whoever figures this out...100 bucks paypalled to them..

[smashed s4]

So i swapped in a replacement m42 into my 91 318is. Kept the existing harness and DME from the old m42. changed a bunch of stuff, h20 pump, timing tensioner piston, VCG, upper oil pan bolts, lower oil pan bolts, did the intake mess blah blah.

anyway, so the car cranks, and barely starts for a split second then dies

sounds like air is escaping from SOMEWHERE, and there is a huge BOOM and rattle from the airbox.


we have diagnosed this:
-getting fuel
-getting spark
-working AFM
-working fuel pump
-fuel lines are CORRECT
-swapped in 2 different CLEAN ICVs

whoever can diagnose, or even come to my house (san jose, ca) and figure this out. i will personally paypal them 100 bucks...

im desperate people

thanks!

[ak-]

If it sounds like air is escaping from somewhere the second it turns off, then it probably is.
Make sure your intake boot is proper and your vacuum lines under and around it are connected.

[smashed s4]

checked all the vac lines! to my knowledge, i think they are correct... really wish i got a veteran m42 guy over to my house to see!

[bmwm42]

Loose spark plugs

[smashed s4]

Nope^ they are snug

[Vivek]

I have this friday off I'll come double check all your vac lines for you.

[bmwm42]

Intake gaskets changed not seated correctly equals your problem

[Massimo]

IDK but sometimes when you buy a new boot some have an extra hole in them. mine did check to see if you do and plug it up if it dose. other wise as mentioned before intake gaskets.

Oh and I believe the is a plug in the air box check to see if that is still in place.

[///digitalme]

is the crank position sensor plugged in??

[absolutdog]

post a video

[alexpage]

Timing, use some soapy water in a spray bottle, to seek out air leaks.

[bmwman91]

Did you plop in a whole, known-running M42?

Did you manually align the timing of the crank & cams? The big BOOM in the air box makes me think that you could have the crank phased 180 degrees off from the cams and the engine is basically pumping air "the wrong way."

[future rs]

Did you plop in a whole, known-running M42?

Did you manually align the timing of the crank & cams? The big BOOM in the air box makes me think that you could have the crank phased 180 degrees off from the cams and the engine is basically pumping air "the wrong way."

This^

If your timing is off 180 the car will sound like it wants to start, but really your valves are open and closed at the wrong time. You are going to be getting combustion in your intake manifold. The car is igniting the fuel/air and dumping the "exhaust"/ igniting when your intake valves are open. I have done this before on a car BIG dumb moment to say the least.

Go through and check all your timing components and settings.

[e30austin]

I had a very similar issue on an M42 a few months back. One of the vacuum hoses came unplugged on the left side of the throttle body (I think it went from the throttle body to under the intake somewhere, it was on the left side of TB) and caused the car to keep stalling out and falling on its face. Eventually figured it out, but did waste a lot of time checking everything else! My money is set on some sort of a vacuum leak.

Just for fun, I would also manually check timing. You never know what someone else's handiwork can do...

GL

[smashed s4]

So it was a full running m42. I know it ran before. How should i go about checking the timing components without actually ripping her open?

thanks!