3.2 FW Position & Speed Sensor Testing - No Start Trouble Shoot Help!
 

After buttoning the hatches after a valve adjustment I try to start my 3.2 with no luck. The engine fires, runs for a second or 2, then dies. Car has run beautifully, without any hint of start hesitation since initial installation 4 years ago. Back then, the builder stated that similar problem existed, but found bad ground connection to the FW sensors, fixed, ran great since right up to said recent valve adjustment.

Reading related threads suggests electrical connections to the flywheel position or speed sensor may have been disrupted while moving around the Motronic wiring harness (gray sleeved motronic wire collection) working around the left intake valve area.

Threads mention to reference sensor testing methods in Bentley manual, but I don't have one. Understanding grounds and connections are crutial to Motronic life. Fuel okay (pump working), spark okay, fires.... seems like it completes start sequence then balks at transitioning to run sequence (suggesting faultly speed sensor connection since it wouldn't fire with bad postion connection right?). I stress connection because all sensors/ relays (FW speed, position, DME relay) are only 4 years old , about 5000 miles on car since replacement, and car ran great before valve adjustment. Neither FW Speed, or FW Position connectors were disconnected during valve adj. Seperated O2 connection inbetween 3-connection vertical bracket (with speed and position) and actual sensor to allow for slack to move header for exhaust valve cover access.

Does anyone happen to have a Motronic wiring diagram of the O2, fw speed and position sensor as mounted in the engine compartment (left side). Namely, where neg or ground tabs are on the box connectors and how to go about testing?

Any suggestions on how to trouble shoot is greatly appreciated!

Thanks!

The sensors should test about 1k ohms between 1 and 2, the lower two pins. A grounded shield on 3. I've read several posts where those connectors on that tree have broken so I would check the integrity of those. Don't know that an O2 sensor would keep it from starting. Ken

Thanks Tigerrat!


Does anyone think that a pinched O2 wire would cause this non-start issue. Another post suggested similar issue when only changing at CAT (O2 only changed or moved). O2 was moved during my valve adjustment, perhaps the wire got pinched in the hole with the wiring harness in the rear tray going back to the DME....

Thoughts?

If you have spark (more than one) your speed and reference sensors are fine.

It sounds like a fuel issue. Like I said in the other thread the OXS heater and fuel pump are powered by the same set of contacts on the DME relay.

Further troubleshooting will require a voltmeter because it is hard to see electrons flowing with the naked eye. ;)

Closing the loop... all fixed. Yep, rick-I you were right, fuel issue. Pinched fuel line starving run sequence.

Many Thanks! Another Pelican forum success story :D