W108 068 280sel 4.5 warm up cycle

[ilpatino]

Hi all,

Today, I started up the 4.5 without the airfilter to look at the throttle-linkage (there seems a lot of play in the accelarator-pedal). I smelled the very destinct smell of raw fuel, and noticed a worn rubber fuel line between the two injector-lines. The engine at idle was a bit hesitant, and the garage smelled a lot like unburnt fuel, and a blackish smoke. When I blipped the throttle, quite a few pops and 2 backfires.

So I must conclude a something is wrong during the warm up cycle.

Also, maybe related, I noticed some days ago, even after a brisk drive, that just of idle, when blipping the throttle, the engine hesitates just a bit, and while cruising, it seems to "surge" a bit, but that could be subliminal .

I already read up on the cold-start valve (part 0000713437), but that seems unservicable. The part itself is also quite expensive.

Then there is the idle air valve, which can be clogged up, but seems servicable, (part 0280140017 ), and is also expensive, even when second-hand.

At moderate temperature (not hot, but definately not cold anymore) a drop in RPM is noticable, but not dramatic. Also at higher temperature, and lower idle RPM, at the exhaust, it sounds as though there is too much "air" that wants to come out. The last muffler sounds as though it is restricted and has trouble expelling the gasses properly. Not the deep bariton sound you would expect, but, well, a bit of a farting noise. (I hope I'm making some sense, but it is difficult to describe otherwise)

I then closed the idle-speed screw shut, but the car kept on ticking over, altough barely.

What am I looking at here?

Rich running at idle? The cold-start-valve that leaks? Is it servicable, contrary to my belief? What about the vacuum? The central locking is inoperative! Can I cut out the vacuum from "the rest of the car to verify that could be the problem?

I will clean the idle air valve with carb-cleaner and compressed air, and fix brittle fuel lines, but any input regarding this matter is warmly welcomed, especially regarding the cold-start-valve.

Have a good one!

[berfinroy]

It is IMPARATIVE that you replace ALL the rubber fuel lines under the hood if they are original, not just the one that is leaking. The fuel delivery pressure on the D jetronic system is high, and the chance of a fire under the hood is also high with old fuel lines.
Also, the leak you have now may make it impossible for the system to maintain propoer pressure to the injectors, which is critical to proper running.
The cold start valve may respond to an injection of 3:1 oil down the throat, but do the fuel lines first.

[ilpatino]

Berfinroy,

new fuel lines are ready to be installed tomorrow, they will be replaced before anything else! Too dangerous!

Is there a way to check the function of the CSV? I read about a check-hex-screw, but that seems to be for the 6 cylinder-cars with MFI. (or the 6.3, for that matter)

[berfinroy]

The CSV (which Bosch calls the "auxiliary air valve") supplies additional air to the intake when cold. Quoting from a Bosch manual, it is tested as follows:

"Remove hoses connected to each side of the air valve. With cold engines (less than 95 F), auxiliary air regulater should be at least partially open. To check the valve, use a mirror and light and look through the valve opening.Turn on ignition and make sure the valve closes within a few minutes."

The cold start injector is ONLY activated during initial cold start engine cranking.

As I said earlier, if the CSV is sticking, some WD40 may free it up. Just squirt it down the throat.

[ilpatino]

Hi berfinroy,

I think you mixed up. The cold start valve (csv) supplies the airintake with additional fuel, while crancking, while the idle slide valve supplies additional air while the car is warming up.

The slide valve will close when the water temperature is high enough, but to my understanding, when this valve is stuck in the closed position it will cause rich running while cold, but it will not interfere when the car is warm, and if the valve is stuck in the open position, it will tend to keep the idle too high when the car is warm, causing a lean mixture at idle. This valve is servicable.

The coldstartvalve does not supplie air, but extra fuel while crancking, the time being determined by a thermo-time switch. When facing the engine, it sits behind the distributor, to the right side of the slide valve. The only issue could be a leaking valve, because that would mean continous extra fuel at any given time.

any way, i'm going to clean the slide valve, and take a closer look at the csv, and see where that takes me.

Next item Is the throttle position sensor and the manifold pressure sensor.

[ilpatino]

Hi all,

this weekend, I found some time to check various d-jet components. The auxiliary slide valve does it's job perfectly, as does the coldstart-valve. I did notice some bucking while cruising at 80-100 km/h, and elsewhere I read that the throttle-position sensor could cause some trouble. So after removing the air-filter-box, I gently removed the black cover of the sensor and sprayed liberal amounts of contact-cleaner. The surging has stopped.

I still feel as though the engine is running a bit rich, maybe I'm being a bit nitpicky here.