Need help understanding my ECU/DME!!

[Zundfolge85]

L-Jet isn't as bad as has been made out. Its got like 3 sensors and that's it. the ignition is completely separate via the vacuum advance distributor. I had L-jet running great on my m20b23 for many years. but its basically a half assed EFI system. 50% mechanical devices and a very very primitive fuel only analogue ecu, so if the engine is not mechanically in perfect condition (vac leaks etc), it will not run properly. it does not have the smarts to adapt to issues. it doesn't even have an 02 sensor for feedback.

I keep seeing people say the L-jet doesn't have an o2 sensor, is it not supposed to? when i got my car the o2 sensor was still in the exhaust right after the header, but the wire was cut. But my engine harness has a connector for an o2 sensor right next to the battery, so i looked on real oem and used that part number to find an oxygen sensor that fits my harness and exhaust perfectly. Just so weird that I've seen so many people claim the L-jet never came with an o2 sensor. Also, did you convert your m20 to l-jet?

[Zundfolge85]

Before you decide to hack up a perfectly good wiring harness, it's best to perform the "wiggle test" first and see if there is a weak spot in the wiring associated with keeping the engine running.



Unless I am missing something here, I think OP might as well delete the ICV system in the first place instead of wasting his time doing the penny bodge; it uses a crap ton of vacuum hoses. It shouldn't take more than like 5-10 minutes to do the job. You can get vacuum caps to plug up the exposed vacuum connections at Autozone for pretty cheap.

The wiggle test produced no results, I was pretty thorough. Also, the car seems to die with no real cause, like it doesn't happen after I hit a bump or anything, and the air temperature doesn't seem to matter. Thanks for the suggestion, makes me a little more confident in the harness.

[Zundfolge85]

Here is a link to the SI board delete: https://www.r3vlimited.com/board/for...-functionality.

I agree that LJet is simple in theory, but! To make it work well in a four season climate is another matter. Temperature regulation is an issue and a perfect coolant temperature sensor is critical! Since the system is not adaptive it relies heavily on the few sensors that it does have and requires other variables to remain constant. For example let's say that the cooling system is not pressurizing properly and the externally mounted thermostat is not able to keep the engine temperature within reasonable parameters, then the FI coolant temperature sensor is not able to do its job consistently (I'm not sure about any limp mode attributes with LJet?). Another example is related to vacuum: One has a few vacuum leaks and therefore the flap/potentiometer in the air flow meter is sending wrong resistance values to the ECU. More advanced FI systems can adapt for external variables.

I agree that a complete idle control delete would be a good idea unless it is obvious that all of the vacuum system there has been maintained to perfection. The penny with a 1/8" hole is for temporarily eliminating vacuum leaks an/or idle control system problems for diagnostic reasons. Running an M10 without idle control in Michigan will be interesting during warm-up in the cold. I had a BMW 2002 heater valve and a cable hooked up on mine back in the day - idle speed was able to be manually operated via a "choke" cable. I have also experimented with locating the idle control valve next to the big air boot like we find on 325i M20 engines.

Thanks so much for the link ill do that. Im actually only driving the car in the summers, so its only ever seeing 70F to 80F degree days. Im tempted to do the ICV delete but wouldnt that mean id have to delete my cold start injector? I feel like even on warm days it would have a harder time starting without that.

[Zundfolge85]

Here is a link to the SI board delete: https://www.r3vlimited.com/board/for...-functionality.

I agree that LJet is simple in theory, but! To make it work well in a four season climate is another matter. Temperature regulation is an issue and a perfect coolant temperature sensor is critical! Since the system is not adaptive it relies heavily on the few sensors that it does have and requires other variables to remain constant. For example let's say that the cooling system is not pressurizing properly and the externally mounted thermostat is not able to keep the engine temperature within reasonable parameters, then the FI coolant temperature sensor is not able to do its job consistently (I'm not sure about any limp mode attributes with LJet?). Another example is related to vacuum: One has a few vacuum leaks and therefore the flap/potentiometer in the air flow meter is sending wrong resistance values to the ECU. More advanced FI systems can adapt for external variables.

