D-Jetronic internals info

Putting the cart well before the horse here for the ES, but I'm wondering if there's any detail information for the D-Jetronic system. I have the Volvo F.I. (Viking) manual, "Bosh Fuel System and Engine Control Manual" and the stuff from the "D-Jetronic history and fundamentals" page, but these pretty much stop at the field service level and don't go into the boxes much.

What else is out there, especially for more serious DJet hacking (for instance, the original B20 in our car has issues, and if it needs to be replaced I'd need to know hwo the various component values need to be altered for different displacements if we went with B21/23x). Is that info out there or is it a matter of popping the case and figuring out the equations (and in that case has anyone done it with a B30 to get two sets of "as-built" values?)

It's an analog computer, so there isn't anything hidden in PAL/GAL or PROM (it would predate PAL anyway).

IPD used to sell a potentiometer to adjust the fuel a bit, but I'd suggest MS'ing it with an 850 TPS, and the stock blue top injectors.

Each MAP sensor has a computer that is matched to it and dependent on the engine and cam.

That said here is what I have on the subject.

There are a few pressure sensors for Volvo D-Jet, probably more for other D-Jet cars(Benz, Citroen, Cadillac, VW, Porsche...) that might work okay. All the Map sensors will work to some extent but the correct one originally installed at the factory is best suited to that engine...until modifications start to happen. For anything even a little tuned(higher compression/headwork, etc.) still retaining D-Jet would usually be best to use an 010 or 015...but there are limitations.

50% or more of the drilled and opened MAP sensors I've seen have been done by people trying to compensate for an entirely different problem. Fuel pump starting to fail - not getting enough power, fuel line/filter(in-tank filter too) blockage, throttle valve, clogged injectors, etc.

Here's the Bosch part numbers for the NA market - note that the E engines were used elsewhere for longer.

B20E -1970 - 0 280 100 010
B20E -1971 - 0 280 100 015
B20F -1972 - 0 280 100 035
B20F -1973 - 0 280 100 035
B30E -1972-74 - 0 280 100 035 (- 059 with auto trans)
B30E -1975 - 0 280 100 066 (- 059 with auto trans)
B30F -1972-74 - 0 280 100 035
B30F -1975 - 0 280 100 066

Click to expand...

I'm with Kenwood. Ms it.

The D-Jet box being an analog circuit has a set of trim resistors that adjust fuel by their resistance values. IIRC the IPD kit w/potentiometer replaces one of those resistors.
The problem with the potentiometer is that given the 12v analog signal, the box carries all the injector currents through that resistor or pot, and the pot burns up in a short time. If you just get a pot and use an EGA or wideband to trim fuel, set a pot a the given spot it works best and then measure the pot resistance and wire in a good 10w reisistor of that value.
A quick web search should uncover the orig IPD instructions on how to do this, published in 1978. I had a copy at one point back in the day.

How did things work out? Did you indeed increase the displacement of the B20?
Would be very interested in pictures of the IPD kit w/potentiometer !

The adjustable IPD box isn't a potentiometer. It's a switch that selects a different value resistor for each position.

http://hiperformanceautoservice.com/images/IPD_AdjustableD-JetECU.jpg


Here's a link to the instructions. I believe the company that did the modification for IPD is still in business and will modify your ECU but they don't rebuild them. IPD had Bosch remanufactured units modified but Bosch is no longer doing them.

http://www.240.se/litteratur/ipd-ecu.pdf

I had one of those on my old 1800E, to account for the 2.1L motor. I always assumed it messed with the engine temp circuit, making it think it was cooler than it was, and getting a little cold enrich going on?

The kit came with a plain resistor you could hook up in those terminals on the box to default it back to '0%'.

The analysis of how the analog circuits work can be found here:

https://members.rennlist.com/pbanders/ecu.htm

That website used to have links to the main and daughter board schematics. Granted I think they were the Porsche versions of the D jet; but, fundamentally the same as the Volvo (head temperature instead of coolant temperature). Those links appear to be broken and the only site that appears to maintain those schematics is Ron Kwas' Swedish Embassy site:

https://www.sw-em.com/bosch_d-jetronic_injection.htm#General_Information_and_Acknowledgements

It would be theoretically possible to modify the analog filters on the circuit board to accommodate different engine sizes / volumetric efficiencies. That is what Bosch did for the different applications that used the D jet. However, tuning the controller requires unsoldering parts and soldering in new parts to alter the tune. This will be inconvenient bordering on painful. The best way to do this might be to model the schematic in SPICE so that you can make an initial estimate of how altering component values alters fuel delivery before you actually start unsoldering and soldering. Aside from the tuning headache. a few more reasons for not transplanting the D jet to a non D jet engine:
- the D jet's cold start system is rudimentary bordering on crude
- the D jet's idle air system is crude and exceedingly difficult / impossible to adapt because of its requirement to be mounted in the coolant flow
- the D jet requires a unique dual tach signal (the dual contacts in the distributor) to issue set and reset signals to the RS flip flop in the injector control circuit
- throttle switches and manifold pressure sensors are unique to D jet and new replacements are generally unavailable. Bosch used to offer a classic rebuild service - for the cost of a new digital EFI system.

Modifying D jet for use on a B20E bored out to 2.1 l would be quite doable. Putting D jet on a 2.1 l engine that is not set up for D jet would be like giving yourself a root canal - repeatedly. If you are switching engines, do as others have suggested and transition to an open configuration digital fuel injection system. I use MSII Extra; but, there are a number of other lower cost 4 cylinder specific systems available.

On that isolated RHD island lives a Benz guy who breath D-Jet. I had a chance to talk with him at Birmingham classic car show at MB club stand. He had made his own test equipment for D-Jet and also had great stories.