Intake cam timing vs injector duty. - PeachParts Mercedes-Benz Forum

Pagz · #1 11-30-2010, 03:49 PM

Hey guys,
I still have a few things to iron out on my setup,one of the things that is really bothering me is the smell of petrol in my oil.

One problem is, I get black smoke under WOT(more so on the dyno) but the AFR's look spot on,apparently this can happen due to combustion chamber shape? ...im not so sure..i thought it could be varying mixtures across the bank but all spark plugs look the same shade!!

One of the tuning difficulties we possibly all face is the intake cam 10 degree advance,what do all of you do here in this situation? the intake cam can take some time to advance based on oil pressure/temp/rpm etc etc so there is no defined line as to its on/off stat. We have set it up so that it comes on at >10%TP and >1500rpm ,it has been tricky to get the AFR's smooth around when it advances and when it retards at 5300.

All this has got me thinking about what angle the injector is initially fired and at what stat the cam is in when they do,i do tend to get some fuel buildup inside my plenum,which makes me think the timing is not ideal...and could this also be why we get some black smoke through most of the WOT rpm band?

Any advice or experience on the cam timing/injector timing from you guys would be great.

Thanks,
Paul

JayRash · #2 11-30-2010, 05:13 PM

Well Paul,
When it comes to Cams i usually jump into action, but this is well beyond me my friend. i say think abt it using logic, i guess with trials u will get to it. and if i come across any info ill sure post it here.

Pagz · #3 11-30-2010, 07:36 PM

Thanks Jay,Im due at the tuners again late this week,just hoping to have any possible problems thought out well before hand as it gets very expensive standing around thinking about it.

I get a strange feeling when we first ran stand alone and rebuilt the engine 5 years ago the timing may have been wrong on the intake cam(and hence the intake cam pickup) and as it was the first time the ECU had been setup on the engine it may be possible that after the last few rebuilds we have changed timing and somthing no longer lines up....another thing to do would be to degree the engine and see when the intake actually opens!....as im pretty sure thats just a guess based on were the piston is in the cycle.

whipplem104 · #4 11-30-2010, 10:44 PM

I turn mine on at a little higher rpm, but I turn it off at around the same around 5250. It is nearly impossible to not get it to lean or richen at the switch on/off point. It is too large of a change. I favor a rich spike over a lean one. It would be nice to have a smoother mechanism for. I look at the spike and I get a boost spike at the same time. I think this indicates that somewhere in the middle of on and off would be ideal at this rpm.
If you are getting fuel in your intake then I think that the cam timing is pretty off. This could be because of your exhaust cam also or exhaust back pressure.
It has to be that when the intake cam opens there is enough pressure to blow fuel back out of the intake port. I would think that your idle would be rough though and your manifold pressure would be jumpy.

JayRash · #5 12-01-2010, 03:05 AM

paul
no matter what u do, line up the markings and then turn the cam exhust side counter clock so that u get retard and not advance once the tensioner is tight

JayRash · #6 12-01-2010, 03:13 AM

paul
no matter what u do, line up the markings and then turn the cam exhust side counter clock so that u get retard and not advance once the tensioner is tight

Pagz · #7 12-01-2010, 03:22 PM

Thanks guys,I will check MAP stability!,im confident the cam timing is correct,i went to great lengths last build to make sure that wasnt an issue!.

I think the bulk of my problems are in the lower rpm range,i tend to get black smoke if i idle for along time then do a WOT run,then if i striaght away go WOT again there is no smoke. The tuner mentioned he had to run it quite rich to get a good idle...there has to be something wrong with injector firing time and intake valve opening at idle!!?,it could also be the fact the cam is switching on/off all day long when under light loads and this may be causing rough mixtures,maybe we should raise the TP switch point to say 15-20% instead of 10% and make sure the injectors are firing when there is sufficient valve opening,if we fire them late enough this may also help avoid any unwanted backpressure deflecting the fuel. Having a very rich mixture at idle(high vac) may explain why the oil smells of fuel.

Hmmm thanks again for the input always good to get more thoughts on the table.

