I got to a point with my 1996 GMC Suburban rehab where I had no idea what was wrong. My scanner kept telling me I had a misfire in cylinder 4 but no other information than that. It was finally “drivable” so I took it to my favorite mechanic who tells me it is a compression issue in that cylinder.
From my research it seems to boil down to 4 possibilities:
[ul]
[li]Blown Head Gasket[/li][li]Stuck Valve[/li][li]Bad Piston Rings[/li][li]Cracked Block[/li][/ul]
The mechanic is quoting me $3000. I can’t afford that. Right now, I’m thinking I either need to sell it to a junk yard or try to fix things myself, and sell it to a junk yard if I screw it up badly enough.
I have replaced the brake lines to both front wheels, changed out the spark plugs and wires, and replaced the wheel bearing module on my wife’s mini van (a single self-contained module, not the separate pieces that need to be repacked).
I figure, if it is a cracked block, I am SOL. Everything else requires pulling the head to fix. Would any of this be outside the realm my abilities assuming that I am fairly handy in most things?
What would be involved? Do I have to pull the whole engine out to replace the heads? Would anyone here be able to provide a ballpark estimate on time and cost of parts?
My mechanic also says there is a misfire on another cylinder on the other side of the engine that is due to not enough gas getting to the cylinder. I’m pretty sure the truck sat in a garage for a number of years and the old gas has gummed up the injectors. Which also makes me think that there is a stuck valve in my other problem cylinder. I’m thinking that I may need to pull both heads, clean everything up and then put it all back together.
Do a compression test first.
On the cylinder that is low, take a reading before and after pouring a teaspoon of oil in the spark plug hole. If the compression comes up to near normal, you need a ring job. If it doesn’t, it’s one of the problems you mentioned. If you have a blown head gasket, you will be getting exhaust gas in the coolant, and it should be pretty obvious.
If you do go through all the trouble of removing one head, you might as well remove both of them. You’ve already done about 75% of the work.
A valve that is stuck open is pretty easy to see if it’s a pushrod engine once you get the head off. A little more difficult if it has overhead cam.
A blown head gasket is usually pretty easy to see. Although the gasket might get ripped when removing the head, there still should be a track or mark on the block and/or head where the exhaust gas was leaking. If it was leaking into the cooling system, usually the combustion chamber is much cleaner on that cylinder.
Like beowulff said, there may well be exhaust gas in the coolant. Auto parts places sell a block-tester kit that can tell if there is exhaust gasses in the coolant. About $50. Are you loosing coolant or is your oil looking milky? Actually I’m somewhat surprised that your mechanic didn’t check that out himself. Maybe you need a second opinion from someone else.
Did he actually do a compression test on all 8 cylinders? It should be pretty easy to narrow it down if we knew the wet/dry compression figures. How exactly is he quoting you $3k to fix it if he doesn’t know what the problem is anyways?
Pulling the head isn’t a small job, but if you’re meticulous about it and take it slow it’s not a bad DIY job. Actually messing around with the springs or valves is probably best left to a mechanic or machine shop, but you should be able to save a lot by pulling the head yourself.
If it is a cracked block or rings, a used engine would probably be the best bet (assuming the truck is in otherwise good shape). There’s about a bajillion 350’s in junkyards so the engine itself shouldn’t cost too much. Engine swaps are definitely something where the labor charges will widely vary, so it’d be worth shopping around on a price. You might be able to even find a shop that will do the actual swap for pretty cheap if you do all the tedious work of pulling the accessories, wiring, etc off the engine.
If it is cyl # 4 I would also check the cam shaft first. This seems to be the one that fails if the truck is ever overheated. Just pull off the valve cover, rotate the engine and see if the valves are going up and down the same as the other cyl. If it was a head gasket you would most likley but not always loose compression on adjoining cyl. If it is a valve there is a good chance you will hear popping or huffing noises in the intake. A cyl will come up with the wet test as indicated. Spend a couple hours checking it out yourself if you are able,
Add a worn cam lobe, a collapsed lifter, a burnt valve, and a cracked cylinder head to the possibilities list.
Cracked blocks are possible but quite rare.
