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Old 12-13-2004, 08:42 PM   #1
tmarcel
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Default UTEC and Modded stock injectors - Experts wanted!

Okay, I've got a lot of exposure with UTEC and have tuned other standalones like SDS. I've come to a place where I'm stumped and need some ideas though.

I jumped on the "modded stockers" bandwagon a while back and have had fun with them. However, I can't seem to get these things to idle correctly. On one of the WRX's, when the rpms come back down - say after blipping the throttle or just pushing the clutch in while coming to a stop, it'll hesitate and stumble but won't usually die out. On the other one, the same thing happens but will usually stumble and then DIE out.

Anybody seen this? The idle is fine with both it's just the stumbling/hunting issus after pressing the clutch back in or blipping the throttle.


Vehicle mods:

Car #1 - UTEC (4.2C), Garrett GT3271, modded stockers, 3" intake with integrated MAF hosuing, and various other bolt-ons

Car #2 - UTEC(4.2C), Garrett GT3276, modded stockers, 3" intake with integrated MAF housing, and various other bolt-ons


OLF param's:

I've tried 390/720, 420/720, 470/720, etc, etc and little affects the stumbling hunting issue and/or just straight cutting off at idle.


Some things I've noticed: both car's AFRs hunt around between 13:1 and 20:1. Car #1 above doesn't hunt as bad as car #2 though. When the stumbling/die out events occur the AFR's go very rich. Car #1 will just stumble and jump back out of it where number #2 seems to go too rich and doesn't recover most of the time.

Who knows about this? Suggestions?

TIA,

Todd
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Last edited by tmarcel; 12-13-2004 at 09:12 PM.
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Old 12-13-2004, 08:52 PM   #2
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Reset the stock ECU. It will zero out the fuel trims and it will relearn for the change in weather. I dont know where you are located, but I had a similar problem with mine so I examined the fuel trims, it was adding fuel like CRAZY. I reset it and it was instantly better.
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Old 12-13-2004, 08:54 PM   #3
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Quote:
Originally Posted by cdvma
Reset the stock ECU. It will zero out the fuel trims and it will relearn for the change in weather. I dont know where you are located, but I had a similar problem with mine so I examined the fuel trims, it was adding fuel like CRAZY. I reset it and it was instantly better.

Both have been reset. Car #1 about 20 times. Car #2 has been reset once. Seems logical though but doesn't help much on these two.
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Old 12-13-2004, 09:06 PM   #4
CMJ
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Quote:
3" intake with integrated MAF
So this intake came with its own MAF sensor? What brand is the sensor?
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Old 12-13-2004, 09:11 PM   #5
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Quote:
Originally Posted by CMJ
So this intake came with its own MAF sensor? What brand is the sensor?

Oops, I should edit that. I meant MAF housing
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Old 12-13-2004, 09:40 PM   #6
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Do you have a way to check STFT and LTFT? If you can get those close to zero and you still have trouble then try and bump the idle up 150-200rpm. Just for kicks you should try the stock airbox, specifically the corrugated hose after the box.
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Old 12-13-2004, 09:51 PM   #7
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I will suggest that you use something bigger than 720. How did you come up with that value? Did you have them flow tested at operating pressure? I ask because I guessing you're talking about modded top feeds. My modified side feeds I ended up at 850. What does your 0% column in your fuel map look like? I would guess that your LTFT is out of whack.
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Old 12-13-2004, 09:54 PM   #8
tmarcel
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Quote:
Originally Posted by CMJ
Do you have a way to check STFT and LTFT? If you can get those close to zero and you still have trouble then try and bump the idle up 150-200rpm. Just for kicks you should try the stock airbox, specifically the corrugated hose after the box.
STFT and LTFT - not at this time. Probably would help so maybe this will be next on the "to get list".

As for the OE airbox, we thought this through. Our intake has four vac posts just like the stock intake tube. All reroute just like stock.

This is just odd
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Old 12-13-2004, 09:58 PM   #9
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Quote:
Originally Posted by StiDreams
I will suggest that you use something bigger than 720. How did you come up with that value? Did you have them flow tested at operating pressure? I ask because I guessing you're talking about modded top feeds. My modified side feeds I ended up at 850. What does your 0% column in your fuel map look like? I would guess that your LTFT is out of whack.

It's because we're using a 3" MAF housing primarily. Taking it to 720 got them close to the overall map to 11:1 in the upper rpms range. It made it easy to tune the rest of the map.

0% has 4 from 0rpms to 2000rpms.
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Old 12-13-2004, 10:06 PM   #10
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Do they both have the same intake? The only time I have seen that same problem is with an intake that was, uh, problematic to say the least. Double check that it is not the MAF setup that is causing the problem.

In the worst case of this that I have seen the car ran fine with STi pinks, but when the customer switched to the modded stockers the stumble began. The logical starting point was the injectors, but the solution was found in the MAF housing. I have no idea if this is your problem here or not, but try switching the intakes, or putting on a different one.
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Old 12-13-2004, 10:25 PM   #11
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Quote:
Originally Posted by pegdrgr
Do they both have the same intake? The only time I have seen that same problem is with an intake that was, uh, problematic to say the least. Double check that it is not the MAF setup that is causing the problem.

