ImprezaGT

Howdy,

I've been trying to diagnose a problem I'm having. The car jerks when I pull off normally or accelerate a bit. On pull off, I need to be very gentle else the whole car shakes.

MAF voltages read fine 1300 on idle going up correctly.
Lambda sensor voltages read correct.
Replaced spark plugs yesterday.

Still does it. Now i'm stumped.

*edit, AFR reads lean on the jerks.

jaytc2003

iTrader: (1)

what is the afr being measured with?
Do you have a power fc? If so I think you can change acceleration enrichment. Sure a mapper will be here soon.
Could it be just clutch judder??

biglad1

hi i had that prob and it was wrong plugs put in it was coffing and farting as soon as i changed them it was a differant car hope this helps

ImprezaGT

I replaced it with the same plugs as previous, HKS 40i or something to that effect. Yes I have a PowerFC. Problem actually started soon after installation...hummmmm.

AFR is measured with a proper wideband. It's def not clutch judder, believe me

jaytc2003

iTrader: (1)

If you still have the original ecu then swap back and see if the problem persists. If it doesnt then I would say it is something to do with the map in the power fc, the fact you say it runs lean when it happens also to me says it could be map related.
Did you map it yourself or did someone else do it? If it was yourself then maybe ask one of the mappers on here for advise. As I said previous, I am sure there is an acceleration enrichment thing somewhere that may help.

ImprezaGT

Original ecu was damaged, I mapped it myself but I dont think its related because it didnt start doing it immediatly. I also tried resetting the Pfc back to std. map, I do have huge injectors though (740) and pretty much nothing on the car is standard.

jaytc2003

iTrader: (1)

I know the standard map is quite agressive, but if you have mapped it yourself you probably know that! I take it the injectors have been scaled on the map etc? Does it just happen at a certain rev range etc, has anything else changed since it started doing it?

ImprezaGT

Yea injectors scaled & everything. Happens on pull off, have to take it really very easy on pull off else the car jumps around...very embarrasing in traffic :P Also on WOT its not very smooth. It does sound like it could be something todo with the acceration enrichment but I've upped the values there by 50% or more before and it didnt help much. Need to fiddle more I guess. Only the battery changed but I've checked voltage and it seems fine. Gonna try tonight with a slightly bigger bat.

jaytc2003

iTrader: (1)

cant see the battery itself causing it, maybe a dodgy earth somewhere but that I imagine would manifest itself at every stage, not just when you are pulling away. You can monitor the voltages on the commander if you have one.

Could it be something to do with running either closed or open loop?

silent running

I've had what may be a similar problem, which did seem to be more apparent since running a Power FC. The best way to explain it is, you know that jerkiness that every car has at very slow speed, where you have to do a lot of slipping the clutch and very gentle throttle to manoevre around? Well that's what it's like all the time. Going from no throttle (or very light throttle) to a quick tap of the accelerator gives a real jerk which is basically down to the engine not picking up as quickly as it should. There is a pause of less than half a second then it comes in with a bang, with no intermediate ramping up of power. Most noticeable when accelerating through the gears - I have to slip the clutch slightly on every single gearchange otherwise it really throws you back and forth when you put your foot down.

Some people have said it's normal. Some have said it's a trait of Subarus and get used to it. Some try and explain it as turbo lag (which I can say categorically it is not). I say it's crap and no fuel injected car with a mechanical throttle cable should have that kind of delayed throttle response.

Messing with acceleration enrichment basically does nothing, at least not the setting that's accessible from the FC Commander. However, I have heard that there are other acceleration settings hidden deeper in the Power FC programming that may fix this. EIther way I'm taking it back to my mapper next week for it to be checked out.

jaytc2003

iTrader: (1)

yeah think the trait business is bollocks, my fc is smooth as anything. (hope in a few weeks when I have a td05 and fmic its still as smooth!)

ImprezaGT

Seems like I found the problem / cure. I had to increase my acceleration enrichment drastically. I mean as in from standard value of 8 up to 50 for 1000rpm, 70 for 2000rpm etc. I fiddled with these settings before but didnt think of increasing them over 500% :-/

silent running

What were your full before and after values? I might give it another go myself. I only went to double the existing values.

ImprezaGT

I cant remember my before (stock) values but, they are all below 10 I think.
At the moment they are:

1000rpm 40 3.5
2000rpm 64 3.0
3000rpm 72 2.8
4000rpm 75 2.3
5000rpm 80 1.7

I'm still busy fiddling those values. Just increase it by 10 at a time, when its better pull them back a bit to gauge where the sweet spot is.

silent running

Cheers, I'll give it a go this morning

ImprezaGT

*bump*

Ok this didnt actually fix my problem, just suppressed it a little. I did some more thinking and came up with this.
The problem occurs when the under bonnet temps go up, in the morning when cold i drive to work no problems.
Afternoon when the temps are higher it starts happening.

ImprezaGT

bttt

please thanks