MAFT bucking letting off throttle

[Baron4406]

YES I did a search, spent almost a week checking here and Full Throttle. I just installed a 3" GM MAF and the infamous MAFT version 2.01. I'm an LT1 guy and just play with DSM's as daily drivers so I had a good MAF laying around. I have a '91 AWD Talon that I rebuilt the motor on last year (its stock and tight) and the car is mostly stock. Only mods are full 2.5" exhaust and boost controller set to 14 psi. I set up the MAF as a draw thru and it went as easy as pie. It actually runs really well, have the Base knob set to 450 injectors ( 2 if I remember right) and the rest zero'ed out. Like I said the car seems snappier now, and even accelerates smoother. It does have one little bug tho, mainly is I get on it good then let off the gas the car bucks hard. I did a few third gear pull with MMCD and everything looks good. Getting zero knock and timing is in the 30's (kinda high actually). I also have an A/F meter and the car seems to be running richer with the GM MAF in place. The MAF is good I put it on my Camaro last year and drove it around for a day and it was fine ( Funny this 3" MAF didn't feel any differant than the 3.5" that is stock on FBodies) Any thoughts?? I may fun my logs a bit longer, to try and see what is happening when the RPM's drop. I remember I was looking for something else and ran across a post somewhere that told of this problem with hacked 1G MAF's.........of course this was before I installed my MAFT and now can't find what causes this.

 

[92awddsm]

Well, when I had a 2gmas, I had the same problem. I even had compensation for it on my eprom. Now that I switced to gm maf and translator 2.01, all the bucking is gone. I do have mine set up as blow thru, so Im not sure whats causing it. I also have a friend with it setup in draw thru and he is also having problems. I will see if he figured it out and if so, I will let you know.

 

[danl]

I had that problem before my EPROM ecu upgrade. I had to run the car extremly rich (high 9:1 air/fuel ratio) to keep knock tolerable. When letting off the gas quicly the car would buck hard. When I put race gas in with no other changes than leaning it out the bucking went away. You need to lean out the WOT knob. If you getting 30 degrees of timing AND your still running rich that tells me that you aren't moving much air at all. Lean it out and try to get 5 counts of knock. Then richen it up a little from their if you choose. That should alleviate the bucking, its very annoying especially when autocrossing.

 

[ucancallmedebo]

my car does that sometime with a 2 g mass. The problem could be if you are recirculating your bov the air going back into the intake disturbs the air going though the mass. This dosent happen with blow through. I think this is why from the factory the bov tube is exstended and angled down to the turbo to lessen the turbulance from the BOV venting on the mass.

 

[Baron4406]

Good ideas guys, I'm gonna do some pulls after backing off the WOT knob and try to get some knock. I think I'm richer than my 02 would indicate, since my timing seems to be very high. This should be a lesson to newbies, the first thing you should get is some kind of logger PERIOD. I'm very experienced with these cars, however I'm modding this car differantly (using the GM MAF) so there is a learning curve. BTW I AM going to a blow thru setup soon. I have a Walbro 190, Supra sudemount, etc. to go on the car. However I add one componant at a time then get it running right rather than throw parts at it. I just threw this setup on to play with and to see how the MAFT worked.

 

[danl]

Just so you know, the draw through works great as well. Thats how I've had mine connected since a month after MAFT's were introduced to the DSM market.

 

[Baron4406]

Lean out my WOT??? BLASPHEMY!!! I'll just turn up the boost thank you

Anyway I'm now at 15 PSI and did some pulls, finally got some knock....most counts I saw were 8 but I richened up the mid knob and it disappeared. Everything looks great I'm not getting as much timing as I thought, at high RPM's I'm in the 21-25 range. One bizzare thing I did notice tho, I did some 2nd to 3rd pulls to see what happens when I shift and right after I shift the timing goes to like 45 degrees. It seems I'm getting mad rich for a split second and that is causing the bucking. However at 15 PSI the bucking seems to be gone anyway.

Also I hit fuel cut a couple of times, first time ever. What's funny is the logs didn't show much of a problem. Im' playing with fire tho, I still have the original fuel pump (144k miles) , so no wonder huh?? I have a Walbro 190 sitting here I'll put in when it gets warmer.

BTW I was getting injector duty cycles of 107% at 6500 RPM's............. hmmmmm those 450's are struggling to keep up even with a 14b at 15 psi.

 

[danl]

Lean out my WOT??? BLASPHEMY!!! I'll just turn up the boost thank you

Anyway I'm now at 15 PSI and did some pulls, finally got some knock....most counts I saw were 8 but I richened up the mid knob and it disappeared. Everything looks great I'm not getting as much timing as I thought, at high RPM's I'm in the 21-25 range. One bizzare thing I did notice tho, I did some 2nd to 3rd pulls to see what happens when I shift and right after I shift the timing goes to like 45 degrees. It seems I'm getting mad rich for a split second and that is causing the bucking. However at 15 PSI the bucking seems to be gone anyway.

Also I hit fuel cut a couple of times, first time ever. What's funny is the logs didn't show much of a problem. Im' playing with fire tho, I still have the original fuel pump (144k miles) , so no wonder huh?? I have a Walbro 190 sitting here I'll put in when it gets warmer.

