misfire under load until boost comes in?

[QuattroFever]

having a bit of an interesting one. I'm getting a misfire like shes running on 4 cyl's at the transition point from -ve to +ve pressure

once its on boost it's fine but when the boost gauge reads 0 - about 5 psi its chugging like a good 'un'

never under vacuum. always seems to be at the point where it just starts to make boost then all of a sudden it goes away and pressure builds and its off like a rocket.

running vems so I know/can see the mixture is perfect.

is there an obvious answer that someone with a bit of experience of these symptoms can answer?

[Flat on my back]

.

Hmmmm...

My gut is telling me plug or connection problem...

Can you tell which cylinder it is?

Them move the 'dodgy' plug/coilpack to another positon.

[QuattroFever]

not sure which cyl. it is. not sure how to diagnose it. unplug the injectors one by one and drive it until it either gets worse or stays the same?

at the point which it stays the same is when i have the dodgy coilpack I guess.

will go for a drive later.

looking at the coilpacks cyl. no.5 coilpack has cracks in the insulation but it is on the low voltage side so i wouldn't have thought that would cause any problems. what voltage are we talking about coming out of the POS's

very strange to get better under heavier load though eh. You would think that when the boost comes on it would be even worse?!?

This thing never ceases to amaze me.

[jade]

Having the same problems with my Vems, I have a ls2 coil packs have changed them one by one no difference, checked earths still no good, change spark dwell from 3.5 4 no change, Getting a little boring now

[QuattroFever]

interesting, must admit i tried the spark dwell too. No change.
Makes me wonder if its not the coils then.
I had no misfires when running motronic.

Are your symptoms exactly the same i.e the change from 0-5 psi?

[Wiell]

i think the vems is acting up. maybe a ignition timing error under low load?
whats the afr when it starts to missfire?

sorry for the bad english.

[QuattroFever]

i dont think its mixture related. Ive changed the bins rich and lean by as much as 8 points in the bins around this area with no luck.

[QuattroFever]

Having the same problems with my Vems, I have a ls2 coil packs have changed them one by one no difference, checked earths still no good, change spark dwell from 3.5 4 no change, Getting a little boring now

What firmware are you running?

[Wiell]

i dont think its mixture related. Ive changed the bins rich and lean by as much as 8 points in the bins around this area with no luck.

ok. maybe the acc enrichment isnt tuned in right? and putting in to much fuel when you are starting to build boost, and when you get full boost the afr is right?

what afr are you running? its easier to know when you are trying figur out the problem.

[Jamo]

There have been reports of this on some higher firmwares including 1.1.80

I run 1.1.74 and haven't had this problem

[A80Avant]

havent had this problem on 1.1.27 either if it helps.

it does sound like over too much accel enrichment if all coil related has been checked though

[th.b.w.]

Hy, have you ramp up the dwell ?

Set : Coil charge time to 3,78
and rampup with Coil charge time MAP Scaled to 10.

Than you have at low load 3,8-4,0 and at high boost 5,5ms....

Thomas

[GazzaG60]

too much accel would make it bog down for a brief few seconds. this sounds like its gonig bananas as it goes positive. vac.

have you checked the map sensor. is it calibrated? is it set to the correct one.

had this on a corrado. it was 02 probe related. whats the afr saying in the logs when it goes.

jamo has a point. if its been reported then it may be new firmware related. 1.1.23rc is running the same as it did when i got it. almost 3 years to the day that i installed vems.

[QuattroFever]

too much accel would make it bog down for a brief few seconds. this sounds like its gonig bananas as it goes positive. vac.

have you checked the map sensor. is it calibrated? is it set to the correct one.

had this on a corrado. it was 02 probe related. whats the afr saying in the logs when it goes.

jamo has a point. if its been reported then it may be new firmware related. 1.1.23rc is running the same as it did when i got it. almost 3 years to the day that i installed vems.

afr is between 12 and 13 on wot

if i feed the throttle in gently it wont do it.

map sensor is pre installed and calibrated as per base map supplied.

Haven't tinkered with that yet. haven't even managed to get any sensible boost curve on it just using overboost fuel cut to get started because the boost vs rpm table wont open in the firmware i was running, upgraded now but thats a whole other story!!

boost cut is working at pretty much bang on what I set it too so I've no reason to doubt the accuracy.

if i feed the throttle in slowly in 1st or second gear it is ok, but if i put it in 4th gear at 1500rpm and feed the throttle in it still does it until it makes decent +ve pressure. I dont think it's accell enrichment. I was playing about with that to improve throttle response so I know it's not vastly out.

low rpm\high load but only as it comes out of vac.

There have been reports of this on some higher firmwares including 1.1.80

I run 1.1.74 and haven't had this problem

what version did you move up from? I was recommended .70 as a stable version. I've read to stay out of the 1.1.6x's

playtime is over for me for now however...Lack of ability to connect to vems at all when it wont start is not fun.