Need help understanding my ECU/DME!!

[Zundfolge85]

Hey all, so I've had this 1985 318i m10b18 for a few years but never had the time to get it running. Its always just died intermittently while driving. When it does its as if it loses power slowly and steadily until it cuts out. Ive gone through almost everything related to the L-jet system and nothing really works. I finally decided to try the throttle position sensor, and when I tested its connector for voltage it gave me some weird numbers. according to the bentley manual "With the ignition on, there should be at least 5 volts VDC between the center terminal and either of the outer terminals of the switch harness connector." when measuring mine, I got 12v between one outer terminal and the middle, and 0v between the other terminal and the center. Because the voltage isn't correct on that connector, I tested the ECU connector according to the bentley manual for power and it doesn't seem to be getting all the power it needs. according to the manual, terminals 13 (ground) and 9 should read 12v when tested with a multimeter while the engine is cranking. after dozens of tests I consistently only get a reading of 0.9v. I also tested pins 13 and 4 (wire from starter solenoid) for 12v and got 0.9v. So I'm sort of lost on what to do next, I really have no idea what I'm doing with electrical but I'm trying to learn.

My question is does anyone know what could be affecting the voltage to the ECU? My guess was that maybe there's a relay that controls battery power to the ECU that could be going bad? or some other electrical component between the ECU and the battery that has gone bad? My 318i has three relays outside the fuse box which are the fuel pump relay, the vacuum advance relay, and the idle speed stabilization relay according to the manual.

I also had a parasitic drain this whole time, so I hooked up a multimeter in sequence with the negative battery terminal and cable and got a reading of .09 amps being drawn. so i went through pulling and replacing each fuse, turns out the drain was the gauge cluster, which runs through fuse 21. so when I have the blue connector on the back of the cluster removed there is 0 amps being drawn. but shouldnt there be a little bit of draw? to keep the clocks memory or something like that? this may sound really stupid but i was wondering if maybe the ecu problem is related to the cluster, like if the cluster is bad then the ecu wont get the right voltage. I dont know. I could really use some help, im depending on this car to make it out west and get an apprenticeship in race fabrication, so Im pretty stressed about it.

[ZeKahr]

Hey all, so I've had this 1985 318i m10b18 for a few years but never had the time to get it running. Its always just died intermittently while driving. When it does its as if it loses power slowly and steadily until it cuts out. Ive gone through almost everything related to the L-jet system and nothing really works. I finally decided to try the throttle position sensor, and when I tested its connector for voltage it gave me some weird numbers. according to the bentley manual "With the ignition on, there should be at least 5 volts VDC between the center terminal and either of the outer terminals of the switch harness connector." when measuring mine, I got 12v between one outer terminal and the middle, and 0v between the other terminal and the center. Because the voltage isn't correct on that connector, I tested the ECU connector according to the bentley manual for power and it doesn't seem to be getting all the power it needs. according to the manual, terminals 13 (ground) and 9 should read 12v when tested with a multimeter while the engine is cranking. after dozens of tests I consistently only get a reading of 0.9v. I also tested pins 13 and 4 (wire from starter solenoid) for 12v and got 0.9v. So I'm sort of lost on what to do next, I really have no idea what I'm doing with electrical but I'm trying to learn.

My question is does anyone know what could be affecting the voltage to the ECU? My guess was that maybe there's a relay that controls battery power to the ECU that could be going bad? or some other electrical component between the ECU and the battery that has gone bad? My 318i has three relays outside the fuse box which are the fuel pump relay, the vacuum advance relay, and the idle speed stabilization relay according to the manual.

I also had a parasitic drain this whole time, so I hooked up a multimeter in sequence with the negative battery terminal and cable and got a reading of .09 amps being drawn. so i went through pulling and replacing each fuse, turns out the drain was the gauge cluster, which runs through fuse 21. so when I have the blue connector on the back of the cluster removed there is 0 amps being drawn. but shouldnt there be a little bit of draw? to keep the clocks memory or something like that? this may sound really stupid but i was wondering if maybe the ecu problem is related to the cluster, like if the cluster is bad then the ecu wont get the right voltage. I dont know. I could really use some help, im depending on this car to make it out west and get an apprenticeship in race fabrication, so Im pretty stressed about it.

