Serious misfire problem with 4.3 csfi.

[EagleMark]

Okay, I went and talked to my mechanic again, it appears that the crank-cam correlation value is out of spec. It is stuck at 6 degrees, no matter what he did. Since the vortec V6's have a non-adjustable distributor, it has to fix the correlation in the PCM. The easy solution is to make it adjustable by swapping out the V6 hold-down with a V8 one. I guess I will pull the one off the 283 this weekend.

I just fixed one of them for a guy who had some work done and they could not get it to run right, I pulled the distributor and moved it one tooth and it was fine!

[1project2many]

Okay, I went and talked to my mechanic again, it appears that the crank-cam correlation value is out of spec. It is stuck at 6 degrees, no matter what he did. Since the vortec V6's have a non-adjustable distributor, it has to fix the correlation in the PCM. The easy solution is to make it adjustable by swapping out the V6 hold-down with a V8 one. I guess I will pull the one off the 283 this weekend.

This is all over the place. Misfire, change everything, problem starts after rarely needed procedure is done, do rarely needed procedure multiple times, and now the problem is claimed to be an issue which won't cause a misfire... not a very methodical approach by any means. It's starting to turn into a drama rather than a helpful thread on fixing the engine.

I've seen cam retard values that are 10 degrees off. The engine runs well and the PCM can still identify a specific cylinder if there's a problem. The only indication of a problem is the check engine light and code 1345. PCM updates cam retard value when engine is first started or when throttle is pressed more than 70% so if that value is off, something is at the heart of it.

My suggestion doesn't change much. Moving the distributor is not likely to be the answer. If there was no problem, then there suddenly was a problem, you should find and fix the root cause. Check the distributor shaft for free play as previously mentioned. Grasp the rotor and try to turn it to check the press fit between distributor plate and shaft. If those two tests don't reveal a failure, forget everything you've been told by the mechanic and start from scratch. Check fuel pressure. Use a spark tester or plug opened up to .070" to check for consistent spark at each cylinder. Force a misfire and ensure the VCM can report the correct cylinder has a problem then check the mechanical condition of that cylinder. I can't stress enough that you're not doing anything besides guessing if you don't follow a methodical approach and when you ask the internet people to make guesses for you they are usually wrong.

[jim_in_dorris]

I am not discounting what you have to say 1project. I am just trying to get a handle on this. I am not getting a 1345 code. That tells me something too. I will test the rotor this weekend when I can actually stop driving it to work. I will also check the shaft for free-play, but the mechanic did say he inspected the distributor because he has seen that be a problem before. My real question is why a CASE relearn doesn't change the cam retard value back to zero? The Blazer is running fine other that the codes. It isn't a real misfire, just being reported as one. You can make any cylinder misfire by pulling a plug wire and it runs like poo. I can't work on it during the week, so I haven't done any of the suggestions yet. I had to replace the Crank Position Sensor because it was throwing a P0336 code. After replacing it I was getting random SES lights (I can't remember what the code was for those) so decided to do a relearn to stop the random SES light. I am getting 17 MPG combined driving, which is what it has always gotten, so have a hard time believing that something mechanical is wrong. It may still be that something is wrong, it just doesn't run like it is. I will also check fuel pressure and look at mechanical on that cylinder if I can get some time with my son this weekend. Obviously I can't really rule anything out until I check it out completely. I only know that it is not the plug, wire, or injector on that cylinder, and that the cam retard is at 6 degrees. Everything else is mere speculation on my part. Unfortunately I do not have access to a scanner new enough to work on this truck, or my mechanic would not have even seen it as money is tight.

[black dawg]

so what exactly does a crank relearn do? What happens if you put the distributor in a tooth or two off and then do a relearn? I have seen many that were 10 plus degrees off with little to no issues.

Why was the crank relearn originally??

