miss in engine

gmc4life · September 13, 2006

I have a 2000 GMC 2500 with a 5.3 L. engine. Lately I'm having a miss in the motor upon accelerating. The engine light came on and we had to change the crank sensor, but the miss is still there. It's worst when the engine is cold. I took it to the dealer and they can't find the problem. It's very annoying, specially when you try to pass another vehicule.

Hope you can help me

Paul

GM-Tech · September 13, 2006

The most common cause of a miss under load would be a plug wire. The dealership should be able to drive it with a tech 2 hooked up and display the misfire graph to see which cylinder it is. That would help a lot to narrow it down.

When you say they can't find the problem, does that mean they're unable to duplicate the misfire or they see the misfire but can't figure it out?

gmc4life · September 13, 2006

The most common cause of a miss under load would be a plug wire. The dealership should be able to drive it with a tech 2 hooked up and display the misfire graph to see which cylinder it is. That would help a lot to narrow it down.

When you say they can't find the problem, does that mean they're unable to duplicate the misfire or they see the misfire but can't figure it out?

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There was some miss in #1 and #6 cyl. After they change the crank sensor those miss dissapeared. We change all the plugs wires and the miss is still there. Could it be a foul plug????

GM-Tech · September 13, 2006

Could it be a foul plug????

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Sure, could be.

gmc4life · September 13, 2006

Could it be a foul plug????

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Sure, could be.

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Just got back from the dealer and they were in contact with some GM tech. The mechanic explain to him what was the problem and his answer was that it could be a broken wheel on the crank to a broken wire on one of the injector coil. So what it tells me is that it will cost me big bucks down the line. They will be going through the process of elimination and it could take a while.....hope it's only a broken wire...lol.

GM-Tech · September 13, 2006

his answer was that it could be a broken wheel on the crank to a broken wire on one of the injector coil.

Dunno for sure what "wheel" he's talking about, but it would seem to me that either of those things would be a constant misfire, not one that just occurs on acceleration.

The reluctor "wheel" on the crankshaft doesn't break that I ever heard of.

gmc4life · September 14, 2006

Before I give this dealer (GM) big bucks I'm going to take my truck to another dealer (Cheverolet) and see if they can come with something else. I don't mind paying for services, but this is rediculous.

The mechanic who was working on my truck told me that having a broken reluctor wheel on the crank happenned before. Also he said that if the crank has any play at all in the bearings, it would make the crank sensor go crazy. But, if there was a problem with the crank, the engine would run funny on idle which is not the case, it only miss when the load is on. To go back to my first post, #1 cyl. had over 18000 miss and #6 had over 20000. That was before they change the crank sensor, but now the miss is still there but they can't pick it up on the scanner. Somebody told me to put a can of injector cleaner in my tank. I will try that tomorrow, it can't hurt it more than it is now. Will keep you posted.

gmc4life · September 20, 2006

After changing the plugs and a injector treatment plus two more trips to the GM dealer and a $300.00 dollar bill, they finely found out what the problem is. They don't know how it happened but the crank shaft is moving back and forth in the thrust bearing, thus causing the crank sensor to act up. This means that the engine has to come out, and I could see the dollar sign light up in the service manager's face ....but it got to be done...Thanks for all the help and keep this forum going. There's a lot to learn just by reading it every day....HAPPY MOTORING.

95Sierra2500 · September 21, 2006

After changing the plugs and a injector treatment plus two more trips to the GM dealer and a $300.00 dollar bill, they finely found out what the problem is. They don't know how it happened but the crank shaft is moving back and forth in the thrust bearing, thus causing the crank sensor to act up. This means that the engine has to come out, and I could see the dollar sign light up in the service manager's face ....but it got to be done...Thanks for all the help and keep this forum going. There's a lot to learn just by reading it every day....HAPPY MOTORING.

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Did they SHOW you that this was the problem? I'd want to see it before I'd believe it...But that's just me. I'd also be doing this overhaul myself and adding a cam and some head work, but again...just me.

GM-Tech · September 21, 2006

Did they SHOW you that this was the problem? I'd want to see it before I'd believe it...But that's just me.

Just crawl underneath and pry the balancer fore and aft. Thrust clearance on the thrust bearing is only a few thousandths of an inch. Basically unnoticeable by prying the balancer fore and aft. If you can noticeably move it, you have a problem.

