Over the last couple of weeks I have installed the following parts to my 2004 Impreza STI:

• MD321H turbo
• Headers/exhaust
• PE 650cc injectors
• Hybrid FMIC & induction kit
• Apexi AVCR - only wired in at the moment, sensors havn't been connected/plumbed in.

I started the engine yesterday and it is running rough, It idles very low and I have to pump the accelerator to get the revs to rise.

I have checked all vac pipes and they seem fine, I can reach the plugs on two of the injectors. I unplugged the injectors one at a time and it didn't make a noticeable difference. I unplugged the MAF and it stalled

Any idea what could be causing the engine to run rough? it stalls occasionally and doesn't idle fast when it is cold.

Should it run ok with the 650cc injectors?

Thanks

 

Did you use the cold air kit supplied with the intercooler? as when I fitted this and ended up fitting the maf sensor the wrong way round and caused similar issues.

You will get issues running the bigger injectors on the standard map, I would pop the standard items back in till you get it mapped.

Banny

 

has it been mapped to run those injectors?

if not then, yes you will nedd a remap as you will be overfuelling badly now (presuming you have gone from standard to these)

 

Your cars overfueling due to having big injectors fitted and no re-map, which irrc could also lead to DET if driven?

If you do your homework on injectors tuners reccomend they are the last thing you install or do them just prior to mapping, as the car will overfuel.

Once mapped, should be fine!

 

I haven't had the car remapped as I was planning to drive it to my mapper off boost, I did use the induction kit supplied with the FMIC, I will turn the MAF around and see if it makes a difference, I hope it does!

 

I would install the standard injectors but I sold them

I went from the standard 550cc injectors to the 650cc injectors, anyone done this before?

 

If you have an adjustable fuel pressure regulator, you could turn the pressure down to compensate for the increased fuel.

I went from 440cc to 550cc on my classic and it ran like a bag of bolts till I adjusted the settings on the power fc commander.

Banny

 

the sti will compensate within 30seconds of idle for the 650cc... they are only 100cc larger and it should drive fine off boost..

Banny maybe on the right lines... good calll

Simon

 

I turned the MAF around and the car is driveable

Thanks for the help!!!

Simon i am ready for a remap, how about surrey rolling road this month?

 

replied to your email etc

 

Hi Simon, how big a jump in injectors can the fuel trims cope with? (idle/cruise)

cheers.

 

200cc give or take a bit..

usually see WRX with Sti injectors - 380cc to 550cc fine cruise and idle
Sti - 550cc - 650cc..

generally larger than 650cc can be troublesome to control on the standard ecu and getting to the point of maxxing out maf and other stuff if you need larger than 650cc so not noticed how well the oe ecu coped as removed in favour or a simtek etc..

Basically the ecu has 25% + and - using the lambda sensor.

Why?

Simon

 

In closed loop it does but only 15% in open loop I believe.

Sorry, grandma sucking eggs etc

 

I would hope with those mods it wouldn't come out of closed loop until mapped

 

How will the ECU compensate for the large change in lag time of the injectors?

It will run poorly and you may find some odd corrections being speculatively applied by the ECU which are far from ideal.

Get it mapped ASAP.

 

I took it out for a little drive last night.

The car idles and revs ok.

I took it for a drive and pulling away gently in 1st gear it drove normally, change to second and it hesitated. I had to keep my foot on the accelerator lightly to stop it from stalling when changing to third. It hesitates in third aswell. When warm it cuts out alot whilst changing gear.

I will plumb in the AVCR solenoid later on and see if it helps.

 

I am planning to drive it approx. 100 miles to get it mapped! the way it drives at the moment i don't think it will make it

 

....just out of interest Simon.


how can it adjust upto 15% in open loop???

 

There are various ranges for fuel learning based on MAF voltages/grams per sec. It remembers what fuel trim was used at the top end of the closed loop range and applies that to open loop. It only has a +/- 15% adjustment available in open loop though.

 

It wont help at all.

You should be driving this completely off boost until mapped.

You have changed so many things, turbo, injectors, FMIC, induction it is a wonder it runs at all.