I am working on tuning my Accel Gen 7 system, while this is not a Gen 7 question but a general tuning question and should apply to all programmable ECM's.

I have my base volumetric table very close, the O2 sensor provides very little correction so I know I am pretty close.

I started tinkering with my A:F ratio's and timing because my Headers are glowing under idle conditions and just off idle and most likely at high RPM's.

At just off idle I have my timing at 24 BTDC and my A:F ratio around 15.5:1. I have had the A:F at 14.5 and timing in the 18* range and have the same affect.

I believe that Rich Mixture and retarded timing cause glowing headers well I have neither and mine are glowing...

Here is what I have, 415 ci SBC, 10:1 compression, Brodix Track 1 aluminium heads, 31 lb/hr injectors and a Hydraulic roller cam with 277/284 duration and .535/.551 lift. I have 1.5"primarys with 3" collectors and 2.5" pipe with 2 chamber flowmasters...

This is what is really getting me, I use to run a Factory ECM with custom PROM, Iron Heads, small cam, 24lb injectors 2.5" collectors and had the same problem but had a nice ping on top of that. The exhaust is different so I know there is not a bad restriction.

Somebody point me in the right direction, I am at a standstill...

Thanks

 

I don't think there is an engine in the world that likes a lean idle so I would start by shooting for like 13-14:1 at idle. A rich mix at idle shouldn't make the exhaust glow but retarded timing definitely will. You say timing is at 24* at off-idle but what about at idle? It's not that it's too much and most likely just right for a loping cam. Idon't know what to tell you other then to add fuel and see. Maybe the o2 is bad. Is it wide band or narrow? Sometimes the o2 is fooled by vacuum leaks or exhaust leaks. I've read that a miss is interpreted by an o2 sensor as a lean condition so maybe it's mistaking your loping idle for a lean condition (which you have programmed for) and now you have even less fuel than you want. I don't know, it's just a guess.

 

Lean mixture causes headers to glow red. I had a professional setup my DFI and he made my idle in open loop, cruise at closed loop, and anything over 30% load open loop again. He had idle at open loop cuz closed loop was trying to lean out the mixture and cause a really bad idle and glow the headers. Now my idle is a lil rich, but it's safe. Of course, all tuning was with a wideband O2 cuz the one that comes with the DFI is hopelessly useless. The stock O2 barely let me pass emmissions!

 

My timing at idle is 22* and I run a narrow band O2 for now until the price drops some....

 

Well I think Markolc has the thinking dead on. Use open loop at idle. And a narrow band o2 is useless for trying to hit a certain a/f ratio so be very careful with that. Timing sounds pretty good, I would start richening it up and in open loop.

 

I have to agree here too. Get you idle AFR down and then keep it out of open loop at idle.

Check real carefully for any vacumm leaks.

 

I like the idea of using closed loop only for cruising and open everwhere else but how do I do that with the Gen 7 software?

All I can find is a switch to disable closed loop but no parameters for going back and forth.

Thanks

 

You should have closed loop parameters that you can set. Like when the rpm is <1500 then open loop.

 

I have my fuel set for 1.5-1 at idle and the ignition timing at 26 degs. Because of my cam(248/248 solid roller) the idle is set at 900rpm in park and 800 in gear. In my case, pulling fuel out resulted in a surging idle.

Is your info correct? A 415ci with Track 1's and you are using 1.5" headers?

www.geocities.com/dzperf

 

They are 1-5/8" primaries with 3" collectors and they are block hugger shorties that exit even with the top of the oil pan.

The headers are made out of 16 guage steel and are not coated, could the thin material be the reason for the glowing? I know the small size of the primaries would be a restriction at high RPM's but I am glowing at less than 1400 rpm.

I did find a chart for changing the O2 feedback based on % Mass Air Flow. But I am having trouble determining if the air flow is based soley on engine RPM or RPM and Load. If it is just based on RPM all I need to do is drive it find my idle air flow, and cruise air flow and change the feedback coefficient for everything except my cruise air flow to 0.

Is my thinking totally wacked?

Thanks...

 

Ok, here's the deal on closed loop fueling with a narrowband (HEGO) O2 sensor in the DFI Gen 7 system:

Since you are running a narrowband O2 sensor, the only time you can truely be in closed loop fueling is at or around an air-to-fuel ratio of 14.5 to 1 (the stoichiometric ratio for gasoline). As your A:F ratio gets further away from the 'sweet spot' of your sensor's range, the amount of fuel that can be added or subtracted by the closed loop control system decays away linearly out to +/- 1/2 of an A:F ratio from the stoichiometric ratio. When you are more than 1/2 of an A:F away from the stoicoiometric ratio, you will be an open loop fueling condition. This is done to prevent the control system from adding/subtracting more fuel than it should as the sensor's response becomes more nonlinear -- and less accurate. So, essentially, you can only run closed loop fueling with a narrowband O2 sensor when your target A:F ratio is between 14.0 and 15.0 to 1(for gasoline). All other target A:F values will cause open loop fueling conditions when using a narrowband O2 sensor.

The HEGO Maximum Feedback Coefficient calibration table allows you to program the absolute maximum amount of closed loop fuel that can be added or subtracted at any given estimated value of Mass Air Flow. This correction can be up to +/- 25% of your total fueling value. The estimated MAF is mostly based on engine speed, load, and temperature. Keep in mind that the value in the table will be influenced by the decay mentioned above when your A:F ratio is not close to your stoichiometric value