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View Full Version : 941 not cranking with glow plugs update



wlf89
01-05-2017, 06:30 PM
i got the new breaker put in and it isnt tripping no more but it still wont crank when 50 outside or below after being heated 2mins. it tries to but wont quite do it. when its about 60 or hotter about 30secs of glow plug and it will crank right up. i took all the battery connections from battery to starter and all the grounds off and cleaned them up but didnt seem to make no difference. it sounds like the engine is spinning fast enough.
any ideas why it might not be cranking like it should?

catdozer876
01-05-2017, 07:36 PM
Check for water in your diesel fuel, cleaned your fuel screen, check for free flow of diesel from the tank and changed your main fuel filters. I have had algae cause a problem very similar to what you are describing. It just was not getting enough fuel to start after sitting over the course of just one winter. When you do change your filters try dumping out the fuel from the fuel filters into a clean bucket and see if the fuel is discolored or smells different than fresh diesel.

Also sometimes if it is really cold I have had luck with cranking the diesel with the fuel in the off position for about 10 seconds. Then wait about 30 seconds, then apply the glow plugs for same duration as you would normally for the conditions, then give it a little bit of fuel, not too much and then crank it. You have effectively heated the engine a little and it can make a big difference in starting in the cold. Also if you give it too much fuel when trying to start it can make it much harder to start form a few tractors I have had. Keep us posted. Have you checked to see if all of your glow plugs are working?

Old Magnet
01-05-2017, 09:32 PM
What's the status and specification of the batteries you are using?

wlf89
01-06-2017, 10:43 AM
just going from memory here old magnet but i think the specs below are correct for the batteries i put in it about 2yrs ago. and it was checking somewhere around 24.8volts to the starter.



Battery Electrolyte Composition:Acid
Battery End Type:Top Post
Battery Purpose:Starting Lighting Instrumentation
BCI Group Size:27
CA at 32 degrees F:1035
CCA at 0 degrees F:840
Freight Class:65
Polarity:Left Positive
Reserve Capacity:140
Terminal Type:DIN
Volts:12

cojhl2
01-06-2017, 11:01 AM
Even though you have the trip fixed, are you sure the glow plugs are not burned out?

wlf89
01-06-2017, 11:36 AM
all 4 plugs are working

Garlic Pete
01-06-2017, 12:40 PM
but if all four glow plugs are working for sure, you have good batteries and the voltage you describe, it sure seems that you just need more heat to get that thing started when its cold. Two minutes at the temperatures you describe is way more time on the glow plugs than I'd expect. That time to me would be more expected at freezing or below.

i'm afraid you may be seeing the effects of a worn engine. If the compression is low because of worn rings or valves not sealing well, it won't make anywhere near as much heat upon cranking. I don't remember you posting any information about blowby. If there is enough wear to cause this starting difficulty, I'd expect you to see a fair amount of blowby when it is running.

If the blowby isn't bad, I'm confused. When you are cranking with it below 50 degrees and the fuel on, are you getting a lot of white smoke? I think in your other thread we pretty much ruled out a fuel supply problem.

catdozer876's suggestion to crank it a bit with the fuel off would really help build some heat, even if internal wear is part of the problem.

You mention that you have 24.8 volts at the starter, but you might want to measure volts at the glow plugs with them energized. Even though you cleaned all the connections, maybe you've got a voltage drop somewhere which means your glow plugs aren't making the heat they should.

Pete.

Old Magnet
01-06-2017, 12:56 PM
Those batteries should be adequate if they are in good condition. I'd note your voltage reading. Batteries in good shape should produce 2.2v per cell = 26.4v for the two 12v batteries.

wlf89
01-06-2017, 02:06 PM
but if all four glow plugs are working for sure, you have good batteries and the voltage you describe, it sure seems that you just need more heat to get that thing started when its cold. Two minutes at the temperatures you describe is way more time on the glow plugs than I'd expect. That time to me would be more expected at freezing or below.

i'm afraid you may be seeing the effects of a worn engine. If the compression is low because of worn rings or valves not sealing well, it won't make anywhere near as much heat upon cranking. I don't remember you posting any information about blowby. If there is enough wear to cause this starting difficulty, I'd expect you to see a fair amount of blowby when it is running.