Some possible causes to your issue:
- bad ignition switch
- G102 is corroded and needs to be cleaned
- wiring associated with ignition switch or G102 is bad

Fuse 21 powers a bunch of things on your car. The “parasitic draw” is most likely the digital clock memory and auto charging flashlight feeding directly off battery power. There is also a memory power input from that blue connector into the fuel economy gauge circuitry - dunno what they need it for in that area though.

[McGyver]

Go to this website to find the Electrical Troubleshooting Manual (ETM) for your car: http://www.wedophones.com/BMWManualsLead.htm

Make sure to save the PDF in case the site disappears!

That will give you info on how the entire car is wired and should answer your questions. Good luck!

[Zundfolge85]

Some possible causes to your issue:
- bad ignition switch
- G102 is corroded and needs to be cleaned
- wiring associated with ignition switch or G102 is bad

Fuse 21 powers a bunch of things on your car. The “parasitic draw” is most likely the digital clock memory and auto charging flashlight feeding directly off battery power. There is also a memory power input from that blue connector into the fuel economy gauge circuitry - dunno what they need it for in that area though.

Thank you thats really helpful, ill check the ignition switch wiring. Just curious what makes you think the g102 ground specifically is at fault? I checked mine and it just goes from the valve cover to the battery tray. looks like its been moved to anpther part of the tray than where it was originally though.

[Zundfolge85]

Go to this website to find the Electrical Troubleshooting Manual (ETM) for your car: http://www.wedophones.com/BMWManualsLead.htm

Make sure to save the PDF in case the site disappears!

That will give you info on how the entire car is wired and should answer your questions. Good luck!

Thanks a bunch!

[ZeKahr]

Thank you thats really helpful, ill check the ignition switch wiring. Just curious what makes you think the g102 ground specifically is at fault? I checked mine and it just goes from the valve cover to the battery tray. looks like its been moved to anpther part of the tray than where it was originally though.

Because the 1985 318i wiring diagram says that your injection control module is grounded by G102 through terminal 13. It does look like G102 was moved by a PO based on what I’m seeing in the diagram. Perhaps they did some weird hackery with it and that’s what’s causing your car to shut off.

[packratbimmer]

Some general things to keep in mind: The L-Jet was upgraded in 1985 at some point so it is imperative to know which parts will be compatible. Previous owners may have swapped out the wrong parts which will physically fit. The ECU was changed in 1985 and will run the previous L-Jet, but not the other way around. I will be frank with you - L-Jet on the E30 is the hardest system to dial in of anything else found on E30 cars. If you have the early version of L-Jet (1984- early 1985) the injection system MUST have a properly functioning coolant temperature sensor (CTS). I have had 318i cars run great when cold and die as soon as they warmed up due to a bad CTS. Make sure to eradicate vacuum leaks (L-Jet does not tolerate them nor adapt), run copper plugs with no exception, make sure the vacuum advance is working on the ignition, make sure to run the distributor that matches your version/ECU and check to see if your injectors are dripping. The throttle position sensor is important, but will not prevent the car from driving if it out of adjustment - dialing it in will be complicated by an improperly functioning idle control system. As far as the harness goes, persevere on wire at a time. They must all be in order to rid J-Jet from the gremlins...

P.S. - on more than one car I have had a rust soup condition in the aging tanks which would allow the cars to start and run but not keep going after the rust particles were stirred up.

[packratbimmer]

If your cluster has a parasitic drag, you could try bypassing the service indicator (SI) board. I can send you a pic of how to do it if you like (this only works on early cluster - BTW). Have you inspected the SI board and batteries? The old boards are prone to corrosion due to the batteries.

