257K miles. One weak cylinder. Rough idle. Possibly poor gas mileage.

'93 Del Sol. Model S. 1.5L. 257k miles. Valve job about a year ago. ECM replaced in June, 2015. Distributor replaced in June 2015.

Suddenly my car idles roughly. When the engine is cold or warm it misses noticeably in low gears.

Pulled wires. When I pulled one of the wires, the engine's idle didn't change. Removed the spark plug, it had wear. I will post a picture, hopefully much later today. I replaced the plug but it made no difference.

I'm ruling out the injector. With the engine running, I put a stethoscope to all four injectors and they all sounded the same, so I'm ruling out the fuel injector. If there was a problem with fuel pressure, would the injector make the same noise as it would when fuel pressure was ok?

I'm ruling out spark. With the engine running, I pulled the wires again and heard the same spark sound at two cylinders, so I'm assuming there is spark.

I'm thinking to do a leak down test on the problem cylinder.

Any ideas or suggestions will be appreciated.

Thank you.

 

The wire you pulled might be a bad plug wire. Check the distributor cap contact terminal for corrosion for that specific cylinder and the rotor may also be worn. How old are the spark plug wires and distributor cap and rotor? With a lot of age I would replace all and even the spark plugs with recommended NGK plugs.

 

have someone try to start it while holding the plug wire. You should get a little shock or if your not comfortable getting shocked just look for the ark. Then just do as the other op said. If its not spark try removing the coil wire and crank it and check spark plug for gas.

 

Do a compression check, dry and wet.

 

Delsolintegra, I'll check but I'm dubious.

Tony, I will do a compression test.

Thanks.

 

Sublimeluder, I will check more for spark and for gas at the cylinder in question. Thanks.

 

Hopefully its just the plug wire or distributor cap. 257 is a lot of miles. Does it smoke and how is the oil consumption?

 

First off, don't just pull plug wires out. That's a fast way to fry a coil, and is poor diagnostics. Second off, you're "ruling out" a lot of things the wrong way. Just because you hear spark doesn't mean you have healthy spark.

Do a spark test. Go to your local parts store and get one of these. Follow the instructions on the package. What color is the spark at all four plugs?



Do a compression test. Remember, engine at operating temperature, WOT throttle. What are your compression numbers for each cylinder?

Once you've done those two tests, and posted the answers, we can work from there.

 

NotaRacist thanks for joining. You're right my check for spark was a poor quality test. I have a similar tool to the one you posted an image of. Compression is: 175; 25; 160; 155. 25 is the cylinder I suspect. So, bad rings on #2 cylinder, correct? Engine rebuild to fix, correct?

Thanks again to all.

 

Not necessarily. Put that cylinder to TDC and pump 15 PSI air into it. If air only comes out your oil fill hole, then yes, bad rings. If it comes out one of the other cylinders it is likely a valve problem.

Also, can verify really fast by following up with the wet compression test Tony suggested. If compression goes up quite a bit from your 25 PSI it would indicate bad rings too.

 

Yep, as TomCat said, a wet compression test should be your next step. If you have access to a air compressor, you can also do a forced compression test, which is what TomCat is eluding to. You can find a how-to for that in my build thread, here. I would use more than 15 PSI, though - You need to force in more than it's holding for a reliable diagnosis. Since you're getting 25 PSI from the compression test, I'd feed it 50 to see where it's escaping.

Air leaking through intake - intake valve problem
Air leaking through exhaust - exhaust valve problem
Air leaking between cylinders - head gasket problem
Air leaking through oil dipstick tube - ring problem

 

The reason I used 15 is when I did 30 PSI with all the spark plugs out, it tended to throw the piston to BDC. But then again my rings are still sealing pretty decently.

15 PSI lets me listen easily without moving the piston around and is how I discovered the valve problem on my wife's car.

Maybe start low and work up the PSI until the piston moves, then back it off a little?

For me I thought of it as a poor mans leak down test. No gauges to get percentage loss but do get the air flow location information.

 

Yeah, I don't know if there's a technical name for it, and I've called it a few different things, but "forced compression test" seems the most reasonable name for it, since you're forcing air in.

I didn't have any problems with the piston moving when I did mine. Granted, my problem was in an exhaust valve, but it's easy to brace your wrench on the crankshaft nut so it doesn't rotate, and you should have one there already to get it to TDC for that cylinder. Seems like the logical way to do things. The reason I say more than 25 PSI is because the cylinder is obviously holding 25 PSI. Feed is less than that, and it should theoretically just hold it there. You need to feed it more to really hear/feel where it's leaking from.

 

The leakdown gauge I bought only uses 15psi.

It's not super loud but in a quiet garage you can definitely here the air escaping.

 

burnt valve.

 

Alrighty gents I'll do a leak-down test. I need to rent a compressor. Since I just had/did a valve job, I'd be surprised if it were a valve but you are all correct. I should nail down what is bad. Thank you.

 

Damn that sucks. 99% of the time if u have low compression its #3 cylinder. I'd recommend doing a rebuild even if its just a valve. If u can't afford OEM u can get a set of king bearings and NPR rings for cheap. Then buy a felpro head gasket set. That's the route I had to go anyways. I wish ya the best of luck with it and hope ya have it on the road soon.

 

Yeah Sub it does suck Not sure what I'm going to do, I'm assuming I need to do a rebuild. Not sure if I should keep it on the road or ditch it. I like the car, it serves me well. I don't know how the cylinders are numbered. If you lift the hood, the distributor is on your left, the bad cylinder is second from left, so #2 or #3. I'm thinking to buy Honda parts and rebuild this engine, does this make sense? And I am still doing the leak down next week. Renting a car this weekend.

What's funny is that the car seems to perform fine at high speeds; although, I suspect it's getting lousy gas mileage.

Thanks!

 

Yea that would be your #3. Honda parts is always the best route but in my opinion not necessary for every build. If your comfortable doing a timing job yourself you could rebuild yourself. 1.5 is a great motor to learn on. You could do a cheap rebuild for $300 . You and a friend could probably get it done in a wknd. Well thats if u dont have to wait on the machine shop for something.Theres plenty of info online. Hell even if I know how to replace a part I still Google it.

 

Cool! Sub. Thanks for the encouragement. I've done two timing belts. I removed the head, intake and exhaust manifolds and handed the head to a machine shop and let them do the actual valve work. I have started looking at the procedures already in the Honda manual. Thanks again!

 

You can definitely do it then. Taking the head off is the hardest part in my opinion. Dang sensors lol. I had to pay $115 for a new knock sensor because it pulled apart when I was trying to on hook the harness. You can also rent just about any specialty tool from auto parts store.

 

This is a 93, no knock sensor. A couple of plugs under the distributor (ECT sensor, 1 wire temp gauge), 3 bolts for the distributor and a timing belt, Intake Manifold and Exhaust Manifold is about all there is.

Draining the radiator first helps as there is a coolant passage in the Intake Manifold that bleeds a decent amount of coolant on the ground otherwise.

 

I was talking about when I rebuilt my 2000 prelude last wk. Obd1 is definitely easier a lot less sensors to mess with.

 

 

I took the head off last year for a valve job. I brought it to a machine shop for the actual valve replacement. The manual suggests taking off the intake manifold, head, and exhaust manifold as one piece. That's what I did. Worked well. Missed one hose under the intake manifold, fortunately my son was there to help.

I'll be bummed if it's a valve since they were replaced last year.