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Old 08-13-2020, 10:31 PM   #1
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When your Diesel cranks but doesn't catch, what's your protocol?

My bus is awesome, but sometimes, if I haven't started it for several days, I can't get it to catch. The first time it happened, we were going to meet with friends to shoot a photo to commemorate the beginning of our dual Skoolie journeys. It took a solid 30 minutes to get it to catch.

For the past two days I couldn't get it to start at all, trying on and off all day, both days. I noticed that the batteries were reading 12.4v, so I left the charger on it overnight. Yesterday I realized that I hadn't closed the roof hatch properly, and thought maybe that was preventing the engine from starting, so I closed it, checked all the emergency exits, and tried again. No luck. I left the charger on overnight again, and this evening, the bus fired up on the 3rd or 4th try.

I guess that either I wore the battery down trying to start with the emergency hatch locked out, and there wasn't enough voltage to get things moving, or maybe I did something else that wasn't right. That leads me to the question: what do you do when your engine doesn't catch? Do you have a routine?

I'll crank mine up to 30 seconds, then leave it off for 2 minutes or more. Sometimes I'll crank it for 7-8 seconds, then stop for about a minute and try again. Both of these routines have worked sporadically, but there has to be a better way!

Two quick questions: Do I need a bigger battery charger than my 12v/15a "smart" charger? Also, is there a minimum voltage that the batteries have to be at for the engine to catch? I'm on a Cat 3126B with 3 1,000Ah batteries.
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Old 08-13-2020, 11:00 PM   #2
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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.
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Old 08-13-2020, 11:23 PM   #3
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Originally Posted by bus-bro View Post
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.
Damn. That is some very useful information! I'll start reading up on air in the fuel lines and see what I can find in the way of diagnostic and resolution. Your experience is much appreciated!
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Old 08-14-2020, 12:44 AM   #4
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CAT 3216 also likes high engine RPM during the cranking. If the battery is not fresh, it may not turn over fast enough.


Any codes? I had a similar situation a few years back. When it did start, it surged while idling. Turned out to be a faulty ICP sensor.
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Old 08-14-2020, 09:01 AM   #5
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Like bus bro suggested, you likely have an air in fuel issue. It can be caused by many sources, but what they all typically create is an air leak on the suction side of the fuel system. This leak allows the fuel to drain back to the tank when shut off. When you go to start it again, the mechanical fuel pump has to reprime itself and the filters, which is what's causing your long start times.

The difficult part is diagnosing it and then finding the leak. Since it's on the suction side you won't usually see the telltale wetness that you'd normally see with a fuel leak.
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Old 08-14-2020, 09:02 AM   #6
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Oh, and a diesel engine in warm weather should start within the first second or two of cranking. If it doesn't you have issues that need addressed.
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Old 08-14-2020, 09:29 AM   #7
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Quote:
Originally Posted by Native View Post
CAT 3216 also likes high engine RPM during the cranking. If the battery is not fresh, it may not turn over fast enough.


Any codes? I had a similar situation a few years back. When it did start, it surged while idling. Turned out to be a faulty ICP sensor.
I haven't checked for codes yet, the "check engine flashing code" trick is something I just learned about. When we had it at the shop getting checked over last month before I bought it, they had it hooked up to the scanner and there were no codes.

The problem may be operator error, but I'm going to follow up with trying to narrow down the issue. I just found out about the fuel priming pump. That's something I could have tried, but didn't know about.

I'll also keep an eye on the RPM when starting, to see if there are any irregularities there. This is helpful, and underscores that I have a lot to learn.
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Old 08-14-2020, 09:33 AM   #8
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Yeah, mine starts instantly even if you bump the starter. Im not even done turning the key all the way and its fired up.
Thats in warm weather.
When its cold it will stumble a bit, but eventually start.

Are you getting any smoke when cranking?
White smoke is lack of heat for combustion or leaky injectors.

I second the air leak in the line posibility. I have a VW TD engine and when a few of the fuel lines went bad it was just like what you described. Sometimes it was so bad Ihad to give it a spray of wd-40 down the throat to get it to fire up.
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Old 08-14-2020, 09:46 AM   #9
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Quote:
Originally Posted by Jsneeb View Post

Are you getting any smoke when cranking?
White smoke is lack of heat for combustion or leaky injectors.
I will check for smoke the next time I have a problem, which might be over the next few days. You are talking about the exhaust and not the blow-by, correct? The blow-by tube had barely detectable smoke when checked after the bus had been driven.
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Old 08-14-2020, 09:49 AM   #10
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From the exhaust yes.
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Old 08-19-2020, 12:50 PM   #11
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Just to correct an earlier post -- the CAT 3126 has an intake grid heater -- this is the reason CAT says never to use ether or you'll potentially blow up the engine and maim/kill yourself

With that warning out of the way -- my bus has a parasitic drain and I've let my batteries go down as low as 12.2v and it still fired right up.

I would get a volt meter and measure what the voltage drops to while cranking the engine.

I would also compare the voltage at the battery to the voltage at the fuse block and at the starter.

