M42 Full Rebuild now won't start

[theTBLACK]

So where are we at now. Are we back to injectors as the cause of the issue? We gotta figure this out

Tell me about it.

Here is where we are at.

Compression is good. Timing is good. Getting spark.

Now it's a fuel issue - I pulled the fuel rail and put plastic bags over the injectors - they weren't putting even a mist into the bags.

Now we have tested the grounds and all of the electrical with the injectors - everything is working as it should and all the voltages are correct.

Not sure what to do next honestly.

[Dj Buttchug]

So where are we at now. Are we back to injectors as the cause of the issue? We gotta figure this out

[theTBLACK]

You could try pulling the injectors and opening them up with 12v and back flushing them with carb/brake cleaner, then in the regular direction to see if you are getting flow through them.

Like stated above though it is very unlikely all 4 injectors are bad/clogged. But it's not unheard of. We're they sitting out for a long period of time before the rebuild?

No sir. They were in the car and it actually idled (shitty, but it did) before the rebuild.

[Balleristic31]

You could try pulling the injectors and opening them up with 12v and back flushing them with carb/brake cleaner, then in the regular direction to see if you are getting flow through them.

Like stated above though it is very unlikely all 4 injectors are bad/clogged. But it's not unheard of. We're they sitting out for a long period of time before the rebuild?

[theTBLACK]

Just hook up the fuel supply and injector wiring with the rail out of the manifold and watch for fuel spray while briefly cranking it. I don't know if the stock ECU always primes the fuel system unfortunately, I never paid much attention to that kind of thing since I knew I was going to ditch it. If they're not firing, getting 12V, and the harness has continuity, either the injectors are all bad (quite unlikely), the ECU isn't working right (inputs are no good, since the ECU itself is ruled out) or the ECU ground (on the PS strut tower) is bad.

I did this and no fuel was coming out whatsoever. Not even a mist.

So they are firing and getting 12V, and the harness has continuity.

The ground on the strut tower is good also.

So bad ECU or what? Could the injectors be clogged, or the fuel pressure regulator be bad? It seems like if i'm getting spark and everything else that the ECU would be okay.

[theTBLACK]

Alrighty, so you get 12V. That is good, at least the supply side is working. Next up you need to check that the ECU is firing the injectors. One pin on the injectors has constant 12V, and the other pin is switched to ground through the ECU.

It would be hard to check that with the injectors in there, so I recommend buying a small incandescent bulb, like 5W or something, with wire leads and using it as a "mock injector" with the harness. This will quickly tell you if the nodes are being switched.

I did exactly this - I used a 5W bulb and set up wires to make a mock injector.

The nodes are definitely being switched as it the bulb flashed while cranking. So I believe the injectors are definitely getting the amount of power they need.

So i'm thinking either my injectors are clogged, or my regulator is bad. What do you think?

The fuel pump is new, the lines are new, and the filter is new. I was getting a very steady hose-like stream out of the feed line that goes into the rail.

[varg]

Just hook up the fuel supply and injector wiring with the rail out of the manifold and watch for fuel spray while briefly cranking it. I don't know if the stock ECU always primes the fuel system unfortunately, I never paid much attention to that kind of thing since I knew I was going to ditch it. If they're not firing, getting 12V, and the harness has continuity, either the injectors are all bad (quite unlikely), the ECU isn't working right (inputs are no good, since the ECU itself is ruled out) or the ECU ground (on the PS strut tower) is bad.

[bmwman91]

Alrighty, so you get 12V. That is good, at least the supply side is working. Next up you need to check that the ECU is firing the injectors. One pin on the injectors has constant 12V, and the other pin is switched to ground through the ECU.

It would be hard to check that with the injectors in there, so I recommend buying a small incandescent bulb, like 5W or something, with wire leads and using it as a "mock injector" with the harness. This will quickly tell you if the nodes are being switched.

[theTBLACK]

Have you cranked with the fuel rail out (injectors attached) and verified that they are firing?

The injectors get +12V from the main relay via the red/white wire coming from Pin 87, leading to the harness box under the intake manifold. Verify +12V is present here when cranking. The ECU grounds the injectors in pairs (1&3, 2&4) to fire them. If you haven't, check continuity of the wires between the injectors and the ECU (pins 3 and 32)

I double checked all of this. There is continuity between the wires and injectors, and I get 12V while cranking.

[theTBLACK]

Next steps are to try Varg's recommendation and verify voltage to the injectors. I'm almost convinced at this point this is the issue.

Today I did pin out every single pin on the DME and everything was in working order, and all of the DME wires to the coils were correct.

I'm also going to press some air through the fuel lines, make sure the fuel filter isn't backwards, and double check the fuel pressure.

One thing I worried/concerned about

Does the fuel pump always prime when you turn the key to the run position? Mine will not do it - even after replacing the fuel pump relay with a known working one.

I could only get it to turn on by jumping the pins where the relay is.

If I recall correctly, usually the pump will come on for a brief moment and you can definitely hear it - i'm not getting anything at all.

Any ideas on that?



I'll keep you guys posted on voltage to the injector rail early this week.

[theTBLACK]

See:


I'm trying to help you out. Please check that your injectors are getting 12V while cranking before going any further or spending money getting your injectors cleaned.

I appreciate the help. I will check that first thing Monday and report back. Much appreciated guys really couldn't do it without you.

[varg]

See:

Have you cranked with the fuel rail out (injectors attached) and verified that they are firing?

The injectors get +12V from the main relay via the red/white wire coming from Pin 87, leading to the harness box under the intake manifold. Verify +12V is present here when cranking. The ECU grounds the injectors in pairs (1&3, 2&4) to fire them. If you haven't, check continuity of the wires between the injectors and the ECU (pins 3 and 32)

I'm trying to help you out. Please check that your injectors are getting 12V while cranking before going any further or spending money getting your injectors cleaned.

[theTBLACK]

Just to check the obvious...the injector wiring harness is plugged into the big black wiring box under the manifold?

Yes. The only thing we haven't checked is from the DME to the injector ports all the way through, and the fuseable link.

[bmwman91]

Just to check the obvious...the injector wiring harness is plugged into the big black wiring box under the manifold?

[theTBLACK]

Yup. It was coming out of the feed line right at the rail. And they weren't rebuilds - which makes me think they aren't firing at all,

At some point, the plugs were wet. But I'm not sure what's happening now.