Hey everyone,
My 02 2WD 4.3L Blazer is experiencing a single cylinder misfire on cylinder #5 when I'm merging onto the interstate and feel a noticeably loss in power. Usually when I hit about 60 mph and shifts into 4th. It will flash the Check Engine light while the misfire is occurring then turn off. Using a bluetooth OBD2 adapter and Torque Pro I monitor the current misfire count for all cylinders. Throughout normal driving a few other cylinders will misfire, current count never gets about 2-3 on them, but never #5 unless I am merging into traffic and it gets up into the hundreds. No others misfire when merging, just #5.

This has been on ongoing problem for a while now. I don't normally have to merge very often so I never looked too closely into it. Some other things to note, it usually only happens during the warmer days 85+. During the winter months I get a "lean" code on bank 1 and 2 every now and then. This was before I had a a scanning tool of my own and had to rely on the auto parts store for scanning. I thought this was due to a loose air intake because after adjusting it never popped the code again.

I'm thinking this could be a few things, but maybe there is something I could be missing. Here is a list of things that have been replaced in regards to the ignition system during routine maintenance:

• Distributor rotor
• Distributor cap
• Ignition coil
• Spark plugs
• Spark plug wires including the coil wire
• Camshaft position sensor

The problem was present before changing all that as well.

I have a compression test kit and I've read how to do the wet/dry tests with the throttle open. As soon as Hurricane Barry passes I will be able to do that test. I'm also thinking that because of the lean code I could be low on fuel pressure. I've read the spider injector system in these can be pretty problematic so that could very well be the problem or at least part of it. Another things could maybe be the fuel pump, but considering the high misfire count occurs on a single cylinder I'm leaning towards injector. Or the engine could just be entirely clapped out and needs a rebuild or 5.3 swap.

This Blazer seems to have already seen a bit of work before I acquired it so what I want to know is is there a way to tell if the upgraded injectors have already been installed? I really really really don't want to have to take that intake plenum off if I don't have to. And as always, any more advice or corrections on my train of thought would be greatly appreciated!!

 

Went ahead and logged what the fuel trim was doing while sitting in the drive way. I got it into closed loop then revved up the engine from idle. I wasn't logging misfires as I wanted to be sure to log these values. I tried to log O2 values, but for some reason they all showed "null" not 0. I might have selected the wrong PIDs.



This is getting a little bit out of my area of knowledge. What could make it get super lean at 2200+ RPM? Fuel pump/filter/injectors? How can I investigate this further? Should I also be looking at smoke testing?

Note: When I'm cruising at 70mph 2.1K RPM both long term fuel trims sit at about 0.74%.

Thanks everyone!

 

Hey everyone,
Sorry to keep posting, but I just wanna get all this information out there in case someone else ever has the same problem. The information on this forum has proved invaluable so I'd like to do my best to contribute to it.

Anyway, since changing the injectors or fuel pump might be the solution and doing either of those it's a good idea to go ahead and swap in a new fuel filter. So I went ahead and got a new filter and took a log of the fuel trims.



Fuel trims still take off when I hit 2.4k RPM, but not nearly as bad as before putting in a new filter. My next plan of action is acquiring a fuel pressure gauge to measure pressure drop.

My understanding is having positive fuel trim means the computer is telling the injectors to stay open X% longer to compensate for more air. I've always read the way these spider injectors fail is they leak and usually cause rich conditions. So that's why I'm leaning towards a bad fuel pump and the fact that a filter seemed to help, even a little. Has anyone heard of these spider injectors failing in a way that causes a lean condition? I find it odd it starts leaning out right at about 2.4k. I'm wondering if the previous owner put some sort of weird tune in it? it doesn't sound like any blazer I've ever heard before.

 

Mine was throwing a code for # 5. All my wires, cap and rotor, and plugs where A/C Delco with very few miles on them. Removed the # 5 plug and found traces of arc lines going to plug. Removed wire added siliconed around boot and pulled boot back to inspect wire terminal. Sometimes I have pulled this loose in past times. But wire was good. Replaced plug with new AC and problem gone. Also added Techtron to fuel tank that I purchased at Costco. Really runs good now. Mine is a 99 with 206000.
Everything I read about this engine is it is really particular about its cap and rotor. To avoid unnecessary problems I use them.

 

Hey everyone,
I found the crankcase vent tube sort of came undone. I'm not sure if that was the cause or I did that when I was checking fuel pressure. It seems to be running a lot better now since fixing that. I haven't been able to test further as I think I might have blown a head gasket. Getting the coolant gurgling sound in the morning when I start it up. No drips on the ground, no white smoke out the back, oil doesn't look milkshakey. Exhaust might smell a tiny bit sweet, but not running poorly or anything, no overheating. The coolant tank doesn't bubble until I turn the car off and not losing a noticeable amount of coolant. Not sure what is going on here. Going to pick up a block tester tomorrow and check for exhaust gas in the coolant.

 

Danny
When you are merging into traffic you are putting a load on the wire on # 5. It could be that it breaks down with that load and other times not much is required and it performs as normal. I know you said that the wires were replaced, but sometimes new is defective. If you have old wires still you might swap #5 out and see if that corrects the problem. I don't have a good meter, but you can check the wire that way also.. Goggle it.
I am sorry don't know about fuel trims. My engine would also throw random misfire codes. I ended up pulling the distributor and found that the drive gear was seriously worn. Also I broke the ear off the hold down for the cap. Purchased a new distributor and installed. I have never had it run this well before!! If you wanted to check this gear, it is not too hard to pull the distributor. There is a really good youtube channel by Schrodingers box; Dec 19, 2012. I have had mine out a few times and it is now easy. Take the cap off and line the rotor up to the number six you see inbossed in the distributor housing. I crawl under the vehicle and use a flex handle short extension and 5/8 socket to align up the two timing marks on the vibration damper. With the cap off I bump the starter to move it too the inbossed 6 on the distributor. When it is close, I finish it with the 5/8 socket. I also pull out the fuel relay while doing this. I hope this helps you.

 

Danny
I also forgot to tell you that these engines are hard on intake gaskets. If you are adding coolant that might be your problem, I would think that more than head gaskets. When I changed mine I had been adding coolant every trip to town and back. I was able to take my intake off without tearing it apart. Which I guess is not the normal way. Took pictures and was not a lot of fun. But don't lose coolant anymore.