Author Topic: 6.9 Normal Operation to a No Start Condition  (Read 669 times)

diametricalbenz

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6.9 Normal Operation to a No Start Condition
« on: 08 May 2020, 08:29 PM »
Hello all. I try to run the 6.9 at least once a month to keep the suspension pumped up and everything else from seizing up. For the last 6 months it’s been in the garage hovering around 45-50F garage. Several weeks ago I decided to fill up the 6.9 since gas as $1.49. Cold startup was normal maybe 2-3 seconds of cranking before a 5 minute warmup before taking off as I normally do. On my 0.5 mile trip the gas station while running at 35mph the car starts to lose power and feels like its misfiring but still running, when I try to depress the accelerator the car stutters and chugs even more losing power but no backfiring. I apply very light throttle to maintain speed as cars are approaching and engine was still somewhat limping with the engine surging at very low rpm 1000-1200rpm (as I recall) at 20mph as I roll into the gas station. Once filled up (5 minutes or so) it starts up fine surprisingly and runs for maybe 2 minutes when at a speed of about 25mph (residential zone) again the engine suddenly the engine start stuttering and losing power and running rough. I stab the accelerator and the engine cuts out. The engine does immediately restart but will only go just above idle maybe 1100-1200rpm. If I try to accelerate the engine cuts out. I ended up limping the car back home with my feet off the pedals for fear of stalling it. Once the car was finally home it simply would not start again.

In my attempts to start (5 seconds of cranking at a time) on the 2nd or 3rd attempt the engine turns over but just for 1 second or less and then nothing after that.
In the past two weeks I have:
- Replaced all 8 injectors (all new Bosch brass body)
- Resistor 0.4ohm
- Resistor 0.6ohm
- Bosch Coil
- Distributor Cap
- Distributor Rotor

I have double checked the spark plug wire order. I have checked one of the spark plugs and the tips are not wet light brown in color but the plug threads are wet with gas. Perhaps too much fuel? I can smell a lot of gas in the engine bay (the air filter is off).

I haven't been able to take the fuel distributor off since several of the injector lines won't budge and even with the flare wrenches the points are starting to round. I have checked the air sensor plate and it does move freely and returns to the resting position with the ignition off. It seems like the plunger is not moving in time with the plate, if depressed completely and then pressing back down a moment later it seems like the plunger is slowly catching up with the air sensor plate. Maybe after 20 seconds its full tension is restored. When the car’s ignition is ON there is a lot more force on the air sensor plate. I can’t hear the fuel pump running when the air sensor plate is depressed but I can hear some fluid movement though the fuel distributor.

I am working on getting the cold start valve off to see if it’s spraying but haven’t been successful yet.

As for the WUR, I have no idea if it’s working or not. Maybe it’s injecting too much fuel?

This is a lot in one post but does anyone have any thoughts!?  :(

daantjie

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #1 on: 08 May 2020, 08:45 PM »
Welcome to the "House of fun" ;D  I think that is a song by British group, Madness ;)

Start simple first.  Make very sure you have no vacuum leaks, there are many spots that may have a poor connection, or the rubber boot connecting a nipple to a hard vacuum line might look fine but actually leaks.

Also to properly diagnose fuel related issues on K-Jet you MUST have a fuel pressure gauge plumbed into the system, no other way.  There are set points and ranges within which the system operates under various ambient and operating conditions, and you have to check these first as a base line before you chase other gremlins.

I am sure other members will chime in as well.
« Last Edit: 09 May 2020, 08:07 AM by daantjie »
Daniel
1977 450 SEL 6.9 - Astralsilber

TJ 450

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #2 on: 08 May 2020, 08:48 PM »
Has this issue appeared after or before the work?

I wouldn't start ripping into the CIS further until everything else has been checked. From what you've described, the fuel distributor is functioning correctly.

I would look closely at the ignition system first, making sure there hasn't been a mistake in assembly etc.

It would be worth checking air hoses and the like in case there is a large vacuum leak.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

diametricalbenz

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #3 on: 08 May 2020, 09:27 PM »
I may have to dig up the vacuum pump and splice it somewhere since the engine obviously will not run. The hard lines have cracked in several places and I have used rubber boots to splice them together.

