Serious misfire problem with 4.3 csfi.

2002 Blazer 4.3 Yes I know about the TSB and all the problems with this unit. I had to take it to another mechanic (who I trust) because my son's work doesn't have a scanner to do a crank relearn. I took it in Thurs. for a crank relearn, and the problems began. First the SES light just came on. misfire code on Cyl 4 and 1. Cleared them and drove back to work. SES light starts blinking. Cr@p! Back to the mechanic. It it misfiring a bunch on Cyl 4, especially above 1700 RPM. replaced brand new Dist. cap with another one. no help. Left it with him to see what he could do. He informed me Sat. morning that he has no idea what's wrong, but the voice mail didn't tell me what he did, so I can't eliminate anything until I talk to him monday. I assume he tried wires and plug (both of which are brand new, and yes the plugs are the correct AC Delco plugs) You can here a lean rattle when it starts misfiring, so I don't want to drive it, but my truck has the entire front axle out of it. It is probably going to stay that way for a while, since I can't afford to fix both vehicles right now. I think that I may have to go with the upgraded spider to fix this, so I am looking for a decent price online right now. It also has a crack in the lower manifold that needs fixing, and I found a brand new entire upper and lower manifold with CSFI and throttle body for $329 plus $30 shipping, I might go that way too. I really don't know yet, I will know Monday what I am looking at.

Did anybody notice what the cam/crank offset number was? I have seen several badly worn distributor gears in 4.3s lately. This causes all kinds of missfire issues

I work on these alot. common problems are dist cap going bad reguardless of age, fuel pump, FPR, injector spider/poppets bad, and worn dist gears. Occasionally we'll find the plastic dist base is egged out causing the rotor to wobble. I would first check the fuel pressure

I can see fuel pressure causing random misfires or misfires on all cylinders, but 1 cyl? We are not even sure it really is a misfire at this point. We need to do more diagnosis. Would a weak valve spring cause this? At an idle, there is misfires, but slow count. Above 1700 rpms the count just flies. The O2 sensor doesn't look like it's going lean, but it has a lean rattle. When we resealed the lower intake manifold, the distributor did not appear bad. The brand new distributor cap was replaced with another brand new one and didn't change symptoms.

yes a weak valve spring or sticking valve could cause one too. I broke a valve spring and had one heck of a missfire once. not a common occurance on these motors though. at least in my experiance.

I would throw in a compression check while your at it.

Check the basics. An ignition scope would be the best way to rule out spark or electrical issues but you can make a spark tester from an old plug by opening the gap to .070". Install the test plug in series with the normal plug. If spark can jump both gaps then you don't have an issue with the secondary ignition system. A fuel pressure gauge should be installed for testing. Pressure should be at the mid to high end of spec and should not drop substantially in the first few seconds after the engine is shut off. Fuel pressure right on the borderline can do strange things with these engines. Manufacturing tolerances can be such that a few injectors will open with a weak spray while others won't crack. Also, leaking regulators tend to dump too much fuel into the manifold which will foul one or two plugs. Drain holes in the manifold funnel liquid fuel to cyls 3 and 4 when there's a problem. If the regulator's leaking you'll quickly see a nice, clean path indicating fuel has been bleeding into the manifold when the upper half is removed but a visual inspection of the plugs is a quick clue as they'll be soaked. Broken valve springs are unlikely but they will almost always show up on a vacuum gauge as a weak pulse of the needle. You need a good gauge that doesn't have a large damping factor for this test to work. Finally, the EGR valve can get stuck open which will cause all sorts of ridiculous symptoms. Problem usually affects more than one or two cyls but a quickie test / fix with a good scantool is to open valve 100% with engine rpm at 2500. Returning to idle after 35-45 seconds, you'll notice a large improvement in idle if the valve was open.

I have rarely had to do a crank relearn. But I have been doing this for over 20 years and ime when a problem crops up shortly after a repair it can frequently be traced back to the repair. If the crank signal is erratic then the pcm will have trouble firing spark at right time, correctly diagnosing specific cylinders which are misfiring, firing injectors at correct point, etc. Assuming this basic sensor is providing correct information could cause many, many wrong guesses.

