No compression...

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cchase

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This is a follow-up to my previous post about the 2002 Malibu with the misfire:

https://bobistheoilguy.com/forums/threads/misfire-troubleshooting.151872/

The mechanic says there's no (or low, not sure but it would have to be really low) compression in the cylinder that's misfiring which I suppose means the head needs to come off.

I'm considering attempting this job myself, with my main worries being the fact that I haven't delved this far into an engine that I needed to get running again, have no experience with transverse mounted engines, and don't know how hard it is going to be because the head that needs to come off is in the rear.

What am I getting myself into with this job in terms of accessibility and possibility. Time is not a major concern.

Also, I'm trying to figure out a way so that the vehicle can be used for at least a week or so. I'm aware that driving a car with a misfire isn't the best idea, but it's the owners only vehicle. I am thinking the best temporary course of action is to disconnect the injector so at least it isn't flooding the cylinder with fuel constantly. Is this a safe course of action or should I avoid it altogether?

Thanks in advance.
 
I'd say it depends on if this cylinder is part of the front bank, or the rear cylinder bank.

Front bank, probably not too hard to take off the head...etc...Rear bank, well, that will be much tougher - may even have to lift and rotate the engine forward.
 
Originally Posted By: addyguy
I'd say it depends on if this cylinder is part of the front bank, or the rear cylinder bank.

Front bank, probably not too hard to take off the head...etc...Rear bank, well, that will be much tougher - may even have to lift and rotate the engine forward.


It's in the rear bank...
 
If you put the car in park and disconnect the front dogbone... release the e-brake roll the car backwards, the engine will roll forwards. Re set the ebrake and lash the engine.

However, there is not "lots" of room, and there is lots of stupid stuff that has to come off. Don't know how much further it is than a LIM job, but the LIM takes many newbies all day.

However you may get lucky and pull the valve cover and find a broke rocker arm or something.
 
Total compression loss usually mean a toasted valve or broken valve train parts.....if it's a burned valve make sure you find and correct the cause for it
 
Originally Posted By: Cause4Alarm
Total compression loss usually mean a toasted valve or broken valve train parts.....if it's a burned valve make sure you find and correct the cause for it


What would be the cause for a burned valve?
 
Usually a lean mixture or ignition timing too far advanced....sometimes if the valve timing is off it can let still burning gases by the exhaust valve causing it to erode
 
I didn't expect the problem to be low compression. I would get a compression gauge and verify it yourself. It's not beyond possibility that the shop did not diagnosis right. See if in fact it is low and how low and if the plug seems wet from fuel. If it is really low just in cylinder 5, I would first want to take the rear valve cover off and see that the rockers are intact and opening and closing the valves when engines is cranking. Could be possible the intake rocker came loose. But does the engine make any unusual noise?

If the problem is found to be in cylinder 5, the rear head needs to come off. The lower intake would have to come off. This will require replacing the lower IMG which it needs anyway if it hasn't been done before (If it has been done before that could explain a rocker coming loose). Then you might as well replace both head gaskets once you are that far in. You'll have a motor that will go another 150K-200k, but I can understand just replacing the rear head gasket.

It depends on your mechanic skills but it is a somewhat involved job. There are a few tricky spots, but for the most part it is pretty straight forward. It's mainly a matter of the lower intake manifold removal, then it is just a matter of unhooking the exhaust and un bolting the head. you will need a a couple of torque wrenches and probably at least an inexpensive Felpro torgue angle gauge for the headbolts. There are some very detailed instructions for the lower intake job on the net.
 
definitely verify yourself. It is an involved job if you are not very mechanically inclined. Hardest part is pulling the lower intake, and getting the exhaust manifold bolts off without snapping them. good luck and keep us updated.
 
Originally Posted By: mechanicx
I didn't expect the problem to be low compression. I would get a compression gauge and verify it yourself. It's not beyond possibility that the shop did not diagnosis right. See if in fact it is low and how low and if the plug seems wet from fuel. If it is really low just in cylinder 5, I would first want to take the rear valve cover off and see that the rockers are intact and opening and closing the valves when engines is cranking. Could be possible the intake rocker came loose. But does the engine make any unusual noise?

If the problem is found to be in cylinder 5, the rear head needs to come off. The lower intake would have to come off. This will require replacing the lower IMG which it needs anyway if it hasn't been done before (If it has been done before that could explain a rocker coming loose). Then you might as well replace both head gaskets once you are that far in. You'll have a motor that will go another 150K-200k, but I can understand just replacing the rear head gasket.

It depends on your mechanic skills but it is a somewhat involved job. There are a few tricky spots, but for the most part it is pretty straight forward. It's mainly a matter of the lower intake manifold removal, then it is just a matter of unhooking the exhaust and un bolting the head. you will need a a couple of torque wrenches and probably at least an inexpensive Felpro torgue angle gauge for the headbolts. There are some very detailed instructions for the lower intake job on the net.


Thanks for your input. I wish I had people like you on speed dial.

