OBD-I s52, has spark and fuel, but won't start

[JGood]

Are your CPS and and Cam sensor mixed up?

It's easy to mix those two up, they are the exact same plug.

They aren't the same. One is female, one is male. If you mix them up, you'll be connecting the cam and crank sensor to each other and the engine harness to itself. The ICV can be swapped with the CPS, but it's not. I get a hum from the ICV with key on, which means it's getting voltage. Voltage isn't supplied to the crank Sensor. I swapped them for shits and giggles, didn't work.

[JGood]

Same symptoms as mine. ended up being the main relay, last 4 #'s on it should be 9004.
Put a check light on a injector and see if it blinks while cranking.

No shit? I didn't even think of testing the main relay, I figured if I'm getting fuel, then the main relay is turning on the fuel relay and it was working. The car the engine/relays came from was in a pretty violent accident, so that's not a bad idea to check them.

[Good & Tight]

Same symptoms as mine. ended up being the main relay, last 4 #'s on it should be 9004.
Put a check light on a injector and see if it blinks while cranking.

[7pilot]

Fuel is good.
Ignition is there but inhibited by either valve timing/sealing or electronic issue. (backfire )
Air is available.
Block is grounded.
head is grounded.
Ign coils are grounded in two spots on the Cam case.

Try a 413 red label perhaps?


m

[Killacortes]

My plugs have been wet before when i was misfiring and i replaced all coils and plugs and that got rid of the wetness on the plugs and fixed the backfire.

if your getting spark and fuel then the cps isnt reading when to fire right. could be the pins on the flywheel to tell it when to fire?

[SamE30e]

Are your CPS and and Cam sensor mixed up?

It's easy to mix those two up, they are the exact same plug.

[nrubenstein]

I bet you don't have fuel. Unless you have actually seen fuel coming out of the injectors, you haven't got it. I've seen plugs come out looking wet with no fuel on them.

Is the ECU grounded properly? If it's not bracketed in, run a ground wire to the case.

[JGood]

The DME is using Bosch M3.1.
The Cam and crank position sensors are tested by hooking a DVOM set to resistance between terminals 1 and 2 on the sensor side plug.
So with the plug contacts facing you and with a single centered rib at the top and two on the bottom, T1 is the left most lug and T2 is center.
I checked the Bentley. According to the Bentley E36 comic book, there should be 1280 ohms + or - 10% between T1 and T2.( I don't believe this is correct. probably 530-560 Ohms)
In the ignition wiring schematic, both sensors are described as identical in construction....Hall effect sensors.

Backfiring on crank/no-start...Valve timing may be off, MAF may be bad, Bad Plugs , clogged air intake.

Injectors... It occurs to me that if you have no scent of gas in the cylinders when you pull a plug, that some of the injectors may be stuck shut.


m

Yes, and I'm getting no continuity between pins 1 and 2. Not no resistance, or too much resistance, but no continuity whatsoever.

From what I understand, the crank and cam sensors are both VR in non-Vanos motors. In Vanos motors, the crank sensor is a VR but the cam sensor is a Hall. It is a known fact that the VR sensors see 540 ohms vs the 1280 that the Bentley reports, so I'm a little skeptical as to what other info in the Bentley is correct regarding those two sensors...

Never said there was no scent of gas. Actually, I said the plugs were wet. That kinda had me concerned...

Valve timing wasn't touched since the motor was removed, valve cover wasn't even removed. Not saying nothing changed, but it would have to be an act of God...

Tried unplugging MAF, still no start. These motors start without a MAF, right?

All of your suggestions are valid, I definitely appreciate the input. I think I've "been there, done that" on the troubleshooting though. The only thing I can think to do is unplug the cam sensor all together. Since the engine should start without it, maybe if it's royally f'd up, it's actually causing more problems then no sensor at all?

[7pilot]

The DME is using Bosch M3.1.
The Cam and crank position sensors are tested by hooking a DVOM set to resistance between terminals 1 and 2 on the sensor side plug.
So with the plug contacts facing you and with a single centered rib at the top and two on the bottom, T1 is the left most lug and T2 is center.
I checked the Bentley. According to the Bentley E36 comic book, there should be 1280 ohms + or - 10% between T1 and T2.( I don't believe this is correct. probably 530-560 Ohms)
In the ignition wiring schematic, both sensors are described as identical in construction....Hall effect sensors.

Backfiring on crank/no-start...Valve timing may be off, MAF may be bad, Bad Plugs , clogged air intake.

Injectors... It occurs to me that if you have no scent of gas in the cylinders when you pull a plug, that some of the injectors may be stuck shut.


m

[JGood]

I just read in multiple places that the DME will resort to batch fire / wasted spark if it isn't getting a cam sensor signal, so it will still run.

[JGood]

The back firing (through the intake??) suggests that the engine is out of spec for static timing. I understand that it ran prior to installation.

I would treat the engine as an unknown and start from square one. Check the static timing, check the engine position/rpm sensors, check spark quality, fuel delivery, and add a new set of plugs(or burn off the fuel varnish on the current ones with a torch).

m
Oh, make sure that there are no rags or objects stuck in the intake tract to keep foreign objects/critters out.

It sounds like a static timing issue to me too. But he pulled this engine out of the car running, then put it into this car. He didn't even pull the valve cover. Timing doesn't change itself on these motors, AFAIK. Even if Vanos was locked the whole way to one direction, it should still start. Going through the process of removing the vanos and retiming the engine just brings more variables into the equation, considering I've only timed a vanos engine twice, so I'm not an expert by any means.

I'd love to test the cam sensor as you suggest, but nobody can tell me how.

New plugs is a good idea. Not sure how to check for spark quality though. I'll also check fuel pressure.

[JGood]

Are you absolutely sure it's getting spark?

It's sparking, I'm not sure how I can be any more sure, haha. I saw and heard sparking as we held the plug against a valve cover bolt and he cranked it over.

[7pilot]

The back firing (through the intake??) suggests that the engine is out of spec for static timing. I understand that it ran prior to installation.

I would treat the engine as an unknown and start from square one. Check the static timing, check the engine position/rpm sensors, check spark quality, fuel delivery, and add a new set of plugs(or burn off the fuel varnish on the current ones with a torch).

m
Oh, make sure that there are no rags or objects stuck in the intake tract to keep foreign objects/critters out.

[Wh33lhop]

My M50 started up just fine on 4 cylinders. If it's your coil packs, 4-6 of them failed at the same time. Are you absolutely sure it's getting spark? I'd look a little further into the cam sensor, is it possible that instead of outright failure (no spark) it's somehow malfunctioning and throwing your timing way off?

[JGood]

are ALL your plugs firing, maybe you have a bad coil pack or two..if you are near a Harbor freight,they have a spark plug tool that has a light, so you can see if they are firing....its like$5-$10 bucks.worked for me ..I ended up having two bad coils...just a thought. Good luck

I suppose it's possible, but I'd be damn surprised. The coil packs haven't been touched since the last time the car ran. I'll check it out though.