been avoided.

Thanks for your insight.
Jeremiah

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