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Old 05-05-2013, 03:05 PM
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restoring low compression??to pass emissions

A buddy of mine has 97 honda civic. Here in Atlanta he can't get his tag b/c the check engine light is on. The computer reads random misfire.
I ran a compression test and found two cylinders(2 and 3 ) built compression a bit slowly, and only built up to 110 psi. About 40 psi short for that 4 cylinder engine. The other two cylinders were fine.
I then squirted some oil into the cylinder to check if the rings were leaking.
The compression was the same, leading me to determine the problem is in the head. Bad valves or seats, bad cam, leaking head gasket

The car actually runs ok, but will not pass an emissions test.

My question is this.
Can I restore compression without pulling the head off and repairing it?
I think it will pass emissions if I can get the compression up to within 10% of the other two cylinders.


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Old 05-05-2013, 04:18 PM
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Do a search here, in the upper tool bar, for "random misfire codes", you get a lot of hits. One that was resolved was caused by leaks around the injectors, some by other leaks, head gaskets, etc.
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Old 05-05-2013, 07:29 PM
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Misfires are detected by one of two methods. One is primary circuit voltage threshold and ringing in the voltage as it lapses, the other is by changes in the rotational velocity of the crankshaft.
A low cylinder does not fire with the same force as others and the velocity of the crankshaft changes across the duration of the cylinder in question on its firing time.
Your going to have to do a valve job to fix it.
If the state does a tailpipe emissions it will fail miserably...every time.
The MIL wont go away until the mechanical problem is rectified.
BTW ... have you checked the valve adjustment to make sure there arent tight ones?
Fixing the car right, will give better dependable service for longer time to come.Just a thought.
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Old 05-05-2013, 08:18 PM
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the car is a piece of junk. 200K + miles, and a rebuilt wrecked salvage title from another buddy. hes not looking to fix it up. In fact its probably "totaled" for anyone who isnt a mechanic. Its just to get him through until
he purchases a real car.

I understand the misfire detection process at work in modern engines. Im not ,however, familiar with adjusting the valves on a Honda engine. Is it similar to the procedure of adjusting valves on, say, older chevy engines-tightening/loosening rockers?

Here in atlanta, actual tailpipe emissions are not tested on OBD2 cars.
Only the computer is read for problems, hence check engine light on= no tag.

And a more general question. How would tight valves leak compression? I've always heard that, but could never wrap my head around it. Seems like tight valves would = higher compression.
What am I missing?

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Old 05-05-2013, 08:25 PM
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Those hondas have been known to have valves that stretch or cup at the head of the valve. When they do...all the clearance dissapears, and I have seen them stretch to the point they hold a valve open and cause them to burn . If a valve is not fully closing , which is what I was reffering to, then the compression will be lower on the offending cylinder.
That would cause a power loss/velocity change on that cylinder, setting the premise for the missfire counter to set a code.
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Old 05-05-2013, 08:26 PM
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Start by checking valve clearnce/adjustment
Then possibly make the adjustment if needed. If the engine is a bucket shim engine, you may need a few parts.
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Old 05-05-2013, 08:27 PM
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Quote:
Originally Posted by 68NovaSS View Post
Do a search here, in the upper tool bar, for "random misfire codes", you get a lot of hits. One that was resolved was caused by leaks around the injectors, some by other leaks, head gaskets, etc.
I'm not trying to determine the source of the misfire. Its plainly obvious in this case, very low compression, most likely from a worn out head. What i'm looking
for is a product or quick fix to get the compression up solely to get a tag for this year. I know its a long shot, but there sure is a lot of products on the shelf claiming to rejuvenate a worn engine. But honestly I dont see how any of those could work for problems in the top end.
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Old 05-06-2013, 09:19 AM
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Quote:
Originally Posted by briansansone View Post
I'm not trying to determine the source of the misfire. Its plainly obvious in this case, very low compression, most likely from a worn out head. What i'm looking
for is a product or quick fix to get the compression up solely to get a tag for this year. I know its a long shot, but there sure is a lot of products on the shelf claiming to rejuvenate a worn engine. But honestly I dont see how any of those could work for problems in the top end.
If it won't hold compression due to valve leakage, there isn't any elixir on the market that will fix that.

Most states have a proviso that if you take a failed vehicle to an approved repair station and spend up to some limit 100-200 dollars usually and that can't fix it, they will then issue a license tag. That may prove to be the cheapest solution to the problem.

Bogie
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Old 05-06-2013, 09:20 AM
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Quote:
Originally Posted by LATECH View Post
Those hondas have been known to have valves that stretch or cup at the head of the valve. When they do...all the clearance dissapears, and I have seen them stretch to the point they hold a valve open and cause them to burn . If a valve is not fully closing , which is what I was reffering to, then the compression will be lower on the offending cylinder.
That would cause a power loss/velocity change on that cylinder, setting the premise for the missfire counter to set a code.

I'd bet money thats the problem. The engine has well over 200K.
It runs pretty good for having such low compression on TWO cylinders.
Maybe thats because it weighs as much as one of my wheels on my silverado.
Thanks for the insight.
Brian
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Old 05-06-2013, 09:08 PM
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Quote:
Originally Posted by oldbogie View Post
If it won't hold compression due to valve leakage, there isn't any elixir on the market that will fix that.

Most states have a proviso that if you take a failed vehicle to an approved repair station and spend up to some limit 100-200 dollars usually and that can't fix it, they will then issue a license tag. That may prove to be the cheapest solution to the problem.

Bogie
its $750 per year in atlanta.
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Old 05-07-2013, 09:36 AM
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its $750 per year in atlanta.
What happened to the free wheeling south? Yikes; smog laws with a vengence!

Bogie
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Old 05-08-2013, 09:41 AM
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Originally Posted by oldbogie View Post
What happened to the free wheeling south? Yikes; smog laws with a vengence!

Bogie
Yup. You cant register or even sell a car without a clean bill of health here.
You are allowed only ONE monitor system to be "not ready". If you want to sell a car with the check engine light on, YOU HAVE TO SELL IT OUT OF STATE.
or scrap it. We do have a smog problem here in this city of 6+ million.
The city spreads out 50 miles in every direction, so you absolutely need a ride
to survive here. But government red tape can wreak havoc in the life of someone who is plagued by that check engine light. I had a van whose tailpipe
emissions was squeaky clean, but the check engine light was on. I couldnt get a tag!
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