Need engine/fuel injection diagnosis help

Woodsrat · June 13, 2005

99 S-10 4.3 "W" V-6 with central sequential fuel injection, 2WD 5-speed

Truck has 107,000 miles. I bought it new and it has always run flawlessly.

The other morning I started it and drove 1/10 mile, it then sputtered for one second and died. It would not restart. An hour later it started right up, idled fine, but if I started to open the throttle, even in neutral, it would sputter and die. Now it will not start at all again.

OBD II scan test: pass, no codes

fuel pressure at fuel rail: consistent 54 psi

good spark, even when it won't start

The fact that sometimes it will restart and idle smoothly leads me to believe it is not an engine mechanical problem.

I am focusing on the fuel injection. Since it has six injectors and this seems to be an all or no problem, I am sceptical that the problem is one or more injectors. Since we have good fuel pressure at the fuel rail. this seems to point to the fuel meter body in the plenum. I removed the electrical connector and the connections are perfectly clean and dry (love those sealed GM connectors).

Any thoughts or additional tests I should do to diagnose the problem?

Thanks!

GM-Tech · June 13, 2005

fuel pressure at fuel rail: consistent 54 psi

If that's the max, it's no good. With the pump running, it should be 60-66 psi. After the pump stops, it should hold 55-60 psi. It doesn't take much of a drop in pressure to cause problems on injected engines.

Woodsrat · June 14, 2005

I rechecked fuel pressure at the rail. When I am cranking the engine over it holds 61psi. When I stop cranking it goes down to 54psi. When the engine was running at idle (which it won't do now), it was holding a steady 54psi. Does that still sound like a problem?

If so, I assume the likely culprits would be fuel filter (which I replaced at 90,000 miles) or fuel pump?

Thanks again.

GM-Tech · June 14, 2005

That sounds like good pressure.

Woodsrat · June 14, 2005

Okay, so that brings me back to the original question. Is the fuel meter body suspect? What other checks should I be doing to narrow down the diagnosis?

Thanks!

GM-Tech · June 15, 2005

Is the fuel meter body suspect?

No.

The first thing I would do would be to pump out a good fuel sample. A 16 oz. clear glass bottle full is enough to make sure you have good, clean fuel with no water. I know this seems unlikely, but I've seen some weird and sometimes intermittent things going on with water or other foreign crap in the fuel.

Then I'd want to make sure I had injector pulse when it wasn't starting. We have a device to plug into the connector and check 'em all. Couldn't say how you'd do that without knowing what's what in the connector. Next I'd put a spark tester on one of the plug wires. This is a device that looks like a spark plug without the electrodes. If the spark can come up out of the porcelain and arc against the body of the "plug", you know the spark is good and strong.

For an engine to start and run, you need compression, spark at the right time, and a decent fuel and air mixture. Find out what's missing and you'll find your problem.