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CPS checks good...no codes on ODBII scanner...no start

B

Benz0

NAXJA Forum User
Location
Richmond, VA.
I can hear the fuel pump hum when putting ignition in the ON position prior to crank...Hooked up a ODBII scanner (http://www.memoscan.cn/en/showproducts.asp?Cid=10) let it sink up and tried to crank. It cranks, crank cranks cranks but no fire. The starter will sometimes just "stop" working and I have to cycle the key a few times to get it to start cranking again

This rig sits for a couple months at a time but I HATE electronic work with a passion...What do you do when testing for a spark? Analog volt meter? Stick the coil wire up to the block and look for an arc?
 
Year/engine--the BASICS?
 
Ok.

You can use a spare spark plug, attach the spark plug wire to it, ground the body to the engine, crank it over and observe for sparking. If you don't have a spare plug, pull one out of the engine, same procedure. Looking for a SNAPPY BLUE SPARK.

There could be multiple reasons for the starter to "stop". Battery, cables, starter-solenoid, starter relay, ignition switch, and the wires in between.

Do you have an alarm/anti-theft system?

Do the gauges work when you turn the key on?

Do you have fuel pressure at the rail?
 
Battery is practically brand new since the last one went bad ~4 months ago

joe_peters said:
Do you have an alarm/anti-theft system?
Click to expand...

None that I know of...there is no remote entry either. It does have those courtesy delay on the head lights though.

Do the gauges work when you turn the key on?
Click to expand...
Yes...but the ignition is a bit touchy and the key needs to be a certain "sweet spot" in for the guages and all to work.

Do you have fuel pressure at the rail?
Click to expand...
I would need to pull the fuel line at the rail to find this out...didn't have much time this past weekend to troubleshoot. I will do a little more this evening.
 
Battery is showing ~13.5v with no load stays around 12 during cranking

Checked fuel in the rail...I don't have a gauge but when pressing in the shrader valve it spews out with a lot of pressure so I am assuming it is getting primed well.

I dont' have anyone at the house right now to crank the motor over while I hold a spark plug and wire grounded to the block LOL...
 
Some more info...I just went out and locked the Cherokee and used my key to open the driver door thinking this might be an ASD issue (Thanks Adam)...but alas no start :(
 
Test your crankshaft position sensor.

Without that critical input signal going to the computer, you will not have spark and you will not have fuel going TO the fuel injectors (even though you may have great fuel pressure at the fuel rail).

There are other possibilities (swap ASD relay in the PDC under the hood, etc), but the crank sensor is a very common failure on the Jeep 4.0

Good luck and let us know what you find!
 
If you have STATIC (engine not running) voltage of 13.5 volts your battery is overcharged/bad. You should have about 12.5 volts static for 100 percent charge. Typo or bad reading?

The ASD relay receives 12 volts from the ignition switch, it receives its energizing ground from the PCM.
 
Yes...but the ignition is a bit touchy and the key needs to be a certain "sweet spot" in for the guages and all to work
Click to expand...

This could be your problem, if the ignition switch is bad and not sending voltage to the asd relay in the crank position then you would have a no start condition
 
If you have STATIC (engine not running) voltage of 13.5 volts your battery is overcharged/bad. You should have about 12.5 volts static for 100 percent charge. Typo or bad reading?
Click to expand...


Actually a 12 volt lead acid battery that is fully charged will have a voltage reading of 13.2 volts.

This is true because each cell in the battery produces 2.2 volts, and if my math skills are up to date 2.2x6=13.2

So if the meter used to read the voltage displayed 13.5 it may be off by a couple of tenths but sounds to me like the battery is fully charged.
 
Mbjeep91 said:
Actually a 12 volt lead acid battery that is fully charged will have a voltage reading of 13.2 volts.

This is true because each cell in the battery produces 2.2 volts, and if my math skills are up to date 2.2x6=13.2

So if the meter used to read the voltage displayed 13.5 it may be off by a couple of tenths but sounds to me like the battery is fully charged.
Click to expand...

Actually, life is not a mathematical formula.

Charging table for a 12 volt lead-acid battery at various temps:

http://www.buchanan1.net/lead_acid.shtml

Again, if you ACTUALLY have 13+ volts you have a problem. Now, you could have a bad meter, but you need to find out which is WRONG.
 
Last edited:
OK update...and a very odd thing. Since I have been troubleshooting this during the day we never really noticed this issue. Friend came over to help out a bit and it was getting dark so I went to start it and the starter is arc'ing when you go to crank...

at ONE start try it fired right up with NO problems. We didn't have enough time to go further but I am THINKING that the positive wire for the starter has a melted insulation and is grounding out somewhere down near the starter maybe on the exhaust or something? This would also cause the starter to just "stop" while cranking if it is grounded out.

Would this also not send a voltage signal to a relay for fuel/CPS related issues?????
 
If the battery wire to the starter is shorting to ground, you'd probably have a fire. It may be that you're just overheating the starter with lots of cranking. Have you verified that you're getting spark while cranking?
 
Okay, so you do have spark. That would point to a fuel issue then, right? Can you feel the injectors clicking while cranking?

If you still think something is goofy with the ignition switch, you could try putting the key into the run position and then manually run the starter. You'd do this by jumping the small terminal on the starter solenoid with the big cable going to the battery with a screwdriver. Don't short to the frame or you'll get big sparks. Please make sure its in park with the brake on too - wouldn't want you to get run over.
 
Benz0 said:
Battery is practically brand new since the last one went bad ~4 months ago



None that I know of...there is no remote entry either. It does have those courtesy delay on the head lights though.


Yes...but the ignition is a bit touchy and the key needs to be a certain "sweet spot" in for the guages and all to work.


I would need to pull the fuel line at the rail to find this out...didn't have much time this past weekend to troubleshoot. I will do a little more this evening.
Click to expand...

Guess what I would fix first.
 
joe_peters said:
Guess what I would fix first.
Click to expand...

The tumbler was replaced...

It's been running since but it still has that stupid "sweet spot" to run...:confused:

I still think it's a CPS but the PO installed a damn 1" engine lift efore he got a SYE and I cannot even "see" the CPS from above so this is going to be a real treat to replace :mad:
 
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