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

[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.

[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]

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?

[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.

[SamE30e]

Are your CPS and and Cam sensor mixed up?

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

[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?

[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

[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.

[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.

[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]

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?

There are no pins on the flywheel, it reads off the front crank wheel teeth. Neither the CPS or crank wheel was touched while it was moved from the old car to the new car. The CPS read 540 ohms, so in theory should be functioning (although could possibly still be bad).

[JGood]

Fuel is good. not verified, but I do have pressure at the rail and wet plugs
Ignition is there but inhibited by either valve timing/sealing or electronic issue. (backfire )
Air is available. check
Block is grounded. check
head is grounded. check
Ign coils are grounded in two spots on the Cam case. check

Try a 413 red label perhaps? check (post #1)


m

Maybe there is a small German man inside these engines, who is the brains behind the operation, and he is just napping in this particular engine? I'll give him a few more days of sleep and try to wake him up this weekend.

[JGood]

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.

They came out smelling like fuel, were very wet (you could touch them and get liquid on your finger that smelled just like gas), and there is just a general strong smell of fuel while cranking the engine over. Not to mention, backfiring is still firing, and you can't have fire without fuel, right? I'm not saying the injectors are letting fuel in the way it should be during the cylinder combustion cycle, but I'm 99.999% sure that fuel is going into the combustion chamber at some point while cranking.

We had it grounded. My m50e30 has the ecu laying in the glovebox, not touching anything metal, and runs great. We also tried that ECU, no luck.

[7pilot]

Are you still using the plugs that were wet?
What brand are they? If they are Bosch, toss them.
If you have not changed plugs, try heating the electrodes with a propane torch for around 15 seconds each.



I'm down to either plugs or the harness adapter and/or a timing problem.

m

[JGood]

Are you still using the plugs that were wet?
What brand are they? If they are Bosch, toss them.
If you have not changed plugs, try heating the electrodes with a propane torch for around 15 seconds each.



I'm down to either plugs or the harness adapter and/or a timing problem.

m

They are NGK. Alright, I'll try new plugs, check the relay's, and try a new cam sensor (it's going to need one even if that's not why it won't start...)