Weird Idling Problem?

[deaz]

I have some sort of weird idling problem. Not exactly a problem thats anything big, just kind of weird. Anyway, I have a 98 Accord LX, 4cyl. When it idles, you hear a sort of "Putting" sound coming from the exhaust, but don't hear anything from under the engine compartment. I poured a bit of oil into the cylinders, figuring it may have been due a leaky exhaust, but no smoke appeared from anywhere in the car. (Except out of the exhaust of course). The car currently has 101k miles on it, and the catalytic converter was replaced about 40k miles ago.
Also, not really sure if this has anything to do with it, but along the exhaust system, pretty much right after it comes out of the headers, theres some sort of heat shield(?), and its kinda quarter-way ripped off due to the 4 inch speed bumps they put into my old development.
Other than that, theres nothing really wrong with the car. I've recently changed all the fluids in the car, oil, manual tranny, clutch, brake, etc.

So, if anyone has any more questions about the condition of the car, or can suggest any thing more I can do to diagnose the problem, please don't be shy to post.

Also, one last thing, the car tends to lose power slightly in second and third gear, not sure around which rpm range, but it is a noticable power drop. Do you think that could be from clogged/faulty fuel injectors? Thanks in advance.

[jeffcoslacker]

Usually is either a misfire or a valve that isn't fully seating so you hear the pulses of suction that wouldn't normally exist in the exhaust flow.

Sometimes you can check that by placing a piece of paper (dollar bill works nice) right over the end of the tailpipe as it idles and watch it. A bad exhaust valve allowing suction will pull the paper into the pipe everytime that cylinder is on an intake stroke.

[deaz]

Okay, so, if it is a misfire problem, what could that possibly be? I tested the sparkplugs with a tester, and they appeared to be operating correctly, and the sparkplugs were replaced maybe about... a month ago. And the distributor cap and rotor were replaced about a year or two ago, and I took a look at them the other day and theres nothing wrong with them at all. And as far as the valve seating, is there a way I can adjust that? I have to replace the timing belt soon, so I guess that would probably be a good time to try it. (I'm assuming I'd probably have to have access to move the crankshaft anyway, right?) Any other suggestions on how to fix this problem would be greatly apprecated, thank you.

[jeffcoslacker]

You might want to purchase a vacuum gauge. It's one of the least understood diagnostic tools, but very helpful and easy to use. They are about $25, I think (haven't had to buy one in a long time), and come with instructions on how to interpret the reading.

Basically you are looking for a good solid reading, no needle shake or wander. It should snap to zero instantly when you pop the throttle, then recover as rpm's level out. Holding the throttle at about 2500 rpm, it should read steady. A slow drop indicates exhaust restriction. A rythmic drop with every crank rev indicates low compression in one cylinder. A rapidly shaking needle is usually a bad valve. A low reading indicates late ignition or cam timing.

The nice thing about this tool is that you can instantly tell if you are dealing with a simple misfire, due to ignition or fuel issues, or an actual mechanical defect in the motor. A misfiring plug or injector will not affect the reading. Only issues that compromise the compression or intake/exhaust flow will show up on a vacuum test.

All you have to do is hook it to a manifold vacuum source.

I don't know about valve adjustments on your motor, but somebody here will. That is a possibility also, a valve out of adjustment and not getting enough lift could create what you are seeing also.

[deaz]

I guess its a good thing I already have one tho. I originally bought it for a different car when I was doing some tests on the EGR valve, but hey, never hurts to have it right? lol, thanks a lot for your help. Oh, also, one more thing, do you think it would be good to maybe clean my injectors too? If so, is there a way I can do it while they are still in the engine, like with something hooked up the the pressure valve to blow anything thats in them out? If there is something like that, any clue where I could get something like that? Thanks again!

[deaz]

Sorry it took so long. Anyway, I just got around to doing the vacuum test. I get a shaky needle reading at around 24 in-hg. Is that a bit high, or is that normal. Anyway, as you stated, it must be a bad valve. So, I guess whenever I get around to doing the timing belt is when I should do it. THe weirdest thing was, that this problem never showed up until after my cat died and they replaced it. Hrm, oh well. Thanks again Jeffco.

[Deadhead]

When i had my car into the mechanic, he was replacing my distributer because the ingnitor went bad (yes, the whole distributer didn't need replaced, but the one they put in there the first time was bad, this was the second one) anyway, the ignitor in the distributer also could cause your car to make sounds like that so says my mechanic, and when he fixed it, the sounds went away a great deal, the only reason it does it now is cause of my rusty exaust.

my 2 cents

[jeffcoslacker]

Originally Posted by deaz

Sorry it took so long. Anyway, I just got around to doing the vacuum test. I get a shaky needle reading at around 24 in-hg. Is that a bit high, or is that normal. Anyway, as you stated, it must be a bad valve. So, I guess whenever I get around to doing the timing belt is when I should do it. THe weirdest thing was, that this problem never showed up until after my cat died and they replaced it. Hrm, oh well. Thanks again Jeffco.

A couple of thoughts....24 in is a bit high, usually 19-21 is normal....was the engine warmed up when you checked it? Cold motor will read a little higher. Make sure you were connected to a direct manifold vacuum source that originates below the throttle plate. Ported vacuum sources will give odd readings.