Okay, I talked with the mechanic today. Here is what he tried. 3 different crank sensors shimmed 3 different ways, multiple crank position relearns, 2 different cam position sensors, 2 distributor caps, changed plug on offending cylinder, changed wires on cylinder, changed poppit valve on injector spider. Nothing changed the symptoms. Still cyl 4 misfire above about 1500 rpm. I found another post on a forum today with exactly the same symptoms, but they never posted a solution. My friend who is a 30 year chevy mechanic at a chevy dealership doesn't have a clue either. So I am driving it with a flashing SES light.

Well, if nothing else your guy was determined! I'd force a misfire on a different cylinder to make sure the computer is able to accurately report the offending cylinder. Then I'd pull the #4 wire and check for good strong spark above 1500 rpm. Finally a fuel pressure check to cover basics. If everything looked OK there I'd perform a vacuum, compression or leakage test. Vortec exhaust valves can sometimes hang open (guides were very tight from OEM) and once in a while they stick while a piston is coming up. Vacuum gauge would show a fluctuating needle that pulsed each time #4 came around.

I have read on other forums that its a best guess by the pcm on what cylinder when it reports a miss. my wifes car was reporting missfire on cyl 1 & 3. replaced #1 sparkplug because it was cracked and both missfire codes stopped. of course I did all this troubleshooting to get a recall from GM a week later for faulty OEM plug wires causing plugs to go bad...

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 think thats called rotor phasing. there was a discussion on s10forum a while back about it. didn't pay much attention to it since my distributor is adjustable. you might be able to grind the tab of the base of the distributor and use a regular hold down to get some adjustment.

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Originally Posted by jim_in_dorris

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.

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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!

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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.

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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.

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.

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??

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

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.

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.

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.

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Originally Posted by jim_in_dorris

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

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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? :laugh:

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

Well, yes and no to the injectors. The PCM is under the hood so you could remove individual injector wires one at a time to disable each injector. It's time consuming but not impossible. You can also buy inexpensive plug wire pliers to which you can add a very simple ground wire to prevent those itchy little shocks that happen from time to time. But really, the best answer (if the wires come off) is to shut the engine off to remove a wire. If there's a difference it will definitely be noticeable.

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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? :laugh:

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First time I ran into HEI was a good one. Other guys saying "that makes a big spark" and "you don't want to get bit with that." Phooey! I've pulled off plenty of plug wires and I've even been bit by a Chrysler lean burn ignition system. This is no big deal. Well that sombinch bit me so hard my head slammed back into the hood. Snapping, crackling, and I swear the spark was leaping outta that cap over an inch to find ground. My hand was sore which was bad, and the upcoming headache was worse. But the really lousy part was watching those two guys rolling on the floor at my expense. Not a bit of sympathy outta those bastahds. And for the rest of the time I worked there they'd call me over whenever there was a spark problem. "Hey, Sparky, got another misfire to check out."

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You can also buy inexpensive plug wire pliers to which you can add a very simple ground wire to prevent those itchy little shocks that happen from time to time.

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D'oh!

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But the really lousy part was watching those two guys rolling on the floor at my expense. Not a bit of sympathy outta those bastahds. And for the rest of the time I worked there they'd call me over whenever there was a spark problem. "Hey, Sparky, got another misfire to check out."

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Sounds like the neighbor kid who always wanted to help! So we had him hold the spark plug wire of a lawmower with his hand on the head, no spark pug in hole so it spun really fast when we pulled the cord! I'd swear his feet were off the floor, man did we get grounded for that one... Ha! Grounded! :laugh:

You guys crack me up. GROUNDED:laugh:. Well, I tried to check the fuel pressure today, but my adapter doesn't fit a gm fuel rail. I will try tomorrow at my son's work. We also tried reseating all the wires in the top of the spider in case one wasn't completely in. Nope. Oh well, it was worth a try. Tomorrow morning I will change the oil in the truck as it is due. I need to dig for my vacuum gauge in the tool shed. Tomorrow. We got side-tracked today working on the yard.

