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Old 09-08-2011, 10:46 PM   #1
fishheadback
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& MK6 GTI

Default Wierd idle problem on EJ20K STi

Ok, I just finished getting my car back together and this idle thing is wearing me thin.

Basic overview of my setup- 2.0 V3/4 STi on the stock 6S ecu for now. Stock pistons, new rings, manley rods, and double drilled crank. New factory headgaskets, Silicone turbo inlet, grimmspeed 8mm spacers, FMIC, shortram intake.


Now heres whats going on with the car.

At idle, the rpms hunt a little bit, anywhere from 700-800 rpms, then every once and a while it will dip down to 600ish. Then while I was hunting for possible vac leaks the motor just died. Didnt sputter and try to catch itself at all. I went around and started it back up without problem. When you give it some throttle everything seems perfect, revs good, no misfires. Let off the throttle and the RPMS go down like normal, then it hunts a bit.

Sometimes I can watch on my wideband, and it leans way out when the rpms dip to 600ish.

NO CELS either.


Any input??

Maybe coolant temp sensor??

O2 sensor??

MAF??

To me it doesnt seem bad enough to not drive the car, but I notice it. I havent driven the car yet either so I might just take it for a spin to make sure nothing else is goin on.


Thanks in advance.
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Old 09-09-2011, 05:53 AM   #2
thoughto
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Small idea. Since your car's engine is nowhere near stock, you could try resetting the ECU if you haven't already done so. This might give it a better chance of adapting as well as it can to the new hardware, isntead of starting form where it left off before you rebuilt the engine.
You are going to use an aftermarket ECU and custom tune aren't you?
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Old 09-09-2011, 07:30 AM   #3
fishheadback
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Quote:
Originally Posted by thoughto View Post
Small idea. Since your car's engine is nowhere near stock, you could try resetting the ECU if you haven't already done so. This might give it a better chance of adapting as well as it can to the new hardware, isntead of starting form where it left off before you rebuilt the engine.
You are going to use an aftermarket ECU and custom tune aren't you?


I reset the ecu a couple times and it seems to get better. Maybe Ill just take it out and drive it and go from there.

I have a Simtek ecu, I just wanted to make sure I had all the bugs out of it before I put that one in.
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Old 09-09-2011, 07:37 AM   #4
thoughto
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Good luck. If you drive around gently the ECU might learn a bit. I would hope all the sensors are OK, espec since no CELs.
Simtek seems a good plan. I can't afford one, so I got an Apexi secondhand the other day and will eventually tune mine.
Simtek seems to be a much more advanced unit, and if the tune is good your car should be great.
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Old 09-09-2011, 09:06 AM   #5
Poppie
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Measure the voltages of the sensors you've mentioned or if you can get a Select Monitor (Subarus diagnostic tool for the GC8) as even though there are no CELs it will still pick up any erroneous readings.

As for the Simtek do you mean this one http://8378simtek.wordpress.com/ ?

If so it's a capable ecu but no knock correction (been waiting 2 years for that ) and they do seem to suffer from persistent cold start problems (mine has had to be looked at a couple of times) and sometimes hot start problems (due to the mapper not equipment)
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Old 09-09-2011, 09:34 AM   #6
pmugabi
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The 2.5 I just pulled out of my car had the same problem but worse. It was due to leaking valves (heavily carbon fouled from when I got it).

However since your engine is newly put together, I imagine the valves are ok (hope you checked them). Best bet is an intake leak. I'm sure you know or can search for the various ways of identifying an intake leak - basically pressure tests.
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Old 09-09-2011, 01:23 PM   #7
fishheadback
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Quote:
Originally Posted by Poppie View Post
Measure the voltages of the sensors you've mentioned or if you can get a Select Monitor (Subarus diagnostic tool for the GC8) as even though there are no CELs it will still pick up any erroneous readings.

As for the Simtek do you mean this one http://8378simtek.wordpress.com/ ?

If so it's a capable ecu but no knock correction (been waiting 2 years for that ) and they do seem to suffer from persistent cold start problems (mine has had to be looked at a couple of times) and sometimes hot start problems (due to the mapper not equipment)

Ill have to dig a little deeper and check voltages as you mentioned.

That is the ECU that I have. I have the customer program kit and thought about throwing the ECU back in there since I can read that stuff through my laptop but I havent gotten there yet.

Where do you find the Subaru Select Tool??


Quote:
Originally Posted by pmugabi View Post
The 2.5 I just pulled out of my car had the same problem but worse. It was due to leaking valves (heavily carbon fouled from when I got it).

However since your engine is newly put together, I imagine the valves are ok (hope you checked them). Best bet is an intake leak. I'm sure you know or can search for the various ways of identifying an intake leak - basically pressure tests.

I had all of the valves done and measured them all myself so that should be no worry.

I did find one tiny leak from one of the injector orings, but I didnt find anything else. I was checking for leaks the shade tree way with carb cleaner though. Ill have to do a good pressure check and make sure nothing else is going on.



