Hard starting on 1989 420 SEL

[89Merc420SEL]

Hello All;

I have a 1989 420 SEL which has developed a problem with starting. When you turn on the ignition you can hear the fuel pump prime itself, then when you crank the car it takes a relatively long time to start and when it does start it runs very rough for several seconds and then the problem clears up. This can happen if the car is cold or even when it is hot. Usually if you start the car and run it for a while and shut it off and go back to it in a few minutes it starts just fine.

I have been told that this is most likely the fuel accumulator. My questions are where is the accumulator and are there any "tricks of the trade" to know when replacing?

Thank-you in advance for guidance.

[126nut]

Could be almost anything. A bit more diagnosis will be in order. My first guess is it is getting flooded, fuel from leaking down injectors will foul the engine up when sitting.

A question, hot starts or cold starts, any difference?

I had similar problems with mine but just replaced almost everything, injectors, plugs and wires and guess I got lucky and the problem went away. You will need to do a bit more work on your own and then come on back and ask a few more questions.

[89Merc420SEL]

I agree that it could be most anything, but I have replaced the fuel distributor, all of the injectors, cold start valve, plugs, wires... my next step is the fuel accumulator. Do you know it's location and do you have any experience/tricks for replacing?

[jriewer]

FYI, the fuel accumulator is housed with the fuel pumps. Check out fastlanes site for a picture of it BUT that doesnt sound like your problem. Lot of posts on hear about symptoms of a bad fuel accumulator losing its vacuum and causing problems during a warm start because the fuel has boiled in the lines while the engine sat. Usually doesn't happen during a cold start.
I have an 87 420 with warm start problems. Cold started fine and hot started fine provided I restarted the car within 10 minutes after shut off. Replace the accumulator and fixed the warm start problem.

And did lots of research on here trying to figure out if it was my accumulator or injectors before I started replacing parts.
And my understanding is a leaky fuel injector usually wont affect a cold start because the fuel mixture needs to be rich and since the engine in cold much of the mixture won't combust anyway and gets blown out the the exhuast. my 2cents.

[89Merc420SEL]

I forgot to mention in my last reply that it has both cold and hot start problems. Once it is running for a few seconds it settles out and runs like a dream.

[jriewer]

One other thing, if your determined to replace the fuel accumulator change the fuel pump check valve too while your down there getting sprayede with gas. Make sure you replace all the copper crush valves too. If your fuel hoses are original I suspect they are very hard and may be difficult to compress to pinch off the flow of fuel form the tank as you disconnect the hoses. If thats the case, I wouldnt mess with pinching those hoses for fear of cracking them, that a whole other can of worms. instead wait until your tank is almost empty, syphon off what ever is left and have a container underneath to catch all the excess that will pour out once you start disconnecting hoses.
if you can pinch your hoses, (I used a couple of C-claps) make sure you release the pressure on the tank by opening the fuel cap first)
Oh, yea one other thing, leave the smokes in the house.

[126nut]

Originally posted by 89Merc420SEL
I agree that it could be most anything, but I have replaced the fuel distributor, all of the injectors, cold start valve, plugs, wires... my next step is the fuel accumulator. Do you know it's location and do you have any experience/tricks for replacing?

Now that is what I am talking about, letting us know what attempts you have made already. I, like most DIY'ers, am guilty of throwing parts at a problem in hopes that I will get lucky, the cheaper the parts the better. Fuel distributors are not cheap so I haven't thrown any of those yet.

Hope you get it sorted out my friend.

[Morocco]

I have a '91 420sel with exactly the same problem. It starts rough, hot or cold, but runs fine when it is warmed up. I can leave it in a parking lot for 10 minutes and when I return and start it, it inevitibly sputters and gasps for a couple of minutes. Once I get going on the road it runs fine and idles fine. A mechanic here who did an overhaul on the engine last year suggested the fuel injectors, but after scanning through here I'm leary about throwing money into fuel injectors on a whim. Of course, I don't have a better idea. What exactly does the "cold start valve" do? I like the sound of that one, but what do I know?

[Theurig]

In my case, as with many others who have posted regarding this, the hard starting was when the car was warm and has been sitting for between 15 minutes and a few hours. starts ok in the morning. Turns out the accumulator need to be changed. Reason why it starts fine in the morning is the cold start valve kicks in with some fuel or something. Do a search on the accumulator and also the cold start valve there is a wealth of info. I love mercedesshop!!!