91 Jeep yj turns over but won’t start - code 11

[Sarahfarideh]

TIA for any advice! So, I have a 1991 Jeep Wrangler YJ 2.5L 4Cyl and it’s turning over but it won’t start. 

Backstory: before it completely stopped working, it was driving horrible. It was jerking and backfiring and then just dying. For awhile we would pop the clutch to start it and then we replaced the starter and since then it has maybe started 4 times. 

we have replaced the starter, ignition coil, o2 sensor, distributed cap, distributed wires, 1 spark plug, and installed a newish (refurbished) ECM. 
 

it’s reading code 11 so I’m thinking it’s the crankshaft or maybe the flywheel. 
 

any advice on how to repair either one of these without replacing?? 

[Moses Ludel]

Sarahfarideh...The Code 11 is either the ignition pickup in the distributor or the CPS (crankshaft position sensor).  I would look first at the CPS and its wiring.  The CPS can get dirty from oil if the engine has a rear main seal leak.  It is not uncommon for the wiring to the CPS to become damaged, especially by an exhaust header.  The symptoms sound like a possible short or intermittent short to ground at the CPS wiring.  The CPS could be defective, it does happen.

Check the wiring from the CPS (at the bellhousing, 11 o'clock above the flywheel) to the ECM.  Remove the CPS and clean it to rule out the pickup being oily or dirty.  The flywheel, unless loose on the crankshaft, is seldom the issue unless covered with oil.  This is a simple hall-effect type sensor relationship, the flywheel is far less likely to play a role here than the CPS itself.

You can check the CPS wires with a volt-ohmmeter to see whether the CPS is defective.  There is a resistance specification listed in the Mopar factory service manual (FSM).

If the CPS and all wiring check okay, there is the distributor sensor pickup signal.  That pickup can also be checked with an ohmmeter, but look for a short or loose/damaged wire connection at the distributor first.

Should the distributor pickup sensor and CPS both check out okay, with all wiring okay, I would look to a fuel supply problem (not a Code 11).  Check the fuel pressure at the fuel rail and also the volume of fuel coming out of the rail with the fuel pump cycled on.  The rail pressure and expected fuel volume are each listed in the FSM for your 1991 Jeep Wrangler.  

Let us know if this works...

Moses