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MP8 no start even on ether


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Hey guys, I’m stuck on another truck again.   I’m working on a 2014 Mack CXU with a MP8 and mDrive transmission.   Bought the truck at auction, so I know nothing about it.    Put fresh batteries in it and a new starter.  I have looked through the fuses and found none burned.  The truck cranks and every now and then sputters like it tries to start but never starts, not even on ether. While cranking engine, the engine sounds fine, no abnormal mechanical sounds present.  Another thing is, the information screen on the dash does not turn on.   Have any of you guys encountered this?   No codes, and as far as I can tell the fuel system is not building pressure, but i may be wrong about that.    

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4 hours ago, 96bulldogpower said:

Bought the truck at auction, so I know nothing about it.

That was a really bad thing to do.

Check compression, timing, cam lifters, valve train, fuel pressure, bad harness(s), bad sensors, power to the ECU, bad grounds, corrosion in the connector pins, more bad sensors, corrosion in the harness, oil in harness,....

Jim

It doesn't cost anything to pay attention.

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I primarily buy trucks at auction for our family business.  I know what you mean about auction truck nightmares, but I bought this truck as a known non-runner. So I guess you can say I dug my own grave.   

 

I’ve chased all the typical electrical connections and all seem good.  I’d like to know which pins at the ecm to test for power, do you happen to know which they are? 

 

Although i haven’t tested compression, the engine doesn’t sound like it is freewheeling or has a dead cylinder as it cranks over. Obviously not a accurate way of gauging compression, but it does sound like it should.  I’m concerned that it won’t even run on ether, leads me to believe there may be something wrong with the timing, what gets me is that it does “stutter” once or twice as it cranks over as if it was trying to start.   The other concern is that the dashboard info screen doesn’t come on, leads me to think it may also be ecm related.

 Everything else checks out good, no shavings or out of the ordinary in the engine oil, everything looks mechanically sound, all fluids are topped off, new cam and crank sensor.

 I’ll do some more checking once the rain lets off, just wanted to get you guys’ opinion 

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New cam?  Definitely need to check timing and the top end.  If your local dealer is some what helpful, see if you can get info about the truck like warr. history or any updates done.  I would need a schematic or chase the ECM power wire from the fuse block.

Jim

It doesn't cost anything to pay attention.

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  • 2 weeks later...

If the eecu wasn't powering up the the engine wouldn't crank over since the eecu provides ground for the starter relay. Loosen the fuel return regulator valve at the front of the head, pump the fuel hand pump and verify you have fuel coming out around the fitting. Try starting the engine then, should have fuel psi while cranking. Could possibly be cam timing, easy check, Remove plug on bottom of flywheel housing and rotate engine until "0" lines up with bump in hole. The cam tdc mark should be between lines on #1 cam cap. If its on the edges or outside the marks then cam timing is an issue, but it being on the edges it should still run, just not so good. Do you have access to software to read faults? That would be helpful.

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  • 3 weeks later...
On 4/12/2020 at 12:23 PM, turckster said:

If the eecu wasn't powering up the the engine wouldn't crank over since the eecu provides ground for the starter relay. Loosen the fuel return regulator valve at the front of the head, pump the fuel hand pump and verify you have fuel coming out around the fitting. Try starting the engine then, should have fuel psi while cranking. Could possibly be cam timing, easy check, Remove plug on bottom of flywheel housing and rotate engine until "0" lines up with bump in hole. The cam tdc mark should be between lines on #1 cam cap. If its on the edges or outside the marks then cam timing is an issue, but it being on the edges it should still run, just not so good. Do you have access to software to read faults? That would be helpful.

Turckster, very helpful! I did what you said about checking the timing.   The timing is right where it needs to be.  I have done a few things since I last reported.  I bought and installed a used ECU and VECU, thinking that it would solve my issues but it did nothing, as a matter of fact the engine wouldn’t even crank with the replacement computers, I did not even get anything on the dash screen just like before. So I reinstalled the factory ECU AND VECU, and I’ve decided to stop chasing electrical issues because all computers are getting power and the truck seems to respond to the gauges most other functions just fine with the exception of the dash screen.   

The truck still refuses to start on ether.  I’ve checked the fuel system and it is getting fuel just fine.  I even went as far as replacing the filters and a new fuel lift pump.   Still no start.  

The engine may sputter a few times while it is cranking on ether however it never actually starts or fully runs on ether.   

 

Any ideas of where to check next? 

Also, I do not have a diagnostic tool or a way to check compression.  

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Right off the top of my head, (1)- possible EGR valve stuck open-- remove the egr cross tube (over valve cover) and try to start the engine. If it starts the egr valve is stuck wide open choking the engine w/exhaust. Normally they would start, just run like crap, but you never know.  (2) DPF plugged to max. Have seen a DPF plugged and it wouldn't let an engine start. Remove the flex pipe at the DPF inlet and try to start the engine. (3) Bad engine brake solenoid- it will cause full engine oil psi to rocker shaft causing exh. rocker pistons to hold exh valves open.  Usually while cranking it sounds like the engine has no compression when the valve goes bad. (4) Bad Injector(s) or badly leaking injector cup(s) can cause a no start. Seen this a lot as well. Loosen the fuel return regulator, prime fuel system until fuel flows out fitting and then try to start the engine (fitting loose). If it starts it will run horrible. With the engine running, take a flashlight and look inside the fuel tanks at the fuel return port/pipe (the top one). If there is a lot of bubbles coming out the return pipe you have bad injector cups. Compression is blowing the fuel out of the galleys and the only proper fix is replacement of all inejctor/cups. 

 

Edited by turckster
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