Cant start without help , runs fine when started. - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > Models > Jeep Cherokee & Comanche Forums > MJ Comanche Technical Forum > Cant start without help , runs fine when started.

Rugged Ridge 8500lb Winch w/ Steel Cable $294.99 Shipped OSmittybilt Products at Oconee Off-Road!Building a Bumper?

Reply
Unread 01-28-2013, 08:52 AM   #1
-PMK-
Registered User
1989 MJ Comanche 
 
Join Date: Jan 2013
Location: Falköping, Skaraborg
Posts: 22
Cant start without help , runs fine when started.

Bought me a -98 Comanche some month ago. (4.0L inline 6)
Got it delivered on a trailer.

Had problem getting it started but got it running little so i got in my garage.

It is impossible to start without giving help, can only get it up and running if i give it some "starter gas", but then it runs just fine.
Without "gas" it can fire some cylinder but nothing more.

Checked every sensor i found and cant find any faults (they are in the specs)
(Unsure about the TPS, it give 0.8V at the flat connector, and hmm was it around 4.5V in the square connector, no deadspots)
New sparkplugs, checked ignitior cap and rotor, cables.
Checked compression:
1=9.6, 2=10 =10, 3=10.5, 4=11=10.2, 6=10 Bar
Though it was low compression first but it should be just fine.

Checked fuelpump = ok.
Spark jumps ~15 mm.
Ignition distributor is ok and "on spot"
Rotor is ok.
Fuelpump relay - Switched place so check.
Battery is ok, turns engine good and last long.
Tried to star in P and N but with the same result.

Im really puzzeled about it so any ideas is more than welcome.

// Petri - Sweden

-PMK- is offline   Reply With Quote
Unread 01-28-2013, 07:42 PM   #2
cruiser54
Web Wheeler
 
cruiser54's Avatar
1990 MJ Comanche 
 
Join Date: Oct 2009
Location: Prescott, Arizona
Posts: 9,791
Test the Crank Positon Sensor

Renix CPS Testing and Adjusting



Renix CPSs 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 as the CPS will test good when in fact it is bad.

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 .35 AC volts range or lower 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 the upper mounting hole to 3/8” from the stock 5/16”, or slot it so the CPS bracket rests on the bell housing when pushed down. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.




Revised 01-26-2013
__________________
Quote:
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
Refresh*Connections*Before*Replacing*Components
cruiser54 is offline   Reply With Quote
Unread 01-29-2013, 12:00 PM   #3
-PMK-
Registered User
1989 MJ Comanche 
 
Join Date: Jan 2013
Location: Falköping, Skaraborg
Posts: 22
The CPS Is fine ~0.8VAC. (with a TRMS digital multimeter from my work)

Was up in the garage and recorded.
First one attempt without any help.
Then with help (the can was empty so it was only gas coming out, no fluid)
, turned it off and tried to start it just after again.
Starts easy with help, dut doesent do anything without, have had it running for 4-5 minutes, turning it off and ot wont start again without help.

www.adlit.se/3.avi

(not sure but you might need to copy the link adress and paste in a new browser window to be able to get it opened in windows media player or similar, or as i need to do, press enter in the wierd looking browser window that pops up.)
-PMK- is offline   Reply With Quote
Unread 01-30-2013, 07:20 AM   #4
hillbilly51
Registered User
1988 MJ Comanche 
 
Join Date: Jul 2009
Location: georgia
Posts: 36
I would check to make sure that I didn't have any vacuum leaks on the intake manifold.
steve
hillbilly51 is offline   Reply With Quote
Unread 01-30-2013, 12:45 PM   #5
-PMK-
Registered User
1989 MJ Comanche 
 
Join Date: Jan 2013
Location: Falköping, Skaraborg
Posts: 22
I'll buy a new can of "gas"
Rubber parts are ok, but intake gasket ect i don't know.
-PMK- is offline   Reply With Quote
Unread 01-31-2013, 09:12 AM   #6
-PMK-
Registered User
1989 MJ Comanche 
 
Join Date: Jan 2013
Location: Falköping, Skaraborg
Posts: 22
Update today:

Couldn't find any vacuum leaks, found out that the little valve at the back of the valve cover was missing - fixed.

Swapped the MAP sensor just to check (wasnt that one either)

Well i took my starter gas can, sprayed liiitle gas out and started it - starts with a horse kick.

Let it warm up for 15-20 minutes, turned it off, Tried to start, 3-4 crank and it is running again.
The idle is just between 1000 and the mark under, guess ~700rpm.
it runs really fine and have good response.

Ohm measured the Water temperature sensor under the intake, and the Intake air emperature sensor, andt the reading is looking good
(Found a table with Ohm <-> Tempareture readings)

Now let it cool down and then i guess it wont start without help again.


And now some hours later, its cold and does same as usual, its a good anti theft system

Last edited by -PMK-; 01-31-2013 at 12:43 PM..
-PMK- is offline   Reply With Quote
Unread 01-31-2013, 12:49 PM   #7
cruiser54
Web Wheeler
 
cruiser54's Avatar
1990 MJ Comanche 
 
Join Date: Oct 2009
Location: Prescott, Arizona
Posts: 9,791
Have you tried this? Cycle the key on for 5 seconds. Turn it off. Cycle on again for 5 seconds. Off. On again for 5 seconds. start.
__________________
Quote:
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
Refresh*Connections*Before*Replacing*Components
cruiser54 is offline   Reply With Quote
Unread 01-31-2013, 01:48 PM   #8
-PMK-
Registered User
1989 MJ Comanche 
 
Join Date: Jan 2013
Location: Falköping, Skaraborg
Posts: 22
Yes.

