After a long stay in the garage and some mechanical (and electrical) difficulties I got the car back out to use for awhile. Havnt done any tuning in a few months so I thought that now would be a good time to check things out sicne there wouldnt be any problems to mask the tuning issues. The P/T stuff looked ok. BLMs looked to be averaging around 128 or so. Did a WOT run, errr, well as close to one as my slipping trans would allow. Found some real glaring problems. On tip in, the engine jsut felt like it was waiting for something and in the middle it had that same dead feeling. I had hints of this before but when got home and in teh datalogs the problems where immediatly aparent. On tip in I was wayy lean! So much so that the O2 went down to around .1 volt and I got a few knock counts, which is probably what caused that hesitation that I felt. Again I had problems when I had to lift all the way off the gas to let the trans complete the shift and stop slipping and got back on it again. Not only did it come out of PE but the lack of pump shot really left the engine hurting for fuel. End result was that I added in about 40 percent more pump shot to the 'middle' values of the Pump shot vs. delta TPS table and added in a touch more pump shot to the Pump shot vs. delta MAP table. Also noticed that the manifold pressure was a bit high considering Im nowhere near WOT. Due to the large holley tbi supplying alot more air then the engine knows what to do with. The stock threshold for PE is set to 50% tps. Set this to 35% tps and wow, all the changes made the engine feel much better. It doesnt feel dead in the middle any more. Much crisper feel under load since its in PE instead of trying to run at stoich. And the throttle response... Gives me a nice kick in the chest when I suddenly open the throttle. Im sure id fail emmisions on the spot for this since it probably sends a nice slug of pollution out the tail pipe but it feels reeaaal nice . Id thought Id share this since alot of guys are using the holley 2" tbi on motors that, like mine, dont need all the addl. airflow. While it can work jsut fine when done up properly without tuning theyd be in the same boat I was. Too lean and no PE when they need it. Im sure with a wide band I would have seen this long ago but at least now that my engines running properly again I was able to see the problem.

 

Nice. Your sure hit the nail on the head with the decel enleanment, really dries a manifold out. There are some values to tweak to change this. Not enough enleanment and it'll back fire out the exhaust on a lift.

RBob.

 

Yeah, I ahd that after I put the holley on w/o doing any tuning. Backfired real bad sometimes. Also backfired out the intake as well, for obvious reasons. In hindsight, I probably should have gotten a stock tbi bored out to 48 mm instead. The two in. holley unit is too big for my engine given its power band. I definatly want to get a WB O2 now. Would have made seeing that much easier and will probably help get it tuned in more precisely.

 

On decel enlean, what are some good values to shoot for, AFR wise? I still ahve it set to 20:1 afr. Havnt done much with the parameters, either but by the stock 02 it looks pretty lean.

 

Took the car out before the weather turned to so some more datalogging. Lookes like its not going noticably lean on tip in anymore. Well, not enough to be seen with the stock O2. Still have that problem of going lean after a long decel. Waht was weird is that before teh engine came out of DFCO (above the circled area) it was like it was hardly even running. Just moving air around. When it came out the manifold pressure dropped and the rpms came up. I ahve some of the params in my tuner cats definition file, ill dig and get some more and maybe take a look at this. What everyone elses opinion? I thought it jsut leaned it out on decel but it looks like its really cutting out the fuel almost entirely.

 

Looking at the data logs I dont think theres going to be any way to see what the AFRs when decel enlean is in effect with the stock O2. 02 doesnt show much so i guess thatll have to wait for the wideband. The engine going real lean after DFCO kinda worries me, though.

 

Decel enleanment and decel fuel cutoff are two different functions in the ECM. Decel enleanment is the cutting back of fuel during a throttle lift. Decel fuel cutoff (DFCO), is where the injectors are stopped, 0 PW. DFCO gets used during coast down.

There is an extra pulse of fuel when exiting DFCO and returning to normal mode. This is to re-wet the manifold walls. While in DFCO the IAC gets retracted by a set number of steps, which then decays out upon exiting DFCO.

All of this stuff can be tweaked in the calibration tables.

RBob.

 

Yeah... Like said above I cant see any problems with the decel enleanment with the stock 02 after lifting off and getting back on the pedal but in the above data log after DFCO it goes way lean. Ive felt this on the highway. This is annoying in that when I get back on the gas after coasting, it stumbles a bit and I get knock counts as well. I looked at the hac for the 8746 and found the stuff for DFCO. I always thought it jsut leaned out the AFR's all this time, but instead it has a multiplier for the pulse width. Now I know. I guess Ill try bumping up the fuel when it returns and see if I can get rid of it. Thanks for the help.

 

interesting stuff. never entered my mind the option to bring in PE earlier on TPS %. in spring when i data log i will need to look at winaldl data to see if bringin in PE earlier may be helpful when i get on throttle. also the AE aka PS i may bring in larger amounts earlier rather than just upping tables globally.

 

Oh one more thing. i disabled the DFCO. issue was car dying when coming off a de accell when exiting the xway from 60mph to 0 on a coast to stop. problem went away.