{"id":4796,"date":"2019-04-02T19:04:47","date_gmt":"2019-04-02T23:04:47","guid":{"rendered":"http:\/\/mikestrawbridge.com\/blog\/?p=4796"},"modified":"2019-04-02T19:04:57","modified_gmt":"2019-04-02T23:04:57","slug":"jeep-4-0-no-start-troubleshooting-puzzle","status":"publish","type":"post","link":"http:\/\/mikestrawbridge.com\/blog\/2019\/04\/jeep-4-0-no-start-troubleshooting-puzzle\/","title":{"rendered":"Jeep 4.0 no start troubleshooting puzzle"},"content":{"rendered":"\n

Weird trouble with first start of my new engine<\/h4>\n\n\n\n
\"\"<\/figure>\n\n\n\n

When I put in my new engine I expected it to start up right\naway. I had carefully aligned the distributor, checked all the electrical\nconnections and bled the air out of the fuel system.<\/p>\n\n\n\n\n\n\n\n

But when I hit the key it simply spun over and never fired.<\/p>\n\n\n\n

I put a light in one of the spark plug wires and it flashed\nindicating I had spark. That meant that the Crank Position Sensor was working.<\/p>\n\n\n\n

I put and LED in one of the injector wires and it flashed\nindicating that I also had the cam sync signal. I verified the fuel pressure\nwas correct.<\/p>\n\n\n\n

I checked compression and added a squirt of oil into each\ncylinder in case the rings were not seated. \nI got a pop or two but no start.<\/p>\n\n\n\n

I tried spraying starting fluid in the throttle body in case\nI had some bad gas.  I got a backfire or\ntwo but still no start.<\/p>\n\n\n\n

I pulled the number one spark plug again and looked inside\nwith a bore scope.  I saw the mark on the\npiston showing .040 over bore and everything looked fine.  I verified the mark on the harmonic balancer\nwas correct at top dead center.<\/p>\n\n\n\n

\"\"<\/a><\/figure>\n\n\n\n

After several hours of various checks, I tested a different\nCrank Position Sensor. Same result.  I\neven tried turning the distributor 180 degrees even though I knew it was\ncorrect. No improvement.  I verified the\nfiring order again and the arrangement of the spark plug wires on the\ndistributor.<\/p>\n\n\n\n

I had fuel and spark and compression but no run. The engine\nsounded like it was out of time.<\/p>\n\n\n\n

I read and re read the shop manual on how the ignition\ntiming is determined.  The holes in the\nflex plate signal the computer to fire the coil based on the input from the\ncrank position sensor.  There is no other\ninput.<\/p>\n\n\n\n

I even took down the transmission and replaced the new flex\nplate assuming something was made wrong about it.  No difference.  I mounted an old bellhousing, so I could\nmount the CPS and see how it lined up with the marks.  It was on the fourth notch at 4 degrees\nbefore TDC just like the manual said it should be.<\/p>\n\n\n\n

\"\"<\/a><\/figure>\n\n\n\n

I was also having a problem that none of the timing lights<\/a> I had on the shelf worked. So, I had to order a new one.<\/p>\n\n\n\n

One that arrived, I was able to confirm that yes, the\nignition timing was off. WAY off.  So far\noff I am surprised the rotor still made enough contact with the terminal in the\ndistributor to give me a flash.<\/p>\n\n\n\n

\"\"<\/a><\/figure>\n\n\n\n

According to the manual, the cam sensor plays no role in the\nignition timing. It only tells the fuel injectors which back of three to start\non. After that, the computer no longer looks at it.<\/p>\n\n\n\n

However, the ECU must see a pulse from the Cam Sync Sensor\nbefore it will allow the start of the engine. \nSo, in this sense it does control the ignition.<\/p>\n\n\n\n

I disconnected the distributor and I got one single pulse\nfrom the ignition, but it was right on the mark!  I was on to something.<\/p>\n\n\n\n

I got my old distributor out of the discard pile and plugged\nit in to the harness. The new one still hooked to the plug wires and bolted\nin.  I found I had to spin the\ndistributor by hand to give it a pulse while cranking the engine but as soon as\nI did, the engine roared to life!<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

The new distributor I purchased was bad and somehow causing\nhavoc with the ECU.  My factory manual\ndid not offer a way to test the sender without an oscilloscope, so I just\ncleaned up my old distributor and put in back in and returned the new one to\nAmazon.<\/p>\n\n\n\n

I had replaced the distributor because I was getting a cam\nsensor fault before the engine swap. But I had traced the problem to a skinned\nwire on the engine harness while the engine was out.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

I have learned way more than I ever wanted to know about how\nthe ECU works but I still don\u2019t understand how a bad cam sensor cause the\ntiming to be way way off.<\/p>\n\n\n\n

The new engine runs great now. I just hope I did not take too much life out of the starter with all the hours of cranking I did while trouble shooting.<\/p>\n\n\n\n

\"\"<\/figure>\n","protected":false},"excerpt":{"rendered":"

Weird trouble with first start of my new engine When I put in my new engine I expected it to start up right away. I had carefully aligned the distributor, checked all the electrical connections and bled the air out of the fuel system.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[210,6,231],"tags":[46],"_links":{"self":[{"href":"http:\/\/mikestrawbridge.com\/blog\/wp-json\/wp\/v2\/posts\/4796"}],"collection":[{"href":"http:\/\/mikestrawbridge.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/mikestrawbridge.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/mikestrawbridge.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/mikestrawbridge.com\/blog\/wp-json\/wp\/v2\/comments?post=4796"}],"version-history":[{"count":1,"href":"http:\/\/mikestrawbridge.com\/blog\/wp-json\/wp\/v2\/posts\/4796\/revisions"}],"predecessor-version":[{"id":4804,"href":"http:\/\/mikestrawbridge.com\/blog\/wp-json\/wp\/v2\/posts\/4796\/revisions\/4804"}],"wp:attachment":[{"href":"http:\/\/mikestrawbridge.com\/blog\/wp-json\/wp\/v2\/media?parent=4796"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/mikestrawbridge.com\/blog\/wp-json\/wp\/v2\/categories?post=4796"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/mikestrawbridge.com\/blog\/wp-json\/wp\/v2\/tags?post=4796"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}