Misfire on cyl. 2

[Huw Powell]

 > Conclusions:
 > 1. There is something wrong with cylinder #2 (not plug #2 or wire #2
 > or
 > cap/rotor).
 > 2. #2 is running way rich (hence the sooty plug).
 > 3. There is not a valve problem with #2 (because the compression
 > checks
 > out OK).
 > 4. This seems to indicate too much fuel to #2, as opposed to ignition.
 >
 > Questions:
 > 1. Do the above assumptions sound reasonable?

Yes

 > 2. How can one cylinder get way more fuel than the others? (Or is it
 > getting way less air??)

Most likely that injector is spraying too much fuel (i.e., it's bad)

 > 3. What should I check next?

You can swap injectors between two cylinders (don't have to undo the 
lines, just pull them out and redirect them).  It's a pain, but if you 
make the problem move you've nailed it.


> Car is a 1991 100 FWD, NF engine.
> 
> I've had a misfire that has been gradually getting worse.  Decided to 
> try to do something about it today.
> Bought new spark plugs, distributer cap, and rotor.  Changed them and 
> the oil & oil filter.  Start it up and the misfire is worse than ever. 
> Take it for a short drive to the village recycling center (drop off the 
> used oil) to see if it clears up with some driving.  No - runs terribly, 
> sounds terrible, and shakes the car - also the exhaust smells gassy, 
> like it is running way rich.  Get home and check the cap and rotor - all 
> 5 contacts look like they're firing.  Pull the plugs, one by one, to see 
> what they look like (the old ones looked uniformly normal) - #2 is very 
> sooty and dark, the other 4 are still almost white (the drive was about 
> 1.5 miles).
> 
> So I start swapping things around to see where the problem is.  Put an 
> old plug in cylinder 2, same behavior.  Swap the plug wires for #1 and 
> #2 (at both the plug and cap end), same behavior.  Leave #2 unplugged, 
> same behavior.  Swap #1 and #2 wires and leave #1 unplugged, engine 
> barely runs (firing on 3 cylinders now).  Put all the wires back where 
> they belong and swap the old cap and rotor back in, same behavior. 
> Finally, pull all the plugs and do a compression check: 185, 185, 190, 
> 185, 180.  Put all the new components back in and come inside and turn 
> the computer on.
> 


-- 
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/