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· Registered
1987 420SEL
11 Posts
Discussion Starter · #1 ·
Need some help.
For some time the car has idled rough.
Recently getting very hard to start.
When it does start, it dies as soon as it goes into gear, recranks pretty easy, keep revs up and I can get down the road.
Checked cold start valve, it sprays.
By-pass air valve, cleaned, seems to function. Disconnect and idle goes up to 2000rpm.
To get home last Friday had to disconnect it to get it to crank and got home.
Due to other projects, it sat till Mon morning and it won't start.
I can smell gas after cranking on it a bit, also poored gas down the throat, no change.
It seems to crank over faster, but only seems to hit on a couple of cylinders when I let off the key.
Checked for spark, pulled plug and grounded it, spark seemed good.
Tried to adjust timing with someone cranking, didn't find a point where it seemed like it was firing better, rotated about 5deg back and forth.
Anyway, I think it may have jumped timing. (194K miles)
Is there an easy way to check?
What jumps first, left bank, right bank or distributor?
Also, I can hear the fuel pump running when I am trying to crank it.
Spark, check.
Gas, I think so.
Air, check.
Timing, don't know.
Compression, I think so, no reason for it to change suddenly.

· Registered
1,658 Posts
quote> For some time the car has idled rough.
When you let a car run like crap when it's hot and don't fix what's wrong someday it won't start and then you will be face with problems on top of problems. You need to check a lot more than timing, but to check timing you pull the valve covers and check the marks on the front cam tower. Dist and crank marks are easy to see.

· Registered
1987 420 SEL
2,125 Posts
Hey Benzical. My advice is for you to take it to a Mercedes Benz mechanic before you really mess things up. Remember this is not a Chevy that you're working with.

· Registered
Depends on the day!
13,419 Posts
You didnt' adjust timing, you just adjusted where the rotor contacts the cap..

If you jumped timing you wouldn't be cranking, you'd be deciding if you were going to spend 4-5K to fix it.

Get that chain and tensioner changed.

I'm wondering if your CPS is still functioning properly. I know in the manual there is a procedure on how to test it.

You can hear if your compression went to hell in a cylinder or two when you turn the car over, it would sound a little dead/less crisp.


· Registered
420 SEL (1989), 190 E (1990)
442 Posts
Had the exact same problem, ended up changing the eight injectors, check valves ($800), plugs, distributor cap (read, not the rotor), OVP relay, feul pump relay,checked cold start injector, these were all for the hard start which did not fix, then one day car dies, after idling rough for a couple of days. SO I check ignition, but in my case there was no spark, I though it was the ignition control module, but checked the resistances and everything in the ignition system and everything was fine, eventually my mechanic said to change the rotor (since it was the cheepest thing on the list of things I was wanting to change) and whola! fired right up. The hard start problem persists, but I am going to change the cold start injector anyways, since it may be fine on a bench test but maybe it throws in too much fuel? Who knows!

Good luck and let us know if you fix the hard start issue.


· Registered
1987 420SEL
11 Posts
Discussion Starter · #6 ·
Went from start fine, to
Hard to start, to
Won't start.
Drove other car to work.
Tried to start each morning.
Then after not running for a week.
Started it, it cranked on first try.
Ran like a new car Monday to and from work.
Tuesday a little worse.
Worse on Wednesday.
Terrible on Thursday.
Won't start Friday morning, AGAIN.
Go Figure.
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