Running the 749 in my tt 5 spd formula, been datalogging, and have got most blm's hovering between 125-133 when cruising, which is no problem at all, but when shifting, the car gets rich as hell and backfires, which is because I'm assuming the stock bin's are for automatics, which shift much faster than I can.

What field should I be looking at to lean down the motor quickly when shifting?

Or when coming to a stop light I put it in neutral, and the same thing occurs, which I also believe is because the bin was made for an automatic.

Also, side note if anyone reads, where should the vacuum line for my blow off valve go to? I have the rear tpi vacuum line T'd, one goes directly into the map sensor, and the other end of the T goes to the blow off valve, is this correct? because for some reason I do not believe that my BOV is working correctly.

PJ

 

Ok, looking at a 88 manual 730 bin, there is a field
TPS% to enable fuel cut off, which looks like this

RPM TPS
3600 62.50
3200 62.50
2800 10.16
2400 0.00
2000 12.50
1600 99.61
1200 37.50
800 12.50
400 15.60
0 .39

Now in the 749 code, there are also Decel fuel cut/off options, but none cross reference rpm with tps%, but there is one table that says,
Throttle Threshold for Decel Fuel Cutoff
3.12%

now, would fooling with this setting possibly fix my backfiring when shifting? Or should others be touched on?

pj

 

I take it the backfire is out the exhaust? Single loud bang or a bunch of burbles inter mixed with pop's and a small bangs?

Look at the DE (decel enleanment) stuff. DFCO isn't what you are looking for.

RBob.

 

Alright I got it. Exhaust leak, from the passenger side, quite bad actually, but it has gotten worse and worse, so I didn't quite realize it at first. Will take off that header, and weld whatever there is to weld.

But I did in fact fix the running rich related backfire coming out of both sides of the motor, by starting up decel enleanment, but mainly from starting up DFCO, which fixed the problem greatly, if anyone's interested, I will post my settings in the $58 code to be used by a manual transmission smoothly.

pj

 

Please do, I am finishing up my single tubo 5-speed.

 

Ill just post the DFCO settings that I am using currently, need a little tuning, but this should get you in the ballpark.

decel fuel cutoff lower rpm limit 1100 rpm
decel fuel cutoff upper rpm limit 1600 rpm
decel fuel cutoff map threshold 80kpa
throttle threshold for decel fuel cutoff 60%
speed below which dfco is disabled 10mph

with these settings, i can still cruise around in 3rd or 4th gear hovering below 1600 rpm so that dfco cannot be enabled, if you cruise at higher rpm then 1600 rpm, then you need to change the decel fuel cutoff upper rpm limit, to say 2000 rpm or so, so that if your cruising down the highway, and your at 2100 rpm, and you let off the gas, it doesn't shut off fuel completely, makes for a jittery ride.

I have throttle threshold set to 60% right now, which means that, if above 1600 rpm, and I let off the gas to shift, under most circumstances, DFCO will be enabled down to 1100 rpm, and then be ready to be kicked back on. I'm still playing with this value, but in stock code, some of the DFCO in a manual bin are 60+% anyhow, in stock 749 code this is set to 2% i believe, which for the most part it is turned off, or would not be of much use to a manual.

and I have dFCO turn off at 1100rpm, but i might change that since it turning off at 1100 rpm doesn't seem to give the motor enough time to catch up with itself, like when coming to a light, and sometimes the rpms drop real low, then jump up again, might set this to 1200 rpm or so, to give the motor more time to fuel up again, and idle around 800-900 rpm.

pj

 

Nice,