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It sounds like the ECM is getting power only once in a while. I would try and locate the ecm relay and swap it with another relay and try it like that for a few days to see if it solves the problem . It may be bad contacts inside the relay.
Also , I would follow the power wires that feed the ECM. They most likely leave directly from the batteries with an inline fuse . I would check the condition of the fuse holder and its terminals to make sure nothing got hot and mayhave lost some connectivity. Ecm power feeds may also leave from the firewall somewhere off of a large relay or a main cab fuse. Good luck ! Hope this helps you!
I will try that when i get back to the shop. could there be a problem with the ecm? the truck runs fine all day when it starts and it never quits!
By the way , the engine warn lamp is supposed to come on for a brief second initially when turning ignition on as a bulb check but it also tells you that the ECM has powered up . So if you don't see the light come on at first , and it doesn't start , it's because ECM has no power so it is not firing your injectors and therefore will not start until you find out why ecm is not getting power occasionally.
Good Luck again !
I work for an International dealership so I am not overly familiar with Cat but most trucks grab their ECM clean power feed dirctly from the batteries with an inline fuse somewhere in battery box . You may simply even have bad connections at batteries for the ecm wiring alone!
Have cleaned the batterys and checked the fuse.All seems well but will check them over again.
Sounds to me like its more like a relay problem because it stays running until you shut off
if it was a loose connection somewhere , you would be cutting out all over the road over bumps.
sounds like bad contacts in a relay
Good luck !
Maybe even disconnecting batteries , to unplug ecm connectors and have a look for spread or damaged terminals there , and if all is good there , sometimes reseating the connnector sometimes corrects intermittent problems too!
Hope this is all helpful to you
Ok will go right to relay panel and search for ecm relay. Thats what I suspected because once it starts it continues to run. will get back to you in a day or so thanks for the info.
ok ! Good luck!\
I WILL BE BACK IN TOWN TOMORRROW AND TRY THE FIX AND WILL REPLY WHEN I GET THE TRUCK IN FOR THE TESTS. I WILL REPLY THEN .THANKS
Any luck at all with your problem?
this truck still acts up. not all the time. i have had it to a cat dedaler and they thought it was the starter and replaced that but it still acts up some times. i guess ill have to wait till it totally quits and does not start at all to figure it out. thanks very much for your help anyway and i will keep you in mind for you services.
So you are saying that sometimes, It won't even crank at all?
I suggest you try disconnecting all large cab main connectors , clean and inspect for damaged pins or terminals in the connectors and if nothing is found , just reconnect . Sometimes , just reseating a main connector fixes intermittent problems like these! I am suspecting that the signal from the key switch is sometimes not making it through the cab connectors down to the starter .
You may also have a problem with a sticky relay or even a key switch acting up ! Does the switch seem loose and worn out ?
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it always cranks and the swith and strter button and solenoid on the firewall has also been replaced
Has anyone checked out the cab connections at all !
It sounds to me like you are not getting the ignition signal down to the ecm . So , if this happens, the ECM doesn't know that you are trying to start the engine(it's still powered down)
ecm connections and cab bulkhead connections have all been checked and cleaned
I would go though the fuse box and relay panels, look for anything marked ECM in either fuses or relays . Now if you find a relay for the ECM, try swapping relays with one from another circuit(could be a defective relay and this test will tell us) . You would have to leave them swapped for awhile to see if problem is gone !
Ok , so cab connections are good . What about at the ECM!
If you disconnect the batteries , unplug the ECM and check those connections for corrosion. dirt or loose terminals.
ecm connections also checked and all look like new.checked and resealed
did anyone swap relays
did someone inspect the wiring from the ECM to the cab connector to make sure there is rubbed out or corroded wiring
yes all relays have been swapped and checked for loose connections and burnt or corroded connectors
Ok then ,
I have another task for you that probably wasn't done
The ground side of the system is often overlooked!
There is a test with a multimeter set to ohms scale for testing all the grounds on the truck for excessive resistance!
at this present the truck has been starting almost evey day but still has those days where it just will not start but just crank. come back later and it might fire right up. some sort of ghost.
This test has to be done with batteries connected as normal , everything on the truck has to be turned off , including doors(dome lamp, etc...)
you will need to extend the leads on your meter but if you connect one lead on the batt ne
someone else suggested grounds so i have taken off every groung wire from batterys to ground and also grounds that are connected to the engine. ihave giving all those a wiggle test to check for any openings in the wires.
battery negative and the other end on the frame rail at a clean spot , you should be reading less than 1 ohm of resistance .
That tells us if the frame ground is good or not!
Same goes with engine ground! one lead on battery negative and the other on the engine ground stud !
Again , you should have less than 1 ohm . If higher than 1 ohm , you need to clean the engine ground !
have not checked it with an ohmmeter but did clean connections with emery cloth and wire brush
And once again now with the cab grounds. One lead on the battery negative and one lead on the cab ground stud . Again , it should be less than 1 ohm. If higher , we need to clean that area better.
thanks will give that a try.
My theory is the ECM may not be powering up all the time because it needs to see at least 7 to 9 volts to power up and you may be losing some voltage due to grounds being dirty
Sometimes it is reaching that threshold voltage and sometimes it's not quite enough to power it up but the fact that warning lamp is not coming on at first sometimes , tells us that ecm is not powered up and that 's why it just cranks
I wish I had schematics for that unit to help you further !
I am an International specialist
But I am sticking to the basics
Do you have something to plug into ecm to check codes and maybe read input voltages ?
yes i have checked with 3 freightliner dealers and a cat dealer and the suggest running a wire to the ecm on toggle switch or wait till it just quits and diagnois it then.
Has it ever died on you going down the road?
yes i do. ihave checked it when then light comes on and the voltage was at least 10 volts and when it did not it would not sen any info to the laptop for any info.
has never died going down the road.once it starts it will start and stop all day but there are just some morning it will just crank and not fire up. come back later and away we go fire right up
What about the key switch
Maybe the next time you go to start in the morning , and it doesn't start , open the hood and wiggle a section of harness somewhere. Then go back in and try again
If you shake the appropriate area , it should do something !
Maybe have an assistant watch the dash for the engine lamp as you shake the harness that same morning that it won't start . When your assistant yells at you that the light just went on , then at that very location on the harness where you just shook and twisted is your problem. You may have to tear apart the loom to inspect the wiring inch by inch and look for rubout or corrosion on wires
I would also look for a section of harness that may not have been secured and may have been allowed to bounce up and down going down the road. What happens here is the wiring itself will end up bouncing inside the loom . On the outside , everything looks fine but on the inside , wiring has rubbed itself down to the copper and now corrosion sets in over time, causing chaos. If you find a loose section somewhere , I would check that area!
we have teamed up doing the wiggle test and had cut all the tie straps and removed protective loom looking for the exact thing to happen but never does, check later or nect day and away we go
if i ever find this gremling i will definetally respond with what i have found out. thanks again.
Wish I could be more help!
Let me know what you find ! I am curious!