How can I tell my car is misfiring?

seotaji · Oct 25, 2005

Someone suggested that I might have a general misfire at idle (to account for the loud engine noise).

I've got a '95 Honda Accord EX with the 2.2L Vtec engine.

I've replaced everything other than the plug wires during a tune up which was less than 10k ago.

Could the wires be causing the engine to run loudly?

I'm trying to get this car to sound like it did when I bought it new (which was 10 years ago).

Thanks for the help.

mechtech · Oct 25, 2005

Misfires are generally FELT, rather than heard.
Maybe you have an exhaust leak [can be a tick or roar], or worn valvetrain components.
BTW, no description of the noise results in no useful diagnosis.

PandaBear · Oct 25, 2005

quote:

I'm trying to get this car to sound like it did when I bought it new (which was 10 years ago).

Wow, thats a lot to ask for.

To check for wires you just need to use a multimeter to see if resistance is 10Ohm or less. To check for exhaust leak, you can spray soap water along the pipe when it is cold (don't do it when hot, it will crack) and look for bubbles.

1sttruck · Oct 25, 2005

A 'trick' that I recently used was to make 1 inch lengths of tubing that will fit in the distributor, between the cap and the wires. Install the tubing, warm the engine up, and then ground each piece of tubing by touching it with an insulated screwdriver that is grounded with some wire. Check for consistent RPM drop. The 'dead' cylinder won't drop or drop as much as others.

Matt_S · Oct 25, 2005

quote:

Originally posted by 1sttruck:
A 'trick' that I recently used was to make 1 inch lengths of tubing that will fit in the distributor, between the cap and the wires. Install the tubing, warm the engine up, and then ground each piece of tubing by touching it with an insulated screwdriver that is grounded with some wire. Check for consistent RPM drop. The 'dead' cylinder won't drop or drop as much as others.

...and you're still here!? My gawd!

1sttruck · Oct 27, 2005

"...and you're still here!? My gawd!"

???? Yes, and I also fill the car with a very volatile fluid on a regular basis.

I guess if you've never worked around iginition systems or other electrical systems then grounding as a diagnostic tool may seem dangerous. It is if you don't know what you're doing, either to yourself or to the system, so don't do it. In the case of the car the danger would be to the ingition system as current levels may become too high in some situations, which is in part why it's not recommended to poke the ignition wire with a sharp, grounded probe like people use to commonly do. The other reason is that it'd not good to have holes in the insulation.

seotaji · Oct 31, 2005

quote:

To check for exhaust leak, you can spray soap water along the pipe when it is cold (don't do it when hot, it will crack) and look for bubbles.

I've replaced the entire thing.

quote:

BTW, no description of the noise results in no useful diagnosis.

It's just loud on idle. When it's first running, you can hear loud valve rattling before it warms up and then it's quieter. I've had the valves checked and they were within spec.

Maybe the headers are bad. I've heard rumors that some OEM headers develop cracks?

My friend with the same car and engine has the benefit of having a quieter/smoother car, despite having treated it very badly. He hasn't replaced anything on his, yet it rides and sounds so much better.

I tried 1sttruck's trick and all of the cylinders seem fine. Pulled the plugs and found that they are all worn evenly with no advanced wear.

I wish I had some sort of futuristic scanner that would tell me what was wrong.

I'll check the egr system again, maybe I missed something.

I'm at a loss at the moment.

ikeepmychevytoo · Nov 1, 2005

BTW, how a misfire feels? Is it possible to only have misfire at the higher speeds, under load?

kenw · Nov 1, 2005

"BTW, how a misfire feels?

normally like there's some power missing. Not necessarily rough, tho.

Is it possible to only have misfire at the higher speeds, under load? "

yes, in fact that's a common time to have it, especialy if the failure is electrical in nature.

ikeepmychevytoo · Nov 2, 2005

hmmm... thanks kenw. Exactly! No go after 65mph!... very smooth at times, as if thrown to N. Eventually will gain speed.

seotaji,
How about the idle quality. I mean, going near the exhaust, away from engine and listening to it; Is it spitting, hunting or smooth... This may isolate the fuel management and ignition problems from others such as header, belts and pulleys.

55Test · Nov 3, 2005

Sounds like it could be plugged EGR ports. Quite common problem on the Accord. Clean them out, do your IAC valve and the EGR valve and it should run like new again. Just take a look at this PDF file to see if it describes your problem.

http://home.comcast.net/~em-engineering/T2T013.pdf

How can I tell my car is misfiring?

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