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...

[1project2many]

Some approve, some visibly disapprove, most simply don't get it...

There are many people over here that can't understand why you'd want to own and drive a car large enough to have a place in the UN. With the cost of fuel today and the knowledge we have about emissions, it's tough to imagine a time when 2.5 - 4.2 km/l was considered acceptable. But I definitely enjoy driving those old monsters around from time to time, just for the experience. It could be worse, I guess. I could wear a cowboy hat while I drive my gas guzzler.

I've been told there's a fairly extensive safety inspection that imported cars must pass before they're cleared for high speed on the Autobahn. I remember speaking with a US serviceman that had quite a time with a turbocharged Ford Thunderbird years ago. As I remember the story, the inspector or inspectors had the attitude that no American built car was ever going to be safe enough to drive at high speed. Did you face any problems like this with the wagon?

With modern engine design practices, we can say the stock 400 Ford engines have some significant shortcomings. Low compression versions tend to suffer from detonation due to the large quench distance created by running pistons with "below deck" height. :( Computer controlled timing is a big step for these engines and I think I would complement this advancement by adding the knock sensor. If you find yourself considering changes for higher top speed and / or greater economy, consider that the 400 produces peak torque and HP at a fairly low rpm. Installing an overdrive transmission might help take better advantage of the engine's power. I'm not as knowledgeable about Ford products but there may be a non-computer controlled overdrive transmission that will work with the GM computer.

[Dr_Grip]

There are many people over here that can't understand why you'd want to own and drive a car large enough to have a place in the UN. With the cost of fuel today and the knowledge we have about emissions, it's tough to imagine a time when 2.5 - 4.2 km/l was considered acceptable. But I definitely enjoy driving those old monsters around from time to time, just for the experience. It could be worse, I guess. I could wear a cowboy hat while I drive my gas guzzler.

I should try the cowboy hat thing some day! By the way, fuel prices over here are at their lowest since 9/11 these days with only around 5 Euros per gallon...

I've been told there's a fairly extensive safety inspection that imported cars must pass before they're cleared for high speed on the Autobahn. I remember speaking with a US serviceman that had quite a time with a turbocharged Ford Thunderbird years ago. As I remember the story, the inspector or inspectors had the attitude that no American built car was ever going to be safe enough to drive at high speed. Did you face any problems like this with the wagon?

Well, now things get complicated. Lean back for a tour through bureaucracy...

The first thing to get out of the way is the distinction between personal vehicles of US servicemen and German citizens. As US servicemen's vehicles are registered on base, which, while in Germany, legally is U.S. territory, their cars accordingly have not been subject to German inspections for the longest time. They had "stealth" license plates that replaced the EU's circle of stars and the "D" country code with a NATO logo and an "USA" country code:
.
Thus, inspection was carried out on-base by U.S. standards. I can imagine that what passed inspection and what didn't varied wildly from base to base and depended on the inspector at hand (U.S. military v.s. U.S. civilian staff vs. German civilian staff). I can also imagine certain special rules for servicemen using their cars in German traffic being imposed by base commanders.

After 9/11 the US forces started to retire these plates cause they made US personell easily identifyable and thus terror targets. All on-base cars had to be re-registered with the local German DMVs and thus, suddenly, had to pass a German inspection. I can imagine that during this process some inspectors, who, especially in towns with US bases where barely road legal beaters were handed down for years from generation to generation of enlisted men, had some prejudices about US cars, imposed top speed limits on cars when handing them their first German inspection (even if legally not having any authority to do so)...

This, by the way, applied to all cars registered on-base, no matter whether imported from the US or bought locally.

Matters are different if you import a car from the US. Like in the US, every car sold in Germany has to be type-approved by our DOT. And unlike in the US, every non-standard part going on a car has to be type-approved as well. Any part without a type-approval for the car it's on has to be approved for the application by a TÜV engineer, a costly process of unclear results.

Which brings us to importing cars. If you import a car that has once been type-approved through it's manufacturer or an importer, you simply have to convert the headlamps from US-spec to Euro-spec and pay a few bucks to get a letter drawn up that states that the car imported is identical to the type-approved vehicle. This not only covers bringing rust-free Euro classic cars (old Mercs, Volvos and VW buses are much cheaper stateside) back from California, but also some classic Mopar iron that has officially been imported in the Sixties and Seventies.

Cars that never got type approval, like my Ford, have to be approved especially by a TÜV engineer. They are basically treated like one huge non-approved aftermarket part and, if headlamps and a few other things are modified to EU requirements, get blanket approval. Which, of course, means that I am at liberty to swap any parts in that were not originally on her, cause I'll swap one undocumented, unapproved part for another undocumented, unapproved part. The downside is that the approval process will cost you around 400 Euros in an ideal situation. But once the approval process is done, you are cleared for whatever top speed the manufacturer claimed. TÜV is not at liberty to impose speed limits on cars, unless the tires on the car have a lower top speed rating than the car, in which case the law requires a huge sticker on the speedo informing the driver of the maximum allowed top speed due to tires.

With modern engine design practices, we can say the stock 400 Ford engines have some significant shortcomings. Low compression versions tend to suffer from detonation due to the large quench distance created by running pistons with "below deck" height. :(

Luckily, this problems mostly affect the smogged-to-death 400s from the second half of the 70s. My 72 spec 400 should be fine....

Computer controlled timing is a big step for these engines and I think I would complement this advancement by adding the knock sensor.