I do not have a fuel pressure gauge unfortunately and was trying to exhaust all of my options before either acquiring one or just taking it to a knowledgeable shop

@Tim The issues appeared before the work. Right up until I drove it to the gas station the car ran fine. I started with the injectors since there is a lot of deferred maintenance which is entirely my fault but it was unclear as to what was causing the no start situation. It has all gone pear shaped now!

I will check all of the vacuum connections again and check the electrical as well. I did my best to photograph and put everything back exactly the way it was before installing the new parts. Does it matter which way the resistors go? I noticed that they interlock and so they are oriented in opposite directions.

revilla

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #4 on: 09 May 2020, 12:08 AM »
I once had the same exact problem. In my case, it was a combination of loose rubber collars (x2) at the bottom neck of the air metering body and a sticky fuel distributor main plunger + plate not well centered (it’s adjustable).
Hard to say you have the same problem, but from your description I had exactly the same symptoms.  The 2 collars I’m referring to are the ones connecting the air metering body and the throttle butterfly assy.  But in reality your air leaks (causing fuel mixture to go out of wack) could be coming from many different places. What is for sure is the fact that the leak is massive to cause that condition.

Good luck in your search.

Please keep us posted.

Ps.: I noticed you’re in Wisconsin. Are you close to Oshkosh? I use to fly/land there every year for the biggest air show in the world. Great memories indeed.
Robert
W116 1977 280SEL & 1979 280SE

rumb

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #5 on: 09 May 2020, 05:18 AM »
Is your fuel pump still good? Quick check to disconnect fuel inlet to FD, Jumper relay or apply 12v directly to pump. There is a spec somewhere about vol\minute.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

TJ 450

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #6 on: 09 May 2020, 05:51 AM »
About the resistors, they do go a specific way as from memory the coil runs at 12v when cranking and drops to 6v when the engine's running hence the two resistors. I'm nowhere near my car at the moment but can take a pic of the orientation tomorrow.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

raueda1

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #7 on: 09 May 2020, 07:23 AM »
I'm going to take a contrarian view here and suggest that it's a fuel problem. At the onset it started OK but then bogged.  To be sure, check the vacuum stuff as suggested.  But get that fuel pressure gauge as daantije suggests and check pressures.  It will reveal much.  Good luck!
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

PosedgeClk

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #8 on: 09 May 2020, 09:39 AM »
Buy a pressure gauge set for $100 USD, and be sure that your WUR is giving you proper pressures.
1979 450SEL 6.9

diametricalbenz

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #9 on: 09 May 2020, 09:07 PM »
@revilla Yes, I am about an hour away from Oshkosh. Airventure is definitely a must see!

@rumb I can unbolt the fuel inlet to the fuel distributor and test the pump. I will try to create a jumper cable and try it as polymathman demonstrated in your post back in 2016 or is that for a different car?

@raueda1 I am somewhat inclined to think it's a fuel issue as well. I had just a few spare minutes and I rechecked and reseated as many of the vaccum fittings as I could see. I noticed the EGR white and red rubber connectors are very greasy and loose from age. Can anyone reccomend replacement hard lines and the rubber connectors in the red and white colors?

I noticed on one youtube video that there is a Fuel Hose/Line; Inlet Fitting between the fuel line and the distributor. Does this have a screen or filter on it? I tried removing it and it's wrenched down far too tight and cannot remove it. I am wondering if it's worth replacing at all?

I did pull the #5 spark plug and set it on the valve cover and cranked the engine. There is a nice bright white spark so I am not immediately inclined to think it's ignition related.

daantjie

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #10 on: 09 May 2020, 09:14 PM »
Yes that coupling has a fine mesh screen and they can become plugged with crud.  Best to remove it and to soak in carb cleaner and to blow it out with compressed air.
Daniel
1977 450 SEL 6.9 - Astralsilber

diametricalbenz

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #11 on: 09 May 2020, 09:23 PM »
I will  have to give it another try to remove it tomorrow. It was probably installed with an impact wrench!

daantjie

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #12 on: 09 May 2020, 09:44 PM »
Try soak overnight in PB Blaster that stuff has saved my bacon more than I'd like to admit  8)
Daniel
1977 450 SEL 6.9 - Astralsilber

TJ 450

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #13 on: 09 May 2020, 11:11 PM »
The WUR also has screen in it too (below the fittings.

You could soak that FD strainer in thinners overnight to remove any crud.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

Randys01

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #14 on: 10 May 2020, 02:50 AM »
It's a fuel problem.
Get a gauge.
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