Rebuilt the motor in my '91 318is, cranks but won't start

[bluecrabmafia]

1991 318is. Motor was rebuilt from the bottom up. Rods, pistons, head reworked, new timing gear, the whole deal. Timed the car using the timing tool set.

The car now will crank, run for a second and shutoff. We are getting spark and fuel. Checked the fusible link in the back and it appears to be good. Swapped the relays on the firewall and didn't make a difference. Pulled the connector for the ECU and we are not finding any constant power with the key off. I tried searching and couldn't find a definitive answer on which pins should have constant power on them. Also I am not getting a CEL at all. Tried the stomp test and I'm not seeing anything. I don't believe my car has EWS since I have the digital OBC. Tried reading out both the cam sensor and crank sensor and they were reading like 0.987ohms which seemed wrong. Checked the injectors and they are pulsing. Car also has coil on plug conversion. Car ran good before the motor rebuild.

 Now I bought the car used and the engine had been swapped out before and let's just say the install was questionable. The car also sat for about a year before the motor got rebuilt and had some water leak into the drivers side from the door seal.

 What else can I check or am I missing?

[DesktopDave]

Your car won't have EWS - that was only installed on E36s. The M42 E30s never got the programmable OBC as an option, so no drive-away 'code' protection. There could be an aftermarket alarm installed, or even the Alpine dealer-installed option.

IIRC the only DME pin that gets constant 12VDC is #26. With the key in 'Run,' the DME switches the main relay by grounding pin #27. The main relay enables the O2 and FP relay circuits. The DME will then wait for a good crank sender signal before it grounds pin 1 to power on the FP relay and pin 37 to power up the O2 relay. I can get you a copy of the E30 pinout, for the 175 DME. It's not the same as the E36 M42 or M44.

Also be sure the coils are installed properly - the car will run with them on the wrong cylinders, but not well.

Be sure you have the 5-pin relay in the slot for the main relay block.

Crank sensor should read about 650 ohms. Cam sensor should be about 1200. Be sure they're installed on the correct plugs - they can swap and it'll keep the car from running.

That's all I can think of, off the top of my head.

[bluecrabmafia]

The white main relay is installed. So if I'm not getting constant +12V on pin 26 what could cause that? Wiring issue or something else?

If you could get me that pin out, that would be awesome. The M42 and E30 are new to me, most of my BMW knowledge is E34's and E38's.

[DesktopDave]

The white main relay is installed. So if I'm not get constant +12V on pin 26 what could cause that? Wiring issue or something else.

If you could get me that pin out, that would be awesome. The M42 and E30 are new to me, most of my BMW knowledge is E34's and E38's.

I think pin #26 is wired right off the battery via that smaller wire with the fusible link. You're getting 12VDC to the top terminal of the positive junction block on the firewall, right? IIRC that upper terminal splits off to all the un-fused components except the starter & maybe alt. Not sure on that. Are you 100% sure all the red wires are connected to that terminal block? There's a bunch of them.

From the ETM, you should have power at all times on pin #30 of both the main & FP relays, pin #14 of the round diag connector, and DME harness pin #26.

You should see the CEL briefly light up every time you turn the key to Run or Start. If you don't, it's a good chance the DME isn't powering up. I'd follow the voltage to see how far it goes...battery to fusible, fusible to junction block, block to DME harness, etc.

I couldn't find the pinout (at least I wasn't 100% sure it was the correct one), but the electrical troubleshooting manual can be downloaded here. I use the '92 'vert ETM since it's more complete than the '91 version.

I've had flaky relays on these cars too - it's possible that the relay is passing a little current but not enough to start the DME when everything else is running.

[timothymcn]

Your car won't have EWS - that was only installed on E36s. The M42 E30s never got the programmable OBC as an option, so no drive-away 'code' protection. There could be an aftermarket alarm installed, or even the Alpine dealer-installed option.

I'm not wise enough to troubleshoot OP's problem, but I just wanted to note that non-american M42 E30s were available with 13 Button OBCs. My Canadian 318is came from the factory with a 13 Button OBC, Premium Speakers, and an M-tech 1 steering wheel. No A/C though!

[DesktopDave]

Your car won't have EWS - that was only installed on E36s. The M42 E30s never got the programmable OBC as an option, so no drive-away 'code' protection. There could be an aftermarket alarm installed, or even the Alpine dealer-installed option.

I'm not wise enough to troubleshoot OP's problem, but I just wanted to note that non-american M42 E30s were available with 13 Button OBCs. My Canadian 318is came from the factory with a 13 Button OBC, Premium Speakers, and an M-tech 1 steering wheel. No A/C though!

That has to be a rare combination! Did you check the build sheet to verify that BMW installed it at the factory? The only option I've seen on most sedans is the 6-button 'external temp sensor' OBC, foglights and sunroof delete (if that counts).

[wazzu70]

Great suggestions so far dave!

I will have to look at my wiring diagrams again to remind myself which pins do what. Red wires should be constant 12V, red wires with a stripe (white or yellow) are power activated by the main relay, and green (and with yellow stripe) are key on power sources. The green with a stripe is a key on power source to the ECU.

If the crank position sensor is not reading correct, your engine will not have a chance of running correctly. Make sure the sensor has the correct resistance first. Then make sure crank and cam sensors are not swapped on the plug in to the wiring harness under the intake.

[bluecrabmafia]

I will check everything mentioned so far on Monday. I'm hoping it's something simple like a wire that's disconnected or something. After going through all the trouble of rebuilding the motor from the crank up, it's a little disappointing that it won't run.

[wazzu70]

It probably wont make you feel better, but a lot of times after a rebuild there will be an electrical issue preventing the motor from starting.

On mine I had the coil connectors swapped accidentially and it prevented starting. Took a long time to figure it out. Got that sorted and it fired up and ran like a champ!

[romkasponka]

Check ground cable.

[Tgoode318]

+1 to Wazzu & romka
Sounds like an electrical issue. First make sure battery and every thing is very tight and free of corrosion also make sure that its charged/holds a charge, then make sure alternator wires and starter are torqued down properly If you smell any kind of hot wire smell that is a good indicator that something is loose. make sure ground straps are connected and free of corrosion.  Make sure coils are installed correctly as well.  Get your ohm meter and bentley manual out and start testing GL

[bluecrabmafia]

Wazzu70,

You hit the nail on the head. The coils were swapped and I'm not sure how. We put it back together the way it came apart, but we must have done something. Thanks for the help gentleman. Need to tidy up a few other issues, but she'll be back on the road this weekend.

[DesktopDave]

Thanks for the follow-up, glad to hear it's running. Bet that's a load off your mind, eh? 

[wazzu70]

Don't worry, lots of people get them swapped "somehow." I thought for sure I had mine on correct...but turned out not to be the case!!!

Not sure why BMW chose not to label the cables, they are usually good about that stuff.


Glad to hear you are up and running!