Why do I have two batteries? I have not had two batteries before.

I have also not has a diesel before.

Is it a glowplug thing?

Tim

 

Hi Tim,

High Compression. Gassers run about 8-10 to 1 compression ratio, and use a spark plug. A diesel runs by compressing the air/fuel mixture to the point where heat is high enough to ignite it. If memory serves me, the compression ratio on a 6.9 is about
22 to 1. It takes a lot of juice and starter to turn that over. The sole purpose of the glow plug system is to help boost the internal cylinder heat on cold starts.

That is essentially it. I may be off on a detail or 2 , but someone else may jump in.
Keep surfing around this forum, I've learned a lot here.

Good luck.
The purpose

 

Yes it's for the glow plugs. They draw a lot of power when it is cold. Also the faster the motor spins the easyer it starts. There is a lot of mass in the rotating parts in a diesel motor.

 

The glow plug system draws about 200 amps.
The starter draws about 300 amps.

Since battery power decreases as temps get lower, you want lots of reserve power to get the engine started.

Look at the battery cable on a car.
Now look at the cable from the passenger side positive post going down to the starter on a diesel.

In Arkansas you can probably get by with 850 CCA batteries.
Up here in WV, I am running 1000 CCA batteries.

 

Thanks for the info. Now I know. This is my first diesel.

Tim

 

Ya, this winter I only had one battery, and had very little crank time before I got a jump start. The battery was effected quit a bit in the very cold weather. I bought 2 new batteries and Bamm that thing starts off much better. Right now Im back to one cause I put the other battery in a minivan someone gave me so Untill winter I guess Im ok.

Also, 2 batteries alows you to crank faster and longer with a lower voltage drop than just one therfore your starter will physicly last longer. Low voltage will kill a starter. Low voltage causes it to pull more amps which generates more heat. Well, Good luck.

 

On a related note: why does my IDI start so much harder than my Cummins? Don't take this as a Ford-bashing question but my Cummins fires with about 1/3 of a second of cranking. My Dad's '97 takes a little more than that but still starts pretty fast. I first thought it may be because the Cummins is direct injected but Powerstrokes don't start as easy/fast either.
Also my Cummins also has just one BIG battery and I've never had a hint of a problem but that may be because of the ease of starting.
It also employs a heating grid for starting in cold weather. I thought maybe it took less power but when you're driving down the road -cold- the headlights really dim when the heating grid cycles, much more than when the glow plugs cycle on my IDI. Maybe it's because of the higher reserve on the IDI BECAUSE of the dual batts. They both have new 130 amp alternators so that can't be making a difference.

 

Hey Dodge, besides the compression ratio being higher on an IDI. There are 8 cylinders compared to 6.

There is quite a bit of difference between say 17 to 18 to 1 then 21 to 22 to 1 when it comes to cranking over the motor.

As far as the power strokes. They don't start very well anyway compared to other engines with the exact same fuel system.

 

The rods and crank are still a lot heavier though, the 6 rods in the Cummins weigh more than all 8 in the IDI and Powerstroke. Actually I'm ASSUMING that because they have quite a bit more bearing surface on the crank than all eight rods in the Navistars.

If your talking about the higher compression ratio and there being 8 cyls. instead of 6 that could be a factor but the Cummins doesn't feel like it spins faster it just starts/fires A LOT faster.

 

Not sure...but mine (6.9) starts in two seconds after I start cranking.

Tim

 

Yeh, the rods in a b series cummins a allot bigger then these IDI's. I don't think the weight of the pieces really matters much when cranking the motor near what the compression ratio would and there two more cylinders that have to run through the compression cycle during a 720 deg. engine cycle.

The Cummins motor does start very well.

As far as the power stroke. That could be, partly, explained with electronics. I don't know how many engine revolutions have to be reported to the ECM before it will allow an injection of fuel. That can vary from one manufacturer to another.

Both of my motors start very well. If they are warm they will start with just bumping the ignition.

 

I wish mine would start with a "bump" of the ignition like my Cummins. Since yours do I now know it's possible, something to shoot for.
Mine starts well if warm and no air is in the system. It doesn't start hard cold either it just doesn't start as fast and easy as my Cummins and I thought maybe there was a reason for it.
If I ever get the air intrusion problem fixed for sure I'll try to get mine to start that easy.

 

When I first got mine, it was a chore to start. But after going over all the common stuff found wrong on em' It started within a full revolution. Even last winter when it was overnight 20's it starts with just a bump.

 

My 6.9 fires within the first full revolution without touching the pedal even in winter. Also tried with a single battery last summer and it did work, just not as well. Probably wouldn't start in the winter on one battery. I run two 1000 CCA batteries and when its hot out it they crank engine like crazy. Actually, it will cold start without the glow plugs on a hot summer day, but it takes a good 5 seconds of cranking then it fires all at once with a huge black/grey puff. The cummins method of preheating the intake would probably work for the 6.9 as well because I used a heat gun to start mine even in winter close to 32F outside. Takes longer, but it was consistent and fired within 3 seconds of cranking each time.

I suspect that newer diesels are designed to allow the engines to turn over several times before allowing ignition as a measure to reduce startup smoke. The hydraulic injectors in the powerstroke also need more time to build the kind of pressure needed to fire the injectors. I don't know how other diesels with similar injectors perform. You might think I'm crazy, but I'm actually thinking wiring the FSS through an oil pressure switch in my truck to have the same effect. As it stands right now, startup is about the only time I ever see any real amount of smoke. Can really suck if some one is standing close by when I start it (not everyone deserves to get fogged).

 

David, They have to turn over a few times so the ECM knows where #1 cylinder is and it can begin to signal fuel injection in the correct timing sequence.