If you have a rapid shake that seems to even out somewhat as the RPMs are increased, then yeah, you are probably seeing some valve leakage. The is an injector flush made by 3M that is a tall pressurized can that connects to the service port on the fuel rail, you disable the fuel pump and pressure regulator and start the motor and let it run off the can until it dies. Cleans injectors, valve faces and piston tops, might be worth a try, if you can get any adapters needed to connect it to your engine cheap enough. Go to a good parts store and get the details. I used to have a complete set of connectors and adapters for cleaning all kinds of systems, but I know they can be purchased seperately.

[jeffcoslacker]

Was the old cat blocked? If so, that can cause exhaust valve overheating. Maybe that's why it coincided with that repair?

[deaz]

Yeah, I'm pretty sure I was connected to the correct port. I'll double check it as soon as I get a chance. And yes, the engine was warmed up. I did the quick open/close throttle test, and that seemed to be working correctly. (The gauge would drop to zero, then go up to about 30, then as the engine wound down, it would drop back to normal.) However, if I did hold the throttle open steadily, the needle was still shaking. About the cat, no clue as to whether it was blocked. I was still under warranty, so they went and replaced it, but didn't tell me the cause of it or anything like that. All they told me when I brought it in the shop was that the cat needed to be replaced. (Also kind of weird considering the fact that the car didn't have that many miles on it), However, when I look at the tailpipe of the muffler, I do see a LOT of carbon buildup all around the tailpipe, not quite sure what that is supposed to mean, but maybe that was due to the cat going, not sure. Also, I was going to do a compression test, since I have a tester. Anyway, When I pulled out all the sparkplugs, for some reason they were already coated with carbon, and had a whitish color all over the electrodes, including the center one. I'm assuming that maybe its running too hot in the combustion chamber? But if that was the case, I shouldn't have that much carbon buildup all over the sparkplugs, because it should have burnt off. So I guess my next question should be this... After I clean the injectors, would any of you recommend that I pull the head off, and check the pistons and cylinders, and if they are pretty bad, as far as the carbon buildup, should I have them decarbonized? If so, would a simple throttle body cleaner and a toothbrush would good enough for that?

Also, about the blocked cat... If there was valve overheating... I guess that probably means that the valves were warped and need to be replaced, correct?

I just wish they still did the emissions test at the MVC. Then I would know exactly what my system is pushing out.

Also, one more questions.. Sorry about this, but where could I pick up that 3m injector flush? Would Pepboys, autozone, or advance auto parts carry it? THanks

[jeffcoslacker]

So did you do the comp test? What'd you find out?

A hot combustion chamber is usually the result of over-advanced timing or a really lean mixture, and the white insulator around the center electrode will be very white, and blistered in appearance on close exam. Don't confuse this with fluffy, flaky whitish deposits, which are normal. They can range in color from off-white to tan, orange, or even red, depending on the additives in the fuel used, but should have an even, ashy appearance.

Black sooty deposits are carbon from excess fuel in the mixture. Lean will produce a hot chamber and the blistering described earlier.

Not having seen yours, it's hard to tell, but I'm wondering, did you have a chance to drive it at high speed since putting the oil in the cylinders for your test? That'll soot 'em up, and takes some hard running to blow off, maybe that's what you see.

You know, something else that just popped into my mind, might be nothing, but that shield you mentioned, pull it off and make sure the pipe isn't dented or crushed under there. That could be the source of your problems.

[deaz]

Actually, I havn't had a chance to finish the test... (I did it wrong, lol) But, as far as I could tell, cyl 3 seemed to build up slower than the rest, which if the valve is the problem, probably means its in that cylinder. And yeah, I've had the chance to drive it at high speed. I generally always drive it anywhere between 75-85 down the highways. Also, last time the car was on the lift, I took a look at it, and didn't see any denting in the piping.. Just that the shield was torn a bit. As soon as the car comes back home, I'll redo the compression test and make sure everything is good and confirm the cylinder problem.

[deaz]

I rechecked the vacuum lines to make sure I was in the correct one... and the weirdest part about it all, was that EVERY line coming from that area gave me the exact seem reading, along with the quick needle shake. around 24-25 in-hg. Could this be due to some sort of blockage perhaps? Or perhaps too much carbon on the pistons and the combustion chamber? I'm going to go and redo my compression test right now, but figured I'd leave this little note about updates, incase anyone else ever seems to have this problem.

[deaz]

Okay, I just redid the compression test... and its coming out at a whopping 220 by the 5th stroke...
Each cylinder hit 120 on the first stroke, but by the 5th stroke, it was already at 220... Which seems a bit high to me, especially since the haynes manual says the standard compression is 180... (unless that means on the first stroke? if that is so, then for each cylinder, I'm not even hitting the minimum of 130-135.) If I am doing it correctly, then basically, what does that mean, a heavy buildup of carbon in the cylinders?

[deaz]

ALso, I've been trying to do some research online about how to decarbonize the engine, incase that is the problem, and unfortunately, I havn't found much.... The best bet I have so far is I found someone who has sad that if you take a spray bottle of water, and slowly spray it into the intake, it should "steam-clean" the carbon out of the system. Others have suggested some sort of chemical decarbonizing... But not sure what sort of chemicals would be required, and how to inject them at all... Only problem I see with the water cleaning, is that it wouldn't help clean the throttlebody at all, but then again, that can always be removed and cleaned with a toothbrush. lol. Anyway, any replies would be greatly appreciated.