Help with Fuel Cut Please.

[WhiteTsiAwd]

Well I have been helping a friend(DSM_23) tune his car since he just got his 190 in, and we're having some problems. His Mods are:
Dejon Tool UICP w/ aftermarket TB Elbow, all free mods done, k&n filter, Dejon Tool 3'' Intake Pipe, Hallman Manuel Boost Controller at 15 psi, Autometer dual guage pod with Autometer Boost, Air/Fuel, Water, Volt, Oil Press. Guages, 2.5" Testpipe, 3'' Thermal R&D Catback Exhaust, 2.5'' Downpipe, Accel 8.5 Race Wires, Walbro 190 w/ Re-Wire, ACT 2600 (not installed), Apexi Super AFC 2, Symborski Shift Kit

It seems as if he isnt getting enough fuel but i KNOW thats not the problem b/c he has stock injectors, if that has anything to do with it.

Ok, well to start his Low fuel trim is 125%. His Mid fuel trim is 98% and his High fuel trim is at 89%. Throttle points set at 35 and 85(were at 30 and 80 but we changed them last night to see what would happen). His Lo-throttle is set to 13-15% up until 3k. His Hi-throttle is set to 22%-28%!!! He is getting absolutly no knock until 5k then he gets only 1-2 counts. Timing is anywhere from 15-22 and O2 starts out at about .89 at 3k and changes to .85v from about 4600k up to 6 where fuel cut says Hi. His boost is set at 11psi but creeps to 15-17psi.

Now some questions we have. On his Lo-throttle on the AFC, should we stop at 3k and leave 3200-7k at 0%? And on his Hi-throttle should we change 1-3k from 0% since high throttle dont come in until 85% and very rarely will you be from 1-3k when the pedal is floored? I know that he shouldnt be in that high correction but no matter what we do it does not richin up, expecialy in top end. He shouldnt be getting fuel cut, i wouldnt think considering he has everythign needed(minus injectors) to take care of it.

Another thing is that he is moving a lot of air. At WOT his AFC reads 2002hz of air. Now our thoughts are leaning towards a boost leak? You think putting the lower honeycombs back in will help anything?

What are normal for the mods he has? (450cc, afc, no lower honeycombs, 190lph w/ re-wire).

We really have no clue other then the boost leak idea which is being checked when he gets off work tonight. Any help will be greatly appreciated. If i get any more quesitons i'll add them.

Thanks,
Cody

 

[talon1979]

w/ that turbo I don't think he should be flowing those kind of hz, which means there is probably a good sized boost leak. I bet if you get rid of the boost leak you will not see fuel cut and your hz will drop quite a bit and the car will run a lot better.

 

[WhiteTsiAwd]

Ya our thoughts exactly. Just wanted to see what some other people with more experience thought about it.

Thanks,
Cody

 

[kpt4321]

Originally posted by WhiteTsiAwd
Ok, well to start his Low fuel trim is 125%. His Mid fuel trim is 98% and his High fuel trim is at 89%. Throttle points set at 35 and 85(were at 30 and 80 but we changed them last night to see what would happen). His Lo-throttle is set to 13-15% up until 3k.

I personally would run more like 25% and 65%, but that's just me.

Those trims are not right. You need to tune it so that the low trim is 100% (ish) and the hi trim is too. Since you're lean at idle, add a little bit of fuel at 1k RPM on the SAFC. Since you're rich at cruise, take a little bit of fuel out at 3k rpm.

Then, you want to use the 3k rpm setting at 4k-7k. You don't want to leave it at zero (0%).

His Hi-throttle is set to 22%-28%!!! He is getting absolutly no knock until 5k then he gets only 1-2 counts. Timing is anywhere from 15-22 and O2 starts out at about .89 at 3k and changes to .85v from about 4600k up to 6 where fuel cut says Hi. His boost is set at 11psi but creeps to 15-17psi.

What is causing you to set it that high? Does it knock if you set it any lower?

You're getting fuel cut because the correction is so high. The SAFC is reading 2000Hz, plus it's adding 20+% onto that, and then sending it to the ECU. The ECU is probably seeing over 2500 Hz! That's certainly going to make fuel cut pretty likely.

He definately needs bigger injectors. I'd say 550's are a must, and something even bigger may be a good idea. 450's are one of the problems here, and there simply isn't a way to tune around them.

Now some questions we have. On his Lo-throttle on the AFC, should we stop at 3k and leave 3200-7k at 0%? And on his Hi-throttle should we change 1-3k from 0% since high throttle dont come in until 85% and very rarely will you be from 1-3k when the pedal is floored? I know that he shouldnt be in that high correction but no matter what we do it does not richin up, expecialy in top end. He shouldnt be getting fuel cut, i wouldnt think considering he has everythign needed(minus injectors) to take care of it.

From 4k to 7k on the lo throttle map, use whatever works for 3k rpm.

