Here in California, Chevrolet is warranting truck poppet nozzle injectors for 10 years or 100,000 miles. If the injectors are stuck closed, we are to replace them. If they work their way open after being closed, we are to only service them with Techron fuel additive. Now you might ask, “how are you supposed to know if they were previously stuck closed?” Good question, Chevrolet has yet, to my knowledge, answered that one… I will usually watch when the P030x code set, how many misfire counts are in history, and if the engine breaks down under load. With that in mind, lets move on to the case study…
A 1997 Full size Chevrolet truck shows up in my stall with an illuminated MIL. There are 79,000 miles on the clock and it is idling slightly rough. Watching the misfire graphic screen on the Tech 2, I could see an occasional increment of the misfire counter for #2 cylinder. That is not characteristic of a stuck closed poppet nozzle injector where you would have a steady incrementing of the misfire counter(s). Raising the engine speed and loading the engine down did not produce any secondary misfiring; the engine actually smoothed right out; more confirmation that the injector is not stuck closed…
Now lets take a look at the stored code(s). There is a freeze frame and the accompanying failure record.
First the Freeze Frame
This is the complete list with some overlap. With the exception of some soft key commands, this is what I saw on the screen. Now lets look at the Failure Record and see if has been updated. As most know, Freeze Frames cannot be updated but Failure Records can be.
The Failure Record
As you can see, the data is exactly the same as the Freeze Frame. This means that the diagnostic has not failed since the failure that set the Freeze Frame and illuminated the MIL. This does not mean that the problem is gone however; the test may not have been run since the failure that set the MIL. Now lets press a soft key and see what that code is for…
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Interesting no? I let the engine cool down for 10 minutes and tested the O2 heaters by leaving the key on with the engine off. All 4 O2 sensors started out at 450mv and were below 175mv within 3 minutes. Oxygen sensor heater circuits are tested upon cold startups while watching for sensor activity. Chevrolet trucks do not currently monitor the actual current. They are tested while monitoring “time to activity” or TTA. |
This Oxygen sensor looks ok. Could it be inoperative at
times? Sure, but I don’t think that is the case. I think it’s tied into the
rough running for some reason. With the Tech 2 and a fuel pressure gauge, I ran
a quick injector flow test. All the injectors appeared to flow about the same.
Although this is obviously NOT a scientific test, experience so far has shown
that it is more than adequate. Now before we stuff a gas analyzer up the tail
pipe, I want to mention another truck I had earlier with a post cat O2 sensor
setting intermittent heater DTCs. I had ran multiple heater tests and allowed
the truck to run its own onboard tests twice, yet after replacing the O2
sensor, it returned with an illuminated MIL and the same heater failure code.
The “fix” was supplied by Chevrolet technical assistance; a redundant sensor
heater ground. Or in other words, oops! We screwed up and have a design flaw (I
had no excessive voltage drops). With that said, I don’t think that this is the
case for this truck. Lets look at the tailpipe emissions since my smog machine
is only a few feet away and warmed up
There are NO vacuum leaks… What do you think the fix for the rough idle was, and would you believe that it took care of the P0161? Note, I am not going to defend the logic of the onboard diagnostics for this one…. <g>