[Zundfolge85]

Because the 1985 318i wiring diagram says that your injection control module is grounded by G102 through terminal 13. It does look like G102 was moved by a PO based on what I’m seeing in the diagram. Perhaps they did some weird hackery with it and that’s what’s causing your car to shut off.

ah ok thanks, ill have to find that diagram on the ETM, still trying to understand how to read this stuff. well if terminal 13 is supposed to ground through g102 i would think g102 should pass through the firewall and connect to the valve cover, not just the battery tray-valve cover. I'll look into that, i think the PO rebuilt the engine so there's been a lot of weird stuff on this car.

[Zundfolge85]

If your cluster has a parasitic drag, you could try bypassing the service indicator (SI) board. I can send you a pic of how to do it if you like (this only works on early cluster - BTW). Have you inspected the SI board and batteries? The old boards are prone to corrosion due to the batteries.

that would be fantastic, i would love to try bypassing it. have not inspected the board, but the gauges are white and the needles are purple so I've always thought it's from an m3 or something so ill have to verify the year.

[Zundfolge85]

Some general things to keep in mind: The L-Jet was upgraded in 1985 at some point so it is imperative to know which parts will be compatible. Previous owners may have swapped out the wrong parts which will physically fit. The ECU was changed in 1985 and will run the previous L-Jet, but not the other way around. I will be frank with you - L-Jet on the E30 is the hardest system to dial in of anything else found on E30 cars. If you have the early version of L-Jet (1984- early 1985) the injection system MUST have a properly functioning coolant temperature sensor (CTS). I have had 318i cars run great when cold and die as soon as they warmed up due to a bad CTS. Make sure to eradicate vacuum leaks (L-Jet does not tolerate them nor adapt), run copper plugs with no exception, make sure the vacuum advance is working on the ignition, make sure to run the distributor that matches your version/ECU and check to see if your injectors are dripping. The throttle position sensor is important, but will not prevent the car from driving if it out of adjustment - dialing it in will be complicated by an improperly functioning idle control system. As far as the harness goes, persevere on wire at a time. They must all be in order to rid J-Jet from the gremlins...

P.S. - on more than one car I have had a rust soup condition in the aging tanks which would allow the cars to start and run but not keep going after the rust particles were stirred up.

man this is so helpful thank you. So i checked out real oem and it looks like the ECU was upgraded in 11/1984. mine is 5/1985, so ill have to go through everything and make sure its all compatible. As far as the L-jet being tricky to dial in, ive started realizing that more and more, this car has been a nightmare for me. I only just recently figured out how to get it to start and start while hot. I just replaced my CTS, but need to do the other two, which are the thermo time switch and something else. not sure how much they affect the car other than operating the cold start injector. as far as idle goes, it seems pretty inconsistent. im tempted to do the ICV delete like I've seen others do. with the harness, would you just start slicing it open? ive never done something like this before and dont know if i should remove the entire harness from the car or just start opening it up while its installed. or maybe ill just replace all three of my relays and see if the ECU gets the power it needs. I just took it for like and hour drive and really pushed the engine hard on some turns, it did great. I just dont get how this issue can be so intermittent. when i rebuilt the distribuor i assumed i had killed the problem because it never died after a month of driving.

[packratbimmer]

Do as many tests at the ECU harness connector in the glove box. Remember always that the ECU relies on resistance values to operate, so be careful if you use leads that they have zero resistance. Since it is summer, drill a hole in a penny or nickel and do the idle control delete until you get it going. There is a factory designed squirrels nest of weird vacuum hoses under the intake to get under control (and figure out). More later...

[e30davie]

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.

[ZeKahr]

with the harness, would you just start slicing it open? ive never done something like this before and dont know if i should remove the entire harness from the car or just start opening it up while its installed.

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.

Since it is summer, drill a hole in a penny or nickel and do the idle control delete until you get it going. There is a factory designed squirrels nest of weird vacuum hoses under the intake to get under control (and figure out). More later...

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.

[packratbimmer]

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.