Here is how it went:

Sprayed Fogging oil into spark plug holes – used a double length straw to reach into the cylinders.
Waited 30 minutes

Turned motor over with the starter. The motor ejected some gasoline, mostly on the left bank, whose FD ports were the first to be flushed yesterday.

Waited 1 more hour to air the cylinders out further.

Installed Spark Plugs. ………………and then:

I started the motor which immediately went into a very satisfying high idle and DID NOT peter out in several seconds.

I observed the AFM plate move down to reveal an air gap. This immediately confirmed my diagnosis of the previous FD being bad. With the old one, the AFM plate did not depress by the action of the motor, causing it to die in 3-4 seconds, unless the AFM plate was depressed by hand.

The motor now ran through its warm up cycle, but started to stumble and eventually died after 2-3 minutes (at about 50F ambient temp). [ This warm up time is consistent with the 056 WUR I now have installed, it is calibrated for a shorter warm up period; I’ll write another dissertation on the WUR in another thread…]

I interpreted this behaviour as fuel starvation – something completely within the realm of reason since the transplanted FD was sitting on the AFM with mixture settings that were not necessarily correct now.

I let the car cool down a bit to induce the warm up circuit into action once more. Removed the mixture plug and turned the mixture adjustment screw right (clockwise) by a ¼ turn.

Started motor, observed the operation …the motor came off the warm up cycle within a few seconds (it was still sufficiently warm) and settled into the low idle and did NOT die.

Lean condition is confirmed!

I proceeded to adjust the now running motor (off the WU cycle) with about 1 ½ cumulative clockwise enrichment turns. The idle kept coming up and I kept adjusting it down with the Idle Adjustment screw.

Very satisfying to rediscover the motor at the point where it responds to “regular” adjustments.

Eventually, since I do not have a CO meter, I settled on a setting which was probably a bit too rich. The motor would diesel lightly when turned off. A ¼ turn in the lean direction fixed that problem.

In the interim, I had ample opportunity to rev the motor through its paces. The sound of a low mileage MB V8 revving it up was music to my ears all night long!!

So what have we learned? For one thing, the FDs CAN be flushed. With the right cleaner and method, they can be self injected (on the bench, using their own plunger), soaked, reinstalled and flushed with the car’s own fuel pump.

Unfortunately, since I received the replacement FD without knowing any of its history, I don’t know whether it was operational. I do know that it had some fuel varnish and residue which washed out from every port.

I intend to repeat the flush technique on the FD I just removed from the SLC. Since this one is confirmed “bad” the next test will be the one to watch.

What’s next for my ’79 450SLC?

[ Oil Change + Fuel Filter Change]

The very next thing I’ll do is perform the basic pressure test (system pressure). I do not know either the condition or the settings of the Primary Pressure Regulator in the replacement FD. It’s pointless to proceed with any further tuning without confirming (and adjusting into spec., if necessary) this, most basic setting.

Next will be a Control Pressure test, followed by a Leakdown test.

Next - the injectors. I have a spare set soaking in carb. cleaner in a small ultrasonic tester (the darn thing has auto shut off, so most of the cleaning is from the soaking action). I will rig up appropriate connections to our Motorvac machine which will allow me to power flush and also check the “crack” PSI, as well as the “leakage” if any.

The clean injectors will go in and then the remainder of the fine tuning be applied, of which the low hanging fruit – the replacement of the many rubber vacuum and molded hoses – is of primary importance.


bostonmish