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Bosch D Jetronic and K Jetronic Troubleshooting

374K views 116 replies 43 participants last post by  ianrandom 
#1 ·
#26 ·
Really good information! I have a question about the hose that goes from the airbox to the inlet manifold at the front end of the engine, it has a gigantic banjo fitting in the engine end.. There's a spring and a big screw, obviously some kind of pressure or flow adjustment is possible here, but what is this?
 
#27 ·
wide open throttle?

Question..
What would happen if the throttle linkage was stuck in wide open throttle position and one attempted to start the car?

I believe in EFI systems that the computer would sense that the car is not started and prevent loads of fuel from being dumped in the cylinders, but what about the k jettronic? my car would turn over but not start, so I pulled the plugs and they were soaking wet, and fuel was actually dripping out of the spark plug hole. I then played with the throttle linkage and realized that the connection between the accelerator pedal and the linkage was broken, and the linkage was in the WOT position.

thanks
Mike
 
#30 ·
Question..
What would happen if the throttle linkage was stuck in wide open throttle position and one attempted to start the car?

I believe in EFI systems that the computer would sense that the car is not started and prevent loads of fuel from being dumped in the cylinders, but what about the k jettronic? my car would turn over but not start, so I pulled the plugs and they were soaking wet, and fuel was actually dripping out of the spark plug hole. I then played with the throttle linkage and realized that the connection between the accelerator pedal and the linkage was broken, and the linkage was in the WOT position.

thanks
Mike
K Jet is mechanical and the injectors will only spray at 45psi or greater.I'd say you have an ignition problem rather than a fuel injection problem.Check the ballast.
 
#28 ·
Hello. Very good information in this post. It have been very useful so far.

We have a w116 280se with D jetronic with starting trouble. It is the M110-engine.

The first problem was that the car was hunting at idle. We changed the spark plugs and checked the following: both temp-sensors, pressure sensor (MPC), throttle switch, aux air valve. We also checked for vacuum leaks and that the fuel pump was running. Nothing helped.

But, when we took out the trigger points and cleaned them the problem changed. Now the engine starts but stops after 5 seconds! When it stops, it also stops the fuel pump. We have connected 12v separately but it stops anyway.

We have measured the trigger points when not installed. But my guess is that they maybe are worn down so they won't work when installed and therefore maybe the ECU stops the engine? I also think the cold start valve helps it start, and when the cold start valve stops, the engine also stops?
 
#31 ·
Hello. Very good information in this post. It have been very useful so far.

We have a w116 280se with D jetronic with starting trouble. It is the M110-engine.

The first problem was that the car was hunting at idle. We changed the spark plugs and checked the following: both temp-sensors, pressure sensor (MPC), throttle switch, aux air valve. We also checked for vacuum leaks and that the fuel pump was running. Nothing helped.

But, when we took out the trigger points and cleaned them the problem changed. Now the engine starts but stops after 5 seconds! When it stops, it also stops the fuel pump. We have connected 12v separately but it stops anyway.

We have measured the trigger points when not installed. But my guess is that they maybe are worn down so they won't work when installed and therefore maybe the ECU stops the engine? I also think the cold start valve helps it start, and when the cold start valve stops, the engine also stops?
How about the fuel pump relay,wiring and ignition switch?
 
#34 ·
Pressure actuator or control unit faulty.With a multimeter,see how many mA you are getting while cranking the engine.

If you read anything,it may just be the control plunger is varnished causing it to jam. Sometimes a rubber mallet tapped dead center on top of fuel distributor will free it up. Overuse of fuel injector cleaner will cause this as well as well as low octane (87)
 
#35 ·
hi Benz
I need help .
Can't get mine going at all. 86 E 300 I get good spark ,replace ignition rotor and distributor cap,sparkplugs,I get fuel to the fuel distributor but nothing out of it.Got a new fuelpump relay,and Overprotector relay,fuel presure is147psi before Fuel distributor and no presure coming out of it.
 
