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I finally received a diagnosis on why my car would not stay running, would barely start, and ran so
poorly I couldn't drive it. I at first thought it was the EGR valve, I had been seeing the EGR code
after driving for an extended period of time, but after replacing the EGR there was no difference. I replaced
the distributor cap, rotary button and the coil with no luck as well. . I have just been told I have low
compression in multiple cylinders and the mechanic feels it is the head gaskets. I have a hard time believing that because the
car ran great until one morning I went to start it and it would barely run. I have seen no evidence of oil
in the coolant, was not smoking at all. The garage checked the valves and beyond a couple slightly
loose the valves were fine. The next step is the heads and they want $3500 do the work.
I am not paying that much for a car I paid $5k for plus I am not convinced this is the issue.
Now the question is do I repair it myself, I can do some mechanical tasks, replaced head gaskets
on a inline BMW six cylinder once and I have some friends that are going to help.
I have to decide at some point, once I get the heads off, if it is more cost effective to cut my losses.
I don't want to get rid of the car so I can either buy a replacement engine (donor car maybe) , take
the heads off and have them refreshed and reassemble and hope for the best.
Any other ideas on what could cause low compression beyond the head gasket?
Chuck
P.S. As you can see the car is in great shape, well except it won't run right now......
PLEASE......Do a compression leak down test on the engine before you start throwing tons of money at it. That will tell you exactly where the problem is (if it is mechanical), and what cylinders are having trouble.
At the very least, the spark plugs in the bad cylinders might show indications of fouling or super clean from coolant getting in the cylinder.
Youtube has videos on how to do this, and you can get the tool for $25 - $30 bucks to get you close enough to check if you have a compressor. If your not up to it, find someone who can help you do it.
What would really suck is to replace the engine, only to find out it was a different problem than you were told.
What he said! I wouldn't be surprised if you couldn't get some form of crate motor put in for under $3500. You have a good looking car and pretty much anything you look at for as a replacement would cost a lot more than that much.
If it was mine, I'd do a compression test and pressure test the cooling systems and see what info that produces. In addition, it's been a long time since I tore and engine down but for that kind of $$ I'd give it some serious consideration.
PLEASE......Do a compression leak down test on the engine before you start throwing tons of money at it. That will tell you exactly where the problem is (if it is mechanical), and what cylinders are having trouble.
At the very least, the spark plugs in the bad cylinders might show indications of fouling or super clean from coolant getting in the cylinder.
Youtube has videos on how to do this, and you can get the tool for $25 - $30 bucks to get you close enough to check if you have a compressor. If your not up to it, find someone who can help you do it.
What would really suck is to replace the engine, only to find out it was a different problem than you were told.
Nice car, by the way.
Last edited by cadmaniac; Jan 6, 2020 at 05:10 PM.
You didn't say how many miles is on the car. It could be the valve seals but more than likely it is the rings. If it's the rings you might as well figure rebuilding the engine if the mileage is up there or replacement engine. I will give you a link on a video of how to determine whether it's the heads/ valves and seals or the rings. Great video to watch will give you a good understanding of how to truly test and diagnose the condition of the engine.
I agree with all the compression suggestions just on principle. Another thing to check might be the MAF or MAP sensor depending on which you have. I have a 91 and it has the speed density system and thus the MAP sensor. My MAP sensor crapped out a few years back and the car wouldn't start and run. It happened at the post office (I got there fine went in and when I came back out it wouldn't start) and I had to flatbed it home to troubleshoot. Anyway, If as you say this happened suddenly and it had not been overheated I would lean toward a problem like that rather than rings, head gasket etc. My $0.02.
Most of the vette specialty outlets on line sell some adapters that you can use to troubleshoot these sensor problems. If you plan on owning/driving a C4 you might want to get some of these, a digital VOM and a hand vacuum pump to do some of your own troubleshooting. There are a lot of automotive techs out there that really have no idea what they are doing or even worse do know what they are doing and take advantage of people. Some of this stuff can be done without the adapters but unless you really know what you're doing it's probably better to use them.
Last edited by wsherrard; Jan 6, 2020 at 09:37 PM.
First, thanks for all the suggestions, gives me a place to start. The leak down test will be one of my first tasks
when I get it home. The suddenness with which this happened, ran great when i parked it and wouldn't run
the next time I started it makes me doubt the blown head gasket diagnosis. The car has never smoked, hasn't
been overheated in the years (3) I have owned it and has 106K on it. The oil and coolant system do not show
any indications of a leaking head gasket. I would prefer not to replace it with another Vette if I don't have to
because I know this car, have receipts for all the work done on it for the last ten years. If I buy another one
I could just end up in the same boat.
If your mechanic knows what he's talking about, you can easily confirm it by checking for combustion gasses in the cooling system. If he's wrong, your mechanic is just guessing, and wants your money! Bad!!
