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Author Topic: cold starting a mechanically timed fuel pump diesel engine?  (Read 2399 times)
zubzub
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« on: November 24, 2011, 07:24:17 AM »

I am heading into the winter with a new to me diesel van.  http://en.wikipedia.org/wiki/Volkswagen_Transporter_(T4)
Mine is  a 97 VW T4 with 2.4 AAB.  The reason I am posting this here is the question has a relationship to cold starting 2 strokes by holding them in the no fuel setting while cranking in order to generate more engine heat.   My engine has nice new glow plugs, but it has fairly mileage. It starts a little reluctantly already at -4C, and I can't always plug it in so I need to maximize -30C start-ability. 
So here is my idea....
If I install a switch on the fuel cutoff solenoid for my engine can I crank the engine with no fuel and generate extra heat? 
When a pump timed diesel is cranked with no fuel going into the pump are there negative side effects?

I know this is not too "bus" ish but it kind of is as you guys know more about mechanical diesels than most.  I also got the van as it was a mechanical diesel engine, with too short a high gear and very low HP engine (77 BHP) so it is kind of like my 4104. 
They used to call the VW vans buses.....
Anyhow any feedback would be apreciated.
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Busgeek
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« Reply #1 on: November 24, 2011, 07:38:26 AM »

You are better off not to shut the fuel off because fuel even though it is not burning provides cylinder lubrication.  A small shot of starting fluid is ok just don't overdo it. Hope this helps.  Happy Thanksgiving.  Bus geek.
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TomC
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« Reply #2 on: November 24, 2011, 07:50:33 AM »

I'm sorry to rebuff Busgeek-but it is NOT ok to use ether (starting fluid) on an engine equipped with glow plugs.  Typically most mechanically injected automotive Diesels have pre combustion chambers with much higher compression ratio.  Using ether can cause a backfire, punching a hole in the piston (pistons on automotive Diesels are just not as strong as a heavy duty Diesel), crack the engine block (don't ask how I know this), blow the pre chamber right off the head, and if the engine also has an intake manifold heater-the ether can explode back into your face.  If it doesn't start with two or three pre heatings and crankings, you need new glow plugs or have a fuel/engine problem.  Good Luck, TomC
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« Reply #3 on: November 24, 2011, 08:04:25 AM »

Right or wrong, this is what I always did with my VW and Mercedes diesels:
Wait for the glow plugs to warm.
Crank briefly, turn key off.
Wait for the glow plugs to warm again.
Crank
Apply pressure to the accelerator until the engine runs smooth, slowly back off the accelerator at a rate which permits the engine to stay running smoothly until at idle.
Drive off.

BTW: I do consider the T4 to be a bus, so this is right on-topic in my book.
Do you have any pics of your T4 to post? This is my 1993 gasoline model:
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Seayfam
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« Reply #4 on: November 24, 2011, 08:19:59 AM »

Tom is absolutely correct on this one. You never want to use starting fluid in a glow plug equipped Diesel. Up here in Alaska I run a synthetic oil and make sure my glow plugs are "all" in good shape, along with the battery. I've started my Diesel pickups at -35f with no problems. I don't try that very often, "only" when I can't plug in.  On some of my older Diesel pickups I have cycled the glow plugs two or three times to heat things up.

Good luck

PS
You would be really suprised how much just one bad glow plug in an 8 cylinder engine changes the cold starting ability.
« Last Edit: November 24, 2011, 08:33:11 AM by Seayfam » Logged

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« Reply #5 on: November 24, 2011, 10:11:03 AM »

  I started an older VW diesel with starting fluid once. It too was a pre-chamber engine. Now in my defense, I bought the car with what I thought was a bad motor, and it wasn't starting any other way, I just wanted to see if it would run. The results taught me to never try it again on anything that you considered to be a good engine.

  2 stroke and other direct injection diesels are around 14-16:1 compression, whereas a VW and other pre-chamber or "indirect" injection diesels are 22:1 and higher.

  Diesels are compression ignition engines, the increase in air pressure during the compression cycle raises air temperature as high as 1000 degrees. But there is never any fuel mixed with the incoming air as in a gasoline engine, the diesel fuel is injected when the piston in near top dead center, and injected into that 1000*F atmosphere it ignites instantly.

