Physics of cold starts - Page 5 - PeachParts Mercedes-Benz Forum

kerry · #61 12-16-2008, 09:39 AM

Quote:

Originally Posted by JimSmith

That would be a bit of magic if someone did it. The injection system is tied to the crank via the chain that also drives the valves. No easy way to keep everything timed and yet be able to turn the pump on and off while the engine is spinning. But, if you could do it, in some cases, it might help. A nice fine mist from the injectors is probably easier to achieve by having them cleaned or assembled with new nozzles and pintels. Jim

I made that suggestion about a year ago after unintentionally getting myself in a situation of 35 below zero and no block heater. I have not experimented with it yet but I think it would be worth a shot if you're in a desperate situation. Hook the Mity Vac up to the shut off valve, pull a vacuum cutting off fuel, have someone else glow it and then engage the starter for a number of seconds and then release the vacuum on Mity Vac. It couldn't make the conditions worse and those first few revolutions of compression with no fuel but glowing plugs might be enough to get you going.

777funk · #62 12-16-2008, 10:06 AM

I don't know if anyone has mentioned this yet... I read most of this but I didn't see it.

Injection timing is typically retarded a bit (chain stretch) in our old MBs. I adjusted mine just a hair more advanced (to make up for the chain stretch) this past summer and both cars thanked me for it. I noticed the white smoke while idling is gone and of course quicker starts both hot and cold.

Of course a new timing chain would also do the same thing... But I didn't want to do the timing chain job.

PanzerSD · #63 12-16-2008, 12:43 PM

Quote:

Originally Posted by kerry

I made that suggestion about a year ago after unintentionally getting myself in a situation of 35 below zero and no block heater. I have not experimented with it yet but I think it would be worth a shot if you're in a desperate situation. Hook the Mity Vac up to the shut off valve, pull a vacuum cutting off fuel, have someone else glow it and then engage the starter for a number of seconds and then release the vacuum on Mity Vac. It couldn't make the conditions worse and those first few revolutions of compression with no fuel but glowing plugs might be enough to get you going.

It'd be easier and more possibly practical if you were to put a solenoid valve inline of the shutoff diaphragm, so that you can push a button while cranking, then release to pump fuel.

milner351 · #64 12-16-2008, 01:08 PM

I will have most of my fuel system taken apart in the coming weeks, the injectors have been out a while, and Bryan recently told me the nozzles are in need of replacement - so hopefully that will fix the old girls issues.... making a long story longer...

I was thinking about the mightyvac as a fuel system "primer" as well.

I will be replacing the DV seals, the injectors, rebuilding the fuel pump, and replacing all the clear "plastic" fuel lines between the lift pump, filter head, and injection pump...

so

there will be huge volumes of air in the system needing to be purged out.

Where could I best hook in the mightyvac to pull fuel into the system and bleed the air out???

bgkast · #65 12-16-2008, 04:59 PM

I just discovered the down side of a mostly diesel fleet, most of my cars would not start this morning.

I think the SD would have started if I would have glowed it a bit longer, but like the OP said, your first try is the best try and I blew it. The strange thing is it started the past few days just fine, and it did not seem any colder today. My F250 Also was close, but would not fire off. My 240D was in the garage for winter hibernation, but it started up fine so I drove it today. Luckily it was clear and dry out.

Rmcfarland · #66 12-16-2008, 06:30 PM

Vacuum on the fuel shutoff was exactly what I was thinking. I have seen it suggested now several times, but has anyone been in that desperate situation, mityvac in hand, and given it a go-round?

PanzerSD · #67 12-16-2008, 06:49 PM

Quote:

Originally Posted by bgkast

I just discovered the down side of a mostly diesel fleet, most of my cars would not start this morning.

I think the SD would have started if I would have glowed it a bit longer, but like the OP said, your first try is the best try and I blew it. The strange thing is it started the past few days just fine, and it did not seem any colder today. My F250 Also was close, but would not fire off. My 240D was in the garage for winter hibernation, but it started up fine so I drove it today. Luckily it was clear and dry out.

your F-250 wouldn't start?? didja plug it in?

It's been -30 and colder for the last few days here..at my shop was a 2008 F250 and it got dropped off on friday, and didn't get move till today, and it fired right up without being plugged in.

bgkast · #68 12-16-2008, 07:01 PM

None of them were plugged in. My F250 has the old International 6.9 IDI engine, it's an '86.

