Optimizing D-Jetronic, Brainstorming.... Options

[pbanders]

Here are my thoughts on a systematic approach to optimizing D-Jetronic for a specific stock or near-stock engine - just putting this down and looking for comments:

1. First step - make sure the engine has no other faults. Mechanicals perfect, all systems present and working. correct part numbers, timing/dwell set to spec, valves adjusted to spec, fuel pressure to spec. etc., etc.....
2. Set the MPS using a dyno
   • Set the basic mixture (inner screw) - goal here is fuel economy and low emissions with reasonable performance (suggested AFM targets?)
   • Set the transition vacuum to full load (outer screw) - goal here is to eliminate flat spots
   • Set the full load mixture (full-load stop screw) - goal here is to set for maximum performance at WOT
3. Get car fully warmed-up and set idle mixture to spec CO - goal here is to reduce emissions and fuel consumption, and to minimize idle droop with electrical loading (the leaner the better).
4. Set idle speed with bleed screw to 1000 rpm
5. Let sit overnight
6. Insert 300 ohm potentiometer into the CHT circuit (make cables long enough to adjust from the cockpit
7. Start car and drive for 15 to 30 minutes, with frequent stops - you're looking for:
   • Proper aux air regulator operation (at least 5 minutes of idle higher than 1500 rpm after starting)
   • Idle stability without drooping, oscillations, or stalling
   • No popping on overrun
   • Minimum idle droop when electrical loads are on (lights, heater, blower)
8. If the conditions above are noted, increase the pot setting slowly until the best compromise performance is achieved.
9. Remove pot from circuit, read value - fabricate 1/4W ballast resistor to insert in CHT circuit of same value.

Comments?

If the intake system has been significantly modified (e.g. different cam, big valves, etc.), then to do the dyno procedure correctly, an assessment of the VE changes would need to be made, and the ECU daughter-card SC circuit would need mods - but this is beyond a reasonable approach for most people.

[pbanders]

If adding a lot of ballast resistance makes your 914 run better, then do it! Be aware, however, that adding too much may make the mixture vary once the engine is fully warmed up, possibly causing drivability problems.

This chart is from my ECU web page:

(IMG:http://members.rennlist.com/pbanders/CTCVoutBallast.gif)

It shows the relationship between the Cylinder Temperature Compensation (CTC) circuit output voltage and the resistance of the TS2 (also called the CHT sensor) plus any ballast resistance. Higher values of CTC Vout translate to richer mixtures. The blue trace is for an 037 ECU with an 012 TS2 and no ballast, the other traces show the effect of increasing ballast, up to 500 ohms. The temperature ranges on the chart were deduced from calibrating the resistance values of the TS2 to actual temperatures.

What you see is that if you add between 50 and 270 ohms of ballast, you richen the mixture only through cold start and warm-up. If you add 500 ohms, now the mixture varies once the engine is fully warmed up. The ECU circuit is designed to linearize the TS2 characteristic and to cut off its effect once the engine is fully warmed up.

[computers4kids]

If adding a lot of ballast resistance makes your 914 run better, then do it! Be aware, however, that adding too much may make the mixture vary once the engine is fully warmed up, possibly causing drivability problems.

What you see is that if you add between 50 and 270 ohms of ballast, you richen the mixture only through cold start and warm-up. If you add 500 ohms, now the mixture varies once the engine is fully warmed up. The ECU circuit is designed to linearize the TS2 characteristic and to cut off its effect once the engine is fully warmed up.

The chart was very helpful understanding what the resistance does...especially after warm-up. Since I currently have 270 ohms...I'm only seeing the effects during warm-up...it will be interesting when I crank up the pot between 270-500+ how that will effect warm running.

Do you suspect the 043 MPS responds simarily to the 037 MPS?
Thanks

[Bleyseng]

If adding a lot of ballast resistance makes your 914 run better, then do it! Be aware, however, that adding too much may make the mixture vary once the engine is fully warmed up, possibly causing drivability problems.

What you see is that if you add between 50 and 270 ohms of ballast, you richen the mixture only through cold start and warm-up. If you add 500 ohms, now the mixture varies once the engine is fully warmed up. The ECU circuit is designed to linearize the TS2 characteristic and to cut off its effect once the engine is fully warmed up.

The chart was very helpful understanding what the resistance does...especially after warm-up. Since I currently have 270 ohms...I'm only seeing the effects during warm-up...it will be interesting when I crank up the pot between 270-500+ how that will effect warm running.

Do you suspect the 043 MPS responds simarily to the 037 MPS?
Thanks

of course as they are the same unit other than different calibrations.

For bench set up the Wavetek works with setting a MPS to known working specs ie Stock...

For a engine with different then stock parts you must tune it yourself or find a motor build thats very close to yours .