I agree that a complete idle control delete would be a good idea unless it is obvious that all of the vacuum system there has been maintained to perfection. The penny with a 1/8" hole is for temporarily eliminating vacuum leaks an/or idle control system problems for diagnostic reasons. Running an M10 without idle control in Michigan will be interesting during warm-up in the cold. I had a BMW 2002 heater valve and a cable hooked up on mine back in the day - idle speed was able to be manually operated via a "choke" cable. I have also experimented with locating the idle control valve next to the big air boot like we find on 325i M20 engines.

So as far as the ECU problem goes, I have a feeling it may be my fuel pump relay going bad. I found some wiring diagrams that are helpful, so right now im just trying to test the connector that the fuel pump relay goes into. according to diagram 1 below, I think I should be getting battery voltage from the ignition switch to the fuel pump relay at pin 15. Im getting 12.40 volts there. So by using diagram two, shouldnt I be able to jump pins 30 and 87 to get 12v to the ECU? I tried this and im still getting .8v to the ECU, cranking or not. maybe im thinking about this wrong though.

[e30davie]

I keep seeing people say the L-jet doesn't have an o2 sensor, is it not supposed to? when i got my car the o2 sensor was still in the exhaust right after the header, but the wire was cut. But my engine harness has a connector for an o2 sensor right next to the battery, so i looked on real oem and used that part number to find an oxygen sensor that fits my harness and exhaust perfectly. Just so weird that I've seen so many people claim the L-jet never came with an o2 sensor. Also, did you convert your m20 to l-jet?

I keep forgetting that you guys are in the USA. Some or all of the us ones i believe had a retrofit o2 sensor setup to meet California emissions or something, but its a bit of a hack job intercepted into the AFM signal or maybe the coolant signal. The euro l-jet didnt have an 02 sensor. I found information on this retrofit 02 sensor somewhere before, but i cant find it again.

this is the e30 L-jet wiring on my euro car, no 02 sensor

https://www.exx.se/techinfo/e30_info/e30_ljetronic_001.jpg

[ZeKahr]

I keep forgetting that you guys are in the USA. Some or all of the us ones i believe had a retrofit o2 sensor setup to meet California emissions, but its a bit of a hack job intercepted into the AFM signal or maybe the coolant signal. The euro l-jet didnt have an 02 sensor. I found information on this retrofit 02 sensor somewhere before, but i cant find it again.

this is the e30 L-jet wiring on my euro car, no 02 sensor

https://www.exx.se/techinfo/e30_info/e30_ljetronic_001.jpg

All US-spec E30s came with an O2 sensor, not to meet California emissions standards, but to meet Federal emissions standards. By around 1980, Federal standards became so stringent that it became nearly impossible to pass them without a catalytic converter. And the catalytic converter needs a very narrow AFR range (ideally 14.7 or close to it) in order to operate correctly, hence the O2 sensor.

Prior to 1980 (I believe beginning in 1974), California-spec BMWs (and I believe all US-spec BMWs in the later 70s) would be fitted with thermal reactors, which were basically kilns bolted to the exhaust manifold to burn up any remaining hydrocarbons. As you can imagine, they resulted in plenty cracked cylinder heads

[e30davie]

ah there you go, someone who knows what they are talking about.

Do you have any information on how they integrated the 02 sensor into the early L-jet systems? I had another look and I still cant find the info I once read.

[ZeKahr]

ah there you go, someone who knows what they are talking about.

Do you have any information on how they integrated the 02 sensor into the early L-jet systems? I had another look and I still cant find the info I once read.

Yep. The O2 sensor for US-spec L-Jet is either a single-wire unheated narrowband sensor for early 1984 cars, or a 3-wire heated narrowband sensor for late 1984 and 1985 cars. There is a single black signal wire. Sensors with the heater have two additional white wires. The O2 signal is grounded through the exhaust bung. The sensor signal input goes straight into the injection control module, which uses it to increase/decrease injector duty cycle.

