1974 280 SE Cold start issue. D Jetronic

[KenM]

Sounds like a curly one Carl, at least you are the man to sort it out, I'm no help but waiting for more news.

[carl888]

This car is giving me the complete shits!  It's a sad day indeed when I have to drive an Italian car, because it's reliable.....

Update so far, the only thing I haven't changed is the ECU.  Testing the entire D-Jetronic system reveals nothing.  Today I pulled apart the ECU, in desperation hoping to find a dry joint or blown component...but nothing.  Only three electrolytic capacitors in total which tested fine for value and leakage, all the resistors are, from what I can tell, metal film Roederstein and the remainder of the capacitors are WIMA MKS and Roederstein metalised polyester which I have never seen fail.

It's pretty easy to get around the ECU but be careful separating the mother and daughter boards.  Two small plastic ferrules atop the daughter board ECU need to be removed along with 4 screws and you can unfold it like a book.  Some pics...

 













The next step is to try a replacement ECU.

[mrkozzy]

We seem to be having the same issue Carl.
My 280 just wont start and I am mystified.

Drove the car in to have the dashboard replaced. That work has been completed and now for some reason this issue has arisen.
Tried to work back and figure if anything under the dash may be amiss, but  I'm being assured all is in order as theres nothing there that would cause this.
 
So after the testing I bought a replacement (supposedly tested on a 114 and working) ECU last week but to no avail. still turns over but refuses to start.

It seems there is no power/signal getting to the injectors.

The testing, (done by others) has revealed all things working and powered right up to the ECU.
From there on nothing.
Obviously with no way to test the ECU, the assumption and gamble was that it was dead.
I purchased another thinking I would keep it as a spare anyway if it wasn't the issue.
I'm at a loss.

My ECU differs from yours just a little.  0 280 001 008
                                                             526
                                                             281
                                                             E
                                                             16

Amongst the work done in the last 6 months.
Fuel pump replaced
Filter replaced
Dizzy serviced and top & bottom points replaced
Rotor replaced
Distributor cap replaced
Spark plug leads replaced with Beru brand

All parts genuine.

Coil?

 

[mrkozzy]

Update.

changed over the "spark Box" today.

It grunted and growled but came to life after quite a bit of turning and prayer.

let it run for a couple of minutes until it decided to run high and then low and then high...............you get the picture.  (idle adjustment?)

A least it has finally started.

More later.......had to go back to work!

[mrkozzy]

tried unsuccessfully to restart the car every day for the past week.

It fired up once!  Idled perfectly then stopped after about 5 minutes.

Today it went on the back of a tow truck to a recommended Mercedes specialist.

Lets see what he says.

As Carl says in another post........."you end up changing parts not knowing where to look"

I'm at that stage. Wondering whether I needed to buy all the replacement bits and pieces in the first place.

More later

[gf]

If your car was only  average condition, would you consider modifying the injection system to something more contemporary as a long term fix? I'm not sure if that's a viable consideration in Carl's case, his car being in stunning condition. D jet = despair jet!

[mrkozzy]

Sometimes it pays to have a professional look at it.
Took the car to a recommended mercedes specialist who mainly handles older models.
Had to book the car 2 weeks ahead.
Dropped the car off Thursday afternoon and he called next morning telling me what was wrong and which parts were needed.
The car is now in "temporary  mode" meaning I can drive it however I need to replace 2 items.

Heres a copy of the report.

Car towed to workshop not starting.
Trace fault to injectors not working.
Remove distributor and clean and repair faulty trigger points.
Start car.
Check for idle speed, and found too fast. Found butterfly open.
Adjust throttle butterfly.
Trace fault of high idle speed to faulty airslide and blocked air slide.
Adjust air slide as far as practical.
Adjust mixture, and tune and throttle linkage as good as possible.
Check and top up levels.
Road Test.
REPORT: 
Gear box requires service (not bad)
Suspension and wheel alignment require attention. (not bad)
Requires trigger points and air slide.
Found high pressure hose air conditioner leaking.


Drove the car home Friday afternoon and had a wonderful weekend taking it for a spin.

Replacement trigger points and air slide arrived yesterday.
Cant wait to have them put on.