Skid Row Joe · #69 12-17-2008, 12:48 AM

Quote:

Originally Posted by bgkast

I just discovered the down side of a mostly diesel fleet, most of my cars would not start this morning.

I think the SD would have started if I would have glowed it a bit longer, but like the OP said, your first try is the best try and I blew it. The strange thing is it started the past few days just fine, and it did not seem any colder today. My F250 Also was close, but would not fire off. My 240D was in the garage for winter hibernation, but it started up fine so I drove it today. Luckily it was clear and dry out.

bgkft, My newly purchased '83 300SD with 90K on it at the time, started @ 5' degrees one morning in Wichita, KS., after overnighting at a motel. This was before I put a block heater in it. I glow-cycled it 3 times, then after the third glow, holding the foot feed on the floor (as per owner's manual) it started with some reluctance the first try. The older diesels, you hold the pedal on-the-floor, while cranking it. That old girl was cooold that morning.

bgkast · #70 12-17-2008, 02:40 AM

I had a bad glow plug in the SD, I replaced it but had to plug the car in and charge the battery to get it started. I'll try it again in the morning after being unplugged all night. It is forcasted to get down to 16 tonight

milner351 · #71 12-17-2008, 08:11 AM

I generally plug in my powerstroke ford overnight - but it's on a timer to come on about 1.5 hours before I would normally start it to go to work. Without being plugged in at work, it's started every day without issue - down into the teens at least.

Obviously it depends on ambient temperature - but, in general - how long does it take our MB block heaters (500w?) to warm up the engine to make a significant difference in starting?

zu! · #72 12-17-2008, 10:31 AM

Quote:

Originally Posted by Skid Row Joe

The older diesels, you hold the pedal on-the-floor, while cranking it. That old girl was cooold that morning.

Whoa there! I was told that we should not even touch the gas (diesel) pedal whilst cranking as the flood of diesel will make it harder to start?

I've been experiencing harder starts that usual especially after leaving the Merc out in the parking lot the whole day at work. She stills fires up on the first glow (geez, don't want to experience the multiple glow situation anyway) but it takes a little more time...and when it starts, its kinda like a really slowww start, like maybe running on just one cylinder or something, then slowly, it picks up speed. All this while, I'm just lightly feathering the pedal (after its started though). Might be a sign of my battery weakening...but I think its jsut cold.

I'll try giving it a shot of diesel before I start today and see how it goes...unless anyone has advice to the contrary?

pizzachef · #73 12-19-2008, 10:38 PM

Quote:

Originally Posted by milner351

Where could I best hook in the mightyvac to pull fuel into the system and bleed the air out???

The return line coming off the banjo bolt on the spin-on filter. That'll at least fill the two filters and the lift pump. From there you can use the primer to purge the injector lines or crank away.

Oops, I just saw you have a '95 (is that the car you're working on?) my info is for a 123.

pawoSD · #74 12-20-2008, 01:12 AM

The problem of the cold fuel soaking the cylinder can be easily overcome, with a battery booster/starter unit.

The problem is that a cold weak battery can't crank it fast enough to make enough heat. With a 100amp boost from a charger/starter I've glowed/ cranked mine up in -13F in like 3 seconds...after a failed/fuel soaked start attempt where the battery gave out too quickly.

If these cars were equipped with ultra powerful batteries that gave full output at super cold temps starting would never ever be an issue unless the fuel gelled.

raslaje · #75 12-20-2008, 01:46 AM

Quote:

Originally Posted by Rmcfarland

I see many references to the cold fuel hitting the glowplugs and cooling them off quickly. I remember someone in a thread suggested keeping the fuel off for the first ~5 seconds of cranking, then shoot it in when engine is turning. Has this actually been attempted, and if so, helped anyone?

I'm out of my element here so those more knowledgeable will have to comment on this: A quick look at the schematic in Haynes (and it appears to be an U.K. schematic at that) shows that shorting the two outer contacts on the terminal block next to the battery will energize the starter solenoid cranking the engine and also supply power to the glow plug relay. If the key is in the 'off' position wouldn't that prevent fuel from flowing? Then have someone turn the key to the 'run' position and you remove the short?