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  #1  
Old 01-17-2005, 12:57 PM
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bad plugs or bad meter?

Just 1 month ago I replaced 4 of 5 plugs and the battery in my 84 300sd. This morning it was a bit slow cranking and no start. Hooked to jumpers, still no start. Start ohm testing plugs and all the new plugs give wacky readings. Most read infinate resistance.
So, is there a scenerio where something can be wrong with the car that screws up the plugs? or is the meter bad. The meter is only 1month old also but it could be suspect cuz it is the Harbor Freight el cheapo. When it is set on 200 you will get .2 reading just from touching the leads together.

Eric Z

PS while installing stereo a few weeks ago I found a wiring harness under the passenger floor carpet that was unplugged. Plugged it back in and fuses pop so I left it unplugged. Could this be related? what does that harness do?
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  #2  
Old 01-17-2005, 01:07 PM
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This is quite interesting.

If we conclude that the meter is bad, then the question remains, "Why does it not start"?

Just for grins, setup the voltmeter to read the voltage at one of the plugs. Turn the key to the #2 position and read the voltmeter. See if you get 12V.
Report back.


Quote:
Originally Posted by angst
This morning it was a bit slow cranking and no start.
What was the temperature when you tried to start it?
Is there a reason why the cranking was slow on this day?
What is the condition of the battery and cables?
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  #3  
Old 01-17-2005, 01:19 PM
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Quote:
Originally Posted by angst
When it is set on 200 you will get .2 reading just from touching the leads together.

Eric Z
set on 200 ohms(if that's what you mean) you SHOULD get about .2 ohms by touching the leads. That's how I check my meter EVERY TIME I USE IT. Remember, you want to measure resistance, so you should expect to measure low resistance across the test leads. Did your meter come with instructions?
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  #4  
Old 01-17-2005, 01:28 PM
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angst,

0.2 ohns is about right touching the test leads together. That is the resistance of the leads and the contact resistance between the leads and the meter.

If any GP reads infinite resistance, that GP is almost always bad. Did you remove the GP cable connector from the GP relay when you measured the GP resistance?

P E H
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  #5  
Old 01-17-2005, 02:53 PM
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This day the only change was a worse than latley cold snap.

Quote:
Turn the key to the #2 position and read the voltmeter. See if you get 12V.
10.8 at the plug and 12.3 across the battery, with the jumper cables hooked up it would go up to about 11.2 at the plugs.

Brought the meter inside for an hour and tried it again and got consistant .4 ohm reading across all the plugs. I guess storing the multimeter inside will be the MO from now on.

I finally got it started after hooking beefy jumper cables and running it hooked up to the truck for a long time with a brick on the truck gas pedal. On many attempts it would spin pretty quick and even fire a couple time which seems should have started the chain reaction combustion going. There was smoke coming out the exaust many times suggesting a partial burn.

After I took it around the block I put the meter across the battery and read 13.8 and then it read 13.14 with the car off.
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  #6  
Old 01-17-2005, 03:13 PM
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OK, we have determined that the glow plugs are fine and the glow plug relay is fine.

So, the issue with slow cranking speed needs to be addressed with this engine. How old is the battery? If it is more than four years old, replace it with a decent battery. Auto Zone makes a battery with 850 CCA for $65.00. It's worth the peace of mind. If it is less than four years old, take it out and have it checked under load to determine its output. I appears that it is not providing the CCA that you need to get a diesel going in very cold weather.

What oil are you using? Engines that are "difficult" to start should be using synthetic oil in the winter months. I use Rotella synthetic, however, Mobil 1 is generally considered a better oil, but it costs more.

How long do you leave the key in the #2 position before cranking the engine? The glow plug light will go out in ten seconds or so. In very cold weather, you should be waiting 35 seconds before turning the key to "start".

What is the conditon of the battery cables? Make sure that the cable to the battery connections are clean and solid.

Keep in mind that a diesel that does not start in the first 10 seconds loads itself up with fuel, thereby making subsequent attempts to start it all that much more difficult. When you go to start it, do not give it more than 1/4 pedal. Excessive pedal will inject more fuel than the engine needs to start and all that fuel must be heated up to combustion temperture or it will not fire.
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  #7  
Old 01-17-2005, 04:59 PM
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Battery is a 1month 850cca monster.
Proir owner says oil is Synthetic and was changed 1000k ago.
Cables could be suspect. You may be on to something there.
Leaving key in plug position untill audible click off but only after failed attempts. See below
Quote:
Keep in mind that a diesel that does not start in the first 10 seconds loads itself up with fuel, thereby making subsequent attempts to start it all that much more difficult. When you go to start it, do not give it more than 1/4 pedal. Excessive pedal will inject more fuel than the engine needs to start and all that fuel must be heated up to combustion temperture or it will not fire.
Ahhh. I think you have hit into something. Figuring I am not going to "flood" it I have been pumping the pedal on reattempts and when finally did start there was smoke billowing all over the neighborhood for a good 4 or 5 minutes. Also on my first attempts I was only waiting about 5 to 10 sec after the plug light goes out and then re plugging.
From what you have told me, I think tomorrow mornings M.O. will be. 1 plug for 40 sec untill I hear the click then another plug cycle and no excessive pedal pumping.
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  #8  
Old 01-17-2005, 05:10 PM
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Quote:
Originally Posted by Brian Carlton
OK, we have determined that the glow plugs are fine and the glow plug relay is fine.
right, but make sure that the 80 amp fuse is good. Boy, the first year I had my car I had that stupid fuse crack, but I didn't know it. My starting got worse and worse until it left me stranded (it was summer). That's when I found the cracked fuse. It's under the cover on top of the glow plug relay. Just make sure it isn't that.
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  #9  
Old 01-17-2005, 08:49 PM
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Quote:
Originally Posted by angst
......... Figuring I am not going to "flood" it .......... plug for 40 sec untill I hear the click then another plug cycle and no excessive pedal pumping.
It sounds as if you may have a little "gas" thinking here. On a diesel, in cold weather, you should never "pump" the pedal. Usually it is best to stay off of the throttle until you have combustion. In fact, hold the key to start for about a 2 second count after you feel it "light". If it is really cold you will then get a little "roughness" in the idle. At this point, give it about 1/4 throttle to "even" it out a little.

