Need advice from experience for an M42 rebuild

[bmwman91]

-Hmm, yeah hard to say from the video. I've seen cars run worse from vacuum leaks and scrambled sensors, but I'd still do the compression test ASAP. You don't really need to warm it up since a cocked valve will probably show up very clearly if present, but I'll cross my fingers for you that it's something else!

Maybe also take a look at the crank damper wheel too. They get old and the rubber rung cracks, which can cause the outer toothed part to get wonky and the computer will lose track of the crank position.

[JonsE30]

Oh man me too. I would cry if I have to rebuild again. Sent from my iPhone using Tapatalk

[roguetoaster]

I also cannot tell what that is from the sounds. However, it's always safe to do as suggested above. If you borrow a tester from an auto parts store do put some anti sieze on the threads of the hose fitting before threading it in.

[JonsE30]

Thanks guys. I’ll try to get my hands on a tester ASAP.

[JonsE30]

Compression test is about 180ish across all 4 cylinders. There was little to no variation between cylinders. This was without bringing up the temp.

[roguetoaster]

Compression test is about 180ish across all 4 cylinders. There was little to no variation between cylinders. This was without bringing up the temp.

Sounds good. Clearly it's time to hunt down the items mentioned above. Start with the crank damper, see if you can tell if it appears to maintain a constant gap at the back relative to some reference point as that's a good way to visually check for issues.

[bmwman91]

Cool, yup time to start looking for the dozen or so stupid little things that it normally is! Consistent compression should at least give you some peace of mind. Well, sort of. If it ends up being the crank damper, that's one that will hurt the wallet! It might be cheaper to convert to the E36 serpentine belt setup at that point.

[JonsE30]

Crank damper pulley looks good. No tears, no wobble, everything looks aligned. AFM and TP sensors were plugged and no sign of any damage on the wires. I cleaned out the ICV and it’s bottom hose was loose so maybe it was a vacuum leak? No more CEL but still kinda rough. I can’t remember if that is just normal. What I did notice was the spark plugs were black on the tips, this could lead to a rough idle right? Temp started rising so I turned her off cuz I don’t have my cooling system in yet.

[roguetoaster]

Probable vac leak from the ICV. Black on the plugs is probably a result of that and a few attempts at starting during the timing work, just clean them and reinstall.

[bmwman91]

Yeah the black on the plugs is normal if you have only run it cold. The warm-up enrichments are fairly significant.

The M42 is definitely not the smoothest idling 4 cylinder out there, but if it does not feel like it is running right then there's probably another leak somewhere. Contrary to popular belief, it will at least have a stable idle when everything is working properly, so if the RPM dips or hunts it is likely that there is a clogged ICV, vacuum leak or worn sensor somewhere.

[roguetoaster]

It's worth remembering that vacuum leaks will appear to clear up above 2500 or so RPM, whereas an electronic issue will probably not. Both types of issues can cause poor transition on and off throttle.

[JonsE30]

seems fine 2500 RPM and up. i think at this point i can end the thread since all the issues i will encounter now are non rebuild related right? i can now go down the checklist haha.

[roguetoaster]

Check, check.

[JonsE30]

actually i think something might have come back to haunt me. as of now i was planning to bleed the clutch slave cylinder. the pedal comes back to its resting positing after being depressed, but there is no pedal back-pressure. i tried bleeding it but i get no fluid when pumping/holding the the pedal and cracking/closing the bleeder valve. i've read where you can take out the slave cylinder out of the transmission and just "bench" bleed or "hand" bleed but i still could not get any fluid. have i not pumped enough or is something else wrong?

i read it could be a bad master cylinder and it would be leaking fluid all over the floor, but it's dry. i dont recall messing with the clutch master cyclinder during the engine rebuild.

could it be like an issue if i installed the clutch fork and pressure plate? but would this even be a factor if it is out of the transmission trying to bench/hand bleed?

[roguetoaster]

Uncheck, uncheck.

Could be a hydraulic system failure, but it does not sound like a component being backwards in the clutch assy. Suggest that you try to crack the next line fitting upstream and see if you get fluid. Bleeding the slave by hand is usually NBD.

Is the clutch engaging/disengaging?