4.0L won't start. No Spark. ECM won't produce 8v signal. Why? - JeepForum.com
LinkBack Thread Tools
post #1 of 2 Old 02-03-2012, 11:50 PM Thread Starter
Registered User
1999 XJ Cherokee 
Join Date: Feb 2010
Location: Boise, ID
Posts: 145
4.0L won't start. No Spark. ECM won't produce 8v signal. Why?

Sorry to cross post here guys, but I was having minimal luck in the XJ specific forum. Since this is really more of a 4.0L issue, I figured I'd post here.

Ok so I have a new problem with my XJ. 95 4.0 Auto. The dang thing wonít start. For the full backstory check out the following thread:


So Iíve just gone through and done a ton of work to this Jeep including: plugs, wires, cap, rotor, air filter, fuel filter, valve cover gasket, rear main seal, oil pan gasket, oil filter adapter seal, power steering pump, front and rear shocks, front sway bar bushings, inner and outer tie rods, transmission mount, transfer case chain, all new transfer case seals, transmission output seal, transmission solenoids, front brake pads and rotors, rear brake shoes, heater blower motor, blower motor resistor, blower motor switch, and serviced both differentials.

Now the Jeep wonít start. I drove it into the garage 2 months ago and slowly went through all of this in my spare time and after everything, it wonít start. I did a quick spark check and it has no spark at the coil. A visual inspection of the coil showed major cracks in the coil housing so I immediately bought a replacement. It still wouldnít start. So I checked for DTC and pulled code 11, crankshaft position sensor. No problem. I can do that. So I buy a new Borg Warner CKP and install it. No luck.

So at this point I rescan the DTCs and Iím still getting code 11. So I break out the DVOM and check to make sure Iím getting 8 volts in to the sensor.

Nope. So I yank the plastic cover off the back of the ECM harness and measure pin 7 (the orange 8v output) at the ECM. No output. So I measure input voltage. 12.2v in at batt in and key-switch in. Grounds show minimal resistance. The ECM is powering up just fine since I can retrieve DTCs. So itís getting correct voltage in but itís not producing any voltage out on the 8v output. I checked for shorts to ground in the output wire and didnít detect anything. According to the FSM and to my logic, this all would indicate a bad ECM. So I went and got a junk yard ECM from a wrecked 95 and tried that.

Exact same problem. With both ECMs, Iím getting no output voltage on the 8v orange output wire. Well, technically Iím getting around 14 millivolts on both. Again, the FSM says that this is a symptom of another bad ECM but Iím not convinced. I pulled the 2nd ECM from a 95 which had been t-boned. Logically, youíd assume that in order to be in a wreck, it must have been running. Additionally, why would both ECMs fail in exactly the same way? My understanding is that there is a voltage reducer built into the ECM which reduces voltage from 12 to 8 volts for the sensors. I guess if the voltage reducer was a particularly fragile part I could see it going bad on multiple units, but I still have a hard time believing that I just happened to have 2 ECMs go bad in the same specific way. Also, strangely, both ECMs are still producing their 5v outputs. Iím guessing thereís another problem. Unfortunately, the FSM is no help at this point since it just tells me to replace the ECM again.

If anybody has faced anything like this before Iíd appreciate some help. I just donít want to waste money on another replacement ECM if the problem lies somewhere else.

I have an illness. It's called "While I'm at it"
Barrishautomoti is offline  
Sponsored Links
post #2 of 2 Old 07-06-2012, 07:24 PM
Registered User
Join Date: Jun 2012
Posts: 3
Man I have the exact same problem I don't know what to do either other than junk the thing! Someone help save jeeps from the junk pile!!
thegreenbastard is offline  

Quick Reply

Register Now

In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Similar Threads
Thread Thread Starter Jeep Forums Replies Last Post
1991 4.0 jeep wrangler won't start and has no spark popcancherokee Engines & Drivetrain 1 07-29-2011 04:51 PM
4.0 cranks over, spark and fuel seem fine, yet doesn't start... craigbru Engines & Drivetrain 8 05-19-2011 10:08 PM
91 4.0 won't start: has spark and fuel. 2PAJeepsters Engines & Drivetrain 3 04-30-2011 08:52 PM
Engine turns over/ getting spark/ won't start mabake Audio, CB & Ham Radios, GPS, & Electrical 4 09-27-2009 01:59 PM
no start/spark help!! eche981 Audio, CB & Ham Radios, GPS, & Electrical 1 02-11-2006 11:46 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome