Hello Everybody,

I've got a 2002 2WD Blazer that's giving me a P302, and I'd like to run it past the forum here for some diagnosis double checking and moral support. The SES light first went on for it and was blinking a few days ago when I started it up so I shut it down and let it be. My first thought is the fuel injectors, because I had the poppet injectors go out on my previous Blazer, but I wanted to check my confirmation bias here and think about what else it may be and run down the list of possible symptoms.

Shortly after buying the Blazer, I took it out on a trip and it sprung a sudden leak in the upper coolant hose and lost nearly all it's coolant. Fortunately it happened in a parking lot kitty corner to a mechanic, and I was able to get it replaced in just a few hours. That same day, about six hours of driving later the engine started running rough after fueling up at a gas station, and threw a P300, but made it another few hours home and has had no SES light since. The Autozone scanner's recommendations for the P300 were to replace the fuel pressure regulator and intake manifold gasket, neither of which I have yet done. I tested the fuel pressure in November, and it held solid at 65 psi. The last tank of gas clocked in at 13 mpg, which was quite low, so I could have just messed up on the odometer reset. It's also run a bit rough on starting on a few occasions since November, but never threw any codes.

I still have my previous Blazer (which was totaled), and it runs and drives (doesn't even have a check engine light on, but a lot more engine vibration and doesn't have the same good looks it once did), and it's got the modern fuel spider/injector setup, so my plan is to pull those out and put them in the new Blazer and hope that solves it. Are there other things I should definitely replace or look for at the same time? Are there other diagnostics I could do to narrow it down? I would ideally move it to the back corner of my apartment parking lot since we're not allowed to do any autowork, would driving it a few hundred feet cause damage?

I generally do my own auto work, but this will be the most work I've done with the engine (I was traveling when the poppets went out on the old one, so a shop put in the spider). I got past removing the throttle body before the holidays, but ran out of time and put it back together. Any advice or common gotchas to watch out for would be welcome. Thanks

 

How does it run, can you feel the misfire?

Does the fuel pressure hold above 55 psi for 10 min?

The first step is to make sure that CMP Retard is within spec or else the misfire data may not be accurate. We have cost effective scanner solutions here that can do this.

Since its one cylinder you can check the ignition wire and plug on #2.

Do you have a recent compression test?

George

 

Thanks GeorgeLG, I didn't get a notification on your reply post, so I'm just seeing it now. It looks like I've resolved the issue for now, but I'd like to do my diligence with other diagnostics that you've brought up as well. The scoop: on Saturday I got down to the intake plenum on the old Blazer to pull the spider, but wasn't going to have enough daylight to clean up the mating surface on the manifold and continue on, so I called it a day. Sunday was too windy and dusty to be opening things up, but it occurred to me I hadn't tried any injector cleaner on the new Blazer, so I put two of the Seafoam injector cleaners in the tank. I continued to get the P302 while I test drove it around the parking lot, then got a pending P302 for the next five-ish miles, and no codes since. I think it's good to go and I'll be putting it back in action. Like I said though, I plan to continue on with your suggestions.

Answers to your questions:
Yes, I could definitely feel the misfire
It holds 55 psi for 10 minutes
I haven't checked the CMP Retard, and am not much familiar with the concept beyond the Googling I did just now. This thread mentions (https://blazerforum.com/forum/2nd-ge...-retard-90496/) a couple of options, is there one you'd recommend?
How would I check the ignition wire and plug? Visually inspect the plug and check the resistance on the wire?
I don't have a recent compression test, but that's on my to do list.

 

CMPR:

As your engine wears the relationship between the spark timing and the rotor position starts to drift (timing chain and distr gear) and eventually the spark can have trouble jumping cleanly to the proper distr post causing weak spark or crossfire. Adjusting CMPR involves modifying the hold down to get back within spec and/or doing the timing chain/distr gear. We have cost effective android based scanners that can measure this.

You can measure wire resistance, inspect for cracks, check the plug and then swap wires/plugs and see if the problem follows. Another good thing to do is mist water in the dark and look for arching.

Fuel delivery can definitely be the cause of a misfire and this injection system is notoriously finicky.


George

 

George,I'll read through these, thanks for posting them. I glanced over the misfires article, looks very thorough and comprehensive - Thanks!

 

An update: I haven't had time to look at the plug and wire on cylinder 2, but am still getting P302 codes intermittently, seems like when the engine is cold.
I got a BAFX Scanner and Car Diagnostic Pro, but an only able to access basic PIDs. I also can't download the manual through the app (I contacted the developer to get the manual) so it may be something I'm doing. Hopefully I can get at and share the data soon to get a better view into what's going on; I'll take a look at the plug and wire this weekend.

 

Ok, so of course as soon as I post about it I figure it out, I was connecting as a generic 96-07 vehicle, rather than GM 96-07. Here's the results for CMP (-9) and misfires, #2 has a over a thousand, and a few from #1 and #3. I'm not sure if it's from when I last cleared the DTC or last start, so it would be with 30 minutes or 15 minutes of driving, respectively.

 

Now were cookin' with steam. Get that CMPR straightened out and take another snapshot.


Georger

 

Ok, will do. I haven't messed with the distributor before, it looks like the bracket where I would make the adjustment for CMP retard is held down by the bolt I have highlighted here, is that correct? Captain Hook mentions in the thread below that the original bracket is adjustable up to 15 degrees total, so hopefully that will get me within 2 degrees. I'm assuming I need to loosen the distributor housing, then loosen the bracket and make the adjustment. Will I be able to loosen up the distributor housing enough as it is (without removing other components) to make the adjustment? My Hanes manual says to remove the intake plenum to get at the distributor, so I'm curious how much work I'm in for.

CMPR Thread:
https://blazerforum.com/forum/2nd-ge...n-83379/page2/

 

You just loosen the bolt and try turning the distr by hand then tighten down. If that doesn’t get you all the adjustment that you need then you have two choices. You can either wallow out the hole in the existing bracket to make it oblong shaped so that you can rotate the distributor even more or you can take that hold down off, use the same distributor and then put an old school Chevy small block hold down in its place and then the distributor is infinitely adjustable. I pulled my distributor out to do all this Jimmy jacking around but after seeing the way the old hold down would pop off the shaft of the distributor I think it’s possible to get it out without pulling a distributor up and risking timing problems if you don’t put it back down correctly, but I’m not sure about that. If you’re going to pull the distributor up Mark the rotor position so you can drop it back down into its proper location. Watch the rotor start to turn as you pull it up because it engages with a worm style gear so you’ll know where to start it to head back down again. nothing in the intake needs to come off.

George