Hey guys this is my first post and first time regestering to forum. Forums help out alot, I have learned alot from all the threads. Now to my missfire, I have a 95 z28 A4 and I got a missfire after doing a few WOT runs to fine tune my shiftpoints with C.A.T.S. ( I really havnt messed with timing too much or a/f so its not the cuase, i have put it back on stock tune and still misses) It misses from idle to about 1500 RPMS but only when motor is warm I put a new cap n rotor with the screws tighly on their with locktie, new wires (none are crossed or arcing or touching exhuast), new plugs gaped at 45 and heat range of 6( It still misses with the new stuff) I also checked the injectors to see if the rings or cups were broken all is fine) its makes poping sound and doesnt set a misfire code (93 Octane fuel Shell gas always) 10-40 mobil1 and the 02 sensors are reading the correct volts( check with freescan) what else can be missing i even ran it in speed density incase the MAF was dirty) Thanks for the help sorry for making it long

 

welcome to the boards ... have you checked you coil?
there will probably be others with more info for you but you didnt say you checked that so you may want to.

 

Any modifications, or is it stock? Was the cap/rotor replaced in response to the misfire, or before the misfire?

No misfire detection or code on a 95.

 

All I did with the coil was clean the tip with a wirebrush and put two washers between it and the block incase heat from the heads was causeing the coil to miss. Is there a way I can check the coil? And the car has cold air intake and no cat and pullies 23% I think with optima battery since alt charge is lower (btw I've had the pullies for a while so miss wouldn't come from low charge just incase)

 

And yes I changed the cap n rotor I'n response to miss as well as wires and plugs

 

How many miles on the engine? Has the valve adjustment been checked? Have the injectors ever been cleaned?

 

120,00 the previous owner had a head job done( I've had the car for 5 months and have done plenty races and never missed) miss started a week ago and I've ran Lucas injector cleaner/ seafoam/ and mysteroil to clean them and I always use shell 93 I won't put anything cheap gas or low octane ever
lol. Could the coil be causeing the miss at only idle and low rpm evernthough I spaced it from the heads and cleaned it?

 

Look for a dead cylinder or at least the one that misses the most.

 

It's cylinders 6 and 8

 

Ok so check those 2 for consistent spark with an inline spark checker or even an inductive timing light.

Then check the injector spray pattern if need be.

Just for giggles, disconnect one of the 02s and see what it does after warmup.

 

K I'll try that but could it be the coil

 

if it were coil per cylinder yes it could be a coil, but is unlikely that the coil is firing 6 out of the 8 cylinders constantly and is not firing #6 and #8. It could be possible but highly unlikely.

Check for injector pulse on those cylinders. A test light will even work for this, that will tell up if the PCM is telling the injectors to work and the drivers in the PCM are sound.

 

How do check that with a timing light ( if it's bad I just change the injector right?)

 

Generally, you need a 'noid light to detect the tiny (2 mSec) pulse width ground supplied by the PCM at idle.

 

Srry I meant test light*