When your Diesel cranks but doesn't catch, what's your protocol?

[BamaBus]

Originally Posted by CoffeeGuy

Okay, I finally got the CAT ET software working on my bus and was able to read the ECM, codes and configuration. The first pair of errors logged are 64-11 and 64-2.

I wonder if this is related to the overspeed light that came on during startup? I believe the speed sensors are behind the compressor.

What did you do to get ET to work? I just got a "nexiq" and want to check out a C7. Working on a laptop with win7 that I can access the hard drive from my desktop but I need it to boot on its own.

[CoffeeGuy]

Originally Posted by BamaBus

I wonder if this is related to the overspeed light that came on during startup? I believe the speed sensors are behind the compressor.

What did you do to get ET to work? I just got a "nexiq" and want to check out a C7. Working on a laptop with win7 that I can access the hard drive from my desktop but I need it to boot on its own.

I’m not sure about the over speed light, I just thought it always came on while cranking. I guess if I replace the sensors, I’ll find out!

With the Nexiq/ET software, I reinstalled a license key for “trucks on-highway” because that’s what I saw in the Nexiq manual, then once I restarted Windows, it just started working. I was really kind of surprised, but then I remembered, unlike Macs, Win machines really like to be restarted after any changes. I rarely restart a Mac to resolve an issue.

[CoffeeGuy]

Originally Posted by CoffeeGuy

Okay, I finally got the CAT ET software working on my bus and was able to read the ECM, codes and configuration. The first pair of errors logged are 64-11 and 64-2. These are related to the speed sensors and a quick search on the web shows other 3126 owners with those errors describing the same random no-start issue that I've been having.

I'll pull the speed sensors and test them, and probably replace them.

Damn, I don't know which is harder, pulling the speed sensors or unplugging the ECM so that I can test the sensors!!!

[CoffeeGuy]

I'm fairly confident that I have isolated the possibilities of what has been going on with my engine to the secondary speed sensor. This is 1 of 2 sensors mounted on a bracket that is in a really awkward place to reach, behind the compressor and fuel filter. I've been able to unbolt the bracket and slip the speed sensors out of the engine, but I can't do much more than that. Trying to remove the sensors themselves seems impossible without pulling the compressor, but I've read that it can be done.

I'm trying to find instructions on disassembly, so that maybe it will give me some clues as to how to do this without removing the compressor. I've read that it can be done, but I still don't know how!

Has anyone done this on a CAT 3126B before?

[BamaBus]

Originally Posted by CoffeeGuy

Has anyone done this on a CAT 3126B before?

Have you read this? Only thing I could find.

[CoffeeGuy]

Originally Posted by BamaBus

Have you read this? Only thing I could find.

Thank you, Eric!! That looks exactly like what I needed to see. I'm going to try that this weekend. Between the code I read from ET and the engine behavior, I'm reasonably sure this is my problem. I had the old bracket and sensors out, but I could not figure out how to remove them. There's 20 years of crud built up in those hard-to-reach parts of the engine. I managed to get a lot of it out with my gloved hands, but I couldn't quite follow the wires back to where they join the harness. I did find one wire tie that I need to cut. Only issue is that once I free the wire at that point, I can't secure it again afterward at the same point. Maybe it's not a big deal, but I'd rather avoid creating another problem down the road.

I managed to put the sensors back in and verified that the engine still starts.

Did you get your Nexiq fired up yet? One thing I forgot to mention, is that you do need to have the ignition key in the "on" position for the communications link to start. That was something I inadvertently discovered when testing yesterday.

[CoffeeGuy]

It took some time, but I can finally report that my sporadic crank, no-start condition has been properly diagnosed and repaired!

The issue was indeed the secondary speed (timing) sensor. This was diagnosed with the CAT ET software, showing codes 64-11 (Secondary Engine Speed No Pattern) and 64-2 (Secondary Engine Speed Loss of Signal).

Once I had those codes in hand, I did a little more research and found other descriptions of my same problem with the same error codes. This was 2nd confirmation. I went ahead and ordered new sensors.

I checked the new sensors for proper resistance, and then removed the old sensors and verified that the primary sensor was good, but the secondary sensor showed a completely open circuit. At this point I was so deep into the removal/replacement work that it helped having that small boost of confidence that I had found the problem.

Finally, I got it all back together and started the engine several times, it caught quickly, and I'm satisfied that I've solved the problem.

I want to thank everyone who shared their knowledge and suggestions as I worked through this issue. I'm learning a ton about my 3126B, and I'm better equipped now to diagnose some problems in the future.

A couple of points worth noting. Getting these sensors out was a bear. They're behind the compressor and below the HUEI pump, and the wire is zip-tied to the frame. It took me a few attempts to get the sensors out far enough to disconnect them.

Once I got the sensors out, I realized that there was so much crud built up on the engine in that pocket of metal that I needed to clean it out before re-installing the new sensors. There might be better solvents, but I had a couple cans of carburetor cleaning fluid in aerosol cans, and that did a great job of degreasing everything.

I thought removing the sensors was hard, but that was nothing compared to getting them back in!!! I ended up making a run to Harbor Freight and buying various long-reach pliers and hemostats to help me navigate inside that small space. I now have a better appreciation for what surgeons have to go through. The hardest part is that there is no way to pull the clip that holds both sensors and the sensors themselves out through the small space available so you have to clip the primary sensor into the clip, then working in a space that is too small and distant for fingers, you have to snap the secondary sensor into the clip at the correct rotation. This requires some finesse and a lot of explicative shouting. I think I worked at it for a good 90 minutes before I figured out a way to use one pair of pliers to lock the clip in place, another to rotate the sensor, and then a screw driver as a pry bar with the entire assembly rotated 180° from the correct install position. Also, there is very little light available while doing all of this, unless you have small, bright lights that can be inserted into the space and not get in your way. I have those, but it didn't occur to me to use them.

I need to especially thank Eric (BamaBus) for linking me to a thread where someone said they've changed out these sensors a hundred times without removing the compressor. I might have given up, otherwise. Cheers!!

[Native]

I read that link you mentioned ... it was a good discussion. I have looked at those particular sensors and understand why the CAT dealer specifies to drain the coolant and remove the compressor as part of their replacement proceedure. I am glad you were able to replace them without all that.


Now I know I need to get CAT ET!

[teknomad]

Originally Posted by bus-bro

Somethings wrong if you need to crank 30 seconds to start in relatively warm weather. The engine should roll and start, though that might take a couple of three cranks. Don't think you got glow plugs, or a grid heater in your Cat. It sounds like you're getting air in your fuel lines when you sit. Your battery charger might be good for a trickle charger, not so much when you drain the batteries. What happens is people crank the engine so much in those no start situations that they drain and eventually destroy the batteries, and those long crank cycles with low voltage destroy the starter too. It can get expensive.

theres so much esoteric information like this. There should be a giant 'bible' thread with nothing but information like this.