[pmkls1]

6 degrees off isn't much on the cam retard value which is why it isn't setting a P1345 even though it is technically out of spec. 1project is spot on with recommendations. Just to be clear, is the truck actually misfiring or not ? If there is no real misfire then I would suspect a faulty VCM as I have seen others do the exact same thing. If there is a misfire then compression, vacuum, and fuel pressure readings need to be taken. These systems were VERY sensitive to fuel pressure and you want to see a steady reading near 60 psi at all times. If the pressure drops even 5 psi when snapping the throttle then the fuel filter and pump need to be checked/replaced. Broken valve springs were extremely rare on vortec 4.3's but sticking/bent valves and cracked cylinder heads were common. Those problems would cause a pretty steady misfire at just about any rpm though so I would doubt that there is an issue there. Between the cam gears themselves or the distributor housing, those are also common problems that will make timing jump around and cause a lot of issues. Also be careful that the cam sensors may be specific to the v6 as I know the distributor is so if your mechanic is throwing other cam sensors in it he may be putting the wrong ones in and inducing issues. The misfire counter is fairly accurate given that the cam and crank sensor readings are correct. When you have a cylinder with a heavy or dead miss the counter will sometimes pickup bogus misfires on other cylinders but it is easy to spot because the counts will always be much higher on the actual problem cylinder. Another possibility is a cracked or poorly sealed upper plenum as I have seen a few. The biggest determining factor here though is wether there is a genuine miss or not and that should be easy to tell. Also, you mentioned something about a lean knock which you didn't elaborate on. If you could give more info on that it could be quite helpful. You really need to start back at the very beginning or else you will most likely end up chasing your tail. Start with the crank sensor issue that spurred this whole mess. Also, how long has it been since other repairs were made i.e. resealing the lower intake, and what gaskets were used plastic or metal ? Also, check all grounds as although they most likely wouldn't cause these issues there are ground wires that get disturbed when removing the lower intake. The breather tube coming off of the throttle body hat and the pcv elbow are two pieces that commonly become brittle and crack causing the MAF sensor to not read properly. I know there's a lot of info thrown at you, but if you take a systematic approach starting with the repairs leading to this issue you most likely won't make it halfway down the list before finding the problem. HTH
Phil

[jim_in_dorris]

Thanks everybody, I am not a professional mechanic, but have been playing with cars my entire life, so i understand that shotgunning doesn't work. Besides that gets expensive. It doesn't appear to be an actual misfire, the engine runs smooth as silk all the way through the RPM range. The lean knock I was referring to was a rattle on revving the engine. It turned out that no knock counts were being set during that time, so the mechanic decided it must be something else. I will check fuel pressure, I actually think I have the tools to do that, so saturday I will check that. Something else that may or may not be pertinent is the fact that the Blazer sat for a year and a half with no battery while we saved enough money for repairs. That may have something to do with what we are seeing, I don't know. If you look at misfire counts while revving the engine, above about 1500 RPM the counts increment extremely rapidly, yet the engine runs smooth as silk. The Blazer has about 3000 miles on it since we completed repairs. Rebuilt tranny, new radiator, resealed lower manifold, new plugs, wires, cap, rotor, hoses, idler pulley, belt tensioner, and serpentine belt. The P0336 code was set about 2500 miles after repairs. We put about 300 miles on the truck after the Crank Position Sensor was replaced before the relearn. I have only put about 100 miles on the Blazer since then.

[1project2many]

CKP variation relearn allows PCM to recognize crank reluctor wheel teeth properly. It does not change cam retard value. I've been hiding under the doghouse of V8 vans for so long now that I can't remember whether or not OE 4.3 distributors can be turned. I know that OE V8 parts can. There are a couple of aftermarket brand replacements which come with their own hold down which prevents the CMP sensor (distributor) from being adjusted. The fastest "fix" for those clamps is to put them in a vice and use a hammer to open the clamp up slightly. Presto chango adjustable dizzy.

FWIW if this had been titled "false misfire" or something similar the recommendations would have followed a somewhat different track. But I would still establish a baseline as previously mentioned. Misfire codes occurring when the engine seems to run fine can be extremely hard to track down and you want to make sure you know the mechanical parts are right before diving into pcm and related wiring.

[jim_in_dorris]

Thank you 1project. When I started this thread, I didn't know that the misfires would turn out to be false misfires. And I agree that I need to make sure everything mechanical is okay. I hope to make a start on the mechanical stuff this weekend. I teach and this is the last week of classes and then next week is finals. I have a week off after that before starting the summer term, so I will have more opportunity to make progress on figuring this out. I intend to continue this thread until it is resolved. Without a scanner like a snapon solus, can I disable individual injectors to induce misfires? I can do vacuum, compression and fuel pressure testing with tools I have.

[EagleMark]

Without a scanner like a snapon solus, can I disable individual injectors to induce misfires?

Being an old guy who has been shocked so many times by pulling spark plug wires, even with good spark plug boot pliers, I found that question quite odd?

Can't wait and hear the answer... sure would be easier on the ol ticker!