MR 688 electrical trouble shooting. No crank

[Joey Mack]

I chased an issue for weeks on an 05' Mack...  It started up but #5 was not doing good.. the owner told me to put all new EUP's and injectors and fuel lines..  Still ran bad and smoked us out..  Well after a bunch of cussing, I decided to pull the heads to have a look..  and here is what I found... of course I started on the exhaust side first..  jojo

[JoeH]

4 minutes ago, Ryanp said:

Well kind of made some progress today. Ran through the valves and they were all pretty close. A few were maybe 3-4 thou off. Ran It again, basically the same. Ive got probably 3 cylinders firing. This afternoon we fired it up and I shorted some of the EUPs as it was stuttering and trying to run. We thought it would show us what injectors were firing and what ones were not. Shorted cylinder 1 and it shut off immediately. #2 no change, #3 shut it off again immediately. Cant remember what the rest did but I plan to take the 5 that I haven't had off yet to verify the little parts inside move. Probably let them soak and get freed up? Not sure how sensitive the EUPs are but I've been keeping things clean inside. Got #2 off and sure enough that little square inside is froze up.

Currently running on 3 ish and fills the shop in thick black smoke in about 2 minutes. I read that these things can get stuck open is that right? Or am I more likely looking at a set of injectors?

Thank you all for the help, Its been great to have things to try. Learned a lot more about Mack engines and controls than I probably care to Lol.

Part of identifying good/bad EUPs involves swapping eup locations around. Take a known "good" eup (one that causes motor to stumple/die when you interrupt it) put it where a bad one is and see if the eup makes the "bad" cylinder fire. Process of elimination you can find whether EUPs are bad or injectors are bad. Good plan to tear down all the EUPs first, if they're stuck and need to be freed up you may get slot more of them firing.

[Ryanp]

Well everyone has been a lot of help.

Yesterday I finished getting the EUPs freed up. They got progressively rustier as I got toward the rear or the engine. I guess that's normal with the exhaust. Got those back on and quick bled the injectors at the head. It started up and sputtered for about 3 seconds then took right off and idled normal. Gave it a minute then bumped it a little bit with the throttle and it seems to run pretty well. No gray or blue or black smoke. Runs right out. Thats a relief. I was beginning to wonder if I bought a big boat anchor.

Now I'm on to the small things. I will be going through the air breaks and see how the transmission treats me. Hopefully easier than the engine lol. I don't want to have to learn too much about the transmission also.

Thanks again for the help and resources! Ill start a build thread on the flatbed and what not when I get the welder out.

[JoeH]

Nothing like a little hands on experience! You should be proud of yourself!