My 94 GS-R was idling rough and seemed down on power. I just purchased this car a day ago. Owned by older people (55+ AARP and such) its entire life. Never modified. Today I am trying to track down the idle issue (which we determined was cyl 2) and I decide to do a compression test on it. Numbers come back
Cly 1:210
Cly 2:35
Cly 3:210
Cly 4:210

After putting a half cap of ATF in cly 2 the compression came back at 60.

There is no smoke coming out of the car, at any RPM, valve train seems quiet and in working condition.
The Oil is completely clean and still fresh, along with the coolant.

I know the possibilities are (in my head)
-Blown Headgasket (not likey as clean as the oil and coolant are)
-Burnt Valve?
-Blown Ring?
-Bent Valve?

Has anyone had any problems like this? It has a 155,xxx miles on it and is in really good condition the only thing is while the older man was driving it (putting around town) he used 87-89 octane in it. But I would think if the car was detonating the other cyl would not be perfect 0% difference across the board. (minus 2 of course). I am well knowledged in automotive engines but I am looking for some people who have had personal experience in something similar happening and what was the culprit. I'm angry since this car was mint but if the engine is no good then... Thanks for the help.


Modified by Mchin at 4:01 PM 3/19/2008

 

Check the valve adjustment. Too tight can cause low compression.

 

Is there a chance that it would cause the compression to be 35 compared to 210? We aren't talking like 20% difference somewhere around 70% difference here.

 

If it is really tight, it certainly could. I would pull the valve cover and look. If the valves are adjusted properly, a leakdown test is in order.

Another possibility for the low compression is a bent connecting rod.

 

Gotcha thanks for the help, I guess the next question is under normal driving conditions what would cause a bent rod, without it having rod knock. Thanks again for your suggestion. Also

Crank the motor over several times, I cranked for about 4 seconds per test and watch the guage climb. In a healthy motor, compression should build up rather quickly. Low compression reading on the first stroke, followed by very gradually increasing compression on successive strokes, indicated work pistion rings. A low compression reading on the first stroke, which doesnt build up during successive strokes, indicated leaking valves or a blown head gasket, which also could be a cracked head. Heavy carbon deposits on the valves could also cause lower than average reading as well as a possibly higher than average reading. Record the highest reading that the guage stops at after cranking for a bit.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mchin &raquo;</TD></TR><TR><TD CLASS="quote">Gotcha thanks for the help, I guess the next question is under normal driving conditions what would cause a bent rod, without it having rod knock. Thanks again for your suggestion. Also

Crank the motor over several times, I cranked for about 4 seconds per test and watch the guage climb. In a healthy motor, compression should build up rather quickly. Low compression reading on the first stroke, followed by very gradually increasing compression on successive strokes, indicated work pistion rings. A low compression reading on the first stroke, which doesnt build up during successive strokes, indicated leaking valves or a blown head gasket, which also could be a cracked head. Heavy carbon deposits on the valves could also cause lower than average reading as well as a possibly higher than average reading. Record the highest reading that the guage stops at after cranking for a bit.</TD></TR></TABLE>

I dunno if this is right or wrong.. but when i do compression tests.. i always pull the ecu fuse, crank untill the gauge stops moving.. also i hold the throttle wide open..

Have you recently done a valve adjustment?

Drain your oil and see if there's any metal shavings in the oil..

I've never personally myself seen a bent or broken connecting rod without a knock

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Jimmy &raquo;</TD></TR><TR><TD CLASS="quote">

I dunno if this is right or wrong.. but when i do compression tests.. i always pull the ecu fuse, crank untill the gauge stops moving.. also i hold the throttle wide open..

Have you recently done a valve adjustment?

Drain your oil and see if there's any metal shavings in the oil..

I've never personally myself seen a bent or broken connecting rod without a knock</TD></TR></TABLE>

ECU fused was pulled WOT also. and 4 seconds or about how long the gauge takes to stop moving. I've own the car for less then 48 hours so no I haven't done a valve adjustment. I might drain the oil tomorrow. Nor do I know how long it has been since a valve adjustment has been done. I would figure it would loosen over time? but is their a chance it would tighten over time if it hasn't been adjusted?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mchin &raquo;</TD></TR><TR><TD CLASS="quote">

ECU fused was pulled WOT also. and 4 seconds or about how long the gauge takes to stop moving. I've own the car for less then 48 hours so no I haven't done a valve adjustment. I might drain the oil tomorrow. Nor do I know how long it has been since a valve adjustment has been done. I would figure it would loosen over time? but is their a chance it would tighten over time if it hasn't been adjusted?</TD></TR></TABLE>

doubtfully, or not enough to cause that low of compression in one cylinder..

