Changed Alternator - Engine Cranks But Won't Start

Update: Problem Solved

It was in fact a bad ECU. I put a new one in and it cranked up without any hesitation.

I learned a couple of useful things from the experience. First, apparently anytime you take a Caterpillar engine to an authorized service center they read the computer and make a record of all the settings. This worked in my favor because after getting a Cat Remaned ECU they needed to "flash" it, or program the computer with parameters for my particular engine setup. Sometimes they can download a file with all of the factory parameters, in my case they were not able to locate that file.
Because I had it serviced in Phoenix over the summer, although I was in St. Louis they were able to download all of the parameters that they read from the ECU when it was serviced in Phoenix and program those into the new ECU. This saved me from having to have a tech come to my rig and assess the engine configuration and guess as to all of the parameters.

The second thing I learned is that I've been seriously abusing my house batteries by discharging them too much while boondocking. My generator is not currently working so I've been recharging using the main engine. This has put too much strain on the alternator which is what caused the voltage regulator to fail, resulting in voltage surging too high and frying the ECU. This makes the list of "Things I Wish I Knew".

I had a mechanic look at it and he confirmed the the ECU is not communicating. I pulled the chassis wiring harness plug off of the ECU and confirmed that it is getting proper voltage. Looks like the high voltage might have fried the computer.
I'm working on getting a replacment and will update everyone soon. Thanks for the input.

Kimoreah wrote:
I have a 1999 Harney Coachworks Renegade with a Cat 3126 engine. I purchased it with 78,000 miles about a year and a half ago, and just turned over 100,000 miles.

When I bought it the voltage was fluctuating a lot and I ended up replacing the alternator. That fixed it, however I recently noticed that the voltage was fluctuating again and replaced the alternator a second time.

Now the engine will turn over fine but not start. I'm pretty stumped as to why the sudden failure. I tried to check engine codes by turning on the ignition, turning off the cruise, then holding down the cruise set/resume switch - but no lights blinked. Not even the code 55 saying there are no codes.

I would appreciate any pointers of what I should be looking at, thanks!

sounds to me like you left off the power supply wire to the fuel shut off solenoid?? must be contained in the alternator wire harness some how???? leave ignition on and check for 12v at the fuel solenoid

Do you have a manual primer pump on the fuel filter?

If so, use it and tell us if it is easy to pump (a problem) or HARD (fuel pressure in system OK).

And, assume engine is turning over at normal speed and if cold ambient temperature that you are waiting long enough for the intake manifold heater to get to temperature.

No codes from the ECU, no engine running...without knowing diddly-squat about your particular engine, it kind of sounds like the ECU is not getting power. Maybe there's a loose connection to it, or a blown fuse, or a ground that is broken or didn't get reconnected properly.

I'm not as well versed on diesel as i should be
But on our Safari with Cummins engine there is a fuel system solenoid that opens the valve to the injection pump and operated by the ignition on

No fuel no run
Diesels turn on and off by allowing full or stopping fuel

Maybe a dropped or loose wire, or a wire that broke inside by being pulled on

A rig that old might have a circuit that comes from the IGN switch, through a diode, all the way back to the alternator supplying a Field Voltage. If there is a poor, corroded, or open in that circuit, you'll get your symptom.

Check your chassis drawings, and the original alternator drawings to see if that's the case.

Note that many RVs in that era switched over to an alternator that supplies it's own field voltage. There's a good reason why some manufacturers kept the old IGN switch to diode to alternator design and it makes sense, I've just forgotten what it was.