  Any fuel mixture in the aspirated air that is compressed, will detonate if the temperature reaches the autoignition temperature. In a direct injected diesel, Ether will "go off" later, nearer to TDC, that it will in an engine with 22:1 compression. That early detonation of fuel is trying to stop the engine and make it go backwards, while the starter, or any injected charge going off past TDC in another cylinder, are attemping to make it rotate forward. It cant rotate in opposite directions withont breaking something, and the detonations have been known to crack pistons, bend rods, and snap crankshafts. For all these reasons, never spray Ether into a pre-chamber, indirect injection diesel.

  I would further add, that 0 degrees F is what I consider to be the absolute limit to be attempting to start a cold soaked diesel without applying heat. If you dont have access to electrical power, how about a couple T-105's tied to an inverter? 1 hour plugged into a 1500 watt heater has always seemed more than enough to light off small automotive sized diesels down to -20*F. You should also consider adding kerosene or gasoline to your fuel if your going to be in extreme cold, read your owners manual. Most diesels allowed some percentage of gas and kero in those conditions.

  Dont forget you can always slip a little pan of charcoal briquettes underneath and keep an eye on it. Shield it off from wind good. Another option is to start it every so often and let it warm back up. 

 
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zubzub
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« Reply #6 on: November 24, 2011, 12:37:10 PM »

hey thanks for all the input.
I'm not using ether to start it.  FWIW when I got it it needed to have some brake cleaner sprayed into the air intake on a warm day to start it.  I reset the timing properly and it started running great.  It was only very recently that I needed to even use the cold start lever (it advances the  FP timing for easier starting).
Our friends over the pond use brake cleaner or similar to start reluctant T4 engines, it is a little frowned upon but mostly as it can melt glow plugs....not tales of out of time explosions etc....
note they use Brake cleaner not ether, they say to never use ether.....I haven't looked at the info on the brake cleaner can so I am not sure what the difference is.  This is my main ride and it is parked on a residential street....If I can't get parking near my house I won't have AC.  The idea of a inverter and a warming heater is interesting.  The bottom of the engine is covered by a huge engine pan that keeps noise down and allows the engine to keep temp at highway speeds in cold weather.  Otherwise i would probably be thinking of coal brickets as it is an old favorite of mine.
The OP was me spit balling the idea that cranking an engine with no fuel might give me more heat before starting than with fuel being injected....
The way the weather has been going probably won't have many -32 C/F mornings this winter anyhow.





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kevink1955
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« Reply #7 on: November 24, 2011, 01:53:33 PM »

Back in my Rabbit Diesel days I would preheat 3 times before cranking on a 0 degree overnight and it never failed to start. I did replace the battery cables with some heavy welding cables with crimped on ends, they almost doubled my cold cranking speed so that helped also.
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HB of CJ
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« Reply #8 on: November 24, 2011, 01:56:58 PM »

FWIW., Our collection of old (1980-1984) VW Rabbit Diesels had glow plugs that, if left up to the engines decision, (thermostat or timer?) DID NOT come up to maximum heat.  The way around this was to just use a 30" piece of #12 wire and short directly across from the positive post of the starting battery to the glow plug solenoid.

Yeah, the cable got kinda hot, but you could hold it.  After several winters with three Rabbits, we got very good at estimating the seconds of time held to bring the plugs up to a temp the engine liked for very quick (instant) starting; even down to like minus 5 degrees F.   The DANGER was that if held too long, we could (and did) burn out a glow plug.

Trial and error and lots of experience.  Other than having to open the hood (after brushing off snow) and fiddle with a piece of wire, it was no big deal.  Later we just placed the glow plugs on a separate circuit with a momentary held on toggle switch on the dash soos we just held the switch closed for a number of educated seconds.  NO ETHER!  HB of CJ (old coot)

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« Reply #9 on: November 24, 2011, 07:22:08 PM »

  If its the kind of deal where you absolutely need it to start, and you cannot plug in to AC power, you could use a portable generator. At -30*F I would also have a charger on the battery. A small 2000 watt portable generator running an hour or so ahead of start time should be sufficient.   
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zubzub
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« Reply #10 on: November 25, 2011, 05:21:20 AM »

  If its the kind of deal where you absolutely need it to start, and you cannot plug in to AC power, you could use a portable generator. At -30*F I would also have a charger on the battery. A small 2000 watt portable generator running an hour or so ahead of start time should be sufficient.   

