Motronic 1.0 problems (E23, but still)

[The Dark Side of Will]

My dad snagged a 1986 735i (E23) automatic with a cranks but does not run condition. It had sat for 10 years or so. It has ~70k miles and was previously owned by a lawyer.

We found that some numbnut had replaced the main relay with a relay a standard relay. That meant the DME was on when the key was off and vice versa. Since the crank sensor plugs had been smashed, we also installed new crank sensors.

We replaced the main relay, put some gas in it and it fired and ran.

It ran rough, but was ok for driving around Small Town, USA while figuring out what was wrong with it.

Suddenly it wouldn't shift out of first. We mistakenly thought that this was a governor problem, since that's what the internets said was typically the problem when a 4HP22 stayed in first.

It also needed a new front exhaust section and simultaneously tore the CSB loose inside its mount.

We pulled the driveshaft and replaced the CSB. While the driveshaft was out, we pulled the tailshaft housing off the transmission and find, duh, that since it's an *ELECTRONIC* transmission, there is not governor. BUT the output shaft speed sensor electrical connector had backed off. We replaced the speed sensor anyway and did a preventive service of the transmission. The fluid was BRIGHT red, so we suspect that it had been manifesting this problem intermittently and the prior owner had it serviced preventively. We also added an inline filter to the trans cooler return line.

We put it back together with a Bosal front exhaust section, and it started up again, although still ran rough. We decided that, due to the old gas in the tank that had only been diluted about 4:1 with new gas, we should preventively replace the fuel filter. We did that and it ran better, but still rough.

I left for the week to go to work, and my dad was using the car to drive around town. Then it wouldn't start. We've double checked everything we can find in the book and can't figure it out.

Things we've checked:
->Spark? None.
->Fuel pressure? None.
->Jump the fuel pump relay to hot wire the pump. [Edit:] Have fuel pressure, but engine still will not start
->Thea above items indicate the DME isn't doing anything.
->DME always on power? Good.
->DME key on power? Good.
->DME crank signal? +10V while cranking, but that should be ok, right?
->Ohmed out the crank sensors from the DME connector. They're within spec.
->Exchanged crank sensors. No change.
->DME voltage measurements were relative to the ground pin in the DME connector, so the ground is good.
->Tried another DME from my dad's (wrecked ) '85 635CSi. No change.

[E30SPDFRK]

If you jumped the fuel pump relay and you still have no fuel, you have a dead pump. That doesn’t explain why there’s no spark, but you can start with that.

[The Dark Side of Will]

Edited for clarity: jumping the pump results in fuel pressure

[tschultz]

ECU transistor failure?

[Das Delfin]

Bad solder joint in one of the relays or the ground at the starter is loose? In e30's if the starter isn't grounded properly weird electrical things happen

[cscracker]

I have a no spark/no fuel injector firing situation on my 533i, very similar situation to yours. New reference sensors, tested with a scope to be good, tested all the wiring extensively (including voltage drop tests), tested all the pins in the ECU connector as working, tested all relays working, new coil, new spark plug wires, new plugs, etc., etc., etc. I've narrowed it down to malfunctioning ECU. This is Motronic ECU #3, a remanufactured unit from Programa. I have come to the conclusion that Motronic 1.0 is a flakey mess and ordered a Microsquirt instead of Motronic #4.

Highly suggest getting the Bentley, has lots of good information for doing the aforementioned tests.

You could convert to Motronic 1.3, but I figure if you're going to rewire the engine anyway, you might as well go all the way.

[The Dark Side of Will]

Bad solder joint in one of the relays or the ground at the starter is loose? In e30's if the starter isn't grounded properly weird electrical things happen

We have power at the DME connector everywhere we should, including the +12V "start engine" input which comes from the crank wire connection to the starter solenoid. That shows 10.x V when cranking. The battery may be a tiny bit weak, but would certainly expect 10 to be enough. Any voltage that can turn the starter should power on the DME.

The fuel pump relay tests good; the DME just isn't turning it on. All the sensor resistance values are what they should be except for the closed throttle switch, which shows a high resistance connection when the throttle is closed. That shouldn't keep it from turning the fuel pump on, though.

Everything really points toward us having two bad DME's in a row. We have a third one around here somewhere, which ran my dad's car before a trucker hit him two years ago. We're trying to find it.

I have a no spark/no fuel injector firing situation on my 533i, very similar situation to yours. New reference sensors, tested with a scope to be good, tested all the wiring extensively (including voltage drop tests), tested all the pins in the ECU connector as working, tested all relays working, new coil, new spark plug wires, new plugs, etc., etc., etc. I've narrowed it down to malfunctioning ECU. This is Motronic ECU #3, a remanufactured unit from Programa. I have come to the conclusion that Motronic 1.0 is a flakey mess and ordered a Microsquirt instead of Motronic #4.

Highly suggest getting the Bentley, has lots of good information for doing the aforementioned tests.

You could convert to Motronic 1.3, but I figure if you're going to rewire the engine anyway, you might as well go all the way.

We have the [Edit: E28] Bentley.

There is a known problem with the ignition output transistor solder joints cracking. A couple of years before his previous car was wrecked, my dad reflowed the solder on those connections in the DME I mentioned above. That's why we're looking for it.

Anyone have a working 261 200 059 DME for sale?

[Das Delfin]

10v when cranking does indicate the batt is getting old, but if you're getting no signal at the fuel pump with the key in the on position, and no spark when cranking, I agree that the simplest explanation is two bad ECU's in a row, especially considering aging bmw solder we all know and love

[The Dark Side of Will]

Zombie thread:

What actually happened was that the fuel pump failed AT THE SAME TIME as we were having these problems. That means that we incorrectly diagnosed the DME since we were using fuel pressure as a proxy for the DME energizing the fuel pump relay. Once we saw that the DME WAS energizing the relay and the fuel pump wouldn't develop any pressure when jumped, the rest was obvious and the car started.