A little corrosion (at the electrical connections) from sitting will go a long way to giving you starting troubles.
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Old 08-19-2020, 02:42 PM   #12
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I would get a volt meter and measure what the voltage drops to while cranking the engine.

I would also compare the voltage at the battery to the voltage at the fuse block and at the starter.

A little corrosion (at the electrical connections) from sitting will go a long way to giving you starting troubles.
Thank you for the tips!

I found that my CAT has a fuel primer pump. I think the next time I have a problem starting, I will give a few pumps and see if it fires right up. That should indicate a fuel problem.

Once we're done removing the walls and ceiling, I'm going to start simplifying the wires. I have disabled the "safety" features and can eliminate any of the copper the is related to those, and I expect that fewer wires will mean fewer problems down the road.
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Old 08-19-2020, 03:24 PM   #13
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Quote:
Originally Posted by CoffeeGuy View Post
Thank you for the tips!

I found that my CAT has a fuel primer pump. I think the next time I have a problem starting, I will give a few pumps and see if it fires right up. That should indicate a fuel problem.

Once we're done removing the walls and ceiling, I'm going to start simplifying the wires. I have disabled the "safety" features and can eliminate any of the copper the is related to those, and I expect that fewer wires will mean fewer problems down the road.
When mine lost prime it took about 400 pumps on the primer.
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Old 08-22-2020, 08:20 PM   #14
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I turned the key today, and because I had just installed a new air brake pressure gauge, I was fiddling with my stop watch before I moved it to the start position.,

Bus wouldn’t catch. I have started it every day over the past few days with no problem. Do I tried the pruning pump and it was very stiff, difficult to pump, which makes me think the fuel pressure is there. I waited a few minutes and turned the key again, and moved to start as soon as the grid heater light went out and it started right up!

So maybe I’m waiting too long to turn the key sometimes? Should I hit the starter as soon as the grid heater light goes out?
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Old 08-23-2020, 12:54 AM   #15
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I wait for the grid heater light to go out before turning the key to start it. If the grid heaters are on, they pull a lot of current from the batteries. That current is needed to turn the engine over as fast as the little starter motor can spin it.


Question: Do you have a CAT 3126 or a Cummins of some form? Your profile has the engine listed as Cummins 3126.
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Old 08-24-2020, 12:50 PM   #16
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Question: Do you have a CAT 3126 or a Cummins of some form? Your profile has the engine listed as Cummins 3126.
Whoops! Thank you for catching that! It's fixed.
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Old 08-24-2020, 05:16 PM   #17
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ok, may be too simple of an idea here and my bus is a very different model and set up but i was having some cranking ussues too.

turns out my battery terminal connections were beat up and you could spin the ground on the post.

i replaced them with the 4 way connecters that offer contact across the full width of the terminal.

once those were on nice and snug with full contact on the cleaned end of cable whoo hoo!!! she cranks strong and fires every time.

any weakness in the current can make all the difference to starters, fuel pumps etc.

good luck with getting her going strong!
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Old 08-26-2020, 11:02 PM   #18
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Quote:
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I wait for the grid heater light to go out before turning the key to start it. If the grid heaters are on, they pull a lot of current from the batteries. That current is needed to turn the engine over as fast as the little starter motor can spin it.
These last few days Iíve been turning the key as soon as the grid heater light goes out and so far itís cranked right up! So maybe it was me, all along? Time will tell...
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Old 08-27-2020, 01:58 AM   #19
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I sure hope it was just the proceedure and not something else.


Want to test it? Just try cranking while the heaters are still on ... it should crank slowly like it did before. At least then you would KNOW.
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Old 09-01-2020, 10:21 AM   #20
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Quote:
Originally Posted by Jsneeb View Post

Are you getting any smoke when cranking?
White smoke is lack of heat for combustion or leaky injectors.
Well today I ran into the issue with no-start again. Here's some background and additional information. I'm looking at which wires are associated with the "school bus" features, particularly the sensors on the doors and windows, since I pulled all of those. They were previously disabled by pulling a relay, but this also disabled the windshield wipers. The goal is to bring back the wipers but not the unneeded accessories (and remove their wires from the loom, to make life simpler).

So I disconnected and labeled seven wires on a circuit breaker busbar and verified that the bus starts by cranking it over and running for a minute. Then I started re-connecting them, one by one. The engine started right up (after cranking a few cycles) with each re-connected wire until I got to the last one. Ah ha! I thought! So I disconnected that last wire and jumped back into the drivers seat. But this time, the engine didn't catch.

Concerned that maybe there was some sort of relay setup that was now engaged, I killed the power to the electrics with the main switch in the engine compartment and let things sit for 30 seconds. Turned back on, tried starting, strong cranking, but no start. I disconnected the accessory busbar entirely (I know the bus will run without it) and tried again, no start.

This time I went around and checked the exhaust, and I did fine some smoke wafting out, as the photo here shows.

What are the likely possible causes here?

Does this look like lack of heat for combustion or leaky injectors?

The batteries are fully charged, the engine is cranking strong, I'm confident it's not electrical, and fuel has not had a chance to drain from the engine back into the tank, as it was running a minute before this happened and I've gone much longer without starting and not had this issue.
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