Intermittent problems…. Ya gotta love them. Under factory warranty, they become even worse for dealer techs. Generous Motors (GM) like many other manufacturers doesn’t believe in paying honest wages for diagnostic services, heck, sometimes GM won’t pay ANYTHING for diagnostic services so we have to find all the shortcuts we can.
California Chevrolet and GMC dealers have been experiencing MASSIVE problems concerning sticking poppet nozzle injectors in their trucks since 1996. These injectors tend to stick closed after the engine is shut down and cools off. Many times they will ‘unstick’ after the engine runs awhile or if it is run, shut down, and restarted.
It is very common for these trucks to show up in your service bay with P030x codes set and running fine. The key to determining if an injector had stuck closed in the past is usually by looking at the ECT (engine coolant temp) and Loop Status in your Freeze Frame and Failure Record(s). What you will usually find is that the DTC will set with a low ECT and OPEN Loop Status; cold startup if you will…. This is the rule but there are of course exceptions brought about by gremlins etc…
The other day, a 1997 Astro Van showed up in my bay running fine and with the MIL extinguished. P0306 was stored in a Freeze Frame and of course, the accompanying Failure Record. Remember that the engine is running fine at the moment, but as you can see with the Misfire Data that #6 was misfiring at one time.
Now that’s a lot of misfires on #6. Typically, if we had a
bad plug wire that caused a misfire under a load, we would not see that many
counts. I am thinking this is probably an injector problem, but we need to
first take a look at the freeze frame and failure record data.
Looking at miles since first failure and miles since last failure, we can see that this freeze frame set upon the first failure and that it was catalyst damaging. That was a pretty serious misfire, but now only 21 miles later it seems to be fine. I started the engine, put my foot on the brake, and loaded it up under varying loads. Feels good…. Sorry, but at this point, since I can only get 18 minutes of diagnostic time paid for by GM, I’m not going to pull the engine cover off to use the ignition scope. Besides, ignition scopes are not GM required equipment, so they can’t ding me in an audit for not using one.
Now we know that this DTC set a FF (freeze frame) upon the first failure 21 miles ago, but do we know whether it has failed since then? One way to find out would be to look at the failure record:
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As you can see, the P0306 also failed 18 miles ago. Our MIL was extinguished upon arrival, so we know we have had 3 consecutive passes. If this had been a customer pay job, I would have scoped it just for the heck of it. But being a warranty job, I figure I have done more than I’ll be paid for, so I feel comfortable with adding a bottle of techron to the gas tank, clearing the codes, resetting fuel trim, and shipping it.
If you work in California, be ready to see a lot of these… |
For those that are familiar with misfire counters and poppet nozzle injectors, this should have been pretty straight forward. We see these almost everyday and sometimes 3 and 4 times a day. I picked this one because it was a bit unusual due to setting the freeze frame when the engine was warm and in closed loop. There is no such thing as a stupid question, only stupid answers, so if you have a question just ask and I’ll do my best to answer in a timely fashion.