About a year and a half ago, my car started occasionally missing when it idled. It would run fine for a week or 2, then miss when it idled for a week or 2. Off and on. I took it to the nearest Acura dealer and they said my valves were tight as hell, and that my compression numbers were 140-115-140-140. This was on a GSR with about 80K miles at the time. The service guy told me that he thought I needed a valve job, but that they would have to charge around $1000 just to tear it down and see what was wrong with it. However he told me that I could continue to drive as long as it didn't get any worse. They adjusted the valves.

I didn't have anything done then, and ever since then, the car has run the same, never burns any oil, consistently gets 30MPG or more, and continues to intermittently miss at idle. Never during acceleration.

Well I decided to get a compression tester and test it again, since I figured out that the numbers the Acura tech quoted were horribly low. So I tested it today, and the numbers were:
1-225
2-160
3-225
4-230

Also the plugs were all grayish/white, which I assume means I am running lean? I know #2 being so low is bad news, but what exactly does that mean? I would think that since the compression is low, but that I'm not burning oil, that its a sign of leaking at the valves instead of worn rings?

Now from what I can tell from reading on here and my Helms, the running lean and intermittent missing suggests dirty injectors/bad o2 sensor(s). I plan on having the injectors cleaned and the 02 sensors checked next week.

Any ideas? My GSR has 123,000 miles.

 

now do a leakdown test to find out where you are loosing compression. rings, valve seals, etc.

 

what do u mean by "Miss at idle" ????????

you mean like the rpms dont hold and fall occasionaly?

 

Is a leakdown test something that most mechanics can do? And what are the costs?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BamaGSR &raquo;</TD></TR><TR><TD CLASS="quote">Is a leakdown test something that most mechanics can do? And what are the costs?</TD></TR></TABLE>

mechanics can do it.. and it doesnt cost that much. do that next. in the meantime, buy some chevron techron injector cleaner and drive it around for awhile. that stuff works.

 

how much would it cost for me to go to the local shop and have a compression test done?

 

Just buy your own compression tester, I got mine for $25. Just pull the ECU fuse, pull the plugs and stick the tester in each plug hole one at a time. Then floor the gas and crank the car till the gauge stops rising.

Pretty easy.

 

I know it's relatively easy, but how much would a shop charge?

 

Not sure, but I'm guessing its not going to be much cheaper than $25, if at all. Why not just spend the $25 and check as many cars as you like for free?

 

Also could the low compression on #2 be due to a carbon build up? All my plugs were gray, suggesting I was running lean. I have used Chevron FI cleaner a coupla times and it didn't seem to help much, but I used STP Octane Booster once and that did seem to help a lil bit.

 

The extent of work I generally do on my car consists of oil changes and tuneups. I guess I just wanna make sure that I get accurate results.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GSRGuy17 &raquo;</TD></TR><TR><TD CLASS="quote">I know it's relatively easy, but how much would a shop charge?</TD></TR></TABLE>


I was told quoted $100 for a compression test...I decided to just go to Kragen and pick up my own tester for less than $30, that extra money was put to good use

 

I was going to do this test myself with my friend who has a compression tester.

I didn't know it was neccessary to pull the ECU fuse. All i thought you had to do was pull the plugs, and crank the car, one cylinder at a time.

You really have to floor the gas, and pull the fuse? Where is the ECU fuse located so I can do this?

 

Also, what is should average compression be? I have a 95 GS-R with 100k miles on it. Is 220-230 average/normal/good compression?

 

I just answered my own question. I need to pull the fuse, so that i don't flood the engine when I open up the throttle.

Number 15amp on the rear of my fuse box, right? I'm pretty sure I got it now.

 

I hate mechanics who rip people off

 

If you want to get rid of carbon buildup, the best thing you can get is stuff called SeaFoam which is available at NAPA, and online.

It works better than all the others, trust me I have used it religiously for years. Follow the directions on the can as there are 3 ways to use it. In the gas, in the oil, or directly into the Intake via a brake booster hose.

Good stuff, get some.

Cheers,
Roy

 

carbon build-up ups your compression...and keeps heat within the cylinder by 'coating' the piston top. can be both good/bad. normal compression is anything above 200psi. anything over 215 is very healthy. there should be no more than 10-15% difference between cylinders.

BamaGSR, im not sure what could cause only one cylinder to crap. maybe one injector not firing? If you want to check for detonation get new plugs (cheapos will do), warm your car up to operating temp and go run it hard up to redline in 2nd, then shut the engine immediately. wait a few minutes to give the head time to cool (dont want to crossthread plug holes), take the spark plugs out and check for white specs on the ceramic insulator nose. of course you'll want to do this somewhere safe.

 

Enough carbon buildup can cause the valve to not seat properly, causing lower compression. With only 123K miles I doubt you have bad rings, but it's a possibility. A bad O2 sensor will throw a code. Dirty injectors is very possible, some suggest cleaning every 30K miles-of course if you run premium gas always it's not as important an issue. The missing could be something simple as sh**ty spark-plug wires, or even wrong spark gap. However, with the lean condition, it points towards a fuel issue, most likely.

I suggest getting the injectors cleaned, especially with 123K miles on the clock. Then, go from there. If it's not the injectors, then check fuel pressure. From there, check vacuum. Vacuum problems are notrious little gremlins that no one ever seems to find, but I'm getting ahead of myself-injectors first.

*edit*
I forgot, you may have carbon buildup on the valve seat and that may explain the shop suggesting the valve-job, also the low compression.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BamaGSR &raquo;</TD></TR><TR><TD CLASS="quote">Is a leakdown test something that most mechanics can do? And what are the costs?</TD></TR></TABLE>

To answer this question, leakdown test fills the cylinder with compressed air and then measures if and how fast the air leaks out. You could have a scored cylinder wall in the middle of the stroke, but the cylinder would still hold air at the top and bottom of the piston stroke. In the middle of the piston stroke, the cylinder would leak, and you would know that cylinder wall scoring is the problem. That's just an example.

 

your story just once again shows that the consistancy of the numbers are far more important than the peak values. Different testers can read very different numbers, as well, different operators have very different techniques.

d

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by daver &raquo;</TD></TR><TR><TD CLASS="quote">... Different testers can read very different numbers...</TD></TR></TABLE>YES! Every time I see someone saying something like 'they should be above 200', I want to

That's ONLY true if you're using the SAME GAUGE.