If the blowby isn't bad, I'm confused. When you are cranking with it below 50 degrees and the fuel on, are you getting a lot of white smoke? I think in your other thread we pretty much ruled out a fuel supply problem.

catdozer876's suggestion to crank it a bit with the fuel off would really help build some heat, even if internal wear is part of the problem.

You mention that you have 24.8 volts at the starter, but you might want to measure volts at the glow plugs with them energized. Even though you cleaned all the connections, maybe you've got a voltage drop somewhere which means your glow plugs aren't making the heat they should.

Pete.

the engine only has about 50hrs on it since i rebuilt it, but i didnt do any head work and am wondering if that is my problem,although they seemed to be sealing good when i inspected them when rebuilding the engine.

mrsmackpaul
01-06-2017, 02:25 PM
Those batteries should be adequate if they are in good condition. I'd note your voltage reading. Batteries in good shape should produce 2.2v per cell = 26.4v for the two 12v batteries.

Old Magnet maybe onto something here as the cranking speed when the motor is cold is critical as it generates the heat and faster it cranks the more heat
Even in my mild climate and our very mild winter motors can wind over at what appears normal speed but still not fire straight up and the problem is its just not making the speed to make the heat
So maybe it is as simple as Old Magnets suggestion

Paul

Deas Plant.
01-06-2017, 03:27 PM
Hi, wlf89.
I would have expected a better figure than 24.8 volts from a good pair of 12 volt batteries connected in series, like somewhere North of 26 Volts. A quick test would be to add another good 12 volt battery to the mix, using booster cables to connect it to ONE battery at a time in the machine and then cranking.

If this makes more difference when connected to one battery than to the other, you may have a weak battery in the machine. If you notice the same change in response from connecting to either battery in the machine, then both machine batteries may be weak.

Some years ago, the starter failed on a Cat D5B that I was operating. It barely managed to start the engine to get the machine on the float/lowboy. I called the boss and told him about it and he arranged for his pet auto-electrician to go the new job to investigate. When we went to start the dozer, the starter was even worse, so the 'sparky' took another 12 volt battery out of his van and used booster cables to connect it directly to the starter cables to give 36 volts to the starter when the key was turned. The engine lit up very nicely, thank you. I took the dozer off the float so that it could leave and the 'sparky took the starter out while the engine was still running. I worked the dozer through the day without shutting the engine down and the 'sparky' had the re-built starter back there to put in again at the end of the day. Food for thought?

Just my 0.02.

rmyram
01-06-2017, 04:01 PM
was the 24.8 volts at the starter when you were cranking the engine? i was always taught 2.1 volts per cell which would equate to 25.2 volts for two 12v batteries in series. I'm not going to quibble, 24.8 volts at the starter when everything is at rest is slightly low and will generate low cranking speeds.

garlic pete may be onto something as well. i have seen and even have a diesel that displays similar characteristics. the valves may be sealing well, but was the valve protrusion checked when the engine was rebuilt. valve recession in diesel engines can significantly alter the compression ratio making it hard to start, especially if the valves and seats were ground during the rebuild.

My old 4020 JD which does not have glow plugs had a complete engine overhaul, but the owner did not check the valve protrusion, they had the head checked for cracks and leaks, then they had valves and seats ground. valve protrusion was just on the edge of acceptable towards the maximum side of the spec, one or two may have been above the maximum spec. it is a cold starting tractor at anything other than warm engine temps. i am opposed to using the ether bunny to get it going so i installed a webasto diesel fired engine heater. at -20 celsius it takes less than 20 minutes for the engine to reach operating temperature, the old diesel fires right up like it was after lunch an a warm summer day plowing.

dpendzic
01-06-2017, 05:24 PM
my 941b started well at 25.4 volts on 15 year old batteries---I think the most economical temporary fix would to be add a block heater.

wlf89
01-06-2017, 05:32 PM
i will recheck the volts tomorrow as i am going off memory from 2 weeks ago

drujinin
01-07-2017, 06:51 AM
In a series connection, you can check each battery at rest and when cranking. Example; at rest battery reads 13.2, while cranking battery reads 12.4. Test second battery same way, this will indicate which battery is the weaker of the two. Then if you would like to use jumper cables and another battery. You can attach it to the weaker of the two batteries to see if it gets your cranking speed up as previously suggested.
I agree to the idea of a block heater being added if the machine is going to be used a lot in cold weather and do understand that it may also not be sitting close to an electrical outlet. Hence the reasoning for attempting to get the charging/starting system up to perfect.