BTW I was getting injector duty cycles of 107% at 6500 RPM's............. hmmmmm those 450's are struggling to keep up even with a 14b at 15 psi.

Turning up the boost is great and all but it won't "lean out" the mixture. If your running too rich you giving up massive power due to misfires that you can't feel and a generally "sluggish" burn that can tend to cause hot pockets in the cylinder causing preignition. I'm all about big boost, I have a boost graph when I was on the dyno on 91 octane boost running 26psi, but just trust me here.

I'd suggest leaning it out, should get tinny sounding and rip harder up high. The timing jumps high between shifts because airflow is reduced, this is normal.

Your not playing with fire if your not knocking. I ran 105mph traps full weight on my stock pump and pump gas. Add your 190lph and lean it out. A 14b on pump gas really is only a 15psi turbo. Run 15psi and lean it out till you get 5-10 counts of knock, this will be fastest. I ran my fastest times on the 14b with 13psi boost actually.

Add some colder plugs and lean it out, you'll see.........

 

[Baron4406]

You are right on, that is great advice. I actually did that. I leaned out my WOT knob until I was getting like 8 counts of knock. The car pulled REALLY hard- but I don't want any knock at all so I richened back up.

Had to put this on hold, the temps here dropped way low lately. Yesterday I found my car was now making 17lbs of boost, and getting massive fuel cut! I left my logger at home so I babied it to work. I see now why guys get electronic boost controllers, it would have been nice to just reach down and back the boost off.

 

[danl]

The leaner you can run the further you can push fuel cut away. 8 counts of knock is nothing, I've logged 100% bone stock healthy DSM's and they will see 8 counts of knock. My car would see 20 counts easilly when it was 100% stock on sunoco 94. For daily driving I like to keep it under 10 counts, you have to make it work a little in my opinion. Check for boost leaks while your at it, you DO have some wether you know it or not, trust me, people always have boost leaks.

Just to reiterate you really can't hurt a healthy 4g63 with only 10 or 20 counts of knock at near stock power levels. The only reason I'd richen up (or take timing out of) a car that hit 10 counts of knock is if the knock kept creeping every gear and didn't stop untill you left off the gas.

That brings up another point, you may want to run a leaner setting and take some base ignition timing out to get rid of the knock. Things usually work MUCH better when you run leaner and reduce the ignition timing. This is due to the general characteristics of a motor and more importantly the abilities of the stock and aging igniting system. Don't get caught up with the "ignition timing bandwagon". More IS NOT better. More ignition timing tells me that the burn is not very efficient. If you could get on a wideband you would see how deathly rich dsm's run and why they need to be leaned out quite a bit and why I'm making such a big deal about it.

 

[Baron4406]

The power levels on my car from 0 counts of knock to 8 counts of knock is very noticable. I was under the impression that ANY knock was bad. If anything playing with this MAFT and datalogger let me know how USELESS reading the O2 in the car is. No matter what....if I'm rich or lean it reads a happy .91v to .93 v. Today we had a major heat wave and it got to 35 deg, the fuel cut and 17 psi were gone. Might even take this car to the track and give my LT1 Trans-Am a break, its really the only place i can make full runs (and logs) and see what works.

 

[Naptaker]

My galant bucks during acceleration up to 4k rpms, then is smooth in boost. I've got the mid and wot leaned all the way, and its still running rich. I have a 255 pump with stock injectors. I also have an 18g and fmic. any idea's? thanks

 

[danl]

The power levels on my car from 0 counts of knock to 8 counts of knock is very noticable. I was under the impression that ANY knock was bad. If anything playing with this MAFT and datalogger let me know how USELESS reading the O2 in the car is. No matter what....if I'm rich or lean it reads a happy .91v to .93 v. Today we had a major heat wave and it got to 35 deg, the fuel cut and 17 psi were gone. Might even take this car to the track and give my LT1 Trans-Am a break, its really the only place i can make full runs (and logs) and see what works.

This is a generalized for YOUR setup but 8 counts of knock is the best comprimise for you. Your nearly stock with a stock ecu. You can give up a little timing by letting it knock a little. Also 8 counts of knock is minute compared to what I've put my engine through. Over 300whp, 30 counts of knock. stock headgasket and headbolts and it doesen't even give a flying f***.

Its dissapointing when I look through posts and see people using the stock 02 sensor as a tuning criteria. I run 0.76 volts on my O2 and that corresponds to 10.8:1 on a wideband. The O2 is absoutley useless any side of stoich.

Take care of the maintenance of your DSM before you take it to the track or beat on it in general. A lot of people pick up somebodys daily driver after 15 years. They add a MBC, filter, and exhaust and go to the track and leave with broken parts that have had 15 years and 100K+ thousand miles worth of daily driver wear on them. F-bodies in general are typically maintained better, the owners are more knowledgable. DSM's are maintained like a honda civic in general and they just fall apart because they are high performance turbo cars that need TLC.

 

[danl]

My galant bucks during acceleration up to 4k rpms, then is smooth in boost. I've got the mid and wot leaned all the way, and its still running rich. I have a 255 pump with stock injectors. I also have an 18g and fmic. any idea's? thanks

PM me, i'll need your setup.