Serial number 7AS07315 arrangement number 154-1062. The truck broke down on the side of the road and we replaced a timing sensor and were back up and running. Two weeks later it died on a job. We have spent 40 hours on it and T&E Cat has spent 40 hours on it. We replaced the lift/transfer pump and HEUI pump and all the injectors. We've also replaced all of the electrical harnesses. The engine will fire with ether but only runs long enough to use up the ether. Nothing else. The Cat mechanic completely disconnected the engine from the truck so we believe this is not a truck problem.
An engine will fire on ether as long as it has compression. What has cat done? Does the ecm have power? Does it smoke? Does he check engine light come on with key on engine off? What kind of truck is it in? Did cat verify all the inputs to the ecm? We need a lot more details
My 3126 (which is pretty close to the same engine, just older), had a crank, no start issue. It ended up simply being a ground issue at the starter. Fortunately I didn't start throwing parts at it. I was ready to start throwing parts, but got stubborn. If the CAT man has been there for 40 hours working on it, its going to be tough to diagnose over the web.
Had the problem with a c9.replaceed the heui . Wasn't the problem The wire from ecm to heui pump was bad.
I’m not proud of this.....I had my own haul truck stump me and did just as you say. 5 amp ECM fuse was the issue.
This is why I’m asking questions. K.I.S.S. Keep it simple stupid. I almost bought an ecm for my Ford when a cummins tech I spoke with reminded me to load test the battery power to ecm wires. Green wires and a couple butt connectors cured my issue.
If the timing sensor "fixed" it the first time. Then I would look at all the connectors that may have been moved when changing it and check for pin fitment and continuity back to ECM assuming the Cat man looked at timing on his/her laptop while cranking. Even with a new harness a sender or sensor pin/pigtail could be damaged. Man shot gunning parts can really make it tougher some times may have to start all over power, grounds, and reference
Seen quite a few VP44 injection pumps deemed bad when it was a wiring issue all along. The more erratic the issue the more I dig into wiring.
Worst part of this whole ordeal is there's already been too many hands in the cookie jar...Nothing worse than getting a job that's been prodded, poked, changed parts,wires swapped, yuch...Did you try swapping out a good ecm? Several times at my last employer with a very large Volvo fleet, even when the TechTool software didn't indicate any problem with the ecm after all other ideas were exhausted, a good ecm from a wreck that I had stashed in my box saved the day...The new ecm had to be programmed to the truck, but the used one will tell ya what you need to know....
we have one of these monster 3126 with allison auto with a problem no one seems to be able to figure out. am going to start a new thread on it and see what everyone thinks
Give us something to work with, Does it throw codes? Register cranking rpm? Does it build actuator pressure? needs to go above 900psi before the ecm activates the injectors. Fuel pressure?
If you can connect to it with cat et there's lots of interesting stuff to do, injector solenoid test for example Or look at delivered fuel volume while cranking.
I dont know if I have ever heard of 40 hours worth of troubleshooting time on a no start engine........by a Cat tech. That's just insane!
Yeah, can't be right.
We replaced the harness. That was our first thought. After that, all parts were at the troubleshooting and recommendation of CAT tech. I hope that's not considered shotgunning parts. I agree on the ether. That just means it's getting air. Cranking oil pressure is like 1200 or something. It's in the good range. CAT is able to communicate with the EMC. They have flashed it several times. When they are connected to it the computer shows all good. I don't know for sure that it reads good fuel pressure but the fuel system is all new. Transfer pump, HIUI, and injectors are all new. All installed by CAT. All recommended by CAT. No smoke on engine crank. Local CAT techs gave up. They have sent this to their engineering headquarters. They sent someone out with a super ohm meter and they weren't "happy" with the readings they got from the timing sensor. They want to take the front cover off and see if the timing gear has come off the crank.
IDE bet something is getting overlooked repeatedly. It doesn’t sound like much else can be replaced, it’s almost like a parts changing scenario from the very beginning. How many Cat techs have worked on this? I have a customer here local that called Cat field service for some A/C work and he is on the 3rd tech in a week.
Also.....did any of the techs have a pin out detail for the ECM? If so, did they even check it? I’ve seen some of those techs that when their laptop says everything is good and it should work.....just throw their hands up in the air and quit.
Was the "super ohm meter" a lab scope that could record and look closely at the wave form? I can see burning 40 hours chasing an intermittent problem but a straight no start you would think would be a straight forward diagnostic. This thing stumping a few cat techs and bringing in the big guns; I sure hope you get it fixed and let us know what the problem was (My money is on something simple that was overlooked, of coarse that is easy to say after you figure it out). Good luck!
All this and they don’t know if it has any fuel pressure? It could have a cracked or blocked line from the fuel tank. Very common in trucks with plastic lines. The timing sensors run off the back of the camshaft and will be easy to check either through the sensor port or taking off the tin plate ahead of the cam gear.
I suspect et said everything was fine. LOL
Update if it matters. The engine is a 1998 3126B rather than a C7.
Has the IPR valve been replaced. If I missed it I apologize.
Ok, Do you have answer to any of the other questions asked earlier in the thread also?
We found that the timing gear on the cam shaft had been pushed partially off. We think maybe during the installation of the truck air compressor the gears weren't aligned and this aided in pushing the gear out of position.