Questions and Answers

S-10 Runs Badly Q. Well howdy there, this is a problem that's been making me so mad for about 7 or 8 months now. Sometimes my truck will start up just fine and run like a champ, but most of the time it wants to hesitate cranking up and just die when it turns over, or it will turn over and will struggle to stay alive and eventually wind up dying.

In the mornings, especially if its really cold, it just will not co-operate with me, it will stay alive for about 5 minutes and all of a sudden you will hear the fan start cranking harder and the engine idle speed jump and fall back down and die.

Once I get the trunk warm, it runs just fine, but I can pull up to the house after its real good and warm, turn it off for like 2 minutes, come back outside and crank it back up and will not want to start.

At first we thought it was the fuel injectors just being clogged since the truck before we bought it had just sat outside of a dealer ship with almost a full tank of gas, I don't know how long, but it was long enough to have carbon buildup on the intake and everything around it. The fuel injectors just weren't pumping enough out. So, we replaced them and I've noticed a little change in it since we did that. But it still did the same stuff.

So I took it down to a shop and they tried to run a diagnostic test on it, and came and told me that my computer in the truck wouldn't communicate with the machine. So they replaced the computer, I go and pick it up and it's running awesome, the truck feels likes its doubled in power. Then I get it home and it's doing it again. Then I replaced that PCV valve, EGR, thought it might even be the catalytic converter being clogged up and not letting the engine breathe, so I replaced it also. I've done a million things to this truck and nothing seems to work.

I've been thinking and I was wondering if it could possibly be the timing, because when it idles you will hear a backfire, not a loud one but you can feel it, and it does this all the time. If it's not jumping timing, could it possibly be the harmonic balancers on the chain, causing it to curl? When it's really acting bad, you can start to push the gas pedal and it will hesitate to move and then it starts to move, and you apply even the littlest bit more pressure and the engine starts sputtering and acts like it's dead until you take your foot off the gas.

One other thing I noticed is that when I was trying to jump off my lawn mower was that the engine was running great. I hooked up the cables, no problem. I let it sit there and run for a minute or two. Then I start to crank the lawn mower, the minute I start it the engine starts that "I'm trying to stay alive" kind of thing and starts to rev up a little and then rev down and eventually dying. Why would jumping a lawn mower of all things, cause this engine to sputter and die? Your help is greatly appreciated.

1992 S-10 Blazer 4-door
4.3 Liter V-6 (VIN code Z, I think its TBI)
4 Speed Automatic Transmission.
Around 154,000
Fuel Injection
ABS brakes: yes
P/S - A/C - Cruise control
Power steering.

Thanks a lot,
Robbie.

PS: I checked the MAP sensor and its fine, the O2 sensor is also fine, and if you don't mind please send me a copy of your response to my e-mail address, it would be greatly appreciated.

A. Robbie, I think it's time to get back to basics. The backfire may be due to the ignition wires. I would put a new distributor cap, rotor, ignition wires and AC CR43TS spark plugs gapped at 0.045". The next thing to do is to set the ignition timing according to the directions on the emission decal under the hood. Next I would remove the idle Air Control Valve (IACV) and the air intake hose at the intake manifold and give the IACV and throttle chamber a good cleaning with carburetor cleaner. You might also want to consider replacing the IACV.

From what you describe to me, the problems all seem related to this basic adjustments. The backfire, stumble and stalling can all be attributed to the timing and IACV.

The best explanation I can give why it would stumble and stall when you jump started the lawn mower is that when you cranked it over, the load sensor detected the load of the alternator and sent a signal to the PCM and the PCM tried to compensate for the load by telling the IACV to open a little more. But if the IACV is clogged or malfunctioning, it can't compensate and hence the stumble and stall.

The timing chain probably has some stretch to it after this many miles. To check that, remove the distributor cap and, by hand, turn the engine until the timing mark lines up with the zero on the timing plate. Then, slowly turn the engine back until the rotor just starts to move and note how many degrees it was. If it was 5 degrees or more, the chain is stretched too much and needs to be replaced.

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