#37 ·
just an update
tapping didn't help,I do get reading to it but no fuel comming out untill I press the airflow sensor plate/ don't know if that is what you call it/ fuel starts comming out under presure from fuel distributor,but floods the engine!!!!,so still no start
Should I replace that duel distibutor or there is cheeper fix.
Thank You
 
#38 ·
Help

Dear Friends,...

i'm Barong,.. i live in Jakarta Indonesia (adityamangoen@yahoo.com)
i own a Mercedes Benz 280 SE (2.8)W116 -1973 which have trouble.
I had an accident,....the engine compartment burned.
I have fixed the body and everything,..and engine overhauled.
The problem is,....the engine can't start.
I have checked :
1. The fuel regulator which have 1 inlet and 2 outlet not working
2. No electric signal to the fuel nozzles. (the wire cheked,...and no problem.
3. I assume the trouble is from the ECU,..

Need help....
1. How can i get the fuel regulator ?
2. How can i fix the ECU or can get the used one but in good condition
3. I need the electricity map/diagram
4. Because of my less knowledge and careless,...now i need a fuel diagram from the fuel tank to the nozzles

I hope you all can help me,...i really desperate,.....

Best regards


Barong
 
#39 · (Edited)
D.JETRONIC - MB 250CE W114/8 1971

Friends,
I have problem in my MB 250CE/71 (mod. w114/8-D.JETRONIC) in the shot. Someone has connection scheme of the fuel hose that focus of the hose that comes from the tank of fuel to return, distribution of nozzles nozzles. It is that my MB is being completely restored and needs of this scheme to connect it. Thank you for this attention.
 
#40 ·
help

:crybaby2:1992 190e mercedes won't start?
never had any trouble with it b4. its got spark. and i can here the fuel pump. and there is fuel getting to the fuel injector distibuatior.but not cuming out of the fuel distrbuator thingy with pressure.i dont have any thing 2 test fuel pump pressure. but we thought it was the EHA fuel valve regulator and we replaced it with a second hand 1 with no luck
 
#45 · (Edited)
Hi Nutz,

I'm a new W116 owner here in the UK, having just bought a 1980 450 SEL. I'm having some trouble with what I think a fuel starvation issue.

The car will start on the button first time and the cold start system seems to be working fine. After a couple of minutes the revs drop to a very rough idle.

If I touch the gas pedal even a little the engine dies straight away. It will restart again no problem but does the same thing everytime I press the gas.

Your words of wisdom would be much appretiated.

Many thanks,

Leigh. :)
 
#48 ·
280 GE gets too much fuel when cold

Hi, my 280GE starts fine when cold, but then starts running rough after a 20 seconds, black smoke and smell of gas..

Funny thing is that the car runs fine when properly warmed up, but until then it's all black smoke and stalling all the time. Obviously getting too much gas. Runs a bit too warm while driving.

Replaced sparkplugs and cables, distributorcap and rotor, tested coldstart nozzle(ok), replaced fuel distributor complete housing because airvalve wasn't moving smoothly, still the same.

WUR was replaced not too long ago, but of course it could be shot again... Or the control pressure regulator maybe, or both?
 
#49 ·
Hi Nuts. You realy did a great job. Than you so much for all the info. :thumbsup::bowdown:

I have a 1971 350 SLC, Djet. I can see some little black smoke out of the exhuast pipe at high rev's which I think is due to mixture of fuel/air.

Is there any way for me to adjust the mixture manually?

Tnx.
 
#50 ·
You can adjust the fuel pressure via the fuel pressure regulator. To adjust the mixture, locate the ECU and adjust the knob on the side of it. Best to make a reference before doing so, so that you can put it back if it makes things worse. Also inspect the hose that runs from the MPS for cracks and such.

When was the last time you thoroughly inspected your ignition system?
 
