MR 688 electrical trouble shooting. No crank

[Ryanp]

[Ryanp]

Hello I'm working on a 2004 Mack MR688. AI300 with the allison hd4560. Last 6 on the vin, 023615.

Sorry for the confusing post. First time and I see that it only works on my desk top. This truck I'm working on was pieced together from 3. Cab, engine/trans, and the original chassis. everything was "VIN matched". So it came as a basket case that was missing some parts but the electrical appeared to be mostly complete. Hard for me to tell whats "extra" because I just need it to run and drive. Its getting a flatbed with water tanks to be a tender truck on our farm. There is still a harness that i believe controlled the front hydraulic pump but its tied in quite a bit to the harnesses that go into the console. 

 

Anyway its got a battery in it now and I'm trying to test everything and get it to fire before i go any further with the project. We can jump the relay at the air filter housing and it will engage the starter, slowly but I've only got one battery in it right now. I suspect there are thing unplugged or missing in the console that aren't giving me power where i need it.

Currently if i jump in and key it on,

1. "electrical malfunction" light

2.ABS light

3.Hearing some relays in the console clicking like you would expect.

4.The keypad for the trans doesn't light up or do anything.

Go to start position on the key,

1.Lights on the dash stay the same and I hear a couple more relays clicking but still no crank.

2.Still no trans power.

3.Not sure if its from the ignition position or the start position but the 4 large relays near the vecu held on by screws get quite warm. Almost hot to the touch.

 

Something is not hooked up or hooked up wrong i assume. I have contacted the dealer who is supposed to send over schematics but haven't seen them yet. Having a hard time knowing what to test for and where, the fuse/relay layout is mostly rubbed of the sticker on the panel and the diagrams I've found are for completely different trucks.

If someone has a schematic or some testing ideas I'm all ears.

Thanks, Ryan

[Joey Mack]

This is a tough one,, those trucks are wiring nightmare's.  The Allison fuse should be #71..  just for kicks, since its a farm truck, cant you just run a starter button to the exciter on the starter, put a 15 amp fuse in-line with it, and crank it over.  by the way, the wiring looks to be in great shape,,  Ive worked on many of these where the dog house was loose or open, and as trash trucks they would get filled with everything under the sun. youre lucky.. jojo

[Ryanp]

Thanks for the reply. Would you happen to have access to a diagram to show where fuse #71 is? I just went through and tested them all and they test good. Jumped all the open fuse locations and found the flashers but no trans power. Also it will turn over if we power the big relay behind the cab that powers the starter up.

I know what you mean about the dirty console. I have a 2001 mr688 that is all oily under there because of oil from the air brake release. Ive cleaned all the trash out but its still dirty and cobbled like no other.

thanks, ryan

[Joey Mack]

I can look. I have many of them but dont recall an MR diagram..  I will go out to my shop in a bit, to look.. jojo

[Joey Mack]

So what I have is for V-MAC III...  Heres a look... jojo

[Ryanp]

Is that book different than what I would have? I see it says 1999 on it. With the AI300 mine is a VMAC4?

[Joey Mack]

yes. I have an older version...  and I dont know how much of the cab wiring was changed between the 2..  Sorry,  jojo

[Joey Mack]

Have you tried to go to the "Trucks dealer portal" and go in through the customer portal, then access "E-Media"  ??  jojo

[JoeH]

Here's the diagram for the 2003 we have been working on. Bergeys had to put in a service request directly to Mack to get this diagram for me. Top rate dealer! Look at fuse #40, check that the fuse is in there good and tight. Also you need to run Blink Code Diagnostics. Key On Engine Off (you can run it with engine running but you aren't there yet), hold the cruise control button (I forget which one) down til the Lightning Bolt goes out. It will then blink out a 2 digit code. Count the flashes.  When that code is done the light will come back on and stay on. Press cruise again to display next trouble code. Repeat until it continues to display numbers it's already put out.

Tell us what the codes are, so we can look them up for you. Also buy yourself Mack Manual 8-211, that's the VMAC III diagnostics book. It's a must have!

[JoeH]

Quality worse than I expected.

