Mackpro

My lucky Friday night of oil changes on the Charger and 2 Jeep’s with some help from Hamms

Fuse 33 in the lower fuse box

Also on those engines, the air compressor gets it fresh air from piping that goes around the back of the engine to the back of the intake manifold. This is all on the turbo boost pressure side. So any leaks in that part equals lower boost pressure. The original intake manifold gasket were standard gasket material and were prone to blow out. The newest gaskets are steel core and more durable. Once you get the after cooler on, hook up the drivers side piping and on the passenger side install a test plug where you can pressure check the after cooler and intake manifold and air compressor intake piping . While there will be air passing through the valves and out the exhausts you can still build enough pressure to check with soapy water on all hoses and gaskets and fittings. My homemade pressure tester .

I pulled up the 1990 Mack tune up manual. A E7 400 specs are 21-37 psi fuel pressure. Pump timing at 19 degrees and boost pressure under a load should be between 20 and 28 psi . .

I sure don’t . Possibly someone on here has had a Ecm flashed. Also look at Rochester Diesel. I believe that they still make high performance turbos and injectors for your engine. I called them years ago and they were very helpful on a project I was working on.

That’s good!

The tech tool only has me checking the start relay and wiring in the fuse panel by clutch pedal. It basically just had me do the same test that I sent you. There is only info on pin 85 when key is in start position. Doesn’t say what it should be with just key in on position. The troubleshooting shooting guide in tech tool for the Mid144 PPID-3 FMI-3 is exactly what I sent you. If 12 volts is at pin 85 when key is in start position then it says “ No fault found” and test ends. When you turn key on is the PTO lamp on in the dash?

Hmmm interesting. I don’t think it should. But I’m still looking

Yes 85 should have 12 volts on it when key turned to start position. But you only have a few seconds to test it. , then you have to cycle the key and try again.

What’s last 6 of vin and I can run it through TechTool

I’ve seen 3.5 to 3.7 volts sent through some circuits to check continuity of circuit. I found this out with the EGR valve . If it doesn’t get the return voltage it will throw a open circuit code. But I’m not 100% sure in your case

The start wire comes out the back of the fuse box and comes through the top 5 pin connector, 4th pin down. Then through the 16 pin connector on pin 9

Testing the relay by it’s self. 80-140 ohms across pins 1 and 2

Pin 85 should have 12 volts when key turned to start position

Very small relay in kick panel fuse box. It must be inserted correctly or no start. The blades must be horizontal. Not vertical.

Your fuse box down by your clutch pedal, does it have a rubber boot that goes around it that sticks out a couple inches along the side? There was a recall on most all CXU, GU and CHU’s. Water was getting in the fuse box and shorting out relays. https://static.nhtsa.gov/odi/rcl/2014/RCRIT-14V078-3643.pdf

Thoses codes are odd and uncommon. I had no notes in my manual on them.

Sometimes the pictures in the VMAC 3 troubleshooting manual are shown from the wrong end of the connector. Sometimes it’s looking at the front of the connector and sometimes from the rear. Best to check the actual wire number on the wire itself . VJ3-08-0.8

The EPA killed the option of some HP upgrades on some pre 2007 trucks. Mostly on the AI engines in certain years. It wasn’t due to they way the truck was spec’ed , just maxed out their NOX and particulate matter (soot) output for the year on all the vocational trucks they built that year. It happened to several friends of mine back then with their CV’s. I looked your truck up and couldn’t find a torque limit switch on your truck . Usually only saw those on 460’s with 18 speeds .

The engine ECM looks at the coolant temp and intake manifold temp and AC high pressure switch and commands the fan to engage. If you unplug the fan harness connector from the fan the fan should speed up/engage. Coolant thermostat and water pump and radiator clogged externally ( behind after cooler) is the more common over heating problems. Is this a farm use truck?

Mid144 PPID-3 FMI-3 is Starter relay output , voltage above normal or shorted high. Possible cause is short in harness or relay