Hey gurus: Need help with engine problem

[ixguy]

99 323i auto, M52TUB25

Just got done replacing head gasket due to coolant leak. While off, replaced basically all vacuum hoses, everything looks good. Checked function and condition of DISA valve, checks out perfectly.

On startup, received codes for minor emissions control leak (pre-existing) slow response on one Bank 1 o2, no response on the other Bank 1 o2, and Seconday Air injection Bank 1 flow to low.

Also more critically, misfire on cylinder 4, and code 1250 which I *think* is Fuel Pressure Regulator Control Circuit malfunction.

We moved the plug and coil from 4 to another cylinder, code did not move, still runs like crap. Replaced the suspect plug, same thing.

We replaced the FPR and (ancient looking) fuel filter, and all fuel lines and vacuum lines associated with those. Started right up, runs like complete crap. Only code coming up now is the 304 -- misfire on cylinder 4.

We are 100% dead sure the primary timing is right. Ran it around 3 times by hand and observed the workings. 99.5% sure the VANOS is built back up correctly too.

Running out of ideas, any gurus want to wade into this one? I'm desperate for ideas...

[Eurostyle]

IMO its a complete waste of time and $$$ trying to rebuild this motor, even if all goes well, they don't last after a year or so...and you are back at the same point.

Did you do a comp test!? Are you sure all valves are ok? Even if the head was rebuild, check again, something may not be sitting right!

[ixguy]

We did a compression test before the head gasket, was ok except one was high (the one with coolant).

Motor was strong and ran well before the service, only it had coolant smoke on startup and consumed coolant.

Looking for troubleshooting advice at this point, we have already committed to this course of action, the rebuild is done.

[ixguy]

Update, compression checks out fine. So I think the head gasket job and valve train are all fine.

We cleared all codes, none are recurring, but it runs rough enough to vibrate the car and stall out if you don't give it some gas.

[TSI]

This may sound daft, but have you checked the ignition? I've had a hidden crack in a spark plug lead give misfires before.

[jabela]

Vibration could be worn out motor mounts. Were those replaced?

[Blackedout95]

Curious, what has the cost been and who did you have do this work?

[ixguy]

Originally Posted by jabela

Vibration could be worn out motor mounts. Were those replaced?

Definately not mounts, it's not running correctly even at idle. I'm familiar with what bad mounts are like, and while this work was being done I had a good look at them, they're in excellent condition.

Originally Posted by Blackedout95

Curious, what has the cost been and who did you have do this work?

My dad and myself have done the work. Cost has been a bunch of gaskets, set of bolts, some helicoils, a bunch of vacuum hoses, fuel filter, FPR, new Vanos seals, a lower rad hose, coolant, oil. Between $300 and $400.

We bought a fuel pressure gauge and and have created a rig to hook (regulated flow from) the compressor up to the manifold to check for leaks. Will report back on those findings tomorrow.

Originally Posted by TSI

This may sound daft, but have you checked the ignition? I've had a hidden crack in a spark plug lead give misfires before.

Not really sure how to do that without replacing the loom? The ignition wires really do look to be in excellent shape and were minimally disturbed during this operation; they all remained in their rail. All the coils offer equal resistance and moving them has no effect on the running, nor does changing/moving plugs. Can you offer any suggestions for testing / diagnosing this?

[Dinanstu]

I would think its timing. Dual Vanos are tricky...

[ixguy]

Originally Posted by Dinanstu

I would think its timing. Dual Vanos are tricky...

For the primary timing we used a good cam-locking tool and observed the TDC and valve behaviour after installation by manually advancing the motor, and we were extremely careful with the VANOS. But, mistakes are possible of course. How would we go about checking for a mistake in that area?

[TSI]

Originally Posted by ixguy

Not really sure how to do that without replacing the loom? The ignition wires really do look to be in excellent shape and were minimally disturbed during this operation; they all remained in their rail. All the coils offer equal resistance and moving them has no effect on the running, nor does changing/moving plugs. Can you offer any suggestions for testing / diagnosing this?

Yeah, just remove the loom. Check both ends of each lead! Pain in the ass, but better to know that it's fine.

[ixguy]

Originally Posted by TSI

Yeah, just remove the loom. Check both ends of each lead! Pain in the ass, but better to know that it's fine.

Alright, I'll have a look at that tonight and do some multimeter tests to see if I can find any crosstalk.

By the way the fuel pressure checked out fine, steady 50PSI.

[ixguy]

After much troubleshooting and testing that the harness for the fuel injectors was loose back where it connects by the brake booster. Once reseated, all is well, car runs great!

Turns out when some of your injectors are not getting a consistent signal to fire all sorts of calamities happen to the motor's operation and it gets ODB code diarrhea.

[Randy]

you and your dad are amazing

[ixguy]

Originally Posted by Randy

you and your dad are amazing

For the record, my Dad is amazing. The guy rebuilt my double vanos motor in his spare time at his house, and he's not a mechanic.

I'm just along for the ride.