[JoeH]

I had same issue on mine, fuse #40 was loose.  # says CB-40 (Circuit Breaker)

Edited February 3, 2022 by JoeH

[JoeH]

https://www.diesellaptops.com/products/diesel-explorer

 

Also download this onto a laptop while it's still free, and when you can stomach the cost buy their $683 Diesel Link Adapter so you can plug into the truck. You can see if all the computers are powering up and communicating. For us, it wasn't listing the Engine ECU, which ultimately was because it wasn't powering up due to fuse connectors for #40 were loose.

[JoeH]

You should be able to figure out Who is Who from these pictures.

[JoeH]

You don't even have #40 installed. It should be a 25 amp Mini fuse or breaker.

[JoeH]

All the way towards the driver seat in the row "above" those three breakers.

[JoeH]

11 hours ago, Ryanp said:

Is that book different than what I would have? I see it says 1999 on it. With the AI300 mine is a VMAC4?

I don't think there's a VMAC4? Correct me if I'm wrong? Yours should be a VMAC III.

[JoeH]

Also on the trans keypad there should be a 20 amp fuse and + and - wires that run from a battery to a plug in the radiator grill. These wires supply "clean power" (power that is has no voltage fluctuations from other systems sharing power feed) directly from the battery.  Clean power comes through that 20a fuse then should go straight to fuse #65 which is 10a.

[JoeH]

I made the mistake of deleting these during our frame job because I assumed they were for the trash body. You may have done similar, or someone else did prior. If you don't know which plug in the grille I'm talking about I can get a picture tomorrow.

[JoeH]

Here is the schematic for the Clean Power. You should see the numbers 343A 2.0 and 336A 2.0 on the wires in the plug in the grille I'm referring to.

[JoeH]

You seem to be hitting the wall I climbed 2 weeks ago!

[JoeH]

13 hours ago, Joey Mack said:

So what I have is for V-MAC III...  Heres a look... jojo

1999 and 2000 had the engine ECU under the turbo. 2001 saw the switch to driver side, which was a good move. I don't know enough to know if the diagrams would match or not. But his truck is 1 year newer than mine so hopefully they're close enough! Mines an ai350 to his ai300. Same trans!

 

[Ryanp]

joeH,

Thanks for all the pictures and insight! I had my mobile mechanic friend come over last night and we determined the ecu was good but that I needed to recheck all my grounds and power connections and clean them up. I will have to get that manual ordered and double check those fuses and relays you pointed out. Also ill look into that trans power. your right I have that harness hanging out in the grille area, thanks for the wire numbers I will have a look to see what I can see.

 

Thanks, Ryan

[Ryanp]

Well everyone has been a lot of help. Today we made some more progress. The "clean power" was sure enough just hanging out not plugged into anything. I had also assumed it was for the garbage PTO pump or what not. Wires were numbered exactly as JoeH had shown in his schematic. Trans powered up and I read some codes off it. I left my paper at the shop and cant remember the codes. The blink codes I also have wrote down at the shop. 4-1,1-4, and 2-3 I think. My research told me ambient air temp, speed sensor, and coolant temp if i remember right. I will get those codes tonight.

This still did not fix my no crank issue Ive been working on. I have been mostly working alone and this afternoon, my uncle got in the drivers seat and was messing with the key when I was bumping the relays and fuses. The neutral start relay had loose connections that once the key was turned and I bumped the relay it rolled over. Thank goodness.

Still need to figure out my codes and get a few other things tied up but hopefully soon we will know if this thing can run.

 

[JoeH]

Sounds like you are moving in the right direction. Loose circuit breaker connections can be squeezed to firm them up.

There's a "patch" repair to backfeed clean power into the EECU. Without looking at your truck in person I can't know for sure if your EECU is actually getting power. I didn't see a breaker in CB-40, which should be the power to three 12v power pins on the EECU plugs. Truck can crank but won't start if the EECU doesn't get power.

If I read correctly, you're working with one battery. It will take 2-3 batteries to start this thing. If the voltage to the EECU drops to 7 (going off memory) the EECU will power off until the voltage normalizes.  The draw on one battery trying to start this thing is significant. 

Trans codes can be pulled as follows: press up/down arrows together, hold for a few seconds. Display will say "d1" then a 4 digit code. Press Mode to move to next 4 digit code. I believe it has 4 code slots? Each one listed as "d1", "d2" etc. Once you get to "dX -" you are to the end of the active code faults.  These are Allison codes, so you will have to sift through Allison data to find what they mean.