I love this one, and so would my neighbors, especially as I only have a 4000 watt generator.  First I wrestle my gen on then I leave it running for an hour on the street.  Still if I am really stuck it is a great idea.  I like the idea of bypassing the GP relay for a hotter boost, I'll wire that up.  I also have some good 31s around so maybe a little house bank wired in for engine heat.  Are there 12V timers/12V engine warmers? I'll have to look.
 No one thought no fuel cranking was going to be hotter but in classic bus nut fashion I will try it anyway as it makes some sense to me, and no one screamed  "you are crazy!"...yet.
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robertglines1
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« Reply #11 on: November 25, 2011, 05:47:35 AM »

Have used shop rag with gasoline splashed on it. let air intake suck in----much less damaging to diesel engine than either. Not recommended for Gasoline engines!!! To much danger of backfire!!!  Old school.  Use with the due caution it requires. Does not take much gasoline fumes to start diesel. Don't let rag get sucked it Shocked.     Usual disclaimer.   when all else fails or you run out of plan a and b starting aids/or just don't like starting fluid.    Bob
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« Reply #12 on: November 25, 2011, 05:57:27 AM »

Are you able to find any reasonably priced Webasto heaters?  Not the large DBW2010 or 2020's like what the big bus would use, but the smaller ones such as were factory options on the VW. Runs off diesel and battery, no generator required.
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« Reply #13 on: November 27, 2011, 09:22:06 PM »

Fiddle faddle...

Upgrade the battery and cables and call it a day.

Everything depends on the speed of the spin, and that the glow plugs are functioning.

On a used vehicle, in cold weather regions, particularly one that is 15 model years old, the new battery and new cables may be considered another cost of purchase.

Just change 'em, find the biggest battery that will fit in the space, and go to a bigger cable size when you replace those, both connections points of both cables cleaned up and doped with your favorite anti-seize or dielectric or whatever, and all will be well. And,of course, confirm the alternator is making a good charge to maintain all this fresh capital.

Move lots of electrons, fast and easy, and there will be no more talk of using your glow plugs to set fire to the sprays introduced.

Perhaps glow plug failure is the reason others haven't had a fire come back out the intake by the use of sprays?

happy coaching!
buswarrior

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« Reply #14 on: November 27, 2011, 09:44:30 PM »


 No one thought no fuel cranking was going to be hotter but in classic bus nut fashion I will try it anyway as it makes some sense to me, and no one screamed  "you are crazy!"...yet.

  My only thought, or concern, is some pumps that are in fuel shutoff, seem to lose a bit of prime when spun over that way too much. IOW, when fuel is turned back on it may have to crank longer to start injecting fuel. And the longer you have to crank at sub zero temps, the less likely your to start. And lets face facts, once the batteries go down, the whole day starts going down.

  The idea of bigger batteries and cables is a good one, as spinning faster does create much more heat. IMHO you have one shot when you hit the starter on a diesel in really cold weather. If it wont light off the first time, the second time isn't likely to offer better results. Mercedes always said if it was firing to keep cranking. My results found if it wasnt running in 15 seconds you need to stop and go back in the house and wait a while.

  My thought with the generator was you could have it in the vehicle, like way in the back. I have seen little 2000 watt Honda's that are so quiet you can barely hear them 20 feet away. They are small and light. If you absolutely have no access to AC power and it don't light off at Oh dark thirty, what else you going to do? And up north in the dark time of year, batteries slowly die by not getting enough charge while running around running lights and heaters. A little juice wouldn't hurt it any. If the block heater warms it up and your battery has a good charge, the only thing you would need to worry about is gelling fuel.
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zubzub
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« Reply #15 on: November 28, 2011, 02:53:35 AM »

well Im still worrried but we will see.  The van already has a 31 in it and I have a twin 31 as a spare.  Appears there might be room for 2 31s in the engine bay....the lower  engine shield really is a pain, as I would gladly put some coals under the engine while I waited for the coffee to brew.   Really depends n how cold it gets.   The last few winters have not had many -30 days.
This little van is also the morning school bus for my kids, otherwise I probably would not care so much.  In the past, if an engine would not start I would cancel the work day(mental health day) stay home and count my blessings.
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