Gearbox rattling at low revs under load- timing?

[kpr]

from memory.  theres a setting to use the table or use fixed.(wording is probably different)  change it to fixed.  

 

or probably just as easy:

 

just put 10 in the whole map.  

 

 

you should start off with timing set low. once you are happy with your afr, which sounds like you have sorted.  start to add timing.

 

its actually quite good to start with quite low numbers when you are road tuning.  as a few degrees  will feel like a big gain. as you get closer to where it needs to be gains will feel less and less. will never get it perfect without dyno. but should be able to get it pretty close.  

[NaN]

NaN

[yoeddynz]

Cheers Nigel. But my shaft is a perfect length. No complaints there.. . I was really careful about that whole aspect as was paranoid about getting it wrong. Was the most timing consuming single bit of measuring and engineering.

[yoeddynz]

from memory.  theres a setting to use the table or use fixed.(wording is probably different)  change it to fixed.  

 

or probably just as easy:

 

just put 10 in the whole map.  

 

 

you should start off with timing set low. once you are happy with your afr, which sounds like you have sorted.  start to add timing.

 

its actually quite good to start with quite low numbers when you are road tuning.  as a few degrees  will feel like a big gain. as you get closer to where it needs to be gains will feel less and less. will never get it perfect without dyno. but should be able to get it pretty close.  

 

 

 

 

just found this on how to check and set the timing. Scroll down this page.

 

http://www.megasquirtpnp.com/docs/mspnp_g2_mk9395.htm

[Unclejake]

 

- what if the input shaft is about 1-2-3mm tops to long... but just enough to bind everything up and cause some strange effects.

Good thinking, but that scenario would destory the engine pretty fast as the crank thrust bearings would get pwnt 

/sorry for spamming your thred Yoed

[yoeddynz]

No wuckin forries UJ.

[yoeddynz]

Sooooo.... the latest on the rattle is that its much better but still there since we loaded a new ignition map onto ECU late this afternoon.

 

On friday I used the timing light at work (mines broke with a blown bulb I cant seem to locate), locked the timing at 10 and checked the timing marks. It was at 12 degrees so I adjusted the 'trigger wheel offset degrees from 50 to 47.5 till the timing light showed 10. Pretty chuffed I had got the trigger wheel so close by eye

 

I created a new map using a generator online just to get a better starting point. It immediately away looked so much better than the previous table- which was the default ignition map that came with the code from Extraefi and was possibly a map for a rover V8 which the fella at Extraefi owns.

 

Anyway we took it out for a good drive and re-tuned the whole VE table to suit the new ignition curves.

 

But the rattle is still present and although I have to purposely try a bit harder to get it to rattle I feel that either I have rattled the box enough that it now needs some love,

 

Or the gearbox was already a bit tired and as previously mentioned by Ta 63-1uze it is now become noticable because of the lower spread of torque from the Piston V6,

 

Or its still there because of my possible crazy unmatched driveshaft yoke angles..which I sort of forgot to check last week,

 

Or I could retard the ignition even further? Hannah has already dropped the numbers in the bins where the rattling is present by a further 3.5 degrees.  We have learned so much more about tuning even in the last hour of driving it and playing with the numbers. A little afraid to keep dropping them but will keep experimenting I think.

 

Overall the car is even better to drive!!! Much smoother about town without the sudden snappyness that the last ignition table with its massive early advance seemed to create. I'm loving this tuning stuff and seeing such dramatic changes.

 

Here is the latest map. The generator made the 750 rpm line all 10s for some reason? Not sure what I should do with that? I totally understand that the table aint perfect. Its a simply generated, pretty linear table created from quite basic info.

I also realise that we will never get if perfect until we use a dyno. But its getting better and we are learning

 

The lines that Hannah knocked back are the 1200 and 1700. The rattle seems to be around the 42~72Kpa   x  1200~2000rpm area.

 

 

I took a small data log but not sure how to share it. Or even read it.. yet another whole area of more learning!

[kpr]

it will be assuming it idles at 750rpm.     so if you get some load at idle the extra timing at 600 will make it want to rev back up/hold the rpm.      that looks alot better than the old map!  you probably need to put more timing in the idle cells.     in the row it idles, plus the one above and below.  try increase the timing by 5 degrees in 600, 750, 1200.  fade out from there on.     becuse 10degrees at ilde is probably a little low. and will be heating everything up

[yoeddynz]

Yeah it idles at 750. Well it should do but I now need to screw in the idle bleed screw a touch as its sitting more about 900-950.

 

Its just weird having a line of 10's. Other thing is that if I stab the throttle from idle it'll pink slightly before revving. Watching the table as I do this the yellow dot jumps up first, under load, then across. But it happens so quickly its hard to see exactly where its happening. I need to learn to read the logged data.

 

Never drove the car today as busy extending out shed. But did start and move car. It started a lot quicker (was never ever a bad starter though) and didn't do the big rev then drop back down thing. I guess because its not got such silly advance now.

[kpr]

line of 10's is fine.

 

can get knock when  you stab the throttle even if the timing is correct.    im not sure if megasquirt has the feature (it should).  but alot of ecu's have "transient retard." so when you stab the throttle it pulls some timing for an engine cycle or so.   

also if your acceleration enrich isn't correct, it won't be helping the cause either

[yoeddynz]

I have the acceleration enrich turned off for now. Another thing to play with!

[flyingbrick]

Is the transient retard there because fuel takes awhile to make it to the combustion chamber?

[kpr]

ah the acceleration enrich  may fix your problem, if its turned off.  make sure its set with tps not  map. 

 

 

Is the transient retard there because fuel takes awhile to make it to the combustion chamber?

 

if the acceleration enrich is set right, usually wont be too much of an issue. group fire the ecu will fire all the injectors like an accelerator pump on a carb.    i don't know the science behind transient retard. but it works if you need it.  possibly something to do with the map reading/ecu, not reacting quick enough to a snap change. (much like why acceleration enrich is required)  since you have more advance at light load, the higher advance maybe used for an engine cycle or so.   transient retard is run from tps, which is a whole lot faster than map

[yoeddynz]

I figure map would be slow on a sudden stab for sure. Yeah I'll set it on tps. Not even looked into the accel enrich at all yet. Probably not noticed a lack of it as I tend not to stomp the throttle under general driving.

[vegie]

maybe not relevant, but I have a Nissan v6 with a factory dual mass flywheel.

 

they are commonly replaced to put a solid flywheel in place of, which usually results in the sort of clattering noise your getting, mostly at idle...

 

was this engine meant to be dual mass in factory manual trim?

[yoeddynz]

Nah it's always solid flywheels on these. Not really a lot heavier than what my cromo item is either. It has a sprung centre standard type exedy clutch too.

Yeah I have read about many dual mass cars having been converted to single mass solid flywheels giving trouble. Often due to using solid centre clutch discs so no give at all.