From 1k to 3k on the hi throttle map, use the 3k rpm setting, or whatever keeps the car from knocking.

What do you mean that the car does not richen up when you use the correction?

Who says he should not be getting fuel cut? I say he sure as hell should be.

Boost leak test is a good idea, but like I said, you're not going to be able to tune around 450's at this point.

 

[WhiteTsiAwd]

I personally would run more like 25% and 65%, but that's just me.

Will give them a try. It makes a little bit more sense i guess then 85%.

Those trims are not right. You need to tune it so that the low trim is 100% (ish) and the hi trim is too. Since you're lean at idle, add a little bit of fuel at 1k RPM on the SAFC. Since you're rich at cruise, take a little bit of fuel out at 3k rpm.

Ya, i knew they needed to be closer to 100% but for some reason they were lower, so that will be changed.

Then, you want to use the 3k rpm setting at 4k-7k. You don't want to leave it at zero (0%).

Thanks, was wondering about that.

What is causing you to set it that high? Does it knock if you set it any lower?

We set it that high b/c kept on hitting fuel cut, and it doesnt knock at all until about 5k and its only 1-2 counts. But didnt even think that adding fuel would not cure the fuel cut problem, only make it worse possibly.

You're getting fuel cut because the correction is so high. The SAFC is reading 2000Hz, plus it's adding 20+% onto that, and then sending it to the ECU. The ECU is probably seeing over 2500 Hz! That's certainly going to make fuel cut pretty likely.

That makes a lot of sense. Didnt even cross my mind.

He definately needs bigger injectors. I'd say 550's are a must, and something even bigger may be a good idea. 450's are one of the problems here, and there simply isn't a way to tune around them.

My thoughts exactly but he seems to think hes fine..

Thanks for the response, i'll let you know how it goes.

cody

 

[WhiteTsiAwd]

Alright, for an update, no more fuel cut. Before it was just completly cutting out but now it will sputter 1 or 2 times about 6400 in 3rd and 4th.

Fuel trims are rather decent, Low at 113%, Mid at 104% and High at 103%ish.

All correction is in the Neg- until 5600-7 then it gets as high as +18%.

No knock until 6000rpm, and even then its only 2 counts with timing at 15-16. Only 2-3 counts of knock between 5600-7 in 3rd. But as soon as he shifts to 4th then it knocks 20+ all the way through with only 3 degrees of timing or less. Could that possibly be Phantom knock?

One thing i dont get though is that does the ECU take O2v into consideration at WOT? And if it does not then should we look at O2v while tuning? Because as of right now O2's start out around .86v and go down to about .80. But as the O2's go down so does the knock. Which i find weird and if someone could explain that to me then that would be great.

Oh, and the MBC is backed all the way out now. Starts out at 10 and will creep to 15-16 in 2nd. In 3rd and 4th, at 6000+ rpm it will creep to as much as 19!!! But still no fuel cut.
Thanks for any input.

Cody

 

[kpt4321]

A couple of things:

First, the ECU ignores the O2 sensor at WOT because it is not accuarate enough to pay attention to. You can use it as a reference, but go by knock and timing more than anything else.

If the car is stumbly, it could be because of several things. Ignition, too rich, knock retard...

If the O2 sensor is dropping that badly at full throttle, then the car must be leaning out. That's probably at least partially the cause of your knock problem.

The boost creep does not help either. You do not want the screw all the way out, you want it as tight as you can get it, for the best boost response, without overboosting.

 

[WhiteTsiAwd]

Well last night him and I were messing around and he hit fuel cut in 3rd again, but probably because of it being about 10 degrees lower last night.

Also, would him getting a AFPR help out so he could higher his base fuel pressure so at higher RPM's the fuel system wouldnt have to work so hard and make fuel cut less likely?

The reason we backed the MBC all the way out is because that was the only way that we would get it not to creep so high so fast. Any other time it would creep to 19 really fast and we would get fuel cut.

 

[kpt4321]

Originally posted by WhiteTsiAwd
Also, would him getting a AFPR help out so he could higher his base fuel pressure so at higher RPM's the fuel system wouldnt have to work so hard and make fuel cut less likely?

It doesn't have anything to do with the fuel system working "less hard."

A higher base pressure means more injector flow, which allows you to use more negative correction on the SAFC and the ECU will see less airflow.

 

[WhiteTsiAwd]

A higher base pressure means more injector flow, which allows you to use more negative correction on the SAFC and the ECU will see less airflow.

So a FPR would make fuel cut farther down the road at this point then?

 

[Mike 99GSX]

Go back and read what KPT said. Airflow count is what contributes to fuel cut. If you had control of your fuel pressure, the you could theoretically turn it up. If you are running more fuel pressure, you will need to use for negative airflow compensation on the AFC to make up for it. This would help with fuel cut.

 

[WhiteTsiAwd]

Alright, thanks. I was just double checking.