This hesitation happens at any given rpm and at any given load or throttle position. I sense it most between 4-5k rpms becuase that is where I cruise mostly. It feels just like a miss. like the spark just didn't fire one time. I thought about it being injectors but there is no a/f change when it happens. There is nothing I can do to make it happen it just does at random. I have changed plugs mulitple times and tried different gaps but I know the spark isn't blowing out becuase it will happen under -psig loads. I have replaced the coils. I have probably 30-40 minutes of aem logs during which it has happened many times and there is no indication of any error. I have pulled the master option list and sorted through the logs many times looking for a spark or a fuel contraint that is out of spec at some time but I can never find anything. I thought is was fuel building up in the exhaust and suddenly burning off but there is a notcible split second loss of power when it happens. It even happens at idle. sounds like the engine is burping. sometimes it happens three times in a 10 second period and then it won't happen for half an hour.

It is aggravating and I don't like not knowing what the problem is.

There is no knock when it happens. The timing map is good. The car makes plenty of power for a 9psi pulley. The bov opens correctly, vents at idle and during cruise and snaps shut when you stand on it. It never did this with the stock SC kit only after the upgrades. I can't tell which part did it becuase I did EMS, UEGO, 550s, 9psi pulley, front mount heat exchanger, bov, all at the same time. I have never been able to get another SC ems cal from anyone to just "check" over everything to see if there were any major differences but I can post mine somewhere if someone wants to see it.

Thanks guys,
Alex

 

Could be your fuel pump.... one of the local guys had the same problem with his fuel pump getting ready to shit the bed during a dyno day.

I would check the pump or the FPR if you've done everything else.

Also consider getting gas somewhere else, slipping belt or clogged injectors.

Just helping you brainstorm.

 

Hmm. That is possible but it has less then 10k miles on it. It would have to be deffective. I use an AEM FPR set to 45psi with the vacuum line unhooked at idle. The ems logs never show the pump turning off when it shouldn't but there could be some sort of clogging problem at the pump itself.

I thought about changing injectors to see if that would do the trick but again they are nearly new and wouldn't clogged injectors be more consistent? and wouldn't I see some sort of anomaly in the AFR logs if it stopped spraying fuel even for a second?

 

im having the same problem. hesitations comes n goes. i also tride swapping out plugs also. we need some more info to get this fix.

 

olskodumie who did your tuning?

 

no tuning yet. stock vortech kit no upgrades.

 

I have the same but always between 3500-4000rpm...it happens once a day that it just misfires one cylinder when I accelerate (even when it's not WOT) but otherwise it never happens. I heard of more people, I think it's the AEM EMS.

 

does it happen at idle?

 

maybe a bad 02 sensor, i went throgh many of these. but my air/fuel ratio would be all over the place, sometimes running normal then running like complete shit. i would check the 02 sensors.

MAtt

 

I don't think that is the problem. My AEM UEGO sensor has less than 5k on it and I never run leaded fuel. (yet). The one OEM sensor than is still in place doesn't do anything. My o2 feedback is set to read from the aem unit and it is wired into the ems. It is just kinda there. I don't have any A/F problems anyway. It is always were it is supposed to be.