I have seen this type of problem before. Had a Camaro with a manual trans that died every time the clutch was pushed in. What was happening was the crank was being pushed forward from clutch release pressure and the crank signal was lost. That was years ago and I don't recall how much play there was.

95Sierra2500 · September 21, 2006

Did they SHOW you that this was the problem? I'd want to see it before I'd believe it...But that's just me.

Just crawl underneath and pry the balancer fore and aft. Thrust clearance on the thrust bearing is only a few thousandths of an inch. Basically unnoticeable by prying the balancer fore and aft. If you can noticeably move it, you have a problem.

I have seen this type of problem before. Had a Camaro with a manual trans that died every time the clutch was pushed in. What was happening was the crank was being pushed forward from clutch release pressure and the crank signal was lost. That was years ago and I don't recall how much play there was.

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Oh I know how to check it, but I'd still want the dealer to SHOW me that this was indeed the problem, I wouldn't want to just take their word for it. It's an awefully big repair, and I think you can understand my skepticism. Of course, I usually do my own repairs so I know things are done and if it's screwed up, I can only blame myself.

GM-Tech · September 21, 2006

If you really have excessive end play, go in and show 'em.

gmc4life · September 21, 2006

Did they SHOW you that this was the problem? I'd want to see it before I'd believe it...But that's just me.

Just crawl underneath and pry the balancer fore and aft. Thrust clearance on the thrust bearing is only a few thousandths of an inch. Basically unnoticeable by prying the balancer fore and aft. If you can noticeably move it, you have a problem.

I have seen this type of problem before. Had a Camaro with a manual trans that died every time the clutch was pushed in. What was happening was the crank was being pushed forward from clutch release pressure and the crank signal was lost. That was years ago and I don't recall how much play there was.

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Oh I know how to check it, but I'd still want the dealer to SHOW me that this was indeed the problem, I wouldn't want to just take their word for it. It's an awefully big repair, and I think you can understand my skepticism. Of course, I usually do my own repairs so I know things are done and if it's screwed up, I can only blame myself.

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I know what you guys mean...but the mechanic showed it to me by prying on the front crankshaft pulley, and beleive you me, there is noticeable movement front to back. But I'm still going for a second opinion because other mechanics told me that it is hard to believe. The thing that puzzle me is that it is worst when the engine is cold like in the morning. When the engine warms up the misses are not as bad. Wouldn't it be the other way around because when the engine warms up the metal expand and would cause the engine to knock. I don't know, it's only my opinion...that's why I'm going for a second opinion. If I take it easy on the foot, the truck works good. Another funny thing is that the service engine lights will come on and go off after a couple of miles.

GM-Tech · September 22, 2006

I know what you guys mean...but the mechanic showed it to me by prying on the front crankshaft pulley, and beleive you me, there is noticeable movement front to back. But I'm still going for a second opinion because other mechanics told me that it is hard to believe. The thing that puzzle me is that it is worst when the engine is cold like in the morning. When the engine warms up the misses are not as bad. Wouldn't it be the other way around because when the engine warms up the metal expand and would cause the engine to knock. I don't know, it's only my opinion...that's why I'm going for a second opinion. If I take it easy on the foot, the truck works good. Another funny thing is that the service engine lights will come on and go off after a couple of miles.

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If the mechanic showed you movement, it was too much. Here's the spec right from our service information...

Crankshaft End Play - 0.0015-0.0078 in

1 to 7 thousandths is not something you're going to be able to see!

So go back to the dealer and ask them about the clearance issue. You don't need a second opinion if they've shown you that it moves an 1/8' (125 thousandths!) or something like that. 125 times the amount of allowable clearance is a lot!

Wouldn't it be the other way around because when the engine warms up the metal expand and would cause the engine to knock.

Actually, when it warms up and the metal expands, it would reduce the clearance and the knock.

gmc4life · September 29, 2006

Well today I got the bad news....My motor is done, kaput, finish. They remove the oil pan and remove the thrust bearing...it's all gouged out not from loose material but from heat. It appeared that it heated up so much that it melted the material inside the bearing and the lobe on the crank is a blue color. The bearing caps are also gouged out from the crank rubbing on it. Also it gouged out part of the block.

The funny thing about all this is that nobody can tell me how it happened. The mechanic, at the dealer where my truck is, thinks that it might be a problem that occured on the production line and the damage is only showing now. He will try to get in touch with the G.M. rep. in the area to come and have a look at it.

New motor from G.M. $3800.00 cdn.

So if anybody out there is having a crank sensor code, be careful.