Misfire

[Beaver]

2000 DX hatchback 260,000km. It has a misfire. It was misfiring last spring so I replaced the plug leads, cap & rotor and the misfire went away. The car only gets driven 4-500km per month so perhaps 3000km since then. It now misfires again. If I creep up on the throttle it will accelerate slowly without misfiring. If I drive normally it misfires under load. If I drive with the RPMs around 4000 it either doesn't misfire or it's spinning too fast to notice. What should I look at next assuming the replaced parts are not crap?

 

[FWDKILLER]

2000 DX hatchback 260,000km. It has a misfire. It was misfiring last spring so I replaced the plug leads, cap & rotor and the misfire went away. The car only gets driven 4-500km per month so perhaps 3000km since then. It now misfires again. If I creep up on the throttle it will accelerate slowly without misfiring. If I drive normally it misfires under load. If I drive with the RPMs around 4000 it either doesn't misfire or it's spinning too fast to notice. What should I look at next assuming the replaced parts are not crap?

check spark plugs to see if any fuel or oil on them , you could have a leak on your spark plugs seals . a few cars I own had a misfire and I kept replaceing spark plugs ever 100 miles or so till I stop being lazy to change it.
the cel codes will only tell you what cyclinder is misfireing that's all , you will end doing the same I just mention.

 

[Beaver]

Plugs are good. I adjusted the timing as far as it would go and it ran fine for a day. I'm thinking my timing belt might have skipped a tooth. If it's not the timing belt I'm fire bombing the f**king thing and buying a Toyota. This thing is like sail boat, just pour money into it. Once I get the motor figured out I'll need to do the transmission input bearing.

 

[Beaver]

Well, the thing is, the CEL light is not on. A friend hooked his reader up to it and guess what, no codes.

 

[Beaver]

If I do firebomb it there will be video

 

[Beaver]

I got the timing belt changed about a month ago. I drove it home about 5km and it ran well. It sat for about a month until I hopped in today and went for a drive. Once it warmed up the misfire was back, as it warmed up more the misfire got worse to the point of being almost undriveable from a stop.

I've changed, plugs, plug leads, cap, rotor, timing belt, coil and fuel filter. Mechanic checked compression said it was excellent.

What else could it be?

 

[Restotech]

Sounds like a coil or igniter to me. You can get ghetto, and when it misfires, unplug one plug wire at a time and see if it gets worse or doesn't change. If it doesn't change, you have found the cylinder with the problem. Then swap wire, plug, injector, one at a time from the bad cylinder to a good one and see if your problem changes.

 

[Restotech]

FYI - This^ test should be strictly avoided as it carries a high risk for frying the coil.

I'm curious as to where this "theory" comes from.

 

[Restotech]

I can see where that is possible. However I, and many other techs have used this method for many years without destroying coils. On hondas you just slide the wire up enough to where it arcs to the plug tube. This same method can be used, unplugging injectors instead of plug wires. It is just a quick way to locate a dead cylinder.

 

[Restotech]

I did mention that is an option also. Then it would require additional tools to check the condition of spark. I did say it was ghetto but is quick and requires no tools. I have never seen or even heard of a coil being destroyed in this way. Not saying it can't happen, just haven't seen it.

 

[civteck]

Iv worked on outboards and 2 stroke skis for yrs and they provide ground posts for the coil leads for just this reason, iv seen many coils go bad and many tech get zapped from a dangling wire (funny as hell on the water) but while your way will work as boofoo stated it can shorten its life as the built up spark finds the path of least resistance and that could be through the windings.
Now i see 8-10 bad coils a week (pic)

Sent from my boujea ass phone

 

[Restotech]

Sorry I mentioned it.

 

[XpL0d3r]

Sorry I mentioned it.

No need to be sorry for bringing it up. Doing so brought up the discussion of potentially damaging components, which I'm sure OP is glad to know of, even if the risk of damage is incredibly low. Better to know something than to know nothing at all.

 

[Beaver]

An update: Although the plug wires had only about 5000km on them I changed them again. The misfire went away. I thought life was good, my daughter drove it all summer then drove it to school. I got a text recently telling me the misfire was back. WTF? I'm baffled, unless the plug leads are just total crap repeatedly what could the problem be?

 

[fabster]

I'm chasing a similar issue on my 99 EX. The mechanic that last worked on it said it was probably a burned valve. I have yet to confirm.