wheeler73

The shutdown override switch allows you an extra 30 seconds or so to pull the truck over before 7t shuts down.

The truck can be running also. The only time it will flash the codes is when the codes are active. The older harness are sometimes sensitive to moisture.

Low coolant sensor, oil pressure sensor, coolant level sensor. What code are you getting. You can pull the flash code using the set resume button with the cruise switch off. Count the flashes. There will be a slight pause between the first and second part of the code.

Yes it goes through relays and the vecu. I have had to bypass the wire from the ignition switch to the vecu with a new wire in some mru garbage trucks as the companys did not want to trace out and repair the original wiring. You can also unplug each ecu starting with the abs and see if you can communicate with the truck as a defective ecu can cause no communication.

Check for power and ground to the data link connector. Also make sure none of the pins in the data link connector are pushed in which will not allow the laptop to communicate. I have seen that several times.

There is a kent moore tool for removing the bolts. I dont have the tool number handy. If I can rember I will get the tool number and a pic tomorr.

Also could have a J1939 communication link issue. Make sure to check all fuses and breakers.

Do the wipers and A/C work? If not I have had some that lost the chassis id in the vecu and would not crank or start with the key. Had to reprogram the vecu and fixed the problem.

The older trucks did not come with front brakes. I believe it was not mandatory untill 1975 or 1976.

They actually work better than the jake brake set up!

It is way different. You need a .045 feeler gauge for the power leash and .024 for the exhaust valve and a 6 inch pound t-handle to set the power leash and exhaust valve. You loosen both lock nuts on the exhaust rocker arm and loosen both adjusting bolts some. Then loosen the adjusting bolt on the end of the rocker arm and push down and insert the .045 feeler gauge under the power leash piston and tighten the adjustment bolt with the 6 inch t-handle and tighten the lock nut. Leave the .045 feeler gauge in and insert the .024 feeler gauge under the rocker arm and tighten the other adjusting bolt with the 6 inch pound t-handle and tighten the lock nut. Then remove the feeler gauges. I find it easier to remove the .045 feeler gauge first. It is a different adjusting procedure than the jake brake set up as you can see.

They usually do. Just make sure all the combustion washers came out with the injectors. If not you will need to get them out. You can use a long pick to get them out. You do not want to double stack the washers. Does this engine have Power Leash if so are you familiar with the valve adjustment procedure?

There is a Kent-Moore tool for pulling the injectors. I believe it is a 1/4×20 bolt but don't quote me on that. I have a bolt I use with a small slide hammer to pull the injectors.

I like to set both rears up on jack stands and run the truck. I have found a lot of vibration and rear end issues this way.

Do you have an APADS on this truck? What is the ambient air temp? Does the A/C blow cold? Could be the high pressure fan switch with or without APADS. if you have APADS could still be the high pressure fan switch or the APADS unit its self. The best way is to use VCADS and monitor the high pressure fan switch.

Have they checked the ride height and driveline angle? Have seen this cause a lot of vibration issues at different rpms. Also have seen injectors cause vibration issues at different times.

Yes that cel is.

Also hope to brush up on my typing. LOL!!

Thanks all! Hope I can help as I see alot of VMAC III and IV issues as I am the triage and lead tech at my dealership. I also hope to learn on here too as I have found everyone sees different issues in different areas that others don't see often. Thaks for the welcome and helmet and I will try to post pics when I can.

Best to use a good marine continuous duty solenoid. They last the longest.

Hi I am a Mack master tech new on here to help and learn. I have been woking foe a Mack dealer for 9 years. Before that I was in automotive for 14 years. Hope to help others out and learn on here.

The only problem with putting the higher horsepower injectors in without the turbo and programming is over fueling.

Look at the heads and valves carefully. Check the H-rings after you remove the rollers. If you have a bad H-ring or rings you have to remove the heads to replace them. There are special tools to check and replace them. This engine should have ceramic rollers and the cam kit only comes with 2 new ones. I always recommend replacing all the rollers along with the eup rollers. Also check the eup roller guide pins as they wear and break also. If you pull the valves replace the valve seals and rotators if there is no head damage. The rotators fail quite often I have found. The new rotators are an updated design that go under the valve springs instead of on top. Also change the valve keepers if you remove them.

Hey bbigrig it sounds like improper installation of the cups. I have seen that before.

Great. I forgot about that valve.