1998 Honda Prelude Low Compression

1998 HONDA INSIGHT
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JDUBSLOPRO
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Okay...here is a dubious one. I have low compression in at least 3 (I think maybe all 4) cylinders. It's been a while since I did my last compression test--my car's been off the road for 9 months. The compression which was normally 200-220 psi last read 140-160 psi. The car will not stay running without some careful gas/brake/clutch finessing. There is no smoke emanating from the exhaust, coolant level is fine/doesn't appear oily. I thought perhaps a camshaft or both had slipped or timing belt jumped, so I adjusted the camshafts and set them back in place, that wasn't the problem. I eliminated valve seals/valves and headgasket as the problem. I've never seen more than one piston ring go at once, so I kind of don't think that is the problem...otherwise it would be pushing oil up into the head and through the crankcase breather to the intake...and the intake is clean...hopefully you guys can give me some helpful insight as to the problem...I have a breaker bar and a free weekend so I may end up taking the head off if nothing else.
Mar 31, 2006 at 2:58 AM
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LOSONE
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DON'T TAKE OFF THE HEAD YET! Actually 160 is pretty good compression. Oil the cylinders and see how much increase. That engine will run fine with 100 pounds. Insure you don't have a rich misture washing down the cyls. All that done ---

It sounds like a vacuum leak. The Brake boosters are a prime suspect on that model. Also check for throttle body build up. They are bad about that. Clean it good with the throttle open on the upper and lower parts. Use a good carb cleaner and a stiff tooth brush. Wipe as much of the residue as you can before starting. It will run crappy for bit until it clears it's throat.

Let me know
Mar 31, 2006 at 5:59 AM
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JDUBSLOPRO
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the car itself has 54,800 miles on it. I replaced a motor once already at 52,000 miles due to a burnt piston ring (nitrous). The compression tester I rented today is garbage, the end spins rather than being fixed so you can spin it into the head. When I first got the car (a year and a half ago, with 42,000 miles) the compression was all around 210 (+-5psi) it is high compression (10:1) so with a lower reading it would appear normal. Everything about the motor is clean, I keep it in good condition, so there is no buildup whatsoever. The car will idle (rough) for the first minute when it is cold, then rpms drop to about 500 and then it stalls, so I have to keep on the gas. Also there is no check engine light. Anytime I've had problem with vacuum leaks (like cruise control for example) it would throw a CEL and run choppy/stall. Once it hits 3000+ rpms it runs almost normally, and VTEC kicks in at 5200 and climbs to about 6000 where I stop pushing it (redline is at 7200). The problem is running rough below the 3000 mark. I poured a capful of oil into each cylinder hoping to get a wet compression test, but unfortunately the compression tester sucked, so I just started it up, and even though it was warm, it stayed running (smoking from the oil though) and actually ran way better than normal. I'm fearing the worst....
Mar 31, 2006 at 6:15 AM
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LOSONE
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Humm, have you tried running through a valve adjustment? Engine cold less than 100F, Intake should be .010 (.26mm) and exhaust should be .012 (.30mm) With those high revs you might have precussed the valves causing them to tighten- Let me know
Mar 31, 2006 at 9:23 AM
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JDUBSLOPRO
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when i first got the motor in and running, it had obnoxious ticking so i had the valves adjusted about a week before it died...maybe something to do with premature failure? ...it would be sweet if all i had to do was readjust the valves...
Apr 1, 2006 at 1:52 AM
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LOSONE
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I would try that first, I think the tech might have tightened them too tight. It is easy to tigten the nut and the valve adjuster will make another turn. They run at almost 0 lash when the engine is warm. It's worth a try. Good luck
Apr 1, 2006 at 2:03 AM
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Suggested Repair

Do not remove the cylinder head yet. First perform a cold valve adjustment (engine under 100F): set intake lash to 0.010 in (0.26 mm) and exhaust lash to 0.012 in (0.30 mm), since the valves may have been tightened too far and can reduce compression and cause rough idle and stalling. Also check for a vacuum leak (brake booster is a prime suspect), clean the throttle body, rule out a rich mixture washing the cylinders, and repeat a wet compression test with a reliable gauge.

Conversation Summary

The owner of a 1998 Honda Prelude reported compression that had dropped from about 210 psi to 140-160 psi, a rough cold idle, and stalling below about 3000 rpm, with no smoke, coolant loss, or check-engine light. A previous engine had a burnt ring from nitrous use, and adding oil to the cylinders made the engine run better, raising concern about the rings. The expert advised against removing the head, noting that 160 psi can still run, and suggested a wet compression test, checking for a rich mixture or vacuum leak (especially the brake booster), and cleaning the throttle body. After further details, the expert recommended a cold valve adjustment first because the valves may have been set too tight.

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