Pagz · #8 12-03-2010, 03:11 PM

Ok,
So went on the rollers again,this time we trialed taking the cam output on the ecu and paralleling it with a digital input,so now when the cam activates the ecu advances the fuel/ignition 10 degrees either way,so far this seems to be working much better than before.
We also got the narrow band running again which works ok but you can feel the ecu trimming under cruise might have to work on that a bit more later.
Also did some fine tuning to startup as it used to puff a small cloud of black on startup,i didnt get a clear answer from the tuners but im pretty sure having the ign/fuel change 10 degrees based on cam has helped significantly with how much of the fuel is actually making it into the chamber at low rpm's.

Did a three hour trip yesturday and didnt see any black smoke,however we did see a nice cloud of blue after a long low load run then full power from a stand still...and with fuel in the oil the only thing that can be is rings,not sure why i cant get this engine to seal,tuners are adamant the mixtures were not rich enough to cause damage....i dunno,i give up^^.

whipplem104 · #9 12-03-2010, 10:33 PM

I would not worry to much about the oil. As long as it is not using very much and it is not causing any problems. I set up an aan motor this year for a rally car and it is pretty loose on the rings and it gets oil if it is running at low load for a long time. But when it is racing it gets tight. Last rally it burned less than a quart which includes blow by out of the crankcase vent.
Also make sure your crankcase ventilation is working properly and that the pcv valve is not broken or plugged.

JayRash · #10 12-04-2010, 02:28 AM

i for one cant understand y ur engine wont seal. Now i have to admit that mercs are not very tight engines, well my M104 3.6 is not shy at taking oil if driven hard and its even written in the user manual of the car that if driven hard expect to add 1 to 1.5L of oil for every 1000km of hard driving. That is no small ammount. Mine takes non for the first 1000kms when oil is fresh but after that it starts to use some like 0.5L for the 2nd thousand and then a little more for the third.

But i dont think i see blue smoke and non of me friends have pointed that out either.
Do u think the rod guides are not tight enough and piston ends up rocking?

Pagz · #11 12-05-2010, 06:34 PM

hmmm it doesnt seem to be using much oil,however the oil smells heavily of fuel which has got me really concerened,On the 4 hour ride home yeaturday i couldn't get it to blow anymore blue smoke,well not enough to be visually seen from the rear view mirror,tonight i hope to have someone follow an observe.

How quickly does your 104's oil get dirty?,my old honda used to take at least 5000km's before there was any noticable colour change in the oil,with the merc it seems to be less than 1000 and its very apparnant.

I have plenty of crank case ventilation,3 pipes to be exact,we even tested pressure on the dyno upto redline and bearly got a reading.

Interesting you mentioned the locating of the rods,when i assmembled it last time i thought the play in the piston to rod was alittle excessive,but because they are stock pistons and rods i thought there couldnt be an issue,surely??...

The only thing we didnt do when i had the engine appart last time was to use a torque plate for honing,I didnt use one because i couldnt find any information which said this engine required it...
I might search for a quality leak down tester(mine was a bit cheap and i drilled out the restrictor)and do another check.

JayRash · #12 12-06-2010, 01:56 AM

well u might have been seeing blue smoke due to the extra fuel that was being thrown into the pistons, before this final retune. Fuel in oil degrades it rather quickly. My M104 shows signs of dirty oil from abt 3500 - 4000km depending on abuse. Merc engins arent very tight like honda and mitsubishi. My fiend's evo 9 tuned to abt 400+ hp on stock internals still only uses abt 1/2 a liter every 4000km.

As for the plate well i cant give any input.

Pagz · #13 12-07-2010, 02:05 PM

I had a friend follow me and there appears to be very little or no blue at all now,however oil wasnt completely upto temp.
Im in the process of changing the oil atm as it really smells of fuel.when i started it up cold yesturday it almost sounded like piston slap or big end play which could be a product of very thin oil,that or massive wear!...
For the first time since iv been building this engine there was some ferous metal present on my drain plug magnet,not much,but i guess it shows the oil was way past usable (mobil1 5-50).
Had the plenum off last night and there is much less fuel residue in there than iv ever found,its nearly dry,so injector timing had to have been an issue before the last tune!...and this could be where all my blue smoke has been come from...
I guess i change the oil and see how it goes,if the same thing happens again im not sure where to go..build it a 4th time?....LOL