Timing all over the place

Discussion and support for MoTeC's earlier generation ECUs

Timing all over the place

Postby chuckk on Fri Jan 25, 2019 12:26 pm

Hi guys,

Running a sbc with an M48 and a distributor. We took apart the engine to change the lifters. I re did the base timing with the CRIP test. (46 seems to be on the ball)

The problem is when I leave the crip test page to go back and start to tune the engine, the timing is all over the place and backfiring like crazy.

If i stay on the CRiP test page with the timing locked at 20 deg for example, I can rev the engine with no issues what so ever. As soon as I leave the page the timing jumps all over the place and I cant rev the engine.

I had no problems before and i dont see any sync/ref problems.

Thanks
chuckk
 
Posts: 12
Joined: Sun Sep 30, 2018 12:15 pm

Re: Timing all over the place

Postby PQatPIT on Fri Jan 25, 2019 3:52 pm

Sounds like a classic problem of dizzie being in wrong position. Occasionally spark goes to wrong "tower" ie. to wrong cylinder.

Remedy is easy. Turn engine to about 20 degrees cyl. 1 BTC. Then check where the rotor tip is pointing. Should be near the cylinder 1 tower. If it is in middle between two towers there is a big chance that spark goes to wrong cylinder.

MSD and others have rotors where you can adjust relative position if the distributor body can't be moved.

Edit: See this: https://www.youtube.com/watch?v=aWMlNwGW0tM
PQatPIT
 
Posts: 73
Joined: Fri Jul 11, 2008 9:51 pm

Re: Timing all over the place

Postby chuckk on Sun Feb 03, 2019 1:08 pm

Thanks !

It was exactly my issue. I re-positioned the distributor a second time, re did the CRIP and now every thing is good.
chuckk
 
Posts: 12
Joined: Sun Sep 30, 2018 12:15 pm

Re: Timing all over the place

Postby chuckk on Fri Feb 08, 2019 12:08 pm

Hello again,

It seems like I am loosing my initial good crip setting. After a few runs on the dyno, the timing is not accurate anymore. Had the timing at idle after 3 runs being off 15 degrees, same crip number...

Did a test with the timing locked at 34 and ended up being at 55 under load.

This car has an MSD 6AL.
chuckk
 
Posts: 12
Joined: Sun Sep 30, 2018 12:15 pm

Re: Timing all over the place

Postby SprinterTRD on Mon Feb 11, 2019 7:48 am

Most likely cause is you are using a magnetic crank (REF) sensor and have selected the wrong trigger edge.

Incorrect Ignition delay time may also produce this error
SprinterTRD
Pro User
 
Posts: 319
Joined: Wed Jul 16, 2008 8:24 am

Re: Timing all over the place

Postby chuckk on Tue Feb 12, 2019 8:17 am

I decided to scope both signals and found something interesting. The MSD distributor has an hall effect sensor for SYNC but after a discussion with MSD, they do not sell any distributor with an hall effect sensor for the model that I have.

Only magnetic sensor (2 wires ) are available for that kind of distributor. I am thinking maybe somebody decided to replace the sensor inside the rotor. The cam signal is not as good as the crank but it shouldn't matter since the sync is for the sequential fuel injection right ?

The crank is indeed MAG and I will try to play with the voltage threshold tomorrow see if it's the issue because it is using a mercedes sensor and using a predefined setting inside the M48.

Here is the scope picture.

I will try to switch the edge and play with the delay but I am not sure where in the menu it is ?

Thanks for all the help, it is much appreciated
Attachments
corvette.jpg
corvette.jpg (119.04 KiB) Viewed 5945 times
chuckk
 
Posts: 12
Joined: Sun Sep 30, 2018 12:15 pm

Re: Timing all over the place

Postby SDean on Tue Feb 12, 2019 8:21 am

Those signals are quite noisy, if that is what the ECU sees then you will have issues with timing control.
Stephen Dean
MoTeC Research Centre Melbourne, Australia
User avatar
SDean
Site Admin
 
Posts: 773
Joined: Tue Dec 02, 2014 9:29 am
Location: Melbourne

Re: Timing all over the place

Postby chuckk on Wed Feb 13, 2019 7:12 am

Just tried switching the crank trigger to falling edge instead of rising and could not get the thing to not trigger an error.

I have 8 teeth evenly spaced on the crank trigger wheel and using a mercedes magnetic sensor. the sensor only has one wire with a shield around it. The wire is going at the ecu pin #6 and the shield is spliced with the other sensor grounds. A little bit weird to me since I was expecting 2 wires with a shield around them. One wire for "+" and one wire for "-". All sensor grounds have continuity at D9 male plug #6. What do you guys think ?

Things I have tried are :

- Scoping both signals. (new wiring will be passed far from the spark plug wires to make sure I get rid of the noise) I tried to add a ground path to the engine block just to see if that would clear up on the scope but it did not seem to do anything. I have read mixed reviews about grounding both sides of the shield.

-Changed the rising edge trigger to a falling edge. Doing that just keeps throwing error codes even after adjusting the CRIP.

- Set up a custom threshold voltage table instead of using the predefined option 2 in the drop down list. Looking at the waveform it seems to be always oscillating from + 5V to -5V so I am not sure what values this table needs.

- Played with the ignition delay. This had the most effect on the system. At 20 uSEC, idle is ok but revving it I am loosing it again. At 35uSec, idle timing is bouncing but catches up while steady state revving it. 50uSEC, forget it, won't start the engine.

-Not sure what the ref/sync mode do but changing it to anything else than 12 throws everything off. So 12 it is.

At this point I am about to drill a hole in the distributor cap to see the rotor phasing like you guys mentioned.

Thanks
chuckk
 
Posts: 12
Joined: Sun Sep 30, 2018 12:15 pm

Re: Timing all over the place

Postby gtihk on Mon Feb 25, 2019 11:58 am

Falling edge seems to be correct. You might want to re-do the wiring for the ref sensor and shield it better against noise.
gtihk
 
Posts: 64
Joined: Thu Jul 19, 2018 12:37 pm

Re: Timing all over the place

Postby gtihk on Mon Feb 25, 2019 12:01 pm

Sorry, my bad. If you want to use Falling edge, you will need to swap the two wires around.
gtihk
 
Posts: 64
Joined: Thu Jul 19, 2018 12:37 pm

Next

Return to M4 and M48 ECUs (including M2R and MLS variants)

Who is online

Users browsing this forum: No registered users and 5 guests