03 Running Poorly/Misfire/Low Compression
 

I could use some advice/suggestions in regards to the news I heard today about my car. My car is an 03 with 102k on it, well cared for. It was owned by an older lady before I got it. It was driven easily and got standard maintenance by mileage but may have missed a few things due to age. I autocrossed it a fair bit this year but do take care of it and do not believe I have mechanically over-revved it at any point. It has burned a normal amount of oil for an ap1 (about 1 qt. per 3k) and has performed great since I've had it. Friday night, I drove the car out to a friend's place. Driving there, it was completely fine as it has always been. As I was leaving, it was driving really weak and stumbling. It did not want to rev and almost felt as if the engine was being choked. I also noticed a "whistling" noise coming from the airbox, particularly noticeable with the cover off. It did not have any terrible metal on metal noises or seemingly catastrophic failure. I drove it about a half mile before pulling off and calling AAA. I had it dropped off at a local performance shop that has a honda specialist/s2000 enthusiast that night and had it checked out Saturday. I used the word misfire to describe how the car was behaving and it was diagnosed as such. I was told the culprit was likely a spark plug with a burnt resistor. I was not sure that it was actually a misfire but was not sure how else to describe the hesitation I was feeling. I had them replace the plugs and still no go. They did a valve adjust as well, with a few out of spec but nothing alarming. They also did a leakdown test with no abnormalities. The compression yielded something like the following results from 1-4: (170-185-180-185) I will get exact results when I can, I was at work talking to the service advisor and kept it brief. Essentially, cylinder 1 was significantly lower than the others but I am not sure exactly how to use the info. It is a bit alarming but I am not sure how much so as the variance is not tremendously high. They advised the next step to inspect the cylinders with a boroscope tomorrow, which I authorized. If that turns up nothing, they will try to check for a leaky head gasket. I believe in the shop and am just looking for anyone with a similar experience or any ideas.

If the issue at hand is low compression, would it really cause the car to suddenly feel as if it is being choked after running fine hours before (Oil light did not come on)? The leakdown test and valve adjust do not indicate any type of head issue or leaking compression. Could something in the intake or throttle body cause symptoms like this? Would restricting airflow to the engine cause low compression numbers? I am going way out on a limb with that theory and did not get to ask if they pulled the intake. I recently replaced the air filter and was wondering if I somehow got something in the intake tube (plastic or towel) that could cause the issues and whistling noise. Could the headgasket cause these symptoms (Shop told me possible but not probable)? Has anyone experienced anything similar to my symptoms?

The only other symptoms I have to add to the story are likely not related but I'll give it a go. The car would sometimes feel bogged down driving in bumper to bumper traffic. It happened infrequently but would stumble a little bit after going slow/being lugged and would clear up after some revs. Similarly, at a test and tune day, when finishing an autocross run, I would be on the high end of second gear crossing the line. I would push the clutch in immediately, shift to neutral, and coast to the end of the cones. At that point, I'd put it in first and pull off. It would break up a bit and then clear immediately. I changed my habit that day and left it in gear while braking and let the revs drop with deceleration. I did not experience any hesitation at that point and the car performed great.

Very nice write-up! I'm don't think I have the immediate answer, but your post is worthy of a reply. :)

The leak-down test being ok. But, the compression test showing low numbers on cylinder 1, may not jive. Was the comp test done at operating temp?

The car never had any CEL errors? Have you ever replaced any O2 sensors? Stock catalytic converter?

Thanks!

It could be just the dreaded bogging that eventually starts plaguing these cars. Check the electrical stuff, you already did plugs, maybe the battery isn't at its best, or injectors aren't great, worse comes to worst could be coil packs or the ecu giving out.

Does the problem persist? Or does it seem to go away once the car starts moving for a while?

As far as the whistling noise is concerned it could be an intake leak, possibly the little rubber grommet in the MAP sensor.

No. Not unless the restriction is massive and obvious. test is done with the throttle open and airbox off.

That'e the only question in your post I can definitively answer.

Other than that, it could be a lot of things.

When I hear bogging under load with no CEL, I suspect coil packs instinctively.

Compression under 200 isn't the end of the world, just means it's a bit tired. The service limit is 135, and the service limit for variation is 28 from highest to lowest.

That they're pretty consistent is all you need to know.

Thank you all for the responses. Turns out, I was wrong on the compression numbers. The lowest was 160 and the highest was 190. This was done as a warm test. There has been some good news though! I never thought I'd say that a potentially blown head gasket is good news but given the context, it certainly is. The tech said that while the engine was warm and running, the coolant was bubbling exhaust gasses. This seems fairly conclusive that exhaust gasses are getting into the coolant. The borescope check did not turn up anything odd looking either so hopefully no cracked cylinders. I am crossing my fingers until it is taken apart and repaired. I will be elated if I am only out a head gasket. It still seems odd that nothing turned up in the leakdown test but they explained low compression readings are certainly possible with a bad head gasket, especially with high compression motors. It does make sense though, in theory since leakdown tests are not done at pressures comparable to cranking cylinder pressures.

Is there anything else I should have addressed while having the head gasket changed? They are suggesting I do ARP studs while in there. I know this is fairly typical with built honda engines and seems to make sense.

Thank you all for the responses. Turns out, I was wrong on the compression numbers. The lowest was 160 and the highest was 190. This was done as a warm test. There has been some good news though! I never thought I'd say that a potentially blown head gasket is good news but given the context, it certainly is. The tech said that while the engine was warm and running, the coolant was bubbling exhaust gasses. This seems fairly conclusive that exhaust gasses are getting into the coolant. The borescope check did not turn up anything odd looking either so hopefully no cracked cylinders. I am crossing my fingers until it is taken apart and repaired. I will be elated if I am only out a head gasket. It still seems odd that nothing turned up in the leakdown test but they explained low compression readings are certainly possible with a bad head gasket, especially with high compression motors. It does make sense though, in theory, since leakdown tests are not done at pressures comparable to cranking cylinder pressures.

Is there anything else I should have addressed while having the head gasket changed? They are suggesting I do ARP studs while in there. I know this is fairly typical with built honda engines and seems to make sense.

Also, I only had one CEL since I've had the car and it was for the EVAP system. That was over a year ago and it went away on its own. During this fiasco, there was no CEL until I pulled it off onto a side street. The CEL flashed twice before I shut her down. It did not overheat, the oil light did not come on, and I did not hear anything that sounded like a catastrophic failure. The night it happened, I thought it may be a bad misfire or something bad but did not expect a dead engine. That was a real shocker. Hopefully the headgasket will get me fixed up.

Lets hope for head gasket. Certainly make sense in a variety of ways. Of course the thing to consider is why did the head gasket fail? Maybe just old age.

Blown head gaskets are relatively rare occurances on stock s2ks, unless the engine was severely overheated.

All that a flashing CEL means is a high misfire count.