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  #1  
Old 07-03-2006, 11:40 PM
slarson80's Avatar
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Can a weak vacuum pump cause difficult starts when warm?

Hello everyone,
Today after I changed the Diff. fluid I took the car out to run errands. When I came out of a store , the car had been sitting for about 15 minutes. The car did not roar to life immediately like it usually does on a warm start. (yes I did glow it) I brushed that one off. But after my next stop, this time the car sat for about thirty minutes. It was again reluctant to start. After about 30 seconds of cranking and two pumps of the pedal it started.

Now usually when warm it takes about ten secs. of crank and no pumping. Today was a little warm out but not much warmer than the usual weather we have been having. The reason why I ask about vac. pump is that I'm pretty sure it is getting weak and a rebuild is about next on my hit list. I did not see any more air in the clear filter or any fuel leaks. The last time this happened I had just changed the fuel filters and had an obvious leak around the top of the spin on housing.

Any thoughts?

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86 190D N/A 2.5L Auto 265k "Ruby" -Sold-
79 300D 242k "Condi" my first -sold- RIP
2013 chevy sonic hatchback - had to for work
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  #2  
Old 07-03-2006, 11:47 PM
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Engine needs vac' to turn it off, not to start it.

Your hot start problems are something else.

Pumping the pedal has nothing to do with it either.

If a diesel is warm, has good to reasonable compression, with a properly operating i/p, it will start.

I would imagine that you have air getting in the system.
Old manual lift pumps will let in air....as will filter seal too.

Tank to line, flex hose do rot.

Clogged fuel tank filter will restrict flow and cause a partial vac' in the supply line.

Need to check all above.

.
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  #3  
Old 07-03-2006, 11:48 PM
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Location: central Texas
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Go to Alldata.com
plug in your cars specs..
read the tech bulletins titles...
there may be one which has the title ' hard start when warm'....
get the number then check here to see if someone has the info .. or call the dealer and ask them about the contents of that title tech bulletin.
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  #4  
Old 07-03-2006, 11:52 PM
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Quote:
Originally Posted by slarson80

Now usually when warm it takes about ten secs. of crank and no pumping.
This is not normal. The problem is clearly getting worse. The engine should start in 1/2 second when warm, without any glow plugs and without your right foot on the pedal.

Have the basics of valve lash, cam timing, and injection timing been checked recently?

A properly running 617 with good compression can start in 1 second when cold (12 degree ambient) after a proper glow cycle.

This one has some serious issues that need attention.
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  #5  
Old 07-03-2006, 11:54 PM
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Another problem that causes a similar situation is a clogged vent line on the fuel tank. Try popping the cap, when your fuel level is a little lower, and see if it changes.
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  #6  
Old 07-04-2006, 12:06 AM
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10 secs

Is an exaggeration I guess, I just meant it usually fires right up. This car is still pretty "new to me" and I have not checked the valve clearances or IP timing. I haven't really felt the need yet as it usually starts and runs fine.

I guess I will start with the fuel system, and go from there.

Thanx for the input!
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86 190D N/A 2.5L Auto 265k "Ruby" -Sold-
79 300D 242k "Condi" my first -sold- RIP
2013 chevy sonic hatchback - had to for work
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  #7  
Old 07-04-2006, 12:13 AM
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they are amazing engines

I had an 81 wagon... used it two years .... suspension worn out, ac had leaks... finally retired it ...over 280,000 miles... it sat 18 months...then person on forum from Houston bought it.... they brought a battery and we stuck it in... we did nothing else to it.... no new fuel , no nothing except battery... he took key and stuck it in....less than 2 seconds till it fired up... I knew it was a good engine.... but I was really surprised that even with the old fuel it started right up... he drove it back to Houston against my advice.. the front wheels were splayed out at the bottom way too much for me...
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  #8  
Old 07-04-2006, 12:19 AM
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When I was under the car

Perhaps I bumped the vent line and disloged some crud in there that is now partialy blocking the line...

At least I hope it is that simple! Oh well, A project for tomorrow.

Thanx again.
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Sonny


86 190D N/A 2.5L Auto 265k "Ruby" -Sold-
79 300D 242k "Condi" my first -sold- RIP
2013 chevy sonic hatchback - had to for work

Last edited by slarson80; 07-04-2006 at 03:12 AM.
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  #9  
Old 07-09-2006, 11:20 PM
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Problem solved

It turns out it was one of the rubber fuel lines under the hood.

What I did was go back and check the clear filter for air and sure enough, when I held a flash light to it I could see a lot of bubbles inside the element. I thought it must be the fitted line that comes out of the tank strainer because I had just had it up on stands replacing the diff. fluid. I was using a hex key and was swinging it around down there and thought maybe I bumped it or something.

I went to our local MB parts dealer and got a fitted hose, Cigar house, and a couple feet of fuel line. I did the fitted hose first, as it turns out I did not need it. The existing fitting was a nipple coming out of the strainer. That made that hose change nice and easy, just cut some line and viola. Since that was the prime suspect I started it after that and there was no difference. Still had to crank for a while (about ten seconds) and a jacuzzi in the clear filter.

So I figured if it was not that line then it must be a line or something under the hood. I checked the other two lines at the tank and they looked alright. I thought I would leave them for last.

This weekend I changed all the rubber lines under the hood. That went well except my primer pump didn't seem to work right. While pumping sometimes it felt like it was moving fuel, and sometimes it would just push in, with no resistance. When All the lines where changed, enough residual fuel was present to fill the clear filter about half full. At that point the primer pump seemed to be doing nothing but make the fuel in the filter rock gently back and forth. But that was it. I managed to start it by cranking about thirty seconds with the peddle held down. I immediately checked the filter and it was still about half full. I took for a drive (about 40 mi.) when I came back the filter was nice and full, with no bubbles. This morning it started right up.
I took it out to run errands and it started immediately every time.

The primer pump I have is the new version, I've read from two different sources that these pumps don't like SVO/WVO. Well apparently they don't like BioD. either. I've been running about B80 for about 1500 mi. and it seems to have killed my new style pump. It seems that this was not the component letting air in the line, But I know this pump used to work well. When I changed fuel filters last time, it only took about ten pumps to prime the system. Now pumping seems inconsequential. Guess I'll pick up an old style pump this week.

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Sonny


86 190D N/A 2.5L Auto 265k "Ruby" -Sold-
79 300D 242k "Condi" my first -sold- RIP
2013 chevy sonic hatchback - had to for work

Last edited by slarson80; 07-04-2007 at 12:37 AM.
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