BMW E30 323 with M20B25
The engine
- Inline 6 cylinder BMW M20B25, 2.5 litres, ignition order 153624.
- Wastefire ignition with Ford EDIS wasted spark coils (stock 60-2 trigger wheel)
- Sequential fuel injection with no cam sensor and low-Z 720 cc/min injectors
- Custom engine harness
Ignition trouble
Measurements on ignition parts were good:
- Coil primary : 0.9 Ohm
- Coil secondary : 10.9 KOhm
- Ignition wires : 5.5 - 7 KOhm (varies with length)
We had no significant 60-2 trigger wheel errors, the only time was during cranking where we got 3-4 wheel errors and then everything was alright.
First step during ignition setup tonight was to connect the coils and set the ignition order right. We layed the spark plugs connected on the valve cover and fired each coil and could clearly see the spark on the two connected plugs of each coil - and then set the ignition order accordingly. We then mounted the ignition plugs and started with no fuel, and strobed cyl 1 and saw that it was accurate at 10 degrees before TDC, as configured in the cranking advance. The primary trigger configuration is taken from an already Genboarded M20 engine, the trigger is identical so it was no mystery that it would match this engine.
To save the plugs from a badly configured VE map initially we configured the TPS high/low to read 100% all the time to avoid any fuel during cranking, and only use the priming pulse to get an initial sputter. We then knew we had the ignition order correct when the engine came to life on the priming pulse alone and never backfired. We activated the TPS again and set proper req_fuel and VE map values and now the engine cranked and ran.
- But : The engine seems to run only on cylinders 2, 5 and 6.
- this can happen, eg. if the injectors have different opening chracteristics (and driven at low 800..1200 usec pulsewidth). We've seen this with Siemens injectors. Try if making it rich starts these cylinders. Since the low-voltage flyback emphasizes problem with crappy injectors, increasing the flyback voltage with "external" (that can live inside the Alubos of course) powerful diode-pack (4..5 BY399 diode and a 0.1 Ohm 5W resistor in series, two of these in parallel).
We determined this through the temperature of the exhaust manifold runners after we had the engine running, but it could be heard that not all cylinders were happy. All plugs were fresh, there doesn't seem to be any spark and we can't get our strobe to work on anything but cylinder 1 ?
Clarification:
- The ignition order on this engine is 153624
- Coil pack is wired 1-6, 5-2, 3-4 and is fired in that order
- Running firmware 1.0.18, with MegaTune r026 ini
Some questions:
- Do only certain strobe lamps work with wasted spark coils? We tried reversing the inductive pickup, we still only got signal on cyl 1?! Not on any other wire.
- Is there a specific way to connect Ford EDIS coils (which we use) to the ECU and car ? The coil pack gets +12V through 1.5 mm^2 wire and is ground through the Genboard with one 0.75 mm^2 wire for each of the three coils.
- What dwell is appropriate for the coils? (currently 3.0 ms @ 14V)
Bear in mind that fuel has not been set properly, including afterstart and other enrichments.
History
I'm helping a local guy with installing a Genboard on a M20B25 BMW inline 6 cyl engine with Bosch L-jetronic electronics and intake and distributor ignition. The M20B25 originally doesn't come in this configuration (Motronic only) but a previous owner swapped out the block and head of the 323 for 2.5 litre parts and retained the electronics and intake (very stupid, engine ran lean on too small injectors). The stock harness will be cut-up and partly re-used and directly wired to EC connectors - a lesson learned from a previous BMW 728 project with similar electronics, meaning the stock L-jetronic connector and box will not be used.