And a box of working spare parts in the boot, including the replacement ECU. (which wasn't the problem)



Once I saw his workshop, I felt good about leaving the car

[kastad]

Have you checked the auxiliary air valve, Carl?
It will cause hard starting if stuck in a closed position.

You can test the starting part by simply disconnecting the air hose between the intake and the aux valve. Then it allows the extra air to let in all the time. This should be similar to the aux valve fully opening when engine is cold.

It doesn't explain the issue with rough running when fully opening the throttle when warm though.

[robertd]

Hey mrKozzy,

which suburb is that workshop in?

Rob

[carl888]

Have you checked the auxiliary air valve, Carl?
It will cause hard starting if stuck in a closed position.

You can test the starting part by simply disconnecting the air hose between the intake and the aux valve. Then it allows the extra air to let in all the time. This should be similar to the aux valve fully opening when engine is cold.

It doesn't explain the issue with rough running when fully opening the throttle when warm though.

Yep, air valve seems fine because I have a 1,200 rpm cold idle, in fact, I fooled it just in case by setting the idle speed hot to 1,500 rpm and letting the car sit for a day, then trying it from cold..............

..............same problem!

I have to admit I won't be going near the car for a while, a bit too much on, plus it's now disabled, it's had brake failure, a front caliper seal failed.  What a piece of shit this car is!

[carl888]

The next step is to try the replacement ECU that I need to collect from robertd.  I have replaced everything, except that unit, the ignition points and the fuel injectors.  Some of the peripheral things I have changed (This is now called shotgun mechanics, you just blast the car with replacement parts).  This is not my preferred manner in which to diagnose faults, I would have preferred to test the ECU earlier but I don't have access to one at present:

Replaced:
Temperature sender 1 + 2
TPS
MAP sensor
Trigger points
Coil
Ballast resistors
Battery
Ignition amplifier
Fuel pump relay

Experimented with:
Mixture
Timing
Plugs
Idle speed
Shorting fuel pump to run continuously

Tested:
All 7 injectors
Fuel pump and delivery rate
Fuel pressure, residual and run
Fuel relay including pump pre start pressure system
Ignition switch
AAV
Distributor
Leads
Rotor
Cap
Points (Ignition)
Low side ignition wiring.
Cold start system
Engine wiring loom
Compression
Valve adjustment
Fuel pressure regulator
Removed ECU and checked connections.  Opened ECU box and checked for dry joints.

I can't help but think the issue is the injectors not firing appropriately when cranking.  I know they are firing, but I do not know what they should flow when being cranked. 

The ECU continues to trouble me.  Every D-Jet "Expert" I have spoken to says:

1. If the car runs, the box is fine.  Really?
2. They have never seen a fault like this!

Rob, Kozzy's place I think is Peter Lennox:

http://www.peterlennox.com.au/index.htm

CJ

[mrkozzy]

His name is Joe.

Trading as Classical Motors (as well as Classique motors))

124 Thistlewaite street

South Melbourne

He's got that German/Bavarian type accent which gives me  a little more confidence, of his  training.

I've rebooked for him to do the trigger points and the air slide. The air slide is a bugger to get to apparently, so I'm just gonna pay him and have it done.
Earliest I can get it rebooked is nearly 2 weeks away. Man is he busy!

[kastad]

This is hard... What about spray pattern from injectors?

[carl888]

This is hard... What about spray pattern from injectors?

Nothing like replying to a thread 13 months late, my apologies.

Injector spray pattern looks great!

It's still playing up BTW!

Next step is to rebuild the starter.  I have an excuse to do this when the exhaust system comes off.  Apart from that, I'll have to continue with simply throwing new parts at it, which is somewhat annoying.  Not much I can fit now, Injectors and ballast resistors is about it. 

Rob's replacement ECU made no difference.  Grrrrrrr.

[Lance]

Don't know if this is the problem, but I had trouble starting my D jet W114 when I first got it, checked everything, turned out to be a little gauze filter inside the fuel pump inlet which was blocked with crud. I cleaned it, re-installed it and it started without a problem. Fuel has what looks like lint which clogs up filters.
Have you checked the manifold pressure sensor?