Author Topic: 6.9 Normal Operation to a No Start Condition  (Read 668 times)

revilla

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #15 on: 10 May 2020, 03:51 AM »
First thing to check is your pump delivery volume. Spec is 1 lt/30 secs.  To do so you need to disconnect the delivery hose entering the fuel distributor (FD) and place a container. Then you need to make the pump run. There’s a less complicated method to do so rather than creating a jumper. In fact is the method recommended in the kjet CIS manual. Locate the blue connector on top of your FD. Remove the securing wire so it’s easy to connect/disconnect quickly. Put your key in position 2 (without cranking the engine of course). Once the hose inside the container, disconnect the blue connector. You should hear the pump running. If not, she’s dead or you have a bad electrical connection or a bad relay. This relay is used in many places in your car. Some people call then ice-cube and they have an aluminum case. Swap one temporarily to check if your pump now runs. If she does, the relay is your issue. But measure the its delivery volume anyway. 
All the above can be done while you buy your pressure gage. There’s a second easy method but it requires 2 people. Place the hose inside the container as explained above. Put your lever in R or D. Try to start your engine, it won’t start of course thanks to the safety switch, but you should hear your pump running while the key is in crank position. One person measuring the 30 seconds and keeping the key in crank position, the other attending the hose/container at the engine.

Please let us know your findings so we can continue to help you diagnose the problem.

Cheers

Robert
W116 1977 280SEL & 1979 280SE

diametricalbenz

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #16 on: 10 May 2020, 11:18 PM »
I am definitely planning to test the fuel pump output tomorrow.

In the meantime is the best CIS pressure tester the S&G 33800 model? It seems to be the most purpose built tester I can find so far.

PosedgeClk

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #17 on: 11 May 2020, 09:36 AM »
There are a bunch of K-Jet units out there. They are usually marketed for Porsches. There is not much to them. It is a fuel pressure gauge, a valve, and a set of adapters. The only thing that really matters is that you have the proper adapters. I bought Tool Aid P/N 33865 and have used it to tune my WUR after I rebuilt it.
1979 450SEL 6.9

Joshwatson

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #18 on: 13 May 2020, 10:08 PM »
I am also having the similar issues you are having.
I brought a 6.9 back to life from 10+ years of sitting. After replacing the fuel pump and filter, I got it to run, it ran fine and started up with no issues at first. Now after I took it around the block, it idles very low (around 550rpms), shakes/misfires bad, and when throttle is pressed, it wants to die and sometimes does. But if I press the throttle then let go of it, it Revs up smooth for a second then goes back down to 550rpms. 
I am thinking that maybe something from the fuel lines/tank got into one or more injectors blocking them off or possibly catalytic converters clogged? But I’m not sure if mine has catalytic converters or if those are just resonators.

TJ 450

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #19 on: 14 May 2020, 02:25 AM »
Something I was reminded of recently is the fuel strainer in the tank. It's a good spot to start for troubleshooting particularly if you suspect fuel delivery issues. You could change the filter at the same time.

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

PosedgeClk

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #20 on: 14 May 2020, 09:45 AM »
When I got my 6.9, I had all these issues, and everything had to be replaced. The gas tank looked brand new when I started tearing things apart, and it had black primer rather than the body paint color. I'm not sure whether it had been replaced at some point recently in the car's life, but it looked brand new. I found rusty garbage in the lines, the fuel filter was clogged, and a brand new pump that the seller had put in was having a hard time pumping. I dropped the tank and had it coated. The strainer's screen had separated from the body and was allowing trash to enter the pump. It didn't make it past the filter, but whatever. The seller was honest enough with me and knew that I knew what I was getting into. The 6.9 had been sitting for 10+ years on his lot, he never got around to working on it, so he sold it. It ran and drove, and he said that it would easily go a few miles but to be really careful about doing that before replacing the accumulators. Indeed, he was able to load it on a carrier trailer, and the persons who took it off the trailer were able to drive it about a mile where it broke down right in front of the house.

It started, ran, and all that, but there were so many of these problems that cropped up as expected that you really can't point your finger at one thing. I ended up replacing all the lines, the filter, the strainer, the accumulator, and the pump. Forty-year-old lines are a fire hazard. I also cleaned out the little metal can (30cc looking thing). Everything was looking good, I was getting good, clean fuel, and the engine was still dying rather quickly, and the idle was terrible. The seller told me in the beginning to replace a cracked green O-ring in the back of the distributor on the mechanism where the system pressure is set, and that actually seemed to help, and it certainly needed to be done, but it didn't solve the problem. He then walked me through adjusting the mixture by 1/16 of a turn in the distributor, and when that didn't solve the problem, he suggested to buy a set of gauges and tune the WUR. I bought the gauges, removed the post from the WUR, put it on a lathe and drilled and tapped it, got some Viton O-rings from McMaster and replaced the O-ring under the metal diaphragm, and got the engine to start and idle beautifully. The seller and one of my Porsche buddies both told me that I had to have the gauges, and they were 100% right about that. Bosch put out some temperature vs. pressure graphs, and you have to go by these. The ones for the 6.9 are in the combustion manual IIRC. That's where I am now, and I am currently working on a new impeller, seal, and shaft design for the water pump as the weep hole was leaking after the engine idled for a while.
1979 450SEL 6.9

daantjie

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #21 on: 14 May 2020, 10:17 AM »
Indeed I am a big advocate of the "base line" approach, and even though it might be pricey to replace all your fuel related components, as well as spark related, I am of the opinion that after 40+ years you need to do this, even if it is just for safety's sake, especially the fuel hoses, "Car - B - Q"'s ain't fun, guys :o

This is also why I favour KJET over DJET, to blanket replace all KJET items is a cake walk and cheap compared to DJET.  KJET was a lot more prevalent and was installed in millions of cars and multiple brands over the years, so you will always find parts for them at reasonable prices, DJET not so much.
« Last Edit: 14 May 2020, 01:17 PM by daantjie »
Daniel
1977 450 SEL 6.9 - Astralsilber

Joshwatson

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Re: 6.9 Normal Operation to a No Start Condition
« Reply #22 on: 14 May 2020, 10:40 PM »
Well I lightly cleaned my injectors today on the 6.9. Took them off and put some cleaner in the feed side and blew them with compressed air.
Now it runs a bit better. It doesn’t want to die now when I press the throttle. It actually revs up. Misfire is still present though. I guess little by little we’ll figure her out.