TheSamba.com :: View topic - 2.1 DJ digijet idle computer relation to mixture

Mon May 30, 2022 12:15 am

So to go trough the complete story.
I bought the van 3 years back and previous owner had some shop do work on the EFI before me as he had issues with rough running.
Van ran fine but cold start was bit rough (not runnig on all four until you give a bit rpm) but after start there were no issues. Car passed the local emission test on first year no problem. Last year I needed to adjust the idle mixture a bit to get it trough. But this year there were not enough adjustment to get it running good.

I took out the injectors and checked the spray patterns and they were nice and even, also replaced the seals. I did not check the amount sprayed while on a car.

Also replaced the temp sensor to new VW item even the old one was in correct range.

Checked the compression pressures, all between 12-13bar, replaced and adjusted plugs, new rotor new dissy cap.

Found out that idle stabilizer did not affect the running of the car when wire removed, replaced the transistor on the idle computer.

After these car ran better then ever on idle, but the idle spiked from 900 to 1400 after I got the idle stabilizer to work.

Adjusted the idle from the throttle body back to 900 and car idle better then ever and cold start do not need assistance from the pedal anymore to get the car to run for first 30sec or so. But still it seems like it is not firing on all four on cold start and needs some rpm to get it running.

At this point I needed to take the emission test to keep the car on the road.

CO2 was still too high and idle mixture adjustment was not enough to compensate. I removed the wire from the idle stabilizer and got it trough the emission test by adjusting the idle mixture.

And now to the real question in digijet with out lambda sensor. How ECU controls the mixture?

Temp sensor, AFM, fuel pressure and idle computer controlling extra air. Or is there something else.

As I have started to think that the previous shop that worked on the car might have adjusted the AFM to compensate for the non functioning idle stabilizer and now that it is working again mixture is too rich. I was planning to install wide band lambda meter before I start to adjust but now just asking for advice before I do something stupid.

Mon May 30, 2022 4:20 am

I know you're in Europe where the 2.1 came with various fueling configurations.
But

Is your 2.1 fueled by Digijet?
Here in the States Digijet was in the 1.9 and Digifant was in the 2.1

Dave

Mon May 30, 2022 5:44 am

Trying a known good Idle Stabilization Control Unit and/or Idle Stabilization Valve would be an easy way to determine if your current parts are faulty. I believe you can use either 251907393A or 251907393C. B & D subcodes might 'work', but target RPM is probably different.

tanhis wrote: And now to the real question in digijet with out lambda sensor. How ECU controls the mixture?
Here are a couple pages from ProTraining on how Digijet enrichment works (ignoring O2 sensor):
https://www.loam.org/vw/Vanagon/VanagonProTraining/FuelSystems/images/DigiJet/52.jpg
https://www.loam.org/vw/Vanagon/VanagonProTraining/FuelSystems/images/DigiJet/61.jpg

Here is the Idle Stabilization Control Unit function and troubleshooting for Digifant, but should apply to yours:
https://web.archive.org/web/20210902203801if_/http...ms/104.jpg
https://web.archive.org/web/20210902203801if_/http...ms/121.jpg
https://web.archive.org/web/20210902203801if_/http...ms/122.jpg
https://web.archive.org/web/20210902203801if_/http...ms/123.jpg

Bosch also has a troubleshooting procedure for DJ engines with an ISCU & ISV, just like yours. Sometimes they refer to using their special test tool, but it's possible to test without it. Pages 66-80:
https://archive.org/download/carchive/VWW-503_text.pdf

Mon May 30, 2022 5:45 am

He says 2.1 DJ and that code DJ engine by definition includes a Digijet version of injection.
That also includes the separate vacuum/centrifugal ignition distributor setup like earlier Vanagons here have.

While the EPA approved gasoline engine Vanagons made for the USA/CA market have Cats and O2 sensors this wasn't the case for most T3 models built for other markets.

Mark

Mon May 30, 2022 6:05 am

RawUmber wrote: Trying a known good Idle Stabilization Control Unit and/or Idle Stabilization Valve would be an easy way to determine if your current parts are faulty. I believe you can use either 251907393A or 251907393C. B & D subcodes might 'work', but target RPM is probably different.

tanhis wrote: And now to the real question in digijet with out lambda sensor. How ECU controls the mixture?
Here are a couple pages from ProTraining on how Digijet enrichment works (ignoring O2 sensor):
https://www.loam.org/vw/Vanagon/VanagonProTraining/FuelSystems/images/DigiJet/52.jpg
https://www.loam.org/vw/Vanagon/VanagonProTraining/FuelSystems/images/DigiJet/61.jpg

Here is the Idle Stabilization Control Unit function and troubleshooting for Digifant, but should apply to yours:
https://web.archive.org/web/20210902203801if_/http...ms/104.jpg
https://web.archive.org/web/20210902203801if_/http...ms/121.jpg
https://web.archive.org/web/20210902203801if_/http...ms/122.jpg
https://web.archive.org/web/20210902203801if_/http...ms/123.jpg

Bosch also has a troubleshooting procedure for DJ engines with an ISCU & ISV, just like yours. Sometimes they refer to using their special test tool, but it's possible to test without it. Pages 66-80:i
https://archive.org/download/carchive/VWW-503_text.pdf

Thanks, I will go trough these and come back here if I can solve the issue with these.

And yes, europe had all kind of weirdness compared to america...or is it another way around ;) so it is digijet as mentioned.

And as a sidenote I am not a stranger to flat fours but this shit is just too modern with injectors, air flow meters and water as a cooling.

Mon May 30, 2022 6:48 am

I would also suggest that you look at the wiring harness. Poor connections and/or corrosion could be effecting the signal from the coolant sensor. The ground wire lug on the engine has also been a source of trouble for some.

Good Luck!

Hans

Mon May 30, 2022 8:30 am

hdenter wrote: I would also suggest that you look at the wiring harness. Poor connections and/or corrosion could be effecting the signal from the coolant sensor. The ground wire lug on the engine has also been a source of trouble for some.

Good Luck!

Hans

Good point, I have extra ground stap on my engine and i measure sensors etc directly from ecu plug to eliminate possible bad connections out.