Ranger0914

Hey Everyone.. I think my problem is a simple one but instead of keeping on replacing parts...I'd give you smart folks a crack at it. I have a 95 Silverado Z-71 pick-up with a 350 4x4. This is my farm truck but the motor runs like a sewing machine. I was coming back from town with it 3 days ago and it was running perfect until I started up the little hill where my house is. It started sputtering and shut off. I was able to limp it the 30 yards or so to my house. My 93 year old Dad who has seen and done it all said to replace the plugs. I did and it didn't help. I started it up after replacing them and revved the engine a little and it was smooth as silk. Until I backed up 10 feet and it shut off. My next idea would be the fuel filter? Anyone got any ideas?

Ranger0914

I tried to see what I could do. It doesn't make sense to me. I can start the truck and give it a little gas and it runs perfect. I try to drive it or leave it at idle and it stalls. The seems to rule out the fuel gauge. Any ideas anyone? Thanks.

jfmorris

It's unfortunate this isn't a 1996 or newer, where a cheap ODB2 code reader might tell you what is going on. There is a computer on the 1995, but it uses ODB1, and those readers are harder to find these days. Might be worth looking for one though, as otherwise, you are just guessing at what the trouble is.

Things that come to mind with the symptoms are:

1. Fuel delivery issue (but it wouldn't crank and run at idle with the slight application of gas)
2. Air delivery issue (mass airflow (MAF) sensor maybe, over by the air filter, or severely clogged air filter even)

Again, just shooting in the dark here, but that mass airflow sensor has caused me similar issues on an old Volvo I used to own. Get a can of MAF sensor cleaner, pull it out of the air intake, and clean it off real good. Building on the tiny wires that sense the air intake can cause it to start malfunctioning. If the computer doesn't know how much air is coming in, it runs with a default value that probably won't work at anything BUT idle with a specific fuel mix. If you unplug the harness from the MAF and it still runs the same, that points to it as the culprit.

That's all I have for now. Start by unplugging the wire from the MAF and see if things change (or not), and go from there.

Gumby22

There’s a few possibilities - I’d start by checking the fuel spray from the injectors during cranking. Remove the air filter and housing and observe the injectors while a helper tries to start it. They should have a clean, even spray pattern - any uneven spray indicates the injectors need cleaning/service.

Check fuel pressure. It should maintain 8-12 PSI at key on, engine off and not bleed down more than 1-2 PSI. If that’s good, check it while the engine is running and see what it does when the engine stalls.

GM trucks with TBI didn’t use MAF sensors.

Ranger0914

JF Morris. I was pretty doggone sure you had it right. I live on a farm and this is my farm truck. We keep a lot of feed and seed so there are no shortage of mice. I pulled a huge mouse nest from the filter above the glove compartment of my wife's 2006 Suzuki Grand Vitara.
I had to remove the air cleaner when I changed the plugs and found a small amount of installation on the filter but no nest anywhere. Yesterday I pulled the top off the air cleaner and it ran perfect for about 90 seconds then shut off. After that I can keep it running like a sewing machine in neutral by giving it a tad of gas. But try and drive it and it will shuts off within 10 feet or so.
I still don't think it is the fuel filter but I don't know what else to do but change it out.

jfmorris

Yeah - I was hoping I had it right too. I even looked last night at my 1996 C1500, and it *DOES* have a MAF inline from the air filter to the throttle body. BUT, my Haynes manual for 1988-1998 C/K pickups does indicate, as @Gumby22 points out, that the MAF is only present on 1996 and later models.

The Haynes manual has an entire section on how to obtain the ODB I trouble codes for 1991 to 1995 vehicles. It involves putting a jumper wire to ground a pin on the ODB-I connector under the dashboard, turning the ignition to ON, and the "Service Engine Soon" will flash out trouble code 12 - indicating if the diagnostic system is working. That is 1 flash, a pause, then 2 flashes in succession. After a longer pause, this will repeat 2 more times. AFTER that, if any trouble codes are present, they will flash out in sequence. If no other codes are present, just code 12 will repeat. They say NOT to start the vehicle with the jumper wire in place.

I am sure there is info online on how to do this. There are 2.5 pages of trouble codes for this system in the Haynes manual.

If you can't find this info online, let me know and I'll be happy to snap a couple of pictures and send them to you privately.

Gumby22

In addition to checking fuel pressure when it stalls, Remove the glove box liner and inspect for a nest on the HVAC box - that’s where the ECM is and I’ve found several nests in customer trucks in that area - There must be an easy access for them somewhere for as often as I’ve found nests.

You can try checking codes as jfmorris suggested but don’t get your hopes up - OBD1 systems (GM or otherwise) are very basic and don’t use the same level of analysis as OBD2.

Key off, use a paper clip or jumper wire to jump terminals A&B at the connector - turn the key on and count the blinks.


OBD 1 Connector


In case the manual didn’t point it out, the primary reason for MAF sensors beginning in 1996 (besides needing to meet OBD2 standards) is because GM started using port fuel injection.

TBI systems operated on speed density principles - essentially, the fuel delivery was dependent on engine temp, speed and load; and oftentimes they were running more on the rich side.

MAF systems measure the incoming air flow/volume & temperature and can more precisely control the amount of fuel needed based on the amount of air coming in.

Ranger0914

JF Morris

I just unplugged the MAS. It was bad when I bought the truck about 15 years ago. The Check Engine light was on...took me forever to find it as the issue. They kept saying it was the O2 sensor even after I changed it. When I unplugged it it seemed to run better in idle. Could be I was just really hopeful. I ran it back and forth a few times and it didn't shut off. Loaded up some trash to take the depot and as soon as I got to the bottom of the hill it shut off. Had to keep gassing it to get it back up the hill. So I assume that's not the problem. Gonna pull the glove compartment next and check for mouse villages.

Thanks So much for your help...............And everyone else too.

jfmorris

Ok - I didn't think your 1995 had a mass airflow sensor (MAF not MAS), but if it does... unplugging it causes the computer to assume the air flow coming into the engine is at a default value that would work in idle. It won't work under load, as it still thinks (with the sensor unplugged) that the idle level of air is coming in - so the air/fuel mix is not adjusted properly, and it most likely is too rich or too lean to run under load.

The fact that it runs longer in idle, without you giving it the gas, to me would say this sensor is part of the problem. Take a good look at it, and use some MAF sensor cleaner to clean it out.

For comparison, here is a picture of my 1996 5.0L engine, with the MAF sensor circled in yellow...

Ranger0914

JF Morris Mine has the MAS and not the one in your picture. It runs perfect in idle. But trying to go uphill is a bugger. Wants to shut off in any gear .....it appears to do this when I come to a stop but not positive. I just cleaned out the HVAC box. I am getting good airflow for my A/C now but didn't help with my issue. Didn't realize my farm truck was so valuable until it didn't run anymore.
I am heading to town after lunch and getting a new one.

Thanks Again so much