I checked with the mechanic that worked on my truck, and he did check the fuel pressure and it was within spec, but he couldn't remember exactly what the pressure was after this amount of time. My son has been busy at work, 2 junkyard engines in a jeep Cherokee in a week, after replacing a head in it 2 weeks ago. Those 4.7L sure love to break valve springs. Anyways, tomorrow I will try to finish up the 67 Chevy I am changing the intake manifold in, find my vacuum gauge and check that. I still have a bunch of work to finish for work that is due monday at noon, that takes precedent over everything, so I will have to get back to it now.

Okay.......... Today the SES light went out. Did nothing to the truck. ???? Then after about 2 miles of driving, it comes back on again. Then later it shuts off for a while. I wonder if the PCM is learning still, only about 2k on it since the crank sensor change.

Given the information that you have given and a combination of past experiences and gut feeling I am really thinking that you may have a bad pcm. I have had vehicles exhibit the same exact symptoms in the past that ended up having a bad pcm. It is not uncommon for a pcm or other module to have an unusual problem such as this and still operate seemingly fine. Just a quick review of the specifics of your problem without re-reading all of the posts. You are getting a p0300 with a steady count of misfires, but the engine is running fine, correct ? I do remember you mentioning a ping type noise while revving the engine in park also. I wouldn't be too concerned about that at this time as it is common to get such a noise under those conditions from certain vehicles. Before you go buying another pcm, though, I would check all engine grounds and I will take a quick look at the service manual. As far as the pcm "learning", the crank variation relearn procedure is instant and once completed with the scan tool that's it.

Well, I think I know what the computer was trying to tell me. Sat. on the way to my niece's house, the blazer developed a rod knock that got really bad really quickly. I must have had that bearing going bad, and the slop in the bearing was causing the computer to think is was a misfire because the crank speed was changing. Irregardless of anything else, I now need a new 4.3 for the Blazer. I hate to put more money into it, but refuse to go into debt and make payments anymore.

Sorry to hear this, especially after you've put so much work and effort into it. Are you going to find a used engine? Out here on the east coast these vehicles are often sent to the junkyard with reasonably low mileage due to rust.

Sorry to hear that as well. I don't know what your plans are as far as a replacement engine goes, but I would repair your existing engine before buying used. The reason for that is the same reason that I got 3 vortec 350 "cores" for nearly nothing. Other than rust, another reason that many vortec 4.3, 5.0, & 5.7 engines end up in the junkyard is due to the bearing damage that results from coolant seeping into the crankcase past failed intake gaskets. More than likely that is exactly what happened with your engine as well. If you were to buy a used engine it may have bearing damage even if it isn't bad enough to notice yet. Depending on your budget and abilities you can repair your engine with as little as a crank kit, timing chain, oil pump, and gaskets which should come in under $500 easily. I have put close to 10k miles on a "core" 350 that already had ~117k miles on it when pulled due to a cracked head. Ideally, a complete overhaul would be better, but isn't completely necessary. I have actually replaced bearings only (engine in the car sitting on jackstands in the driveway) on engines that had developed a knock due to oil pump problems and put several thousand miles on them with no further issues. Although that is not advisable, it just demonstrates my point that you could easily repair your existing engine. No matter what you choose to do, you are definitely better to keep what you have rather than go into debt for something else like you said. Good luck and I hope things work out.

The failed intake gasket syndrome is probably what toasted this engine. It is past a simple rebuild at this point, it went from running without a knock to complete failure of at least one rod bearing. By the time I got home, the poor engine was making a real racket. My guess is that both the crank and rod are shot. I also need to replace the intake mainfold that broke when we fixed the gasket leak. I would actually consider replacing the bearings and intake manifold gaskets on a pulled motor that was complete, it would be quicker than rebuilding what I have. I have also looked at a remanufactured long block, but then I have to find another intake, and swap everything anyways. Since my son works at a dealership, I can get the goodguy price with a 12 month warrenty, so this next week we will start calling.