Fuel Cut 50-trim 660cc 3" GM MAF-T 255 Walbro

[le0net]

Been searching and searching and find a lot regarding fuel cut, but not anyone with the setup i have, usually people have a setup with something stock and gets fuel cut.

My car runs just fine when not boosting more than 12-13psi, but where is the fun with that

When i boost 18-20psi i get fuel cut at 5000rpm on 3rd gear, haven't tested bigger gears after that, knocks bad and o2 drops down.

My setup on my 1990 Eagle Talon TSI
Timing 5 BDC
FPR 38 PSI (vacuum disconnected)
Revired Walbro 255

50-Trim Turbo, internal WG, FMIC
HKS SSQV Dump
3" MAF Blowthrough mode MAF-T set to compensate for 660cc DENSO injectors, all other ZEROED
Stock Intake Manifold.
RRE Downpipe 2,5" - > 3" and 3" downpipe back, no CAT.
EVOIII exhaust manifold, EVOIII O2 housing.
SAFC II and logging with Pocket logger.
SAFC Settings around +40% to get no knock and a good o2 value (0.9)

Since fuel cut comes from the ECU seeing too much air, and it thinks the stock pump and injectors cant handle it, it shuts down. I have found that running a GM MAF shouldnt have this kind of problems, so how should i proceed to see whats going on. Tested to see leaks after the MAF, since that is the only place a leak could have someting to do with it, but nothing. Should i log something specific?

Could i try to lower the FRP settings so the ECU wont find that much pressure, or would a timing retard help, read that -90 DSM has a more aggressive timing map.

Any suggestions?

Leif

 

[JayRolla]

Hmm that is a little wierd, but I dont think you should be adding so much fuel at wot with your setup. Do you have a wbo2??

 

[mavisky]

You shouldn't be adding fuel, maybe just a hair if the maf-t isn't spot on with it's correction. I'd get a wideband on that thing to figure out what's going on.

 

[le0net]

The MAF-T is setup for a 3" GM MAS and 660cc Denso. Í have been looking at knock levels, the o2 that is built in and the sparks. Cant get rid of knock below the values i have now, around +40%, o2 shows 0.9-0.94 at WOT and the sparks are a bit whitish, not tan brown as they should. If i remove fuel the knock levels raises at once.

 

[matthewdesigns]

Boost leak test before anything else.

Is the SAFC correction necessary for you to run knock-free at 12-13psi? Because that's a huge positive correction on the SAFC. I'm surprised that you aren't seeing fuel cut way before 5000rpm. The 40% correction you use is roughly the difference in size between stock 450cc injectors, and the 660's you say you are using. So, first I'd triple check that your MAF-T is set for 660's, and not 450's. Because, if it's set for 450's, then you'd need to be dialing in that 40% to make up the difference. Second, are you sure they are 660's? Did you buy them new, or used? If used, perhaps they aren't as big as you think they are.

How much airflow are you seeing? Perhaps you are overrunning the injectors...they seem to be borderline size for that turbo, even if they are 660's. Those are more like an ideal injector for a big 16g.

Since you have 2 ways to correct for fuel (MAF-T and SAFC), try to get as close as possible to a good tune using only one of them, then fine tune with the other. You at least eliminate one variable doing that. Try zeroing out the SAFC, and adjusting the MAF-T until you're getting no knock at your current boost level of 12-13psi. I know that may seem counterintuitive, but if your injectors aren't what you think they are size-wise, then doing that may put you in the right track. That, plus eliminating any boost leaks, ought to give you a good baseline.

 

[mavisky]

He should be removing 40% of fuel to go from 450cc's to 660cc's, not making the correction on the maft and then adding that much.

I had the maft set for 660's on my FIC 650's and the car ran the times listed to the left on pump gas. There was no other correction being made. In essence your s-afc is almost cancelling out the adjustment you're making with the maft.

 

[le0net]

Hi Again...

Bought the denso injectors used, looks correct for me, but how can i be sure..
Realized sparks are really old, should i go with NGK BPR8ES with 0.028 gap? Or choose stock....

Well, did a couple of runs yesterday, after some corrections. Double checked my Base Fuel Pressure, and i had it wrong, it was 43psi with the vacuum off, took it down to 38psi.

After that raised boost to 18psi, please look at the logs below, no creep, no fuel cut..
MAF-T zeroed exept for Base Settings for 3" MAF and 660cc (Switches 1-4=OFF, AUX=1, BASE=8) SAFCII around +40-45% up to 5000, 50% the rest.

Looks like Injector D/C is maxed out at higher RPM, seems i need to increase the fuel pressure to get them under 90%.
o2 goes down too much and timing is too high, planning on retarding base timing.

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Pocket Logger

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Regarding the Injectors, they are Blue, see the picture, and Blue Densos should be 660cc.
Some people say Denso 660cc flow more than 660cc, up to 720cc. In that case i would need to change the injector sizing in MAF-T, could that help me to not max out the SAFCII?

