Timing all over the place

[chuckk]

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

[PQatPIT]

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

[chuckk]

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]

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.

[SprinterTRD]

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

[chuckk]

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

[Stephen Dean]

Those signals are quite noisy, if that is what the ECU sees then you will have issues with timing control.

[chuckk]

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

[gtihk]

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]

Sorry, my bad. If you want to use Falling edge, you will need to swap the two wires around.