Hey guys, I'm still struggling with this setup.
680's, 190 lph pump, 3" maf, and Maft 2.xx. 16G Other mods in my list if needed.

Basically my battle goes like this. I'm running 17PSI or so, and I've gotten things nailed down pretty well I think. I'm knocking in the 1000Hz+ range(WOT knob) at anything over 5000 RPM, 2nd gear and up. So, I richen the WOT knob up one click, and then the car rich bogs, with little to no knock. I lean it out one click, and I'm knocking again.

So, I'm not sure where to go from here. My timing is at 5 degrees, so I don't feel that should be a problem at all.

The only other 2 things I can think of is a) a boost/vaccum leak or b) FUEL
a) I've tested a couple of times and found nothing for leaks, seems ok to me, so lets move on.
b) I've a couple of theories...
-unmatched injectors. They're brand new, but maybe I should get them flow tested?
-not enough fuel pressure. I have the 190, rewired, so I wouldn't think that this is a problem? I've heard stories that the #1 cylinder recieves the least amount of fuel, maybe it's receiving less fuel, and knocking. Is an AFPR and gauge in the works or what?
-not enough fuel pressure. I read somewhere that the stock lines aren't sufficient to support even 190lph, and to run SS lines all the way.

Any ideas, anyone? Would the DSMlink help me out here or what? Does it have finer adjustments than my MAFT? Thanks guys.

If you have the latest version (which I believe you do) then you can leave it where you get a little knock then switch to WOT fine adjustment mode. This will give you 2% adjustments instead of the 5%. Had the same problem as you and as soon as I switched to fine adjustment I was able to bring the knock down to less the 4 (still tuning). Goodluck.

How about telling us what your MAFT settings are, then telling us how much boost you are running. For the most part, it's damn near impossible to get a car to run correctly at part throttle, when you have a stock ECU and MAFT. When you set the MAFT for 680's, you put the ECU into such a high timing map (due to chopping the airflow signal down so much), that the car will basically bog and buck at part throttle, until you get moving. Your other option is to set the car to like 600cc base setting, then deal with the car running pig rich.

the funny thing is that I am having the exact same problem. I need a bit more of fuel but can't add a click (5%) because it would bog...I've tried every other part of the car that doesn't said ''horsepower in a box'' and i still have the problem...I have tried the finetuning mode and can't get rid of the bogging. I don't knocw you but in my car it would bog mostly on 1st gear, sometimes in 2nd, just a few times have done that on third gear. The strange part is that even if I add fuel by the fpr, raising the pressure, psi by psi, it would do the same. I managed to do low 12's on race gas, but on pump gas I can't use more than 16psi...

i had a similar problem awhile back, it would knock, and as soon as i richened it, it would bog like all hell...my problem ended up being shitty gas...as soon as i put in race gas it hauled balls...so i suggest trying some of that...also try starting from the beginning...set your shit to 0 and go out and drive 65 mph to set your base, it should cycle around 100, once that is set you can do the rest...dont go off the paper, thats just estimates for injector size and is nothing close to what mine is...definatly do a boost leak test and try some different gas

...sounds like bad news to me, I thought it was a bad MAF or just the box, I was going to try another one from a friend but seems that it wont be solved. I have the exact same problem as you Devilsperm, and racegas didn't solved it, just avoided it, let me explain... since I have a Keydiver eprom for my 750's I have to set for 450cc inyectors. Idles is at +15, mid 0 and wot 0...at that setting, with pump gas, it is ideal for about 17 psi, with little knock...If I try to raise the psi, it would knock, so I set wot at +5 and there starts the bogging thing. With race gas, since you have to tune leaner, I had to put it in -15%...Problem "solved" . Now I have a couple of more psi, and a bit more timing with race gas and my wot knob is at 0 but with 25psi and race gas, I did 12.2 like that, but I really cant add more fuel if i want to raise boost because It would bog even on race gas at +5%...and that is pissing me...I was thinking...and "probably" the problem is at the hz that a stock or 2g MAS should overrun...when the stock maf overruns, you are just tunning by rpm (when using 1g or 2g mas +safc). And since the MAFT is meant to emulate a 1g or 2g mas...probably there's something up there...at high hz...I'm just assuming but if somebody have a better idea, It would be good to hear it

I had this problem on my 2G. If I gave it enough fuel to elliminate knock at 16-17psi, it would bog down and buck and stutter. If I took that fuel away, butt loads of knock above ~5500rpm. Only thing I could do was turn down the boost. My weak link turned out to be the stock intercooler. Right after a FMIC install, I could boost 18psi on the same tune with no knock. Then actually remove 10-15% fuel and still get no knock. All that head ache and i wasn't even anything I could change with a/f settings.

seems that you also have the same problem, but I already have an fmic...hope someone finds the cure

HAD the same problem Hope you guys find the problem

Easiest way to fix those problems is to quit running such huge injectors. The stock ECU does NOT like anything bigger than 600cc injectors coupled with the MAFT. You are taking so much of the airflow signal, you are sending the timing maps thru the roof. Put your 450's in and take a drive. See how much timing you initially get. Then put in your 660/750's and set the MAFT for those. IF you can get the car to move, look at your timing. That's the problem. That is why the car bucks so bad when you first take off. Way too much timing advance initially.

