Compression Loss
10-10-2011, 12:41 PM
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Compression Loss
So I finally was able to get ahold of a compression tester, and what I was hoping against was , of course, what I got.
My car is a 1990 Base CRX with the 1.5L SOHC PGMFI engine with 166k. I jusr purchased the car for my son, and it had ran fine for about 3 weeks. Last weekend it developed a severe miss.
I just ran a basic compression test, and I have a dead cylinder. I got about 150psi on the other 3, < 30psi on the bad one.
So my questions are:
1. Is there a "typical" issue with these engines. I assume its either bad valves or rings. Is one or the other more common?
2. If it ends up being a head issue, I figure if I am going to rebuild a head, I may as well go for an upgrade. Is there any "better" head than the stock one, that does not require any additional changes to the car...a "bolt on" if you will. Or would it be just as easy to just work the stock head a little for some extra performance?
A little background; I'm another old "Chevy 350" kind of guy...new to the import style. I have raced circle track for years, and got pretty good over time squeezing HP out of stock heads due to rules.
Do the same types of modifications (porting and polishing, multi angle valve job, ect.) have as much effect on these little cars?
My car is a 1990 Base CRX with the 1.5L SOHC PGMFI engine with 166k. I jusr purchased the car for my son, and it had ran fine for about 3 weeks. Last weekend it developed a severe miss.
I just ran a basic compression test, and I have a dead cylinder. I got about 150psi on the other 3, < 30psi on the bad one.
So my questions are:
1. Is there a "typical" issue with these engines. I assume its either bad valves or rings. Is one or the other more common?
2. If it ends up being a head issue, I figure if I am going to rebuild a head, I may as well go for an upgrade. Is there any "better" head than the stock one, that does not require any additional changes to the car...a "bolt on" if you will. Or would it be just as easy to just work the stock head a little for some extra performance?
A little background; I'm another old "Chevy 350" kind of guy...new to the import style. I have raced circle track for years, and got pretty good over time squeezing HP out of stock heads due to rules.
Do the same types of modifications (porting and polishing, multi angle valve job, ect.) have as much effect on these little cars?
10-10-2011, 12:59 PM
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Re: Compression Loss
Drop about a capful of oil in the the 'dead' cylinder and do a compression check again.
If the compression comes way up, then likely it's your rings.
It could be other things too though.
Are yu pulling all the spark plugs out before testing any cylinder's compression?
Are you disconnecting the fuel injectors before testing?
Does the exhaust smoke at all?
Are you losing any water?
If the compression comes way up, then likely it's your rings.
It could be other things too though.
Are yu pulling all the spark plugs out before testing any cylinder's compression?
Are you disconnecting the fuel injectors before testing?
Does the exhaust smoke at all?
Are you losing any water?
10-10-2011, 01:14 PM
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Re: Compression Loss
Did the oil test...no change at all, still just barely moving the guage.
Yes, all plugs out when testing.
No on the injectors. I may be wrong, but the FI looked more like Throttle Body style to me. (again...old chevy guy. Do these cars have a fuel rail style injection?
No smoke, at all.
No water loss, or other signs of head gasket failure. Oil is clean, coolant is steady.
The car actually "runs" pretty good, except has a hard miss at idle. Get it above 2k RPM, and it runs smooth enough that you would never guess it was running on 3 cylinders.
Other things I checked.
Timing belt is in good condition. Has definitely been replaced somewhat recently. Cam timing is "visually" correct. (TOP is up, and marks on gear are horizontal with engine at TDC. Timing marks are pretty hard to see, but it looks like ignition timing is somewhere around 18 BTDC.
Cam seems to be visually OK.
I am hoping for something as simple as a stuck valve, or worst case, bent valve or bad guides. Im honestly not sure that it doesnt correct itself at higher RPM, it really runs ot pretty smooth once you get moving.
Yes, all plugs out when testing.
No on the injectors. I may be wrong, but the FI looked more like Throttle Body style to me. (again...old chevy guy. Do these cars have a fuel rail style injection?
No smoke, at all.
No water loss, or other signs of head gasket failure. Oil is clean, coolant is steady.
The car actually "runs" pretty good, except has a hard miss at idle. Get it above 2k RPM, and it runs smooth enough that you would never guess it was running on 3 cylinders.
Other things I checked.
Timing belt is in good condition. Has definitely been replaced somewhat recently. Cam timing is "visually" correct. (TOP is up, and marks on gear are horizontal with engine at TDC. Timing marks are pretty hard to see, but it looks like ignition timing is somewhere around 18 BTDC.
Cam seems to be visually OK.
I am hoping for something as simple as a stuck valve, or worst case, bent valve or bad guides. Im honestly not sure that it doesnt correct itself at higher RPM, it really runs ot pretty smooth once you get moving.
10-10-2011, 01:26 PM
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Re: Compression Loss
It is TB style, but it will still shoot fuel when you are cranking.
That can wash out your cylinder walls and give you messed up readings.
Sounds like a bad valve, leak down test would be next on the list to absolutely verify the loss of compression and to show if the loss is in the head or block.
Maybe run some injector cleaner or sea foam to free up any deposit build up that might be causing valve sticking.
That can wash out your cylinder walls and give you messed up readings.
Sounds like a bad valve, leak down test would be next on the list to absolutely verify the loss of compression and to show if the loss is in the head or block.
Maybe run some injector cleaner or sea foam to free up any deposit build up that might be causing valve sticking.
10-10-2011, 01:35 PM
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Re: Compression Loss
One thing I want to point out right off the bat... An engine is an engine - given there are specifics but the basics are all the same. I am strictly Chevy and Honda myself, and am only on here because of my son. With that being said - don't use that as a crutch - it's still a gasoline engine.
Now with all the drama theatrics out of the way, you have a DPFI (Dual Point Fuel Injection) system unless previously modified. There are not any "typical" problems with "these" engines with regards to your specific problem. What has been seen a time or two is valves chipping away. Typically this is with the next generation D15B7, but I have seen it on the D15B2 as well. As you should know (and a fellow circle track racer myself) a compression test is a caveman's way to find out the condition of an engine. Do a leak-down test in conjunction with the compression test; This will PIN-POINT your problem rather than guessing. Until then (or if you tear it apart) its all just assumptions. With that being said - there is still a high possibility of physical damage rather than gasket/rings being in need of replacement.
I personally would test it before a teardown so you have a baseline to help guide you after your repairs or if future problems arise.
Now with all the drama theatrics out of the way, you have a DPFI (Dual Point Fuel Injection) system unless previously modified. There are not any "typical" problems with "these" engines with regards to your specific problem. What has been seen a time or two is valves chipping away. Typically this is with the next generation D15B7, but I have seen it on the D15B2 as well. As you should know (and a fellow circle track racer myself) a compression test is a caveman's way to find out the condition of an engine. Do a leak-down test in conjunction with the compression test; This will PIN-POINT your problem rather than guessing. Until then (or if you tear it apart) its all just assumptions. With that being said - there is still a high possibility of physical damage rather than gasket/rings being in need of replacement.
I personally would test it before a teardown so you have a baseline to help guide you after your repairs or if future problems arise.
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