Fuel Issue after MJ install??

bflan2001 · Post by **bflan2001** » Sun Nov 09, 2008 11:07 pm

1978 BMW 320i (M10 2.0L), stock k-jet mechanical fuel injection

I've got everything installed properly, double-checked all the wiring, everything looks good. I'm getting spark, but no fuel. The fuel system worked fine before installing the EDIS, so i'm pretty sure they're connected somehow.

Last year I had the motor replaced, and the shop was having a problem getting fuel. The problem was a missing ballast resistor inline with the ignition coil + wire..After installing the resistor, the car ran fine. Right now both the original coil wires are disconnected. Do these need to be connected to something??

Post by **brentp** » Sun Nov 09, 2008 11:30 pm

Not being familiar with the k-jetronic mechanical fuel injection, it may be that it needs some sort of signal from the original ignition coil- perhaps to get an RPM signal..? Or perhaps, it's a safety fuel cut mechanism. Pure conjecture on my part.

Anyway- you may try re-enabling the old coil, having it fire into 'nothing' and see if that restores your fuel system. If that works, you may inquire with experts on that fuel injection system and see what it would take to fool the system into working with the EDIS configuration.

Oliver Sedlacek · Post by **Oliver Sedlacek** » Mon Nov 10, 2008 9:50 am

Is the fuel pump running? If not, it's probably because the fuel pump relay will only enable the pump when it sees ignition pulses. This is a safety feature, as it stops high pressure fuel from being pumped out of a split hose (e.g. after an accident).

Alexander_Monday · Post by **Alexander_Monday** » Mon Nov 10, 2008 2:15 pm

By what I can see, the fuel pump relay does indeed need a tach input.

Looks like you should be able to disconnect the wire from the relay that goes to the ignition and connect it to the tach out of MJ.

Oliver Sedlacek · Post by **Oliver Sedlacek** » Mon Nov 10, 2008 2:47 pm

If the tacho out of the Megajolt wont do it, you could try the PIP signal out of the EDIS

bflan2001 · Post by **bflan2001** » Wed Nov 12, 2008 8:01 am

thanks a lot for the help guys, i'll try using those signals to get the relay to work..for now we just jumpered the connection to get the pump going. we've run into another issue now though. the spark is very weak. we double-checked all the wiring again, swapped the vr sensor wires, wired the ground directly to the battery, but still a weak spark. any suggestions?

Gilesy998 · Post by **Gilesy998** » Wed Nov 12, 2008 6:54 pm

How about this -
Junk the Tachymetric relay (that all K-jet cars use to run the fuel pump) and use a cheap, standard 12V relay. The relay can be feed a permanent 12v into pin 86, pin 85 connected to a user programmable output on the ECU, and the software set to trigger the output a 500rpm - as long as the enigne's at idle or faster the relay is closed and the pump is fed. If the engine dies, the pump shuts down, just as with the original setup.
If 500rpm is too high and wont run the pump to allow the enigine to start, fit a momentary push-to-close switch between relay pin 85 and ground, so you push the button and turn the key - hiding the push-button might make a handy immobliser too

Yvan · Post by **Yvan** » Wed Nov 12, 2008 7:50 pm

brentp wrote:Anyway- you may try re-enabling the old coil, having it fire into 'nothing'...

DO NOT DO THAT!

That's how I destroyed my original ignition coil.

Connect one sparkplug to the HT lead, and ground it (English is not my native language, I hope you understand what I want to say). Only than start the engine, and do further tests.

DannyP · Post by **DannyP** » Thu Nov 13, 2008 12:30 am

Gilesy, I like that idea, just add a second relay(or second trigger for the first) off of the starter position so the pump runs during cranking also. Problem should go away then I would think.

Hiperformance71 · Post by **Hiperformance71** » Wed Nov 19, 2008 8:28 pm

Hello,

I have had a similar problem with a LH jetronic, the version with the electronics all in the MAF, this sistem takes the tach signal from the original coil but using a wasted spark coil arrangement with the MJLJ and EDIS the problem is give the correct signal, without the bosch system don't work. I have solved the problem with a little ciruit using a pullup resistor and two diodes connected to the 2 signals of the coil A abd B. Usually, the signal for the LH-Jetronic is HIGH but when the EDIS give the ground signal at each coil, the signal for the jetronic goes to LOW state and the system works properly. I dont know if your jetronic works like mines, but if do you want, i can post a schematic diagram.

best regards,

(sorry for my english, isn't my native language.)

Gilesy998 · Post by **Gilesy998** » Fri Nov 21, 2008 9:43 am

Hiperformance71 wrote:sorry for my english, isn't my native language.

No need to apologise mate, you make perfect sense!

Some of us Brits, Yanks and Aussies write in worse english than yours