1995 Sierra Hesitation/stalling Problem

1995 Sierra Z71 XCab, 4x4, 5.7 TBI, 102,000miles.
I had and intermittent service engine light coming on for the past three months or so. Performance didn't seem any different up until mid December. I had hesitation when accelerating and a deep bog when shifting to second. It also is harder to get started. No service engine light when this was happening. I tried to get the codes read, but OBD1 reads aren't available at Checker, or Auto Zone anymore; only 96' and newer cars.

Changed plugs, cap, rotor, fuel filter, and O2 sensor. Marked improvement, but still a slight hesitation and the truck will suddenly die at idle occasionally. The service engine light comes on intermitently, but only after around ten minutes of driving. Had the battery and alternator checked today and they were ok. One odd thing is that if the truck has been running at idle for a few minutes and you turn the fan motor to high the truck either dies immediately, or the rpm and volt meter dip down and the engine almost dies before returning to idle. Before I take it in to the shop I wanted to at least have an idea what the problem is.

My best guess is that the fuel pump is dying slowly. Is there a code for this on OBD1 vehicles. Any ideas would be appreciated, this one is really bugging me. :screwy:

To read the codes all you need is a paper clip.

Find the ALDL connector beneath the dash. Use the paper clip to short out the A and B terminal. A is the top right and B is the second from the right on the top row.

Turn the key on, the check engine light will blink 1,2.....1,2.....1.2
This is code 12 and is not a trouble code, it just lets you know you are communicating with the ecm.

Any trouble codes will be stored after the code 12 flashes 3 times.

Turn the key off and remove the paper clip.

If you have a Chiltons manual go to page 4-37 for the procedure and 4-38 for a pic of the ALDL connector.

Hope this helps.

James

find out what the fuel pressure spec is for your vehicle, have fuel pressure tested. if it's below spec, or even at the low end of the spec, fuel pump very well could be the problem. even though it may be at low end of spec-have still seen these cause problems.

Thanks for the info guys. Here's what I found. Code 1111 1111 which I am assuming is 44. If I'm looking at the right code it's oxegen sensor or circuit - lean exhaust. I just changed the O2 sensor so I am assuming that the code is because of the seeming fuel starvation scenario.

I tried a little experiment. I started the truck and cranked the blower fan; rpm dipped slightly, but no problem. I ran the truck at idle for around three minutes and then cranked the blower fan; rpm drops immediately then the engine dies. If I use the pedal to raise the rpm to around 1000rpm and crank the blower motor the rpm drops slightly, but very little. If I hadn't had the alternator and battery checked twice I would think the alternator was going.:screwy:

Fuel delivery/pressure is looking more like the culprit. Looks like my next stop is a shop with a fuel pressure gage. Is there a port under the hood for checking fuel pressure. It's a TBI system.

Is there a port under the hood for checking fuel pressure. It's a TBI system.

No service port on the TBIs (unfortunately). You have to either buy a tool that replaces the fuel filter and then use a standard fuel pressure tester or you need to buy a fuel pressure tester that includes a small adapter that goes in front of the fuel filter.

If you have not replaced the fuel filter recently, then that should be the first thing to do with a code 44; otherwise, it could be a fuel pump going out or dirty injectors.

//2000CAYukon