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[le0net]

He should be removing 40% of fuel to go from 450cc's to 660cc's, not making the correction on the maft and then adding that much.

I had the maft set for 660's on my FIC 650's and the car ran the times listed to the left on pump gas. There was no other correction being made. In essence your s-afc is almost cancelling out the adjustment you're making with the maft.

Do you mean i shouldn't set the Base Settings to compensate for the 660cc injectors, Just leave everything to Zero??

How come everyone tells me to put MAF-T to compensate for Injectors but leave everything else to Zero?!

Leif

 

[JayRolla]

No your are fine, use the maf-t to compensate for the injectors, and use the safc for fine tuning only. I would still invest in a wbo2 if I was you to be safe.

 

[matthewdesigns]

He should be removing 40% of fuel to go from 450cc's to 660cc's, not making the correction on the maft and then adding that much.

Thanks, that's what I was trying to get across.

How come everyone tells me to put MAF-T to compensate for Injectors but leave everything else to Zero?! Leif

Answer -

In essence your s-afc is almost cancelling out the adjustment you're making with the maft.

Your two devices are fighting each other for control of the injectors/airflow. Use the MAF-T to adjust for the injectors, and leave the SAFC zeroed out. If you figure out how much your injectors actually flow, then your MAF-T adjustments will take care of them on a grand scale. Then you use the SAFC for minor adjustments (+/- a few percentage points).

 

[le0net]

So basically what you are saying is that i should Zero the SAFC-II, tune the car with only the MAF-T until i get a drivable mapping and after that fine tune with SAFC-II?

I started with SAFC zeroed but got extremly high knock at boost, but i will try that this weekend.

L

 

[le0net]

He should be removing 40% of fuel to go from 450cc's to 660cc's, not making the correction on the maft and then adding that much.

Does this apply even though i dont have the stock MAF, the 3" GM should flow much better?

 

[mavisky]

That means nothing.

When you set your maft to correct for the 660's it is subtracting about 40% of the airflow signal to your ecu, then you have your s-afc connecte and you're adding 40-50% of the airflow signal back in.

If you can't get a decent low boost pull with just the maft set for the 660's then something else is going on that you need to get ahold of quickly before it causes bigger problems.

 

[JayRolla]

If I remember from my buddys maft setup you can set it to a certain size injector and dont have to do any tuning. It auto adjusts for the size of injector you set it at. This should put your car near the same afr it was at with the 450's.

Now when you start to add boost you will start to add fuel but should only be a little to keep a good afr. You need a wbo2, it helps so much with tuning and takes all the guessing away.

 

[le0net]

Made a boost leak test, pressured around 8bar and heard a very small hissiing sound, so there are no leaks to talk about.

BUT, i had the MAF-T setup wrong, or should i say, i thought i had the 2.0 Version but had the 1.3, so the settings i had was wrong.

Changed the settings to apply for 1.3 version and 650cc (no 660cc available) and seems much better.
Dont need to add as much fuel as before, will be making some logs with 22psi.

Leif

 

[matthewdesigns]

Congrats. Now just use that SAFC to make small adjustments and you'll be on the right track. If you can't get your hands on a wideband, then just make adjustments until you aren't seeing knock anymore.

Good luck!

 

[nfernotalon]

I know my set up is nothing like yours but I added the slightest bit of fuel with my SAFC and it sounded like a stutter box at low rpms I turned it all down to zero and runs perfect idk *shrugs*

 

[le0net]

I will try to get my hands on DSMlink and bigger injectors, but until that i want to run these safe, i will slightly rise the fuel pressure to get the injector d/c down, is the safe value 90, or can i go above that?

I will tune for 0 knock, and will meet a friend later with a wb02 to check the values.

L

 

[matthewdesigns]

i will slightly rise the fuel pressure to get the injector d/c down, is the safe value 90, or can i go above that?L

The number I've generally read as a safe upper limit is 85%, so 90% is not that far off. The concern is that you'll go lean if you keep them too close to 100% all the time. Keep in mind that you'll be a little rich at idle/low rpms by increasing the fuel pressure.

I can't log IDC's on my 2g, but I'm pretty sure mine operate above 85% pretty regularly. My fuel trims are always high, and I throw a fuel trim cel every once in a while. So just be mindful of what's going on. I tune for no knock as a general rule, and feel pretty good about my tune, even with the (supposedly) high IDC's. It may not be optimal, but it's been safe so far.

 

[1gDSM4g63]

Go the KeyDiver and have your ECU chipped. That'll eliminate the fuel cut and depending on which stage you get there more mods.

And as for having 660cc that's too high for a SAFC. I think that max is 550cc and beyond you'll need to eliminate fuel cut.

 

[matthewdesigns]

He's using a MAF traslator primarily, and the afc for fine tuning. So he's fine with respect to the injector compensation.

 

[oldman420]

Sorry for stealing the thread, but I was wondering if anyone one has tuned a big 16g with all fuel upgrades(afpr,255lph,PTE680'S), with only a SAFC with no maft?