The same old 450 SEL idle problem..

[koan]

Also, these cars have a electronic diagnostic plug-in in the engine bay. If a shop had the right equipment, what type of things can you find out from these?

Close to nothing, just some ignition voltages and a trigger pulse for some sort of ignition analyser.

koan

[TJ 450]

With the diagnostic connector, it is used in conjunction with an exhaust gas analyser in the same machine, in line with what Koan said.

From what I have seen, the machine tells you everything you need to know about the ignition, and the CO as required.

In reality though, all you need to do is take the car to a mechanic and have the mixture set to the value given in the manual, once you have ensured that there are no major air leaks. The ignition timing also needs to be set, as too much advance will give you a high idle speed as well.

Tim

PS; an incorrectly set up or faulty switchover valve, or a faulty advance mechanism in the distributor will also cause the idle speed to be high... This is easily ruled out by checking the ignition timing too.

[WGB]

A functioning switchover valve and an empty A-C system will cause fast idle problems.

My 6.9 would idle at 1100 rpm with the aircon turned on and the sytem "flat" which made for fun driving when the A-C was on  until the leak was fixed and the system regassed.

Bill

[skatinblind815]

Hi everybody. It's been a couple days, and for some reason I never saw the second page of responses. Thanks for the help you guys, I really appreciate the input.

I'm still waiting for my new auxiliary air valve, which comes with a guarantee that it will close all the way  . I will let you all know what happens.

After I get the AAV in, I will go about checking the fuel/air mixture and timing. As far as the timing goes, it might be off currently. A few months ago, when I was in the beginning of finding the source of my high idle, I retarded the idle via the distributor, and the idle slowed massively, but there was almost NO power in acceleration. So I put it back where it was. I know for a fact that my fuel/air mixture is off because last Sunday I pulled the spark plugs and they were covered in a black gooey buildup. No bueno.

I am nervous about what you guys said about the air conditioning though! My A/C hasn't worked since I bought the car last August! I think there might even be some components removed, per the work of the previous owner. And I know A/C parts are friggin' expensive. What to do, what to do?


Have a good day guys!

[adilali]

Hello everyone..I'm new to this forum but let's see how I do on my first post. I have a '78 450SEL (4.5), RHD model. I did a major engine and transmission overhaul about 4 yrs back, since then I've always had hard start issues, or hard start when engine is hot (after about 10 mins). Recently I observed even harder starting, to the point where I couldn't get it to start (from cold) without putting some fuel into the intake (below the air filter housing)..  I observed that the 2 wires that connect to the connector on the WUR are a bit chaffed. I also observed that if I slacken the nut for the fuel input tube on the fuel distributor and put the IGN ON in Drive, there's fuel coming out of the tube (so i know there are no pressure issues- after all the pump and filter have only about 300kms on them). What confuses me is that it gives this problem on a cold start, as well as after a 10 minute delay when it's warm (it starts immediately if warm and is switched off and then on right again). Reading from your posts I see possibility of several issues. Can anyone help me narrow these down to one or two places to start?

[TJ 450]

Hi adilali,

It sounds like you may have a case of the system loosing pressure due to a failed accumulator or other leak. For cold starting, what happens if you pressurise the system first?

Tim

PS, It's a good idea to start a new topic for these sorts of questions.

[Type17]

Hot start being an issue only after 10 minutes is almost certainly the fuel accumulator (been there, done that). Additional hot-start troubleshooter question: after more than 10 mins, does it start and run ok for about half a second, and then take ages on the second attempt, or is it rubbish on the first attempt that you make after more than 10 mins?

The cold start issue could be many different issues - leaking injectors, faulty WUR, faulty system pressure regulator, to name a few - you can try guessing and replace parts on spec, but the only way to be sure is to do a pressure test, or get one done.