7747 on a Ford 400 - still not getting a backfire issue sorted

[Dr_Grip]

After sorting out the general setup, my ignition timing and DFCO with the help of this community, I sill can't find a way to tune out an rather elusive backfire trough the intake.

The issue appears only when accellerating from a cruise speed of slightly below 30. I don't have the problem at higher speeds, lower speeds or when flooring her from a standstill. The fact that it only happens during a small speed/rpm window makes the issue hard to reproduce. In accordance with Murphy's law, it seems to only occur when I really need instant throttle response to start an overtake or catch a yellow light :)

I attached my bin and the log file to this post. In the meantime, I already adjusted the VE table to get rid of the 135 BLM seen in the first screenshot.

EDIT: Triple-Checking, the TPS values do not seem to change enough for this being the right point in the log... But it has to be right after I left the Autobahn, so the general time frame looks right.

This is the last data point before the backfire:


This is almost the exact moment of backfiring, note the INT value going crazy:


And this is the data point after:


Here's the monitor view, as well:


Any help, as always, is highly appreciated!

Here's a pic of how she runs when she does not backfire :D

[1project2many]

First, thank you for that photo. It's rare to see one of those old wagons here. I can only imagine the reactions you get over there.

Here's the same area in the log with data I generally view during tuning. Notice the increase in TPS (top window, light blue line) at 19:08? This should be matched by an increase in O2 voltage (top window, orange line). Optimally the O2 increase should be within milliseconds of the TPS increase. Realistically it can trail TPS by a few hundreths of a second without causing a noticeable problem. In this case O2 gets so lean it drops right off the log. When I add BPW or IDC it looks like the AE isn't contributing enough. There's a slight chance it's an issue with the fuel supply system but I think you'd see other issues as well. So I'm going with the tables.

AE is an extra burst of fuel which prevents the mixture in the intake manifold from going too lean when the air density in the manifold suddenly increases. The greater the manifold volume, the more AE is generally needed. You're using unmodified TPS and MAP AE tables from the original ASDU calibration. The Chevrolet smallblock TBI intake has a much smaller volume than a 400 Ford intake and requires less fuel during AE. By comparison, look at the TPS based AE tables from a 7.4 liter Chevrolet engine compared to ASDU. The 7.4 used a carburetor intake with an adapter to attach the throttle body. It had far greater volume than the 5.7 and the tables show a dramatic difference in how much AE fuel is delivered.

I'd look over your logs to see what amount of delta TPS causes a lean condition. It looks like you're good below 10% and you may be good at 100% but it appears that you're lean around 10% -20%.

The attached calibration has increased TPS and MAP AE contribution for viewing and / or trying out. Good luck.

[Dr_Grip]

Thank you for the input, that makes lots of sense! :)

I will get the WB o2 sensor back under her after the holidays and test-tune the big block AE tables!

What I find interesting about people's reactions to her is how people in the US, when I did a roadtrip before fetching shipping her to Europe, all talked about the car like it's an old friend - lots of fond memories spent behind the wheel (or, in more than one way, in the backseat) of family members, friends or first girlfriends station wagons. Over here, people look at her with a sense of disbelief at her sheer size. Some approve, some visibly disapprove, most simply don't get it...

Here's two more recent pic:

[damanx]

I don't mean to throw a wrench into the gear box here, but when I was working on trying to get a 7747 ECM to run with my 60v6, I was having issues with trying to correlate spark latency tables along with the table that refers to the INT Delay vs Airflow due to the difference in exhaust setups.

Hope this might help and not add more confusion.

[ony]

something changed in the picture dash the last one shows tps from hack the first 2 tps from voltage, eagle mark was talking about using tps from hack but I don't remember what it was about. I think it is in paremiter coments iam not for sure. you may have just changed the edit on the sensor. looks funny seeing 110 mph on a data log don't never remember seeing any one tunning over 75 as a cruise log. looking at the blms you got it down pat have you got a working knock sensor hooked up?

[Dr_Grip]

Thank you for your reply!

One of the two aims of the cruise log you are seeing was to find out the real-world top speed of the car, so we pushed her hard on an empty stretch of Autobahn. In "normal" cruise I seldomly go faster than 90.

Regarding the TPS value - I somehow managed to change the display between screenshots, sorry. And I don't have a knock sensor installed - the Cleveland engine starts to run rough and lose power some time before misfiring, so I am pretty sure my ignition timing (based on an article in Hot Rod magazine and the stock dizzy curving) is not harming the engine...