Probabally been beat to death already, but

would a CPS (crank) going bad cause my '88 MJ 4.0, 5speed to crank longer and what seems like a little longer every time I go to start it? It is getting REALLY ridiculous, esp. when warm, to sit there and crank it for 5 seconds to sometimes almost 40 seconds before it finally starts. Fuel system is within spec., TPS in spec., probably need to change o2 sensor judging by ring of soot on tail pipe tip. Have also checked manifold bolts for tightness and all being there.
Thanks in advance,
Ren

RENIX (1987-1990 4.0) is known for long crank times. Make sure your battery is always fully charged, since that effects cranking speed (the CPS is usually an all-or-nothing deal.)

The RENIX control system looks for two things before it starts sending FI and ignition pulses - 1) 300rpm at crank, and 2) a valid SYNC signal from the distributor. It is capable of operating without the SYNC signal - I believe that would cause a series of "misfires" while the ECM was guessing where the #1 cylinder was.

If you're cranking smoothly - just longer - check battery voltage and see if you're self-draining overnight or something. If you're cranking longer and having some "stumbles" during operation, check CPS. If you're misfiring on crank and your fuel mileage goes all to Hell at once, check your SYNC sensor.

5-90

Okay, so I might possibly have s bad sync. sensor since my gas mileage is getting gradually worse and every once in while, the motor does seem to have a misfire at start up. Wonderful, I guess I need to look under the dist. cap tomorrow, and maybe see if there is any oil build up, or do you think that maybe I should just go ahead and swap dist., since I have a couple of extras?