 

You sure its not burning oil, it could be eating up oil if the oil rings on it is gone. Might be a valve seal gone bad. Could be just a headgasket leak. Tell someone to look behind the car and rev it and if they see any smoke see what color it is. If its blueish then its oil burning then its the rings, if its white then its a gasket leak. If its real black its just running rich. You might not see smoke but others might if they are outside the car.

 

Not entirely true. I just slap on my rebuilt gsr head on my car last night and my cylinder #1 had almost no compression. Recheck all my valve lash and some were very too tight, some were loose. Readjusted the valves, now the engine runs kick ***.

 

Bent or broken exhaust valve. Thanks for all the help.

 

if doing a compression test....make sure you disable your fuel and ignition and crank engine at least 7 times at wide open throttle....then record your reading

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mchin &raquo;</TD></TR><TR><TD CLASS="quote">Bent or broken exhaust valve. Thanks for all the help.</TD></TR></TABLE>

how did you figure this out?

 

did a leakdown test it was coming out of my exhaust

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Blahblah718293 &raquo;</TD></TR><TR><TD CLASS="quote">

how did you figure this out?</TD></TR></TABLE>

if you have air coming out of your tailpipe while doing a compression test or a leakdown test...then thats a sign of a burnt exhaust valve

 

correct, now I get to take off the head and see how bad the valve seat is messed up. I also have a B16 head laying around at the shop. Would it be worth it to put that on to save me some downtime that I might need to machine the B18C1 head? I know the basic's like it needs a different intake manifold and such but would their be a problem with a 99 SI head if I have my 94 non OBD2 engine setup?

 

anyone?

 

throw the b16 head on with the gsr dizzy...call it a day

 

too bad you would have to mill the b16 head like .045" just to get it back up to stock gsr compression. you would have a better intake manifold either way you go tho; b16 or itr/aftermarket.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mchin &raquo;</TD></TR><TR><TD CLASS="quote">correct, now I get to take off the head and see how bad the valve seat is messed up. I also have a B16 head laying around at the shop. Would it be worth it to put that on to save me some downtime that I might need to machine the B18C1 head? I know the basic's like it needs a different intake manifold and such but would their be a problem with a 99 SI head if I have my 94 non OBD2 engine setup?</TD></TR></TABLE>

The P72 (B18C1) head is better. It will give you a higher compression ratio and flows the the same as the B16A in stock form.

 

Correct from my understanding its a .2 difference so 9:8:1 instead of 10:1. If its a burnt valve they said I could just lap them to seat the valves correctly again. But I thought these heads has a 3 angle valve job from the factory? If not I might just lap the valves to get them to seat again.

 

Ok so update just incase others have the same problem as me.

Took the head off today and cly number 2 exhaust valves look different. We put some brake clean down the exhaust runner and it starts pouring out of the valve (around the seat area) the Intake valves are black and the exhaust valves are white, is this typical of these engines? Just wanna make sure i don't have a lean/rich issue. Next stop is the machine shop with my head to find out exactly what needs to be done as far as new valves or cutting new valve seats. I'll post pictures here in a little while.

Cly 1


Cly 2


Cly 3


cly4

 

Were there any marks on the pistons on the exhaust side? Look for a slight mark in the carbon coat.

 

I will double check tomorrow, but I am sure the carbon on the pistons looks uniform. More likely (from what i have been researching) the valve has burned out. So the machine shop should be able to tell me if I can salvage them. If not someone in my area is selling omni power valves, guides springs ti retainers ect. So if I need new valves that might be the way to go. I figure if I wanted to do a set of cams I could be all prepared for it without digging this deep into my motor again...

 

even if you can't salvage the factory valves ( I wouldn't) just get 2 OEMs till u have money for nice valves. I burned out a valve on an LS years back, slapped in some cheap valve from a local auto store and it drove great for another 3 years. (person who bought it threw a rod to finish the engine).

It wasn't a bent valve, but still, just grab some replacements and possibly get the guides changed out. Whatever within your budget