NO start issues.....then start fine. Let me explain.

I have a 1989 Jeep Comanche. 4.0 Renix, 5speed, 4x4.
About two week ago, i went out to my jeep to leave work and it would crank and crank and crank, but no start. I couldn't understand what the issue was. I turn the key and you can hear it pressurize.
So i was thinking well if the starter is bad, I will pop the clutch. Well I wasn't on much of a slant of a hill so i didn't get enough pressure to start it. But when i got back into it and turned the key it started right up.

So i drive home, no issues. When i get home i back into my driveway like normal. Try to start it, it starts right up. I drive to work pull thru my parking spot, get off work, try to start it, no start, until i push it a little ways and try to pop the clutch. then turn the key over and it starts. Drive home and back into my drive way, next day it starts fine.
I have noticed that as long as i back up before i park, i have no starting issues. If i try to pull through and stop it won't start.

So my thoughts are the crank shaft position sensor or the camshaft position sensor.

Any ideas? My thoughts for one of the above is it seems that the cause has something to due with proper alignment of timing or something internal. I am not a jeep guru, but I try to figure these things out before paying someone else too.

If you have any ideas please let me know. Just by chance i moved my MJ from the driveway to the curb last night without thinking about the issue and now the jeep is on the street and won't start.

Crank position sensor. You don't have a cam sensor in a Renix 4.0.

Unplug the CPS. Probe the two wires going to the CPS with a multimeter set to AC volts.Crank the engine over and read the meter. Should read .5 volts AC or 500 millivolts depending on which scale the meter is set on.

cruiser54 said:

Crank position sensor. You don't have a cam sensor in a Renix 4.0.

Unplug the CPS. Probe the two wires going to the CPS with a multimeter set to AC volts.Crank the engine over and read the meter. Should read .5 volts AC or 500 millivolts depending on which scale the meter is set on.

Click to expand...

Renix has sort of Cam sensor, in the distributor to tell the ECU if it is a compression or exhaust stroke cycle, but X2 on checking the voltage on the one (CPS, CKP, Crank sensor) on the bell housing. He may not know where it is?

It is a two pin connector near the firewall, drives side that leads to a CPS on the tranny bell housing.

Also suggest having a second person crank while you check for a spark at one of the plug wires (pull one and see if it will jump the air gap to the cap stud or engine block. Also try holding the gas peddle to the floor after a no start. That will tell the ECU to turn off the fuel injectors. If it flooded, it will start. If that works, look for a leaking fuel injector.

No spark usually is a bad CPS on the jeep. By the way, if it cranks, the starter is good, it will not crank with out a working starter, so your post was a bit confusing on that issue???? Is not cranking at times, or not firing up? Which is it?

Not cranking is usually a bad battery, bad cables and dirty contacts at the battery and or starter, or a bad, dying solenoid on the starter itself, or the brushes or other parts in the starter on their last legs.

The OP has a "crank-no start" condition. Do as Ecomike and I have suggested to get to the bottom of this.

Cruiser is right, it is a crank no start issue. I bought a new crankshaft position sensor and thought about changing it late last night until I figured out how hard it is to get to the two blts. I am going to switch them tonight and see if it fixes the problem.

Try this first to find out. A $15 meter will determine whether it's the CPS or not.

Renix CPS Testing and Adjusting
　
　
Renix TPSs have to put out a strong enough signal to the ECU so that it will provide spark.
Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue.
The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark.
Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS, crank the engine over. It won’t start with the CPS disconnected.
You should get a reading of .5 AC volts.
If you are down in the 3.5 range on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from Napa or the dealer.
Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off.
A little trick for increasing the output of your CPS is to drill out it’s mounting holes with the first drill bit that just won’t fit through the original holes. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.

So I did as instructed, I borrowed a voltometer and tested as instructed.
While the engine is cranking, the voltomete was registering .3 ohms if I was testing correctly and I believe I was.
I plan to pull the crankshaft position sensor, clean it up and see if it is working better, if not I bought a new cps.

The test is for AC volts, not ohms. Did you mean to type AC VOLTS?

I would just replace it with a new quality unit. Can't hurt to drill out the mounting holes though.