Piston rings worn to the point of causing a misfire are not very common. However, it’s important to determine the cause of the low compression, as replacing the rings is a lot – and I mean a LOT – more involved than repairing any of the other items, and replacing the camshaft is a whole different animal from removing and replacing (R&R) cylinder heads.
Cylinder head R&R is major engine work. “Book time” is the 12 hour range, and that’s for an experienced mechanic with all the right tools and equipment. For someone doing it for the first time, it could take 2-3-4 times as long. The heads will need to go to a machine shop for resurfacing (to make them perfectly flat), pressure testing (to find cracks, if present), and checking – and if needed repairing/replacing – the valves, seats, springs, etc. (could take days depending on the machine shop’s schedule and exactly what needs to be done). A torque wrench will be needed to install the heads. You should have a good set of tools, a good repair manual, and a good source of expert advice available.
For more detailed advice, we’ll want to know the exact model (1500? 2500? 2WD? 4WD?) and engine size (should be on an emissions sticker under the hood, can also be determined by the 10th character of the VIN).
Maybe your mechanic did this and just didn’t relate it to you, but you don’t want to dive in without a definite diagnosis. If he doesn’t know the specific cause, further testing and/or disassembly should be done to find out.
If you have a compressor then rent a compression gauge. If it’s leaking out of a valve you’ll be able to hear this in either the exhaust or intake manifold and if its in the rings it will leak into the crank case so you should be able to hear it in the oil filler tube. but as Gary T said it would be rare for a ring to cause a misfire.
Now if it’s just misfiring that could be a worn timing belt or chain or even problems with the ignition. Ignition arcing can be seen at night by spraying water on the wires while the engine is running.
Another problem could be an intake gasket leak. You can test this by spraying starting fluid around the outside of the intake manifold. If there’s a leak it will be sucked in and a change in RPM will occur. Never spray it INTO an intake manifold while an engine is running as it will backfire if a valve is stuck and blow a plastic intake manifold off the car.
The mechanic did a basic compression test on the cylinder. (#4 if that makes any difference.) I was thinking of having him do more testing to tell me the exact cause of the low compression. I don’t have the diagnostic equipment and I’m not sure I want to buy it for such an infrequent issue.
I don’t know if he tested all 8 cylinders or just the ones that were in the scanner codes.
The $3000 estimate is probably ballpark for pulling the heads, fixing the issues, etc. based on his past experiences. It’s a small shop with only 2 mechanics and they’re only open from 9 to 5. So a 12 hour job is one guy dedicated to the task for a day and a half. Once he saw these major issues, he was wary of putting too much time into it as he was worried that I would just junk it anyway.
The Suburban is a 4WD 1500. I’m pretty sure it is a 5.7L Vortec engine.
Approximately how much will a machine shop charge to resurface and test the heads once I pull them?
Right now it is really cold here in Chicago and only going to get colder. I probably wouldn’t start on anything like this until March or April. I just need to know what to tell my mechanic.
You could also look into the cost of a longblock. Be careful though, the last one I bought didn’t have the heads bolted on properly. Had to pull them and re-torque them properly which defeated the purpose of buying it in the first place. Could have bought a short block and saved a bunch of time.
As for using the right diagnostic tools, you want a leak-down tester. Buy it, use it, sell it for half the cost if you can’t rent it.
Doing an evaluation of the heads once you’ve removed them won’t cost you much. They will have to clean them up, then magnaflux to check for leaks/cracks. They’ll also disassemble and check for weak valve springs, bad valves and seats an how much play you have in the valve guides.
At that point they can give you a firm estimate and what it will take to fix them. Maybe $500, maybe $1500. All depends on how much stuff and work they need.
Assuming a serious/internal problem, Greasy Jack’s suggestion w/regard to a used engine is the way to go. A word of caution…get educated on smog laws in your state. Here in CA, one needs to be careful about the specific engine.
Before I put 3K into a 18 year old truck, I’d look at how much you wanted it. 3K will buy a reman 350 vortec. Installing it might be another 500? Look at the cost. If the engine has a fuel rail problem, that might get cleaned out, used parts might be good for that.