In the worst case of this that I have seen the car ran fine with STi pinks, but when the customer switched to the modded stockers the stumble began. The logical starting point was the injectors, but the solution was found in the MAF housing. I have no idea if this is your problem here or not, but try switching the intakes, or putting on a different one.
Interesting. The only difference between the two is the type of metal and the angle. One is straight made from SS and the other is made from aluminum. The SS one is 3" and completely straight. The other is aluminum, 3" and has a 45 deg bend. The MAF housing designs are identical on both except the fact that one is aluminum where the other is SS. They both seal extrely well with the o-ring on the MAF sensor.
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Old 12-13-2004, 10:34 PM   #12
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What does your LTFT look like?
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Old 12-13-2004, 11:12 PM   #13
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Originally Posted by StiDreams
What does your LTFT look like?

Like I said above above, I don't have a way of checking it but may get it this week.
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Old 12-14-2004, 12:04 AM   #14
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The injectors don't flow like 750/850s at idle. Or even cruise. Closer to 550s. Not sure if its a pulse width problem, or if its the spray pattern (I think spray pattern), but you gotta give them more juice at lower RPMs.

If its hunting, its lean - so the car starts adding fuel, and ends up overcompensating... you go mad rich, and the car pukes. With a 3" maf, thats going to offset the larger injectors almost perfectly at idle. Try just turning on the car with the stock numbers, see what happens, I think you'll be surprised.
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Old 12-14-2004, 12:17 AM   #15
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I have seen this, you need 0% fuel modification. It's what DarthChicken says, the modders flow a little strange.

You will have to monitor the LT/ST fuel trims to work out exactly what is going on.

It's a fine line. I usually live with the idle issues while I'm doing the WOT tuning based on the UTEC injector size. I then adjust the UTEC stock size and 0% fuel to get it to idle and rev up correctly. Don't touch the UTEC injector size when doing this.
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Old 12-14-2004, 09:52 AM   #16
tmarcel
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Quote:
Originally Posted by DarthChicken
The injectors don't flow like 750/850s at idle. Or even cruise. Closer to 550s. Not sure if its a pulse width problem, or if its the spray pattern (I think spray pattern), but you gotta give them more juice at lower RPMs.

If its hunting, its lean - so the car starts adding fuel, and ends up overcompensating... you go mad rich, and the car pukes. With a 3" maf, thats going to offset the larger injectors almost perfectly at idle. Try just turning on the car with the stock numbers, see what happens, I think you'll be surprised.

I think this may be it! Can't wait to give this a shot today. I'll go 420/550 to start. I can imagine that the upper 60-100 columns will need a lot of fuel augmentation.

I'll let you guys know.
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Old 12-14-2004, 04:55 PM   #17
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DarthChicken made my day! I loaded car #2 with 420/550, reset the ECU and let it warm up. One up to temp, I revved and blipped the throttle, little hestitation and the motor did not come close to dying this time. The AFR doesn't seem to load up nearly as bad now when returning to idle. Whe i get back to the shop tonight, I try lowering the the values to 420/530 or so and see if that helps smooth it out a little more.
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Old 12-14-2004, 05:00 PM   #18
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I kinda had an advantage here, I use stock modified injectors in my car, with a Perrin BigMAF to pass DEQ when the time comes
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Old 12-14-2004, 06:02 PM   #19
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Quote:
Originally Posted by tmarcel
DarthChicken made my day! I loaded car #2 with 420/550, reset the ECU and let it warm up. One up to temp, I revved and blipped the throttle, little hestitation and the motor did not come close to dying this time. The AFR doesn't seem to load up nearly as bad now when returning to idle. Whe i get back to the shop tonight, I try lowering the the values to 420/530 or so and see if that helps smooth it out a little more.
What you have found is that you need about 110cc spacing between the two settings. Instead of running 420/530 try 610/720, that way you won't have to retune the open loop map.
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Old 12-14-2004, 09:42 PM   #20
tmarcel
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Quote:
Originally Posted by CMJ
What you have found is that you need about 110cc spacing between the two settings. Instead of running 420/530 try 610/720, that way you won't have to retune the open loop map.

Good point. I'll give that a try as well and see what's the outcome - much appreciated guys. Got to hate it sometimes when things are too black and white
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Old 12-14-2004, 09:51 PM   #21
tmarcel
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Quote:
Originally Posted by DarthChicken
I kinda had an advantage here, I use stock modified injectors in my car, with a Perrin BigMAF to pass DEQ when the time comes
Cool man. I don't care either way as it works. Couple of questions:

1.) What's your MAF housing size?

2.) What's your UTEC injector sizing both xxx/xxx?

3.) How much add/delete fuel do you have in your map?
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Old 12-14-2004, 10:46 PM   #22
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My example won't work for you - I can only bring you this far. I don't have a utec anymore, and when I did I used it over a JDM ECU that was reflashed. For emissions, I swapped in my US ECU, got the utec close on cruise, ran it through emissions and yanked it back out.

Sorry
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Old 12-14-2004, 10:59 PM   #23
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Originally Posted by DarthChicken
My example won't work for you - I can only bring you this far. I don't have a utec anymore, and when I did I used it over a JDM ECU that was reflashed. For emissions, I swapped in my US ECU, got the utec close on cruise, ran it through emissions and yanked it back out.

Sorry

Argh, just looked at your sig. You've got a Hydra. Thanks anyway man
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Old 12-15-2004, 02:53 AM   #24
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I am going to be putting modded stockers in as well, I have a second set just waiting to go in but I want to get a pump first...anyway when you first put them in and reset the ECU should you initially run them at the default 420/420 numbers and check idle? Or what should you initially set them to to make it easiest to tune them? What if you plugged them in as 720/720, what would that do?
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Old 12-15-2004, 10:17 AM   #25
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420/720 provided that you are running the stock MAF. Get LTFT right in cruise and idle and you will get less hesitation. Work your way up from there. I think that you're going to end up with a bigger number than 720 even with the top feeds.
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