[Sunnyledge]

In reference to you only measuring 0.8v to the ECU (pin #9 or #13), be sure you are using the correct pin out diagram for the wiring harness connector. A few years ago I was doing some diagnostic on my 84 318i using the trouble shooting guide in the Bentley manual. I was getting all sorts of weird values. The pin out diagram for the harness connector in the Bentley manual is wrong. Pin #1 and #14 in the connector are adjacent to the harness. After using the correct pin out things made more sense.

[packratbimmer]

Deleting the idle control system is straightforward, but keep in mind that coming up with a spec for the throttle plate as well as the throttle position sensor can be tricky. Idle will drop with a/c and alternator load. That's why I liked my "manual" air valve setup using a BMW 2002 heater valve. I could set the throttle plate and throttle position sensor to stock specs and then fine tune the idle speed to any condition using my manually operated cable. BTW: you might be able to clean up your relay contacts by polishing with micro-fine sandpaper (1-5K grit) followed by electronic cleaner spray.

[packratbimmer]

Thanks so much for the link ill do that. Im actually only driving the car in the summers, so its only ever seeing 70F to 80F degree days. Im tempted to do the ICV delete but wouldnt that mean id have to delete my cold start injector? I feel like even on warm days it would have a harder time starting without that.

That's a great question about the cold start valve. I never had a problem starting in winter, but maybe it was not functioning?

[ZeKahr]

Thanks so much for the link ill do that. Im actually only driving the car in the summers, so its only ever seeing 70F to 80F degree days. Im tempted to do the ICV delete but wouldnt that mean id have to delete my cold start injector? I feel like even on warm days it would have a harder time starting without that.

Instead of deleting the cold start injector, first do an unplug test and see how the car starts up without it. I did that on my old 325e and the engine started up fine when it was over 40F outside. However, when the temps hit 40F and below, the car would crank and not start up until I plugged the injector back in. This car was kept outdoors at all times. I don't think you'll have much of an issue during 70-80F summers. If you see no issues, go ahead and delete it.

If you're going to do this, make sure your injectors are atomizing the fuel well and your ignition system is in perfect shape as fuel has a harder time vaporizing at colder temperatures (only about 50% of fuel vaporizes at 60F, that drops to 20% at temps near 32F). If you go by the realoem part number for the thermo-time switch (which controls the opening time for the CSV) and the Bosch PDF document located here, the cold start valve on your car is designed to operate for a minimum of 1 second at coolant temperatures above 35C (95F) and a maximum of 8 seconds at -20C (-4F). At 70-80F, the cold start valve is only open for 2-2.5 seconds.

[Zundfolge85]

In reference to you only measuring 0.8v to the ECU (pin #9 or #13), be sure you are using the correct pin out diagram for the wiring harness connector. A few years ago I was doing some diagnostic on my 84 318i using the trouble shooting guide in the Bentley manual. I was getting all sorts of weird values. The pin out diagram for the harness connector in the Bentley manual is wrong. Pin #1 and #14 in the connector are adjacent to the harness. After using the correct pin out things made more sense.

Ok, just to finish up this thread in case anyone runs into similar issues, my problem was the fuel pump relay. swapped in a new one and the car no longer shuts itself off while driving. As for the ECU not getting the right power, I took Sunnyledge's advice about swapping my pinout diagram, and sure enough, pin 1 starts at the cable end of the harness connector, meaning both the Bentley manual AND the ETM have the wrong diagrams for the L-Jet pinout. the correct pinout for the connector is mirrored on the actual ecu connector. The fuel pump relay was providing insufficient power to the ECU, swapped it out, and got 11.5v.

[Zundfolge85]

also thanks for all the help, I learned a lot about my engine and DME Sunnyledge packratbimmer ZeKahr e30davie

[randomInteger]

Nice, good on your for resolving it! Thanks for coming back and expanding on the solution.