Didn't even think of that. ^He's got a good point though, I never had that problem because of a custom eprom chip.

Good point, but that´s why I have a Keydiver Eprom, and the timing is just fine, just as stock.

anyone with the same problem but with 1.3 maft?

Yea I had the same problem and I did everything. You wanna know what fixed the problem for me? I bought a 2g socketed ecu and stuck a dsmlink in it and made a wireing harness!!

My car runs heavenly now, and I havent done one bit of tuning.

haha, but you still using the maft? I'm going to change my inyectors for 880's, put the cams, and vpc and see if nothing blows up, and next step, standalone (drooooooooool)

friend of mine told me to try a 3.5" maf, probably mine is reaching it's limits since I am reaching 400AWHP...what do you think?

talon_boy69 said:

friend of mine told me to try a 3.5" maf, probably mine is reaching it's limits since I am reaching 400AWHP...what do you think?

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Only if youa re runnign a stock 1G MAF you are getting close to the limits. 3" GM MAF will handle close to 600whp. Leave your 3" in there.

Here's another question. All you guys having problems with these MAFT's. What size injectors are you running? What kind of boost are you all running? What turbo? And how much power are you making? I think 90% of the people out there are just running way too much injector for the amt. of power they are making.

I was at 95% injector duty cycle on pump gas with my 660's, 45psi base, and 50 trim. However, on race gas, it was in the mid 80's. If you guys aren't running lo 11's or faster, you don't need anything bigger than 660's. You can only do so much with huge injectors and a hack (AFC/MAFT), then the ECU says "#### you" and you run into these problems.

I am running 750's righ now 92% duty cycle on race fuel (116) at 25psi...have run 12.2@116 with an scm 61...I know...those are 14b times :laugh: ... but well...I am just hitting the problem.

just reading throught this thread and I cant figure out why you guys are having problems. I just installed my 3" maft setup(V2.01) a couple weeks ago and its been great to me. Base mods are:

680cc injectors
Denso 255
otherwise stock fuel system
MAFt and AFC
GT30-10
FMIC
HKS 264s

I havent even played with the maft settings too much.....so far Ive just set the injector compensation on it( 630cc from what I remember). I just logged the car at idle then adjusted the injector compensation until my fuel trims were correct( or close). I then took the car out for a test run and adjusted via AFC for my low and mid trims. Once I had them in spec I went for a WOT tune. My AFC settings for the low and mid trims are all within 5%. Though on my WOT tune I had to take -19% off the upper rpms. Running 20psi on pump(94oct) and no knock at all. My timing advance isnt a problem..

All in all..........my car idles perfect, part throttle is soooooooo smooth and WOT is fun as hell.

I think thats the problem.If you don't have a good fmic then you can't run the higher boost period although I just ordered a water/alco injection and will see how that works for me even with stock sidemount but that is just temporarily until get a fmic.Combined water/alco injection and the fmic should be great even on our 91 octane crap.

The maft can be touchy like you guys said one click up too rich and stutters.one click down and knock.But thats on my stock sidemount too.Lower boost until you get a better fmic.Or run race fuel or mix your own.

Girvin said:

All in all..........my car idles perfect, part throttle is soooooooo smooth and WOT is fun as hell.

Click to expand...

I'll second that. I really get sick of hearing people blame everything on the MAFT. I don't even have an SAFC and mine runs damn near perfect (I do have a custom EPROM to elemiate that excessive timing problem w/ big injectors). Not to say you guys are making excuses or anything, I just hope you all don't give up on it.

well...in my case I can't blame my fmic because the problem disappears with 2g mas or vpc...also, my fmic isn't suposted to be that bad, I think, but I plan to upgrade it for a bigger side to side unit.

this is my fmic
http://www.turbochargers.com/Accessories/FMIC.htm

also, i had same problem with a 60 trim i had for 3 months, upgraded to an scm61 because i got it cheap

I have had my share of nightmares with MAFT as well. Once interesing find that I made, is that my A/F ratios change drastically from day to night. The temp. difference from day to night varies as much as 40' here, and GM MAFT doesn't have any kind of temp. compensation, since it's preset. This might actually affect car's response quite a bit. I can run 22psi with no knock during day time, but come night, I'm knocking badly.. Obviously re-tuning it every day and night is not most pleasant.

Has anyone else experienced and temp-related anomalies?