Digifant open loop vs closed

[MarkWard]

Not trying to tune anything here. Someone was seeking stock fuel ratio numbers for a WBX. The point I was making was that I was not aware of any factory fuel mixture values, only HC CO values, but you could probably find the correlation between the fuel mixture and HC CO, which you did.

I mentioned the air cooled vw vanagon engine only because I came across quite a few melted pistons from running too lean and probably too much timing. When preforming tune ups on all the VW engines from the 70s and early 80s, by law we were required to tune them to spec. Once O2 sensors came on the scene, you were always going to be in a tug of war with the sensor.

Smoothest idle and best off throttle response came from adjusting the engines to run as rich as possible within the EPA spec.

I was surprised to see that from the table you linked how close the mixture was to stoichiometric at the lower CO percentage. I learned something new.
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[Jake de Villiers]

[Wildthings]

The primary adjustments in the AFM need to be made at full throttle full rpm so that you get maximum power when the O2 sensor is off line when pulling a grade. You want to see an AF ratio of somewhere around 12.5:1. All the sensor need to be checked and corrected first before any adjustments are made to the AFM while the idle mixture will be adjusted after any adjustments to the AFM.

One rule of thumb for adjusting the AFM is adjust for where you live and not where you play, this assumes one usually goes up in elevation to play.

[jerryherb]

Thank you all for chiming in.

I will have to check the AFM CO screw as it appears now it has been messed with.

I did not mean to criticize, just posting my findings in the bentley (CO%) in correlation with the AFR value table for future reference if someone else needs them in the future while tuning in open loop with an MTX-L or similar device in place of the original O2 sensor.

i did not use any sealant on the brand new injector seals, should i?

I went through all sensor checks and vacuum line mechanicals at least twice now, but plan on doing it again by eliminating everything but TB, AAR, FPR and dizzy out of the vac loop. If AFR is still lean I will tune the AFM with just the CO screw as the black cover appears factory sealed and i want to keep it that way. AFM temp sensor 1 is the only one i did not yet test at the ECU plug as it came with the "new" AFM, which was replaced after previous tests were complete. Will also throw the tantalum cap in line just to make sure i get a clean/steady signal.

again all vacuum lines are new and tight and all tune up parts, which came from a reputable source (with a cookie) have been replaced. fuel pressure/volume is also in range (brand new bosch pump installed)

[MarkWard]

You should not need sealant on new injector seals.

Found this vacuum leak on an 85 vanagon recently. Took some time to find it. The mounting stud for the coolant pipe that crosses the engine had snapped off, but was hidden by the bracket hoses etc. Found it with a smoke test.

Mig welded a 6mm bolt to the intake runner to seal the hole and secure the coolant pipe. That one was difficult to find.
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[Wildthings]

[jerryherb]

it so happens that i took the header pipes off, cleaned, sanded and painted with 3 coats of high temp. i dont think i have a leak there as those screws are nice and tight, thanks for the pics.

[jerryherb]

Happy to report that i found the AFM CO screw to be 8 2/3 turns out from the bottom. no wonder Beast was running lean in open loop. Adjusted back to base (2 1/2 turns out from the bottom) and got almost a perfect stoichiometric mixture coming off acceleration. adjusted further to 13.9-14.1 AFR oscillation (per bentley altitude graph) at 1 1/2 turns out from the bottom in open loop. Beast, with an occasional miss (156k on old tired engine), now purs like a kitten. 14.6-15 oscillation on the AFR in closed loop.

Will have to see if i can get her to 12.5 under load in real life conditions, and if not i know which one of her screws to twist

Thanks for all your input! Hope this thread helps someone in dire need of truing their pre-owned AFMs

[jberger]

That's great. Just remember that it takes an incredibly long time for the full throttle enrichment loop to kick in. Like minutes. It's almost useless.

J

[jerryherb]

[lucianosanchez]

Man I need to do this to mine; just read the thread and I am a bit overwhelmed on what I need to do. Too many terms and things I do not know. I wish I had one of those O2 testers, they are expensive though!

Anyone want to come by my place and go through tuning my van? I got beer

I can do the test shown here with a voltmeter right? I don't need one of those expensive O2 testers?

I am planning on sending my injectors in for cleaning to rule one thing out and trying to tune my van because right now it is not running well. It acts like it is going to stall as soon as I stop at a red light. It also idles weird; it idles fine and all of a sudden it sounds like it is going to stall, then it goes back to normal.
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1983.5 Aussan Brown Westfalia | 2016 to 2020
1983.5 Beige Westfalia | 2019 to Current

[jerryherb]

not as easy to get the AFR reading with a volt meter as the original sensor is narrowband. i screwed around with it for a few weeks and went to get the MTX-L. its the easiest way to get an easy readout by just replacing the O2 sensor with the wideband one that comes with MTX-L kit. i either got mine on sale or with some coupons. it was around $100-$130 and i dont regret it a bit. it also has a lead wire (brown i think) that simulates the signal of narrowband sensor that you can connect to the O2 plug leading to the ECU. Im in GA, otherwise i'd take you up on the beer.

First step: just replace ALL vacuum hoses and seals instead of screwing with spraying crap on them, you will save a lot of time as some leaks are impossible to find.

Second: go through the FI Pro service manual for your particular Fuel Injection management system (AFC, Digijet or Digifant).

Third (you can try that first if you're feeling adventurous): open up the cap over the O2 adjustment screw on your Air Flow Meter and count the number of clockwise turns it takes for the hex screw to bottom out (lightly). record that number so that you can go back in case things get worse. base setting should be about 2.5 counter-clockwise turns out from the bottom (per experts' opinion i found elsewhere). more in runs rich, more out runs lean. just remember that O2 will compensate for the mixture (eventually) hence its easiest to do this adjustment with an actual AFR meter (MTX-L) with the O2 wire to ECU disconnected.

[zoti]

Digging this out from the past.

on the 2.1L Digifant, at what point does the ECU goes closed loop (use the O2 sensor for adjustments). Is it based on the engine current temp reading from the Temp 2 sensor and if yes, what is that temp that triggers it.

At what point does the Idle Stabilizer unit starts working? I know it has an input from the ECU that can turn it on and off. Is it the same as when the system goes closed loop?

[Wildthings]

[zoti]