M52 is angry. chain tensioner?

[broach328]

So after 3 years and roughly 25k miles of happy motoring, my m52 experienced its first mechanical issue. Starting about a week ago, its been sluggish to start. I would let it turn over several times let off the ignition then hit it again and it would start about the 3rd time and run quiet and smooth the rest of the time its running so i thought okay spark plugs. Then I drove it two nights ago and it took a little longer to start, and while sitting idling, engine warm, the rpm climbed to 1500-2000 on its own with no throttle input then went back down to idle. So that kind of threw me off a little too but I still felt the car was in no danger. Not even a mile later as I am slowing down to a stop sign I downshift 3rd to 2nd rolling about 20 mph and it makes a knock noise and cuts off. Once stopped I start the car back up and its making a stomach turning knocking noise and wont go over 1500 rpm without the misfire being so bad that it floods and bogs out. So my current position is this: car is sitting 300 miles from home(Im off at school) and I am trying to diagnose the issue and possibly make repairs if its something small as I do not have specialty tools with me and any engine work will have to be done at home. Before we jump to conclusions and say vanos, why did it happen randomly out of the blue? Why did it occur when the motor was decelerating?
What has caused this epic misfire? I might also add that it is obd1 (not for much longer) and the diagnostic port does not function courtesy of the wiring harness adapter so determining which cylinder is misfiring is also out of the question. Spark plugs are NGK v-power which is a copper plug and has low lifespan. They have no been replaced in a couple years could they be contributing? the noise is without a doubt coming from the valve train and if you feel it, the tapping is much more evident at the front end of the motor over the vanos unit. I will post a video later this afternoon of the glorious sound. Thank you all in advance and any input or suggestions is greatly appreciated.

[luckysnafu]

Sure sounds like a vanos issue. My m52 has the vanos rattle when dropping rpm's in the range of 2200 down to 1200 or so. Sounds like marbles rattling around in a metal can. Very noticeable and obvious to tell where it's coming from. I'm going to replace the vanos seals myself one of these upcoming weekends.

Your misfire is weird though, and I don't think related to the vanos. Sorry I can't be of more help.

[broach328]

its all good, i thought vanos too but its something worse i am fearing. somehow the valves got warped. my buddy said timing chain problems but I cant find anyone with a similar issue.

[butters]

while sitting idling, engine warm, the rpm climbed to 1500-2000 on its own with no throttle input then went back down to idle.

vacuum leak. check ICV and all vac lines. may seem trivial but could happen suddenly and will cause problems, so this seems like step 1 to me.

vanos can make marbly noise, yes, but I don't think it can cause such severe symptoms as "knocking" and stalling out etc.

you go on to call the noise "tapping" and that makes me think it is suddenly lifters (due to lack of oil pressure?)

[broach328]

the night that it happened it was a sudden noise while under deceleration around 2-2.5k revolutions. As of right now it is not getting fuel because of a fubared crank sensor which I will be ordering the next couple of days along with possibly a new chain tensioner. After a lot of contemplating and frustration I am narrowing the issue down to possibly the lower tensioner failing. Does the lower tensioner gradually fail like the m42 tensioner or is it possible that it can suddenly collapse? Additionally, it seems as if to have a vacuum leak possibly as well. I am going to go through it and make sure the icv, intake boot and lines are are all in good order with no leaks. In the meantime, here is a video of start up and some blips of the throttle.



In case thats messed up, heres a link: http://www.youtube.com/watch?feature...&v=mM9QfqOupEc

[broach328]

any thoughts? anyone experience similar issues?

[10Toes]

Stomp test doesn't work?

[broach328]

I have tried it in the bast with no results. I might have been doing it wrong. I plan on making a new wiring harness or possibly switching to OBDII. For whatever reason, the diagnostic port is not getting power and I really have never had any issues in the last 3 years so I havent messed with it but now may be the time. What I would like to know from the ecu is if there is possible o2 sensor issues and which cylinders are misfiring so I can have a place to start. It might possibly just say random multiple misfire I really have no way of knowing. Its OBDI with TRM chip, s52 cams, m50 manifold.

[butters]

I would go after the vanos, do the Beisan DIY route or the Dr. unit. Do the upper chain tensioner while in there. Lower chain tensioner is quite easy.

[broach328]

I would go after the vanos, do the Beisan DIY route or the Dr. unit. Do the upper chain tensioner while in there. Lower chain tensioner is quite easy.

yeah thats my thought right now. dont much feel like spending the holidays rebuilding the timing components but I guess if it needs it. the guide on the upper tensioner is fairly chewed up but i figured that was somewhat normal over time. cant imagine such distinct noise could come from the upper but if i do rebuild vanos then the upper will be replaced as well. I saw beisan rattle solution as well so I may do that and see.

[broach328]

update: crank sensor, lower chain tensioner and icv hose to Intake manifold connector on order.

[328ijunkie]

Crank sensor? Fur why?.

[broach328]

mine was fubar. the plug was broken apart and there were wires hanging out. and the resistance wasnt even close. :(

[328ijunkie]

Forgot you were still running OBD1 :P

[broach328]

yeah i need you to make me a proper OBD1 adapter im not ready for obd2 yet!