Will include one in my next RockAuto order, thank you for the advice!

If you find yourself considering changes for higher top speed and / or greater economy, consider that the 400 produces peak torque and HP at a fairly low rpm. Installing an overdrive transmission might help take better advantage of the engine's power. I'm not as knowledgeable about Ford products but there may be a non-computer controlled overdrive transmission that will work with the GM computer.

I fear that with the already huge loss in the non-locking torque converter adding an aftermarket overdrive like a GearVendors unit would mostly result in more loss in the tc.
As the Ford 400 has a big block bellhousing, the matching overdrive Ford transmission is the E4OD, which actually fits with almost no modifications to the car (rear gearbox mount has to be moved and driveshaft shortened, that's all) and comes with a locking torque converter. Sadly, it needs an electronic gearbox control unit - but the MegaSquirt II can provide this with a daughter board, so should I ever find a way to get a low-mileage E4OD shipped on the cheap I shall move on to the MSII.

[Dr_Grip]

So, I tried two different things.
1. I first used the 5.0, 5.7 and 7.4 bins and an Excel sheet to find out where the approximate AE values for a 6.6 machine should be. The bin #34 attached was the result.

As can be seen in the log "notenough", she still backfires.

2. I then copied all the AE values from the 7.4 bin to bin #35. Not only is the backfire issue still there (see log "stillbad"), I stopped logging right after the backfire to make the backfire easier to find in the log. But throttle response felt even worse than before, so I also did a fully warmed up log ("warmedup" keep in mind it was 14F and snowing during the logging run, so any hectic throttle activity is backing out of slides).

As always, any input is appreciated - I truly am at a loss.

[lionelhutz]

It appears you run at really low rpms so is this backfire happening at low rpm?

I'm thinking maybe you don't go into PE at the low rpms which leads to a lean condition after you give it a little gas. The AE works for the first bit then it backfires once the AE is done and it goes lean due to no PE.

Maybe try playing with these parameters to see if they help;
PE-Enable vs TPS% - lower these so you enter PE mode with less throttle
PE-RPM theshold for PE - lower this. I don't believe you can enter PE until above this rpm so I think this might be the main one you need to adjust.
PE-AFR - make it richer in the lower rpm's might help

You can look at the other parameters and try playing with other stuff that you think could help.

[ony]

hy, this may not be a problem or it may be the way it works on a conversion. to me it looks like the tps and map voltage don't corrusponed to each other as on a stock chevy. seams the tps is reading a little low or the map is reading a little high. if you use the digiatal dash you can put them side buy side and watch. it may not be anything wrong but one of the sensors may be lazy. I don't know if this will help or hurt, if you are running lets say 10 btdc at idle try setting inicale timming in your bin to what it is set with a timming light at the crank pully. I think it not only affects the spark but also when the injectors fire.

[Dr_Grip]

hy, this may not be a problem or it may be the way it works on a conversion. to me it looks like the tps and map voltage don't corrusponed to each other as on a stock chevy. seams the tps is reading a little low or the map is reading a little high. if you use the digiatal dash you can put them side buy side and watch. it may not be anything wrong but one of the sensors may be lazy. I don't know if this will help or hurt, if you are running lets say 10 btdc at idle try setting inicale timming in your bin to what it is set with a timming light at the crank pully. I think it not only affects the spark but also when the injectors fire.

MAP values definitly are different from a Chevy engine (and even from a Ford Windsor). The Cleveland/M-Block is an... interesting engine, to say the least (some people claim the M-Block plainly sucks). You can see how I had to change MAP values for DFCO to get it to work, for example.
Timing's set to 0° on the engine and in the bin. I've checked multiple times, spark advance according to hack in the log file matches what I see on the pulley +/- 1°.

[Dr_Grip]

I changed the PE-RPM to 1200 while reverting to my guesstimated AE settings. A first drive looks like this has cured the problem.

But I won't know for sure unless I got a WB o2 under the car and did some actual, structured test driving instead of a random cruise through town.

EDIT: Additionally, I found a factory-fresh MAP sensor in my parts pile. Will install it over the weekend and check if that changes MAP readings, just to be on the safe side.

[Dr_Grip]

I celebrated too early. The backfire's still there. You can find one in each of the logs attached. In the first one, it's easy to find right after the WOT run at the end of the log. In the second one, it's somewhere in the first third. In any case, I am at a loss by now.

As you can see from the file names, I also changed the MAP sensor, just in case... to no avail. :(

Any more ideas? Anyone? Especially with her running so brilliantly the rest of the time, this issue is really bugging me...

[buddrow]

" I fear that with the already huge loss in the non-locking torque converter adding an aftermarket overdrive like a GearVendors unit would mostly result in more loss in the tc.
As the Ford 400 has a big block bellhousing, the matching overdrive Ford transmission is the E4OD, which actually fits with almost no modifications to the car (rear gearbox mount has to be moved and driveshaft shortened, that's all) and comes with a locking torque converter. Sadly, it needs an electronic gearbox control unit - but the MegaSquirt II can provide this with a daughter board, so should I ever find a way to get a low-mileage E4OD shipped on the cheap I shall move on to the MSII. "

If you are interested, I have been building a stand-alone transmission controller for some GM transmissions, I could easily put together one for the E4OD. I could set you up with a complete package from transmission to controller and everything in between. Just a thought.

Buddrow