LS1 24x - Lost sync Reason 91 - bad rpm signal, won't start.

[pac1085]

Hi,

My first time installing Ms3/MS3x on a LS1 24x (only familiar with 60-2 wheels from past experience)

U7 is not an LM2904. I made sure to replace it with a MC33072

Engine won't fire. RPM's seem to cut in and out. Pot settings for crank and cam were per the manual....

crank:
"c) With a small screwdriver, turn the pots, R52 and R56, about 12 turns anticlockwise (sometimes you may feel a "click" when the end position is reached, they can't be damaged by turning too far.)
d) Turn R56 back about 6 turns clockwise. "

cam:
For LS1 type sensor or logic modules inputs
a) Ensure JP7 is not jumpered.
b) Turn both pots (R11 and R32) 7 turns anticlockwise (sometimes you may feel a "click" when the end position is reached, they can't be damaged by turning too far.)
c) Then turn the top one (R11) 3 turns clockwise.


I am not sure how to understand the composite log. Does anyone have some insight?

Thanks!

[elutionsdesign]

Well, the top signal is the cam, that looks fine. The middle is the crank, you are getting a signal, and bottom in red is the sync loss. There is lots of that, it shows as error reason 91. You'll have to dig through the documentation to find out what that means.

[ashford]

take a pic of your board, some times the pots don't match the build instructions and get installed backwards

[pac1085]

Thanks, but this isn't a new board - the pots worked fine on the last engine (not an LS, but used both crank and cam sensors) before I switched it over.

Anyone happen to know what sync loss reason 91 is? It is not documented anywhere that I can see.

[pac1085]

Ok, I found a post referencing what reason 91 is. something with the cam.

I put it in semi-sequential and wasted COP and i get a stable RPM signal now.

[pac1085]

Still having issues starting the car, even in wasted spark/semi seq mode. I don't see any lost sync though, and the RPM looks ok..

[pac1085]

can anyone tell if there may be a mechanical issue with the engine timing based on the composite log? I installed the cam dot to dot with the crank and it appeared fine, but I can't rule it out. It is a new engine I built, never fired before.

BTW, I confirmed that all of the fuel and spark outputs are wired correctly in output test mode. Had a nice big backfire when I tested the ignition coils in the car.. (so the fuel is there )
Thanks!

[elutionsdesign]

Can't tell any physical timing issues from the composite log. Have you checked that the commanded timing and the actual timing coincide?

[pac1085]

I haven't yet (trying to avoid cranking it as much as possible, since the engine is new) However, I'm starting to think it may be related to the crankshaft input? If I look at the composite logs, and compare them to this, I notice the crankshaft signal isn't even close to matching:

Capture2.PNG

Would this be related to the R52 and R56 settings? I have them set exactly as listed in the manual.

Thanks for the help so far. I don't mind shooting over some cash via paypal to anyone that can help fix it

[jsmcortina]

This is nothing to do with the pots settings.

It looks like the cam is maybe 90 degrees out?

If you reconfigure for wasted-COP and semi-sequential fuel, the engine ought to run without the cam input.

James

[pac1085]

Thanks James. I'm positive the cam was installed correctly - "dot to dot". I checked it many times before putting the front cover on. I don't see how it could be 90 off (unless a manufacturing defect by Comp Cams). I also checked with the company that designed the cam (Speed Inc) and they said that is the correct way to install it.


Is it OK that my crankshaft signal doesn't seem to match up to the one in the LS1 manual? It seems to have a completely different pattern in the composite log, vs the printout from the manual. I looked at other posts of people having scoped the LS1 crank and it seems to match the diagram in the manual.

[racingmini_mtl]

The polarity of the crank signal seems to be inverted.

Jean

[jsmcortina]

Find attached a composite log from my own LM7.

The cam transition needs to occur around the middle of 5 pulses of one polarity, then 5 pulses of the other polarity. In my log this is showing as 5 "long-short" then 5 "short-long". If it isn't happening like that (yours is not) then something is out of phase between crank and cam.

James

[jsmcortina]

Graphical view from that composite log.

lm7-complog.png

James

[pac1085]

Thanks James, I now understand why you are suggesting the cam may be 90 off. It also explains why the car still won't start in semi-seq/wasted COP mode. I will pull the front cover and check tonight. This seems really odd. If I have to, I will put the stock Lm7 cam back in.

[pac1085]

Ok, you can take my MAN CARD away. I installed the cam 90 off. Thank you again James, for pointing me in the right directions by looking at the datalogs.

[jsmcortina]

Ok, you can take my MAN CARD away. I installed the cam 90 off. Thank you again James, for pointing me in the right directions by looking at the datalogs.

Ooops!!!
No bent valves I hope?

James

[pac1085]

No bent valves It seemed to be exactly 90 off - the exhaust valve would open when the intake should have, and vise versa... quite interesting to see.. lol.