Help Reading LM-1 Logs

[Maffett]

Can someone help read these A/F ratio logs? I'm fighting a rough running problem with my 74 2.7 CIS.

At first I thought I had a fuel delivery problem, but the fuel pressures checked out OK.

I bought the Innovate LM-1 device during the fuel system investigation. I found I was running very rich. I was able to adjust the mixture closer to 14.7 and now the car starts, idles, and runs better. But I'm still getting a bucking / cutting out problem at light load / part throttle. Once the bucking starts, the only way I can get out of it is to disengage the clutch or push the gas to the floor.

The Logs looked to me like I was loosing spark, so I switched over to investigate the ignition system. My Permatune unit failed a bench test, so I procured a used Bosch unit and a MSD coil.

The Bosch unit seems to be operating OK, but I still have the problem. The car runs the same.

Thanks for any opinion of what to look for next.

[Maffett]

Bump

Thoughts anyone?

[ischmitz]

Hi,

It's very hard to say what we are looking at in your LM-1 graphs. I don't see a load signal (not easy to get with CIS) or an RPM signal. So the A/F ratio alone is not very telling. I wonder what made you think you lost spark?

The load signal would be the vaccum in the intake - you'd need to rig up a sensor. The RPM signal under WOT would show how the A/F behaves a little better. With part throttle you always see very lean conditions once you lift. And I don't think the A/F is a way to determine a bad igntion. Missfires due to lean conditions will look the same as no spark....

In general I wonder what threw the mixture off in the first place on your engine. With CIS you need to check your control pressure, make sure you have absolutely no vaccum leaks and take it from there. And you check the CO level to determine mixture if I am not mistaken. What did you do to adjust your mixture?

The LM-1 wouldn't be my first choice to tune a CIS engine. I'd get the proper CIS gauges. And make sure your timing is corrent and the advance is working properly.

Ingo

[Maffett]

Ingo,

I've got a pressure gage installed on the fuel supply line between the filter and the fuel distributor. It reads 60 psi steady. Seems like this should be closer to 75 psi. I relocated the fuel pump from the rear to the front several years back. This probably reduced my system pressure a bit, but until now it hasn't been a issue.

I've got another pressure gage in the control line between the WUR and the FD. It ramps up from 25 psi to max out at 44 psi at 180 F. At this point I can valve off the WUR with no affect to engine speed or change in idle. Once again these pressures seem low. Maybe I should be focused more on getting these pressures up to spec.

I set the A/F mixture using the LM-1 and adjusting the FD set screw and bypass screw. The car runs much smoother now, but the bucking still hits in part throttle.

I've checked all the normal places for vacuum leaks.

The spikes in the LM-1 log look like rhythmic misfires to me. The uniform nature makes me think it's an ignition problem rather than a fuel problem. But having not looked at an A/F log before, I'm not sure if I am reading it right.

[evill]

Looking at your graphs, you look too lean. While 14.7 AFR at idle is text book nice, it is not a reality for our engines. Try setting your idle to 13.5 AFR. The bucking could be lean surge. My 2.7L needs to be around 13.1 - 13.5 AFR to be happy.

Ed

[Maffett]

Ed,

I'll set the mixture to 13.5 and give it a run.

What system pressure are you at? I've got 60 psi in the supply line before the fuel distributor. I've got 44 psi in the line between the distributor and the WUR when I shut the valve. At WOT I've got 44 psi to the WUR with the valve open.

Thanks

[356RS]

If you extend the time line on your data sheet so you see like a 3 to 5 min. period instead of the 9 min session you will be able to see the AF numbers better. And it is running lean.