Strange goings on.

Discussion in 'Mack Forum' started by Tow Bandit, Jul 29, 2012.

  1. Tow Bandit

    Tow Bandit Bobtail Member

    Jul 28, 2012
    I live in Australia and have just purchased a Mack with an E7 400 motor. Its a 1993 CHR series. Now...... it has recently decided that switching off is the game. It only does it in the morning. You can leave it all day and it will be fine. Its only in the morning. It will run for about 10 - 15 minutes and then cut out. Sometimes it will start straight away, other times you need to leave it stand for a few minutes. I have attached a scan tool and it shows nothing even though the light is on. I have tried pumping the fuel, no go.

    Questions.1. Does the ECU have a maximum oil pressure it will allow before switching the engine off to protect itself and if so, what is it?
    2. Does the ECU/ injector pump have some cold start system built into it and if so, can it be tested?

    Our local dealer is a bunch of ............and are not interested at all. Too hard basket. It has to be something based on temperature or pressure. I live in a very hot place and it gets nippy in the evenings hence the higher oil pressure in the morning and some sort of cold start system which deactivates once a certain temp is reached. I am a mechanic by trade and have tested what I can, knowing what I do. These things tend to be something silly that will end up making you look like a cake. As per normal, the flux capacitor will be blamed.

    Any ideas?
  2. bender

    bender Road Train Member

    Jul 20, 2010
    Don't Kid Yourself
    I would be looking at the fuel solenoid and control circuit.
  3. Tow Bandit

    Tow Bandit Bobtail Member

    Jul 28, 2012
    In an update, after adjusting the TEM sensor, my truck starts much better but still cuts out. BUT....if I hold the engine shut off button when shutting down and holding it when i turn the key on and releasing when cranking, it doesn't cut out anymore. The next time I started without pushing the button, it cut out within 20 seconds. According to the vmac book, the engine shut down button is also an override feature which is supposed to give you and extra 30 seconds if the engine light comes on. I can go all day. I will find out whats causing this and have Thor's tool of choice awaiting the culprit.
  4. Pablo-UA

    Pablo-UA Road Train Member

    Oct 11, 2010
    Borispol, Ukraine
    old VMACK is not so sufisticated unit. Engine protection only with low coolant, low oil pressure, overheating of coolant ore oil (optionally) and low oil pressure ore implausive oil pressure value.

    As I remember engine shuts off with over 6 BAR oil pressure, but oil pressure limiting valve is 7 bar, so I sugest bad (blocked) valve ore clogged oil filter
  5. chalupa

    chalupa Road Train Member

    Jul 22, 2010
    My E-7 started that crap today. cost me a load too. Move 100 feet, alarm goes off then the engine.

    Thank god for paperclips! Found the culprit to be the oil pressure sensor o'top of the filters. Unplug it, jumped the to side by sides and off we go. You get an electronic malfunction light but it wont shut off cause of this anymore.

    Humped it up to the dog house for a new one....98 freakin dollars !!! It was 42 last year!!! I swear!!

    And then the dipstick broke while I was checking the oil.....gawd! That will be 42 dollars when it gets here plus she ate a battery this week.

    Just should have stayed home.
  6. Tow Bandit

    Tow Bandit Bobtail Member

    Jul 28, 2012
    My search for my demon appears to be at an end but as with all demons, they do you when your smiling. This is what has been done. The mack computer shows no fault codes making the diagnosis more fun. The fuse box contains thermo fuses which are self resetting. These are now on their way to the tip having been replaced with standard plastic fuses. This dramatically reduced the number of times it died. When it died again, I was sitting in front of the fuse box with the cover off and heard which relays was clicking. There are two relays, one main power and the second is for the engine brake. Both activate when ignition is switched on and are both somehow linked as they both preformed. You would assume that it was an ignition source problem except fuse 15 powers them and had constant voltage. On testing, it appeared that the relay had a high resistance which was making the thermo fuse click out. They are also on their merry way to the tip. Your fuse box is on the other side and self resetting fuses have no visible signs of being blown. This makes it even harder and as you can not see high resistance, catching the culprit is a cat and mouse game. End result.....fine so far. I can actually drive with out clenching my butt cheeks.

    This now leaves me more time to concentrate on the war between caravans and trucks.
  7. Tow Bandit

    Tow Bandit Bobtail Member

    Jul 28, 2012
    OK, this will be my last post on this. After 6 months of hair pulling, I finally nailed the problem. There are a bundle of wires which go into the injector pump. The two brown wires are the key. The one comes from the main fuse and the other goes to the ECM, through an electro magnet. This magnet is what controls the fuel. This is NOT the fuel shut of solenoid it is the rack enrichment thingy, it adjusts fuel mixture by pushing on a rod which controls fuel to the rack. If you have 12V going in, you need 12V coming out when the ignition is on and engine not running. If you don't then you have resistance in the terminals inside the injector pump. I removed the end cover, crimped the wires inside, which are attached to the internal plug.( I suggest that if your personality involves a hammer when you get your ### out, I suggest you get someone else to do it as there is an anti tamper seal on the one bolt in the worst place possible and you have to remove it to get the back off. If its gone then that means your pump has been opened before and not by Bosch.) This resolved my fluctuating voltage. The ECM requires 12V from the injector pump to function and the loss of voltage results in the ECM not registering any fault code. This faulty connection/ high resistance, will give you sudden loss of power, engine shut down, black smoke, poor pulling power and make the truck run like a bag of s..t. This will only happen whist its doing its thing and switching the truck off and back on usually fixes it until next time. This has been tested for a while now and made my truck a pleasure to drive. All of the above posts are are linked to a common fault. When anything that goes through the ECM is activated, it creates extra draw on the power wire to the ECM from the injector pump, hence it looses contact and you cut out/ loose power. This electro magnet thingy has rarely been known to have internal faults and is something that is not normally changed when you have your pump reconditioned, if your problem is actually the electro magnet, you get your old fault back when you recon your pump. I tested my voltage before start up, after breaking down and when it fixed itself, all pointed to a loss of voltage on the brown wire. It has finally fixed my problem. Good luck!
    P.S. All of the above is done with the pump still on the truck and should take about 2-4 hours.
    QUALITYTRUCK Thanks this.
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