I have a Cherokee -89 i bought really cheap (fully driveable if using earprotectio, bad rear axle)
Ill start to switch over some elektronics from that to Comanche.
Removed ignition coil, MAP sensor, whole throttlebody with idle motor and TPS. will remove ECU and the temperature sensors too ect.

I know where im spending my time this weekend
-PMK- is offline   Reply With Quote
Unread 02-02-2013, 09:33 AM   #9
-PMK-
Registered User
1989 MJ Comanche 
 
Join Date: Jan 2013
Location: Falköping, Skaraborg
Posts: 22
Been little in the garage.
Replaced:
MAT sensor (checked it first to a diagram)
Idle stepper motor
Remeasured the TPS.
Cleaned all the connectros i found.
Remeasured the CPS but i need my professional multimeter from work to measure the low AC voltage. (ill test with the other CPS, but its a pain to remove from above i guess)
Cleaned and doubeled the grounding from battery to engine and from engine to firewall.
Rechecked for vacuum leaks (no leaks)

When warm it starts very easy, when cold it doesent give any life signs.
When ~40 celcius, it is fiering/misfiering but really hard to start, usually start when i hear it fire up and then release key, then 6/10 times it starts.
-PMK- is offline   Reply With Quote
Unread 02-03-2013, 09:41 AM   #10
-PMK-
Registered User
1989 MJ Comanche 
 
Join Date: Jan 2013
Location: Falköping, Skaraborg
Posts: 22
Replaced CPS and tested another ECU - Still same -.-

!"#¤2@ now ill get me a beer + sauna :P


***
beer + sauna didnt come yet, read that injectors doesent get signal from ECU if cranks speed isnt ~300Rpm.
went t o the garage again and counted flashes from my "stroboskop ignition set lamp", got ~36 flashes in 30 sec = ~144 rpm in crank speed.
Could it be that my starter is bad and isnt turning the motor fast enough? (battery is ok).

Last edited by -PMK-; 02-03-2013 at 10:24 AM..
-PMK- is offline   Reply With Quote
Unread 02-06-2013, 04:41 AM   #11
cruiser54
Web Wheeler
 
cruiser54's Avatar
1990 MJ Comanche 
 
Join Date: Oct 2009
Location: Prescott, Arizona
Posts: 9,791
Could be.

Renix Ground Refreshing

The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.

The components grounding at the dipstick tube stud are:

Distributor Sync Sensor, TCU main ground, TCU “Shift Point Logic”, Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.

The factory was aware of the issues with this ground point and addressed it by suggesting the following:

Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.

Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.

While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.

Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.

First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4” socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.

A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18” long with a 3/8” lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.

A further improvement to the grounding system can be made using a #4 cable, about 10” long with 3/8” terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.

For those of us with Comanches, it’s very important to remove the driver’s side taillamp assembly to access the ground for the fuel pump. Remove the screw holding the black ground wire. Scrape the paint from the body and corrosion from the wire terminal. Reattach securely.



If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.


Revised 12-04-2012
__________________
Quote:
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
Refresh*Connections*Before*Replacing*Components
cruiser54 is offline   Reply With Quote
Unread 02-06-2013, 05:25 AM   #12
-PMK-
Registered User
1989 MJ Comanche 
 
Join Date: Jan 2013
Location: Falköping, Skaraborg
Posts: 22
i have done that, cleaned and doubeled grounding.

Modified the CPS bracket so from 0.56VAC i now got 0.69VAC today.
Today i cleaned the ignition coil connection (the ones you see when you remove the 2 small torx, didt it as then its done too)
Mesured the voltage drop over battery when i crank, from 12,7V down to 11,4V
Removed starter so mabye tomorrow ill dissassemble and check it too. (connections looked quite rusty under all the dirt/oil)
-PMK- is offline   Reply With Quote
Unread 02-06-2013, 05:58 AM   #13
cruiser54
Web Wheeler
 
cruiser54's Avatar
1990 MJ Comanche 
 
Join Date: Oct 2009
Location: Prescott, Arizona
Posts: 9,791
Good work. The starters are easy to disassemble and clean. If the valve cover or oil filter adapter seals have been leaking, the starter can be all oily inside.
__________________
Quote:
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
Refresh*Connections*Before*Replacing*Components
cruiser54 is offline   Reply With Quote
Unread 02-07-2013, 05:28 AM   #14
-PMK-
Registered User
1989 MJ Comanche 
 
Join Date: Jan 2013
Location: Falköping, Skaraborg
Posts: 22
Dissassembled the starter, bearings looks ok, but the collector isnt ok (sort of black coating on it), brushes is ok.
Planetary gearing turns nice, and looks ok allso.
-PMK- is offline   Reply With Quote
Unread 02-07-2013, 05:55 AM   #15
cruiser54
Web Wheeler
 
cruiser54's Avatar
1990 MJ Comanche 
 
Join Date: Oct 2009
Location: Prescott, Arizona
Posts: 9,791
Commutater or armature is black? Clean it off. Your brushes may be worn down too far. I'd try cleaning it all up and putting it back in.
__________________
Quote:
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
Refresh*Connections*Before*Replacing*Components
cruiser54 is offline   Reply With Quote




Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.