Thanks for the help guys. I appreciate it.
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Old 09-09-2011, 09:21 PM   #8
fishheadback
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Well I took her out for her maiden voyage tonight. There deff has to be a vac leak somewhere. Under light throttle you can fell a light buck and it feels like its running out of fuel almost.

Then from 5in/hg to 0psi it feels like its falling on its face.

Im going to fab up a pressure tester tomorrow and see what I can find. There has to be something leaking somewhere.

Will update with what I find.
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Old 09-11-2011, 08:35 AM   #9
Poppie
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This is a Select Monitor

http://www.ebay.co.uk/itm/Subaru-Sel...item4aaea5a1c8

Have no idea though if this available in the US though

There does seem to be something called Evoscan which seems popular.
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Old 09-11-2011, 10:50 AM   #10
Jaxx
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evo scan does prettymuch the same thing i have a usb cable hardwired to my ecu
search this forum for it
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Old 09-11-2011, 03:42 PM   #11
fishheadback
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Well, I did a pressure test and found one of my fmic connections leaking, and a bad t-bolt clamp that wouldnt seal. I fixed those issues and drove the car for a while.

Now it would idle ~ok but there was a dead spot around 5in/hg-0psi where the car felt like it didnt want to accelerate.

Then when I would accelerate from a stop you could feel one spot where the car would hiccup around 1500-2k rpms.

I also noticed that when I would drive it on the highway, decelerate with the car in gear. Once the rpms would come down around 2k, you could push on the gas and for the first 1/4 throttle nothing would happen. It was like you had the car turned off. Then all of a sudden the motor would kick in like normal. If you wouldnt use the accelerator to keep the rpms up the motor would die, and it would be PIG rich. Then I would have to shut the car off, start it back up. Sometimes that would work on the first try, sometimes the 4th and the car would run like normal for a little while.


Now, fast forward to this morning. I decided to put my Simtek ECU in so I could see what the tps, coolant temp, and O2 was doing. Well, I swapped it in there, did some slight tweaks to smooth out my afrs, and go figure the thing runs like a top.

That leads me to believe that I had a problematic MAF that would give me intermitent issues. It just shocks me that there was never a CEL. The Simtek only uses the MAF for IAT and everything else is off the factory MAP sensor.

Soo, I might replace the MAF, but Im not to worried about it since Ill be using the Simtek ECU anyways. Just wanted to share my findings in case anyone else has a related issue.
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Old 09-12-2011, 08:58 AM   #12
Poppie
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I've found the CEL only illuminates when the sensor is seriously knackered,rather than failing as the ecu seems to try and compensate for it.

May i ask why you're not using the Simtek straight away as I don't see the point of buying a MAF (as you only need the wiring that goes to the MAF) when you have a MAF less ecu?
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Old 09-12-2011, 10:31 AM   #13
eg33GC
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Don't rule out the 02 being junk. It is implied that you were having all these issues in CL, which would be a huge indicator of the 02.

What does the Simtek do with the 02 readings at CL?
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Old 09-12-2011, 01:53 PM   #14
fishheadback
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Quote:
Originally Posted by Poppie View Post
I've found the CEL only illuminates when the sensor is seriously knackered,rather than failing as the ecu seems to try and compensate for it.

May i ask why you're not using the Simtek straight away as I don't see the point of buying a MAF (as you only need the wiring that goes to the MAF) when you have a MAF less ecu?

Well I figured that I would just run on the stock ecu to get any bugs worked out of it. Just eliminating variables mostly. I didnt want to have to tweak the ecu straight out of the box just to get the car running again.

At this point Im not going to worry about the maf. Im just going to keep the Simtek in there.


Quote:
Originally Posted by eg33GC View Post
Don't rule out the 02 being junk. It is implied that you were having all these issues in CL, which would be a huge indicator of the 02.

What does the Simtek do with the 02 readings at CL?
Readings on my laptop seem to show that the o2 is working ok at the moment.



Just swapping to the Simtek from the factory ECU made a night and day difference. Even on my old tune drivability is a million times better with the Simtek. The only thing that leads me to believe is that the MAF is junk.


Now to decide if I want to get tuned as it sits, or if I should upgrade the turbo/injectors then get tuned.
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Old 09-12-2011, 02:13 PM   #15
TommyAtomic
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One of the most contructive things I've done on my gc8 was replace all of the origional rubber vacuum lines with silicon. Many/most of them were brittle/cracked. Vacuum leaks galore. Especially on the lines going to the boost controller and fpr.

You just replace one hose at a time and in some cases replace the little hose clamps that dont hold so much anymore. Eyeball your vacuum/boost guage and note the level of vacuum and rpm @ idle.

Its amazing what $10 worth of rubber/silicon vacuum line will do for you.

As for the new ECU. If your not using MAF readings with the new ecu its still a good idea to verify that the MAF was the problem. The new ecu may be compensating more than the old factory ecu.
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