Interesting thought on loose rocker. The lower IMG was replaced about a year ago. But as you ask, the engine doesn't make any strange noises right now. Does that rule out the possibility that it is a rocker? I would think that would make some noise if it was rattling around, but perhaps it does't necessarily?

I like to consider myself mechanically inclined but this is certainly more involved engine work than I've ever undertaken.

I do have a compression gauge and at this point I am probably going to fly down there to drive it back here with the owner anyway, so I should be able to stash a compression gauge in my bag (and hopefully TSA knows what it is).

I'm a bit surprised on the low compression myself because the engine isn't particularly high mileage (low, I would say), it gets good fuel, is driven lightly and mainly very long trips and very reasonable oil change intervals...

Thanks again to everyone for your thoughts, please keep them coming as this is fairly involved and there's no such thing as too much input.
 
Originally Posted By: mattd
definitely verify yourself. It is an involved job if you are not very mechanically inclined. Hardest part is pulling the lower intake, and getting the exhaust manifold bolts off without snapping them. good luck and keep us updated.


Exhaust manifold bolts have me very concerned as well. Hopefully I can get a torch in there or some penetrant.
 
Originally Posted By: cchase
Interesting thought on loose rocker. The lower IMG was replaced about a year ago. But as you ask, the engine doesn't make any strange noises right now. Does that rule out the possibility that it is a rocker? I would think that would make some noise if it was rattling around, but perhaps it does't necessarily?



Well normally you would expect a rocker coming loose to make some racket but not always. It's possible it did make some racket for a while until it backed out the bolt and pedistal completely and basically is freewheeling and the owner didn't notice, but that is probably unlikely. Most likely scenario is the rocker pulled the threads out of the head maybe due to being over tightened during the gasket replacement. The rocker arm threads stripping is a somewhat known issue. This could be fixed without removing the intake and head.

Of course maybe the engine really doesn't have low compression or if it does it is something else. But we won't know for sure until you get a chance to verify compression. The pushrods are different length and have to be kept in order, but I'm getting too far ahead. You'll read up on all that for the intake removal. I'm thinking if the head has to come off you can leave the exhaust manifold attached and that might make it easier to remove the exhaust bolts
 
Originally Posted By: mechanicx
Originally Posted By: cchase
Interesting thought on loose rocker. The lower IMG was replaced about a year ago. But as you ask, the engine doesn't make any strange noises right now. Does that rule out the possibility that it is a rocker? I would think that would make some noise if it was rattling around, but perhaps it does't necessarily?



Well normally you would expect a rocker coming loose to make some racket but not always. It's possible it did make some racket for a while until it backed out the bolt and pedistal completely and basically is freewheeling and the owner didn't notice, but that is probably unlikely. Most likely scenario is the rocker pulled the threads out of the head maybe due to being over tightened during the gasket replacement. The rocker arm threads stripping is a somewhat known issue.

Of course maybe the engine really doesn't have low compression or if it does it is something else. But we won't know for sure until you get a chance to verify compression. The pushrods are different length and have to be kept in order, but I'm getting too far ahead. You'll read up on all that for the intake removal. I'm thinking if the head has to come off you can leave the exhaust manifold attached and that might make it easier to remove the exhaust bolts


Do I even want to know what the solution is if the rocker arm threads are stripped?
 
Sorry I updated my post. I think if you're careful it could be repaired with a helicoil kit while the head is still on the engine.
 
Now that I think about it with the intake gasket being replaced it is not unlikely at all that the rocker arm bolts being overtightened led to the rocker pulling out. They are suppose to be tightened to only 124 in-lb (10 ft lbs) plus 30 degrees. Probably little chance the shop will take responsibility and fix it if it turns out to be the rocker arm bolt pulled out.
 
Originally Posted By: mechanicx
Now that I think about it with the intake gasket being replaced it is not unlikely at all that the rocker arm bolts being overtightened led to the rocker pulling out. They are suppose to be tightened to only 124 in-lb (10 ft lbs) plus 30 degrees. Probably little chance the shop will take responsibility and fix it if it turns out to be the rocker arm bolt pulled out.


Trust me, at this point I'll be glad if it's "only" the rocker bolts pulling out. Well, actually I'd be most happy if it is the injector.

I have a plane ticket booked, hopefully I can bring some tools with me without an issue at security.

Many thanks to all and especially mechanicx for their input, more is always appreciated as this is anything but resolved at this point.
 
I'm with mechanix on this. I've personally seen the same car (3.4 Alero) come it twice and (and once prior to my starting) for the very thing he's talking about. I guess the kid somehow jacked the transmission into reverse while trucking down the highway and pulled a bunch of studs out.

We just fix each new pulled with Heli-Coils.

I really can't add much to the conversation as he's got it pretty well covered. There are some minor tips and tricks to the LIM, but as mechanix has already said, it's a bit early for that....
 
Originally Posted By: Cause4Alarm
Never was a fan of the GM 60deg V6.....way too many design issues


So far, I'm not seeing a design issue with mechanics using an impact wrench to tighten a bolt that should be 12 lb-ft into an aluminum head.

Let's keep on topic please.
 
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