#51 ·
Thanks Nuts for the help & sorry for late reply as I was out for some biz. I will try to do as you said & will let you know the result.

last time was more than one year ago & of course some mechanic did it for me.

about a year ago I changed the fuel pressure regulator with new one & some body told this regulator is saeled by MB & I should not touch it/adjust it.
 
#52 ·
D Jetronic troubles

Hi Nuts,

I saw your posting on the D Jetronic system and it is the most informative and easiest to understand explanation I have found on the net. So, that means since you were a good guy for posting that info, I have to torture you with a question about the problem I am having with my 74 450sl.

Here goes:

Car would not start. Pulled out the spark plugs, they were soaked with gas. Hooked up a fuel pressure tester. When you turn the ignition on, the pressure went up to about 10lbs and then bled off to zero as soon as the fuel pump stopped. I pulled off the fuel rail looking for a leaky injector and found when I turned the ignition on, every one of the injectors fires full blast until shortly after the fuel pump stops(pump runs for about two or three seconds) injectors spray until there is no more pressure in the line.

I am pretty much stumped on where I should be looking next. I was wondering if you had heard of this before or if you had any ideas on where I should start looking for the problem?

Thanks
 
#54 ·
Hi Nutz, thanks for getting back to me so quickly.

I do have spark. Starving is not the problem, it's actually the opposite problem. The reason it only get's up to 10lbs and then goes to 0 is as soon as I turn the key on, all of the injectors fire full blast at once. The lines never get a chance to get up to full pressure because every injector is locked on and dumping the fuel out almost as quickly as the pump can send it. Something is telling the injectors to all fire continuously even though the engine is not running. Sometime today I am going to try and test the various sensors and see if maybe one of them has shorted out. Let me know what you think.

Thanks
 
#55 ·
does the 74 have the injector trigger points in the distributor like the 73??
if so there are only two things that controll the injector... one is the trigger points..the other is the ECU..
if i had to guess based on my limited understanding of the system would be the ECU..
please...someone correct me...
 
#56 ·
Here is a little update. I disconnected each sensor and the distributor 1 plug at a time. No change. Then I started counting the clicks on the throttle switch and only came up with 18 instead of the 20 it says at the beggining of this thread. While I was playing around with this, the problem went away. I readjusted the throttle switch(still has only 18 clicks). It was a little hard to adjust, it seems a little twitchy getting the setting right. Now the problem is gone and the car is running. I had to stop working on it for today. The problem is, I am not at all confident this is fixed. Does any of this seem like it may be the throttle switch?
 
#57 ·
could it be the throttle sensor was reading WOT and firing all the injectors??
maybe a good cleaning is all it needed??
just throwing out things. when i think i have the answers i need on ours, something else pops up.

good luck
 
#59 ·
1985 380SL Starts but will not run

I just bought my 1985 380SL from a friend. Had the car towed from her mechanic (bad Start I know). The mechanic said it had the same symptoms starts but would not run. He thought it was from rust in the tank. I pulled the tank and treated it with POR 15 to remove the rust, prime and seal it. The mechanic had replaced the fuel pump, filter and spark plugs. I also replaced the in tank filter. The pump runs for a few seconds then stops.
Where do I begin? How can I check the pressure from the pump. My friend who is a Mercedes master mechanic says that it is either the fuel distributor or the that is gummed up but I do not know how to check either and he is too busy with work to come by soon to help. I have a pressure gauge just need to know where to start.
 
#61 ·
Hi Nutz,

I have finally narrowed down my intermittent starting problem as a bad ECU. Car won't start, hit ECU with rubber mallett, like magic it comes back to life. Here is the question I have. My ECU # is 0280002005 have found some with this number on Ebay but they want $300 used with no warranty. Found a junkyard with one out of the same year 450sl but the ECU # is 0280022008 for very cheap. Do the numbers have to be an exact match? Any idea if this will work?

Thanks for the help,

Smitty
 
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