Author Topic: why won't she start!  (Read 2440 times)

1980450sel

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why won't she start!
« on: 09 June 2011, 09:07 AM »
Hi All,
 
A few weeks ago I drove my car (1980 450 SEL 4.5L) to work. I filled up that morning. I went out 2 hours later to move it and it wouldn't start. Eventually it did and ran really rough for a few minutes. Then it settled out and I drove it to an auto supply shop to get some fuel additive as I thought I might have gotten a bad tank of gas. No such luck as the car needed to be towed from there. I thought maybe it wasn't getting enough fuel pressure to the distributor so I checked the tank and fuel strainer, all good. I put in a new fuel pump and still no starting. Just to see if it would start I sprayed ether into the intake and it started and ran for a few seconds and that's it. There is lot's of pressure up to the distributor. If anyone has any ideas I would greatly appreciate it.

Scott
« Last Edit: 10 June 2011, 11:20 AM by 1980450sel »
1980 450 SEL

1980450sel

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Re: why won't she start!
« Reply #1 on: 10 June 2011, 07:55 AM »
I would like to ask something else. If you remove one of the lines that goes from the fuel distributor to the injector, should fuel spray out of the distributor where the line was? I did this and no fuel came out.
1980 450 SEL

koan

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Re: why won't she start!
« Reply #2 on: 10 June 2011, 03:27 PM »
I would like to ask something else. If you remove one of the lines that goes from the fuel distributor to the injector, should fuel spray out of the distributor where the line was? I did this and no fuel came out.

Only if the fuel pump is running and the air flow sensor plate is depressed.

With the key in run depressing the air flow sensor plate should run the fuel pump and you should be able to hear it at the right rear wheel area.

koan
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1980450sel

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Re: why won't she start!
« Reply #3 on: 14 June 2011, 08:09 AM »
Hi koan and thanks for your response. The fuel pump is working is brand new. I guess what I am wondering is, could the fuel distributor not be distributing. It's mechanical so could something in there have broken so that it's not pushing gas to the 8 injector lines?

Scott
1980 450 SEL

koan

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Re: why won't she start!
« Reply #4 on: 14 June 2011, 02:10 PM »
I guess what I am wondering is, could the fuel distributor not be distributing. It's mechanical so could something in there have broken so that it's not pushing gas to the 8 injector lines?

No, there's only one moving part really, that's the metering piston and if the sensor plate is pushed down the piston will move and fuel should come out of the lines.

If it doesn't it could be either no fuel being delivered to the fuel distributor or a seriously blocked/gummed up fuel distributor including the primary regulator (screwed in rear of fuel dist).

The fuel distributor is not a pump but metering device.

koan
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s class

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Re: why won't she start!
« Reply #5 on: 14 June 2011, 02:17 PM »
What's the hp fuel filter next to the pump like?

'76 6.9 Euro, '78 6.9 AMG, '80 280SE, '74 350SE, '82 500SEL euro full hydro, '83 500SEL euro full hydro , '81 500SL

1980450sel

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Re: why won't she start!
« Reply #6 on: 14 June 2011, 10:02 PM »
Thanks guys for the info. The filter is brand new as well. I was under the assumption that there was spinning inside the fuel distributor much like the rotor spins in the spark plug distributor so that fuel only goes to the injector/piston needing fuel at that moment. Typing this out may only highlight my ignorance.

Scott
1980 450 SEL

calvin streeting

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Re: why won't she start!
« Reply #7 on: 14 June 2011, 11:53 PM »
no.. it is basiclay a 8 or 6 way valve. And as the plunger (controled by air flap) gose up and down it varrys the ammount of fuel. (Continous injection system). This movement is then restricted by the control preasure as the car (wur) warms up..

Calvin

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Re: why won't she start!
« Reply #8 on: 15 June 2011, 01:35 AM »
If you want to know more about how K-Jetronic works, look here and here.

This book is also worth buying if you want to go further (also covers D-Jetronic and other variants)

koan

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Re: why won't she start!
« Reply #9 on: 15 June 2011, 05:20 PM »
I was under the assumption that there was spinning inside the fuel distributor much like the rotor spins in the spark plug distributor so that fuel only goes to the injector/piston needing fuel at that moment. Typing this out may only highlight my ignorance.

What you are describing is a system I've seen on a couple of old cars, I think Peugeot used it and a couple of english makers as well. There is a rotating "swash" plate that actuates pistons that deliver fuel, the plate tilts on a shaft to vary the amount of fuel. Might have been SU or Lucas made.

koan
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bostonmish

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Re: why won't she start!
« Reply #10 on: 28 June 2011, 09:37 PM »
Below assumes you have confirmed that your FP relay is operational.

CIS systems are very sensitive to any restriction in fuel delivery. If this were my car, I'd drain the fuel tank and remove the strainer at the fuel tank to FP outlet, then clean (OK) or replace it (better). Next, I would remove the fuel delivery hose into the Fuel Distributor and remove the inlet fitting. That fitting has a mini-strainer inside as well. Again, clean or replace. Test motor operation after each improvement.

From this point I would do a fuel delivery test, per the manual. BTW, before anything else, you start at the FP and first check whether you have a minimum of 12V at the FP. Then check delivery volume. Next is the fun part. Check your system and control pressures. At some point you will detect a deviation from the spec. which will indicate where the problem might be.

Assuming you have proper fuel delivery, make sure to check your Cold Start Valve and control (thermo-time switch). Also, make sure your Air Slide Valve (Auxiliary Air Valve) is not stuck in the closed position. Your Enrichment Compensator (Warm Up Regulator) will need to be examined. Contrary to what some think, it's fairly easy to open and clean them. ...but you better be good.  WURs suffer from fuel varnish and contamination, but can be revived. I hope you don't need to, but it's even possible to bench rebuild a FD, but make sure you have been led there by testing, not guessing.

Another perspective: CIS systems are also extremely sensitive to unmetered air (vacuum leaks). Before embarking on deep testing, I'd recommend a very careful examination of all visible hoses and air passage lines. Skipping ahead, your CIS motor will run with vacuum leaks, but to really tune it well you'll need to eliminate them.

Of course,  before doing any of the above, make sure ALL of the basics are in order. ...like a properly charged battery, good ground, clean air filter, etc.

-
Michael Stoic
Boston, MA
450SEL ...long ago
450SLC now...