Manager Forum

WE PUT A NEW ENGINE IN THIS JEEP AND NOW HAVE CODE P1391. WE REPLACED DIST, CRANK SENSOR, FLYWHEEL AND SET EVERYTHING BY THE BOOK. WE USED DEALER PARTS AND STILL HAVE THE CODE. WIGGLE TEST DOES NOTHING. MODIS SHOWS GOOD WAVE FORM ON BOTH CAM AND CRANK SIGNAL. HAS ANYONE ELSE COME ACROSS THIS BEFORE.

Welcome to the Forum.

I doubt you're going to catch this glitch with a Modis. That Modis data is processed by the PCM. You need a true scope and backprobing at the PCM to see this. When you do this, you'll need to scope both so you can see the relation between the two signals.

Also make sure you have the dist in correctly. On some models, you need to grind the locating tabs so a very minor adjustment can be made to sync these properly. Usually happens when a new engine is installed.

We did use the scope and back probe the cam and crank sensors at the sensor connections and the modis showed that they were in sync in the pid data. How do you know if the dist needs to be adjusted slightly?

If you superimpose the two signals, you can see if they're are correlated or not. The other way is to have a sacrificial cap and drill a hole where number one goes and align everything and see if it points EXACTLY to number one. If it doesn't, grind the tabs so you can get a little adjustment. Don't need much.

The code went away when we put the dist. in with the center of the rotor button 1 tooth past cyl #1 towards #3. Thanks for the help.