I am getting major misfire above 5000 RPM and above 1bar boost. I have run into this probelm before and last time it was caused by the VTEC not switching over and the non-VTEC map not being tuned very well. However, this time VTEC is definately switching over as I can hear it in the exhaust note. I just changed my plugs and gapped them down to .025 with 8 step cold NGK Vpower plugs. It is almost as if the VTEC cam lobe is switching but maybe it is still using the non-VTEC map. AFR is good... right around 11.5.

I am going to try and take the boost down to .5bar and work my way up to see if it starts breaking up at a certain level of boost. I am not getting the misfire if I go part-throttle and rev it out.

Any ideas?

 

What ignition setup do you have on the car and what do the plugs look like? It could be a ignition timing or plug gap problem.

 

Ignition:
Stock Distributor
MSD Cap
MSD Blaster Coil
MSD Plug Wires
FYI... I did not make a change to my ignition setup... I just all of a sudden started running into this misfire probelm

Plugs:
Just put new plugs in... last ones looked a bit rich but I had not changed them for a while and the plugs tend to foul out after about three months.

Timing:
Did not change timing when the missfire started

The only big thing I have done was change the clutch. I may have bumped a wire or messed up a ground somewhere when I took the tranny off.

 

try to bring the gap down on the spark plugs.

 

Smaller than .025? I have searched around and saw a few people going as far as .020-.022.

I am running a T3/T67, high boost is 25psi with methanol injection so maybe .022-.023 would be better for me. Strange thing is that .028 used to work fine, that is why I dropped it down to .025 with the plugs I just put in.

Another thing I was thinking of is maybe one of my injectors is cloged. My idle is perfect and engine sounds good cruising around town.




Modified by LST2 at 12:08 PM 10/23/2007

 

Update:
Haven't closed the gap yet on my plugs but I did lower the boost level. It looks like it is not RPM or VTEC related b/c I am not missing on lower boost levels at full throttle. Seems to start breaking up at around .9Bar. My AFR seems to have gotten a little rich too... about 10.5. I am going to lean it out a little and see if I can up the boost. Seems like I am eigther too rich or plugs need to be gapped smaller. We'll see tommorow.

I should also check the grounds since this started hapenning after I took off the tranny. There are two major grounds right? One on the transmission wire braket thingy and the other on the thermostat? Any others?


Modified by LST2 at 4:37 PM 10/23/2007

 

which map sensor is this?

-luke

 

GM 3bar

 

Sounds like ignition problems. Usually at higher boost and rpm. distributor, coil etc....

 

I chased a similar problem for a while.I fixed a lot of small problems but it was a new (used) igniter in the distributer that cured the problem.Ran great on the street but wouldn't turn over 6K at the track under power.

 

Well I somehow fixed the problem by changing a few things. I thought is was gapping the plugs smaller. It worked for a while but now I am misfiring again. I tried gapping the plugs closer and now it is down to .020.

The only other thing I did was recharge by battery which went dead. Another thing I noticed is that my lights are really dim, so dim that I can see my car cast a shadow from the cars lights behind me. I am wondering if I have a problem with my alternator, battery or bad ground and that is causing a weak charge to the coil and thus the misfire in high boost. I am going to Autozone to get my alternator and battery tested and I am going to clean up all my grounds. Could this be a potential cause of the misfire?

 

did u clean up ur a/f? u said u changed the clutch. maybe u didnt put one of the boost clamps on good. i did that to my car when i changed my clutch. the car was running way richer. turned out i had a boost leak (even though i was still getting the same psi on the guage)

 

A/F is all good 11-11.5. I did put in a new clutch. I don't think I have a boost leak as I was able to get rid of the missfire for about two weeks. During that time I was able to hold a steady 27psi. The missfire just came back.

 

Does it do it when the car is still cold?

Mine was doing the same thing. Full throttle at full boost, I would get a misfire, but only when the engine is hot after a 15 minute drive.

I changed the ICM (ignition control module) in the distributor, and the misfire went away. Autozone has the part for $65.

 

was there a retune after vtec was fixed?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bigb16 &raquo;</TD></TR><TR><TD CLASS="quote">Does it do it when the car is still cold? </TD></TR></TABLE>

I am not sure. I try not to boost hard unless the card the warmed up. I hear it is bad to boost if the oil is not warm yet.


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bigb16 &raquo;</TD></TR><TR><TD CLASS="quote">I changed the ICM (ignition control module) in the distributor, and the misfire went away. Autozone has the part for $65.</TD></TR></TABLE>

Thanks, I'll add that to the list of potential fixes.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Snailed EF &raquo;</TD></TR><TR><TD CLASS="quote">was there a retune after vtec was fixed?</TD></TR></TABLE>
Yes

 

check your wires make sure they fit.
I had the same problem and it was just spark plug wires.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LST2 &raquo;</TD></TR><TR><TD CLASS="quote">I am not sure. I try not to boost hard unless the card the warmed up. I hear it is bad to boost if the oil is not warm yet.

</TD></TR></TABLE>
I didn't mean cold, but I meant not-very-hot... I would never even move until my car gets up to running temps.

 

Well, I think I found the problem. I went to check my alternator and battery and the alternator was pumping out 14v+ so it was OK. But, when they put a load on it the car died. Turns out my battery is toast. This kind of makes sense as the misfires stopped for about a week after I recharged by battery at home.

I have not done a high boost run yet so not sure if this fixed it. I am out of town for a few days so I'll post back on Wed with results.

 

Well that was not it. Back to the drawling board. Going to change the plugs again. Also, I am going to see if it has somehting to do with my meth/water setup. I could have potentially mixed in too much water last time, and b/c I inject a lot of the mix (1,000+ cc/m) a little to much water could probably cause some misfire. It seem the misfire is happening around the same boost level where the meth/water kicks in. Going to play around with the trigger point and see if it moves the point of missfire around.

 

That was it. Something when the water/meth injection kicks in. I think there was too much water in the mix. Going to run straight meth and see how it runs.