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Hello,
My '99 Chevy Astro cargo van is having a problem. Pretty much at my wits end.
Symptoms include
* Intermittant stumbling off idle, at low RPMS and loads.
* Occasional hard starts - you crank and crank and crank and no start.
* OBDII codes of * P0300 ( misfires on various cylinders )
* and P0155 ( malfunction of R/H oxygen sensor heater )
Troubleshooting history:
This problem started about 2 years ago. At first, I took the P0155 trouble code at face value,
and replaced the R/H front oxygen sensor. No joy. I figured that the "heater test" just looks at the
signal from the O2 sensor and expects it to come "live" in a few seconds. If not, bad heater, right?
Well, maybe not. Other failures can prevent the mixture from being in a reasonable range.
Then I thought it was electrical. I replaced the
sparkplugs, wires, distributor cap and rotor, all to no effect. I hooked up an oscilloscope and
saw that misfires coincided with very high voltage readings.
Then I looked at the fuel system, because spark voltage is dependant on mixture strength. I read
that these vehicles have a history of sticking fuel injector poppet valves due to California gas.
I bought a cannister fuel injector cleaner - the kind that you hook up to an air compressor. With that
tool, I was able to get the truck running fairly well - well enough and long enough to pass smog.
For the intervening two years, I put up with it. When there was a hard start, I would trot out the
pressure cleaner and get it running again. Long trips would make it run better.
I did take the car to the GM dealer with instructions to check it for sticking fuel injectors.
And, hopefully to replace them on the GM extended emissions warranty. They said
that the fuel injectors were fine, but that I needed a new oxygen sensor aft of the
catalytic converter to correct the P0155 code. And that I owed them $240 for diagnostic. I paid them
the $240, took my truck home, and replaced the aft oxygen sensor. No change.
Now it needs to be smogged again. Per the instructions in GM special service policy 99066G, I replaced
the fuel injector spider with the new improved MFI system. This replaces all six fuel injectors with a
new design with no poppet valves, and also replaces the fuel pressure regulator. I also replaced the
fuel filter.
I really expected the fuel injector replacement to fix the problem once and for all, and was very
disappointed when it did not. The truck still intermittantly stumbles off idle, and occasionally starts
very hard. Hard starts generally coincide with dark, cold, rainy days. Cleaning with the pressure
tool fixes it. I am also still getting OBDII codes of P0300 and P0155. The
I decided to look at the ignition again. I did not connect any diagnostic equipment to it, but just
got a spray bottle of water, set it to "mist" and liberally misted the entire ignition system while the
engine was running. No effect, the engine didn't miss a beat.
Now I'm pretty stumped. The only guidence left from GM bulletin 99066G is that the fuel filler pipe
may need replacement because California gas eats it and the melted plastic goes through the system....
Seems farfetched to me, but I have a new pipe on order.
I have hooked up a pressure gauge to the injection rail. Am seeing the following readings:
* Engine not running, turn on the ignition: 61PSI
* Turn the ignition off, wait 10 minutes: 45PSI
* Engine idling: 54 PSI
* Stomp on the gas, running full blast up the hill: 58PSI.
Anybody seen anything like this? Thanks in advance,
- Jerry Kaidor
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