Your favorite auto parts store probably has a tester you can borrow for free (deposit required). It uses a fluid in the tester (extra cost, about $8) to detect for combustion gasses in the radiator. It's an easy test.
not sure if it has been said already but head gaskets don't ALWAYS blow out going to a water jacket, they can break between cylinders also causing problems. but regardless, 3500 for head gaskets sounds like highway robbery to me, you can pull a set of heads off with a pretty basic set of tools and a nice afternoon, with not much expeirence at all.. that should be an l 98 engine correct? its still a gen 1 small block base and easy to work on... maybe the mechanic was high siding it in case the heads need sent to a shop to get checked for flatness and cracks and all the other stuff though but even then maybe 500 for shop work 100 for gaskets. thats 3 thousand labor, i think last time i worked in a garage an entire engine R&R only pays like 40 labor hours
Good point made about cyl to cyl leak. Leak down test is your friend here. Its a bit time consuming but will diagnose the gasket or a valve seat leak.. you will know if its valve seal by listening to the intake with the throttle wide open. This would also verify the shop did the diagnosis correctly. By the way did they provide the PSI values per cyl? If they did not I suspect a guess which is naughty.. you didn't mention them so I bet not. No shop that actually did the pressure test would not offer up this information. If you happen to have an oscilloscope you can verify with that as well. Just put a current meter on the starter cable and run the starter. Look at the amp peak and duration per cyl and they should all be even. if not you have a leak. If your car won't start this is not a small slow leak. I suspect this shop did not do the work.
If I'm wrong and the shop did do the work:
If it were me and miles were low Id do the head gaskets/head rework. Pulling an engine is no easy job. If you get into it and the heads and gaskets are fine and now its bottom end you can go with a new engine then. Pulling the heads and replacing is a big job and you dont want a shop just slamming out cars as fast as possible doing this work. this is your baby, your fun car (im assuming this is not your primary vehicle) and it should be done with care. Now is the time to consider some performance upgrades as well. If its the whole engine its wide open, if its the heads you could slice the heads a little for some more compression, and do a cam. opening the valve holes is an option too but not sure how much gain there is there and that can get expensive.
If there is any carbon build-up on piston tops now you can clean that up as well. I would also use this opportunity to detail your engine bay, replace all hoses, water pump etc.
Look at this as an opportunity and just out of curiosity let us know what happens with the pressure test. Sorry about your trouble but this is life..not always easy.
Barchetta1, I have considered doing what you said and upgrading while I have the heads off. If it turns out I have valve issues upgrading the cam & lifters
and cleaning up the heads would be easy to do at that stage. The question is, and I am reading through the numerous posts on this site to get information
on which cam I could use, is what is the best mild cam to help it breath better without causing other issues? If I had the heads shaved a small amount to
up the compression does this require other upgrades that I have to do now or can I set it up for future improvements?
For the record I had work done two thousand miles ago, started out with a leaking water pump and ended up replacing timing chain while replacing a
leaking timing chain cover gasket. That required removal of the oil pan so I had the oil pan cleaned up, no indications of metal from the bearings in the
oil pan, painted and also had a new fuel pump, fuel pump relay and put on because the old one was not providing the required fuel pressure.
All the hoses were replaced while it was apart, new thermostat, throttle body gasket, and the throttle body was cleaned. The previous owner replaced
the fuel injectors, radiator, throttle position sensor, heater core, and new high flow catalytic converters. All of the above mentioned above has been
done within the last 8k miles. The motor was running great, has been reasonably taken care of which is why the low compression surprised me.
anything you do would need to be mild or you are looking at a tune.. I dont know much about the l98 (assuming that is what this is).. but what you could do is find a tune designed for a specific setup (cam, rockers, compression) and then design your engine around that chip (I think the l98 needs a chip tune?)..
Driveability would be my concern with a cam.. and whether Id need to do the torque converter.. its all about time and money. Since I just like to play with my car on weekends now and then and dont want to spend a ton of money on my car Id go with a mild cam and appropriate lifters, rockers, springs.
Regarding cutting the heads.. if its a l98 I dont know how much wiggle room you have there.. I dont even know if it had knock sensors. Id be looking for max compression that I can run pump fuel on or possibly pump with a small amount of race fuel. I do not believe shaving the heads would require any other upgrades.. its pretty common to do with warped heads.. I do not know how much meat are on your heads to shave away. You'll need to research that. When I did a race motor once the shop did all the work and I used clay and bolted the heads on with no gasket and made sure there was no valve to piston contact. but I suspect if you went that far you'd be on race fuel. I wouldnt mind havng to do a small ratio of race fuel because I love the smell
When you had the water pump issue did you overheat? If so that is likely what caused your current problem.
EDIT: sorry, it occurred to me if you shaved your heads you might need to do push rods. Not sure how much adjustability there is on l98 rockers.
Last edited by barchetta1; Jan 7, 2020 at 08:18 AM.
I think the rims are sweet. Very period. I dig 'em. But that's not the OP's problem at all. I agree with the posters who gave GOOD advice about compression and leak down tests.
$3500 head gasket replacement
