Hard Starts Lately - PeachParts Mercedes-Benz Forum

imagesinthewind · #1 06-23-2008, 12:38 PM

78 300SD, my car.

Lately the car has been really hard to start. Cranks forever but starts eventually.
I was hooking the battery up to a charger (hard starts are bad for the starter and battery) and found the vacuum line to the top of the IP was off. I replaced it and it seemed to start quick and fine. Maybe it had been off for a while and I didn't know it. What does that line to the IP do?

Also while the car is cranking, the oil pressure gauge will go to 2 and tap it's way up to 3. As soon as the needle gets to 3 the car starts.
It only starts if you let it crank really long, I know very bad for the starter. But if you give the starter time to cool, then the needle on the oil pressure loses it momentum. It goes back to 2 and I have to start over again.
There is no difference in how fast the car cranks as the needle moves. It just suddenly starts. After it starts the car will start again easily for several hours. 4 hours of sitting though and the car will be hard starting again.
This morning the car had a full battery charge (on charger all night) and it was hard to start.
Any ideas as to why?

On a side note, the gresecar was doing the exact same thing. Not driven it though since the keys got misplaced.

Thanks guys. Sorry for my absence, life is overwhelming right now.

kerry · #2 06-23-2008, 01:23 PM

Your glowplugs are not working.

imagesinthewind · #3 06-23-2008, 01:30 PM

The light comes on and stays on for 8 seconds or so.
All 4 plugs were changed out in October.

kerry · #4 06-23-2008, 01:43 PM

How about the 5th one?
You need to check the resistance on each plug to see if they are working. Should be less than one ohm for each plug. You should also confirm that they are getting 12 volts with the ignition in the glow position. Given current temperatures in Colorado it would seem that none of them are working to cause that problem.

imagesinthewind · #5 06-23-2008, 01:56 PM

4 was a typo. All plugs were changed.
If plugs were bad would the light come on?
I don't have the tools to check the plugs. . .

kerry · #6 06-23-2008, 03:02 PM

A multi-meter at Harbor Freight is usually on sale for about $3, that's all you'll need.

Yes, plugs can be bad and the light work.

imagesinthewind · #7 06-23-2008, 03:12 PM

Should I just change them out?
I have 5 new ones. . .

kerry · #8 06-23-2008, 03:20 PM

I'd do some diagnosis before changing them. The problem might be elsewhere in the system.

Thecorrupterx · #9 06-23-2008, 03:50 PM

mine was having a hard time starting taking 10-15 sec, I have yet to change my glow plugs, but that is next on my list. the things i did to help with hard starts; check electrical supply, battery condition and cable connections that brought it down to 4-5 sec, and change both of your fuel filters that brought it down to 2-3 sec. just doing that solved my hard start problems. also I later added a 2 farad capacitor onto my stereo and that made it crank up even more readily 1-2 sec now. the only thing is i know my glow plugs are going out so i run them 4 times (they only stay on about 1-2 sec) and the times given are considering that. im sure it will crank with no problems after i change the glow plugs.

Eric Eliel · #10 06-23-2008, 05:35 PM

This bears repeating:

The light for the glow plugs is only a relative indicator for "attempting to start".

The glow plugs continue to glow for up to one minute in the glow position.

Try placing the key in the glow position, wait 30 seconds, then try starting the car. If that helps, your glow plug (or more than one) may be nearing their replacement stage.

If you can "glow" the plugs for one minute and it doesn't help start the car, you have issues.

As the glow plugs age, you'll need to glow them longer for the same start performance.

barry123400 · #11 06-23-2008, 06:09 PM

Since you do not have a meter handy at the moment. When the dash glow light is on the interior light should be dimmer. As the glow relay switches off the light should brighten. If it remains the same through these steps there is no current of any consequence getting to the plugs.
Next possibility if the light does visually dim is you have a couple of glow plugs burnt out. For this you need at least a test light to place between the positive battery terminal and each separate glow plug wire.

Your car is a 79 I believe you mentioned. It may have the older glow plugs with the squiggly wires between the plugs. This is a horse of a different color. All those plugs are wired up in series like christmas tree bulbs. A quick test although not conclusive is you should see those squiggly resistance wires glow a slight red color in the dark if the system is working. This of course while the glow light on the dash is lit and towards the end of a reasonable cycle. Still the interior light will still dim when and if the glow plugs are on.

Or wet the end of your finger and lightly touch the squiggly wire about the same as you would do with a hot household clothes iron. There has to be some elevated temperature there even if the glow light only stays on ten seconds. Thats if the plugs are getting reasonable current. Remember those wires will be very, very hot. Test with your finger at the start of a cycle so the temperature is bearable. Not required if the car does the dimming interior light test during the glow plug cycle though.

There should also be a fuse present. If the sqiggly series plugs are in the car follow the #5 cylinder glow plug wire back to it. If the squigly wires are not present there might be a fuse in the relay box if it is out on the drivers inner fender. It may also still be out on the fiewall if the relay click is coming from around your knee area as it turns off. You can locate it by the click as it goes off. I have tried to keep this as simple as possible with no meter.

If you establish you have a problem you will probably need a meter to locate it. Splurge and bypass the 3.00 one in favour of perhaps a ten dollar one at the same source. Many other uses with time including around you business and home.
I just went back and reread your post. You own cars that span the two systems of glow plugs. The dividing line is 80 or 81 I believe. Even if pre 1981 the car could have had a semi updated system of glow plugs installed. If so there will be one continious wire from each glow plug to the next.

Hatterasguy · #12 06-23-2008, 06:15 PM

Strange this time of year a 617 with no GP's should light right off, unless the compression was horrible. Heck it was horrible in my SD, without the oil cap it looked like a locomotive puffing up a hill.

Could be fuel. If I remember correctly this is a WVO car so all bets are off, could be anything.

kerry · #13 06-23-2008, 06:23 PM

Quote:

Originally Posted by barry123400

Splurge and bypass the 3.00 one in favour of perhaps a ten dollar one at the same source. Many other uses with time including around you business and home.

They are the $10 ones, it's just that they're almost always on sale for $3.XX, cheap enough to keep one in every glovebox.

barry123400 · #14 06-23-2008, 06:33 PM

Quote:

Originally Posted by Hatterasguy

Strange this time of year a 617 with no GP's should light right off, unless the compression was horrible. Heck it was horrible in my SD, without the oil cap it looked like a locomotive puffing up a hill.

Could be fuel. If I remember correctly this is a WVO car so all bets are off, could be anything.

Strange but some engines want a little glow plug activity even when hot. I have not found those engines to be particularily low on compresion either.

Otherwise you crank and crank to get it going. Then there are some engines that will not start with only one glow plug out or with great difficulty. Some with two plugs out just refuse to start period. No fixed standards exist.

Skippy · #15 06-23-2008, 11:26 PM

True. Different engine, but I've seen low-mile IDI 6.2 Detroits that wouldn't start without the plugs in Guam weather.