Scan
01-07-2017, 07:37 AM
When I worked for AJ way back and the 941B's came out with the scroll metering injection,often they would not start due to the kicker that moves the rack sticking in the stop position or low idle resulting in none or not enough fuel been injected so have a look at the stack and see if there is plenty smoke when you are cranking,AJ had the drivers schooled to put the throttle to on full after stopping as this would ensure the rack was in run for starting next time,its a good practise with all diesels with mechanical control pumps to put the stop to run and the throttle to full after stopping.
Tony

Old Magnet
01-07-2017, 10:30 AM
I'm not sure of the s/n of this machine but they started out with the compact/scroll metering system and changed to sleeve metering at 80H4676-up.

wlf89
01-07-2017, 03:40 PM
the batteries checked 12.7v each and 25.3v together

old magnet the serial is 70h617

Old Magnet
01-07-2017, 03:54 PM
Those battery readings are good.
You have the early scroll fuel injection.
There is a cover plate at the end of the rack that you can remove to check if the rack is sticking. Same cover plate that you would remove to install the micrometer for setting the rack.

cheshire cat
01-07-2017, 03:57 PM
Lazy starter , dirty and or wrong grade of oil, parasitic load from a hyd pump etc , cables wrong size bad connections , poor quality batteries
or a combination of these things , but I would put my money on the starter being on its last legs !!!...

dpendzic
01-07-2017, 04:45 PM
how about a worn engine with poor compression????

edb
01-07-2017, 04:51 PM
Hi Team,
along with what has been suggested by others, the scan below is Yellow Fathers view on the subject.
He suggests that 100 to 120 RPM Cranking Speed is needed.

I believe he is suggesting these speeds are for PC engines with working glow plugs, and DI engines without.

I would also think that with a good electrical system the direct electric starter motor would crank both engine types at these speeds--due to the designed gear ratios involved.

From memory, both types seemed to crank at same sounding speeds if cranked without fuel on--as when starting a reconditioned or long storage engine for the first time to get oil pressure up even though we had pre-charged the system with a pressure pot and line to the oil system.

Cheers,
Eddie B.

rmyram
01-09-2017, 11:24 AM
chesire cat has an interesting observation about oil, you could try changing the viscosity of the oil, if you are running 15w40 or straight 30 weight that oil can be pretty stiff when cold and will definitely effect cranking speed. up here i run 0w40 oil year round as i don't use my equipment enough to change oil more than once a year, the 0 w 40 lets them crank a lot easier in the winter, even with the block heaters plugged in, or the espar or webasto heaters working.

cheshire cat
01-09-2017, 04:49 PM
chesire cat has an interesting observation about oil, you could try changing the viscosity of the oil, if you are running 15w40 or straight 30 weight that oil can be pretty stiff when cold and will definitely effect cranking speed. up here i run 0w40 oil year round as i don't use my equipment enough to change oil more than once a year, the 0 w 40 lets them crank a lot easier in the winter, even with the block heaters plugged in, or the espar or webasto heaters working.

My take on old equipment and hard starting is often not just one thing wrong but a combination of things so too thick oil will slow an well used starter which draws a big ampege thru old cables also giving the batteries a hard time , lower compression and poor injector spray pattern means the engine won't start unless its turning over at a good rpm ,
So yes just a simple change to the 0w 40 or even just 10w30 oil might make all the difference , one thing for sure you don't want a single grade oil in anything diesel these days now we have the multi grade stuff, 30wt is like molasses in the winter and piss in the summer !!!

dpendzic
01-09-2017, 07:03 PM
straight 30w is all i use in my machines winter and summer--haven't had any problems so far