News:

The Org - Serving W116 Enthusiasts since 2004!

Main Menu

D-Jet hard to start - Ideas?

Started by mrkozzy, 14 June 2018, 10:12 PM

mrkozzy

Hi all.
My 280se D-Jet M110 is proving hard to start. Once started and warmed up it runs beautifully.

Heres the starting sequence;

Not touching the accelerator I,

Turn the key and turn over the motor 10-12 times. Then Stop.
Turn key again and on about the 5th - 6th turnover it fires up.

No choke cuts in, (electronic or otherwise) and the engine will slowly idle at about 4-500 rpm. Almost wants to stop idling but doesn't.
Its at this point I  give it some "gas" and idle it up a bit.

After about 10 seconds I step out of the car and it resumes its very low idle. From here it wont konk out.

As I sit there and enjoy the coffee I brought along with me, it will "idle Up" to the 800 mark as it warms up.
After about a minute I can confidently get in and drive away and it won't miss a beat.

My mind tells me its the fuel pump however its been tested as running. Some 5 years ago all and any rubber fuel lines were replaced including the ones to the injectors. (remember its a D-Jet).

The only noise I do not here nowadays is the fuel pump priming as you turn the ignition key to the 1st turn. That Buzzzzzzzing sound it came with from new.

Is it possible the pump works but is not priming? ( Does that even make sense?)

The "Y" piece manifold exhaust is cracked and breathes through the crack when its turning over and running. Might this have a bearing?

As mentioned earlier, it starts every time and runs well, so fuel is definitely getting through the system.
The fact it can (just) idle at such low revs at start up amazes me, but I believe its still well tuned. I sense nothing else to the contrary.

Over to the brains trust, ANY suggestions on where to start?
MrKozzy

Alec300SD

#1
I have never worked on a D-Jet system,.
My 1979 245DL Volvo station wagon had the K-Jet Lambda Sond  system.

At any rate, here is a link to  "D-Jetronic from A to Z"  by Dr D-Jet, that maybe a bit helpful...I hope.
My gut instinct is that there may be a problem with the thermo time switch and/or the auxiliary air valve.
It sounds like you are not getting adequate cold start enrichment.

https://oldtimer.tips/en/d-jetronic
78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

TJ 450

Yep, I would suspect idle speed control issues first. It may be that the aux air valve needs to be thoroughly cleaned and tested (cycled in boiling water) after cleaning and lubricating.

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

Alec300SD

Also check the condition of the rubber hoses connecting to the auxilary air valve, and the o-ring on the idle adjustng screw (if it exists in your application).
Minor vacuumn leaks from aged rubber components can be problematic, and prevent a smooth idle.

Cleaning the throttle body  of fuel varnish buildup (and replacing the paper gasket if it exists in your application) may be beneficial as well.
78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

mrkozzy

Thank you to all (once again). ;)

I will follow through with the tips and advise.
MrKozzy

marku

There are manuals available for the D-jet including a reprint of the original Bosch which is invaluable. The D-jet is so complex that any hit and miss approach is going to take time and not really guarantee solving the problem.
1974 450SE silver green/bamboo velour/green vinyl roof