If you pump cold fuel into a cold engine, the cylinder will take "mucho" cranking to warm to the point of combustion. Since it takes heat for combustion in the diesel, it uses a little different technique.
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  #10  
Old 01-18-2005, 01:34 AM
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According to the owner’s manual, if temps are below 32 F.
It say’s to put the accelerator pedal to the floor until car fires, then
Let off as RPM’s climb. This is for a 87 300SDL.
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  #11  
Old 01-18-2005, 09:45 AM
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Quote:
Originally Posted by guage
According to the owner’s manual, if temps are below 32 F.
It say’s to put the accelerator pedal to the floor until car fires, then
Let off as RPM’s climb. This is for a 87 300SDL.
While I don't like to disagree with the manual, I think that the procedure in the manual is perfectly valid for a brand new engine with very good compression. The theory is that you can give the engine too much fuel and the heat of compression will fire it all off without any problem.

If you think about it for a moment, the engine has no use for any additional fuel above the amount of fuel required to idle at the ambient temperature. If you give it too much fuel and the fuel lights off, then there is no issue other than quite a bit of smoke.

However, if the engine has 200K on the clock, its compression is no longer at the same level as a new engine, so starting it in colder temperatures is more difficult. If you now dump in much more fuel than you need, you must heat up all this fuel to combustion temperature in order for the engine to start.
This may happen, but, if the engine is marginal, it may not.

On engines that are down on compression and have "difficulties" in cold temperatures, you don't want to inject any more cold, liquid fuel than is absolutely necessary to run at idle.
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  #12  
Old 01-18-2005, 10:51 AM
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This morning it still took jumping off to start it. I didn't do any pressing of the pedal. It would spin fast but just not fast enough. Temp on the dash gague read -4c. (again I have a 1 month old 850cca battery)
Here is what my owners manual says. "Temp below 0c, press accelerator to floor, turn key clockwise to the stop, release key only when engine is firing regularly and back off accellerator slowly. Do not interrupt the starting process. If the engine is very cold it is possible that it will not start on subsequent attempts. In temps below -18c depress accelerator three times prior to starting"

Perhaps the 'no interrupting the start process' is a key element in the mix. The result of stopping would be the loading up that Brian mentioned.
I am going to take the battery to Autozone for testing for a second opinion on its quality.
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  #13  
Old 01-18-2005, 11:13 AM
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Here is something that bit me with a "slow" starter. Before you start replacing things. Check your grounds, battery-chassis-engine. Physically, make sure they are both clean and tight. Loose or dirty connections, even if they "appear" clean, will definitely give you a slow starter.

On mine the engine grounding strap was tight but the bracket it was mounted to was loose. (325K mi. and vibration, go figure ) This caused a lot of frustration (2 starters later )until I "found" it with the help of someone on this forum.
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  #14  
Old 01-18-2005, 11:48 AM
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Quote:
Originally Posted by angst
This morning it still took jumping off to start it. I didn't do any pressing of the pedal. It would spin fast but just not fast enough. Temp on the dash gague read -4c. (again I have a 1 month old 850cca battery)
Something is definitely wrong. -4°C. is not very cold. The battery is brand new. As SD Blue has mentioned above, you need to go on a mission to check all cabling from the battery to the starter and back from the engine to ground. That starter should spin the engine quite fast and it should start immediately at this temperature (presuming decent compression).

When you say that it "took jumpin off" to start it, please provide more details. How long did you crank it on the initial attempt? On the second attempt, how long did you glow it before the crank? How long did you crank it on the second attempt? How many attempts did you make until the battery weakened? What was the total number of seconds for cranking?

All of this info is valuable and relevant.
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  #15  
Old 01-18-2005, 01:34 PM
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Bad battery post connnection?

You could have a poor connection at the batterry post/ cable clamp. You could have a strong battery acting like it is weak. If this were the case, using jumper cables would by-pass the poor connection and provide for a normal start.

Check connection quality at the batterry post/ cable clamp with a voltmeter while cranking the engine. You should have a very low value. A high value will indicate a poor connection. Just place one voltmeter probe on the post, the other on the clamp and have someone crank the engine while you observe the value.
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