what will cause volts to drop on semi

April 07, 2022 Post a Comment

I've got an 07, 9900i with the c-fifteen acert with a voltage trouble that I have non seen in any of the threads. The truck starts and runs fine, the problem is the volt meter drops down to 12.five when under ability. At idle the voltage is xiii.5 / 14.0. raise the rpm, no alter, when under power, starting off, climbing a loma, passing another vehicle, the voltage drops. when I allow up on the pedal the voltage comes back up to normal. batteries are new, alternator is practiced, all cables are make clean and tight. I've had true cat techs look at it along with a couple of different IH dealers and no 1 can find what is causing information technology to drop. Anyone ever seen this problem before ?
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Have yous checked with a voltmeter it's really dropping?
My first guess would be slipping belt. Could be voltage regulator or wire to the batteries. Simply considering a wire looks good on the outside,doesn't hateful it's 100%.
The belt is tight, replaced the tensioner hoping that was the problem. replaced the alternator twice to no avail. all the cables were ohm'ed and checked out OK.
Ok, this can exist tricky. Chances are there is nothing incorrect with the batteries, belts, alternator or chief cables. The volt gauge in the nuance is really data feed from the engine ECM. The voltage the gauge shows is the same voltage the ECM is getting. Under high engine loads the ecm is commanding a college pulse width from the electronic injectors which uses more current, that is why the volt estimate is dropping off under a heavy pull. Basically the ECM is starting to starve for power. The volts should not drop off like that. This is an indication of a bad or weak principal ECM ability supply. Your ECM will accept its own dedicated power harness from the batteries. Follow this harness from the batteries to the engine, bank check all your connections, pins and fuses and pay shut attending to whatever spots where the wires may be rubbed through and partially corroded. Make certain the actual battery information technology is connected to is properly continued to the other batteries and getting properly charged.
Thanks for the idea's. I've been dealing with this for near 4 years and nobody including cat could help me figure this out. I'll let you know if this does the trick
If you desire to become a bit farther, the truck harness connector at the ecm is where the power and grounds become in. Ultimately this is best identify to cheque for proper power and grounds. The wiring should be "load" tested. This is using the excursion to power something that takes a lot of current, similar a caput light bulb. If you have a bad wire information technology volition still show total bombardment voltage with a digital multimeter or bones 12v test light, because those practice not have much amperage to piece of work or read. A head light bulb takes a lot of amperage to be bright and and then if the wiring is weak or bad somewhere it cannot supply the caput light with the current it needs to be bright, so it will be dim instead. You would remove the ECM connector. The main battery positive terminals are 48, 52 and 53. The master grounds are 63, 65 and 67. If you connect a wire from one of the positive pins, to a caput lite, then from the head light dorsum to one of the basis pins, the head light should be nice and bright. All powers and grounds should be checked. It is mutual for ane chief power lead or 1 principal footing lead to split and power or basis multiple terminals. The splice connections can go bad and cause 1 of the ability or basis leads to accept loftier resistance. Primal switch power comes in on pin lxx of the same connector.

double yellow Thanks this.
Thank you for the info. I was wondering how I was going to figure out which pin is which.
wconner, I have the same truck/engine fix every bit you and I've been having the same issues since I bought the truck 4yrs ago. I agree with HeavyD, information technology'due south probably something in the feed for the judge.
On my truck the gauge will show 13-14 volts under normal load, at no load it will jump to 14-14.five volts and under a heavy load information technology volition drop downwardly to 12volts so jump dorsum up. I hooked a volt meter up to the 12v feed on the dash and it reads a constant 13.three-13.viii(depending if I have the lights on, fan on loftier,etc)even when the judge is moving around.

Like you I replaced everything and even went as far equally replacing the power board for the banking concern of gauges the volt gauge is on and nothing has fabricated a divergence. I got tired of messing with information technology and have only given up on it and alive with the gauge moving around.