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Old 05-02-2003, 12:42 PM
Walter Ebner
Posts: n/a
Question Severe hesitation in 1987 300E

I have a 1987 300E and am experiencing some engine problems. The car starts normally but idles rough and when the accelerator is pushed down at a normal rate, the rpm's drop and occasionally the engine will backfire. If the accelerator is let up somewhat, or pumped, the rpm's will increase. This occurs when the car is in neutral (i.e. no load) as well as when in gear. The severity of this condition varies with time. It started out as only a minor hesitation but now is to the point where the engine sometimes will not rev above about 2000 rpm.

The problem started a few weeks after the fuel pumps and fuel filter were replaced. Since then, we've replaced the spark plugs, the oxygen sensor, and have checked the ignition distributor and rotor. This work was all done in the shop, but the mechanic there was not able to get the engine running smoothly again. He suggested replacing the fuel distributor and fuel injectors, a very expensive proposition, but could not promise the car would run any better afterwards. The mechanic did check one fuel injector and found it to be working properly.

I suspect some dirt in the fuel lines/system somewhere and have been looking at the other posts on this website to try and get some ideas on how to attack that problem.

I'd greatly appreciate any help you can give me. I'm not a mechanic, so please explain things in layman's terms.

Thank you.
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Old 05-02-2003, 01:05 PM
Registered User
Join Date: Mar 2003
Location: Southern California
Posts: 2,011
Is this an intermittent problem or continuous, during engine warm-up or when the engine is fully warmed up? Is this just a transient problem while increasing engine speed and load? Will it hold a steady load and speed without misfiring?

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Old 05-02-2003, 03:53 PM
Registered User
Join Date: Sep 2002
Location: Denmark
Posts: 412
Welcome to the forum Walther.

If it backfires, i would spend some more time checking the ignition system.
You said you have checked the ignition distributor and rotor.
From what i have read on this forum, these parts are responsible for a lot of problems if they're not working perfectly.
I know how expensive they are, so the best thing would of course be if you could borrow the parts from a fellow 300E owner or from an extremely kind shop, just to make sure they're not the culprits.

Have you got the correct spark plugs? (ie. NOT the Platinum plugs) And are they in good condition?

Bad/corroded electrical connections?

You can spend a LOT of money tracking down defective parts on a 300E. -Take my word for it! So try the cheap stuff first.

Never criticize someone until you've walked a mile in his shoes. That way, when you do, you're a mile away -and you have his shoes!

'86 300E optically converted to '95 E300 (Sold)
-Blauschwarz on silver
-Black leather
-17" AMG & 15" AMG for winter
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Old 05-02-2003, 05:34 PM
Walter Ebner
Posts: n/a
This is not an intermittent problem and is present during and after engine warm-up. It is mainly a problem while increasing enginge speed. Load does not seem to be a key factor. Once you get the reves up, it seems to be able to hold a steady speed.

The mechanic changed out the distributor cap and rotor with new ones with no effect. I will check on the plugs but putting new ones in had no effect. How do you distinguish between the platinum plugs and the proper ones?

Thanks for your inputs.

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Old 05-03-2003, 08:57 AM
Posts: n/a
Since this is NOT an intermittent problem, you would be money ahead to find a good, honest shop in your area that can troubleshoot and repair this for you. Replacing parts by guesswork is an expensive proposition.

I have done some shotgun troubleshooting on the same problem with my 300E, but mine is VERY intermittent so there's no since taking it to someone who knows the system well because it's guaranteed that it will behave itself perfectly while in their hands.

The best I've been able to do is get help here based on symptoms and no testing by the technician. Even the very sharpest troubleshooters cannot help if the problem is not actually there when testing.

You did not put in your signature where you are located, so we don't know if you are near one of the known good shops or not.

Good luck,
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Old 05-03-2003, 09:23 AM
Registered User
Join Date: Oct 2002
Location: Toronto, Canada
Posts: 700
I'll fix it

Bring the car to me I'll fix it for you. My 190 had the same problem and it took me months to figure it out, no mechanic would offer to look things over to the detail that i have looked them over myself, every one just wanted me to replace things, even I sometimes wanted to do the same, but in the end, I could have fixed the problem with nothing more then a multimeter and a 3mm allen key, but I replaced all the usual parts, distributor cap, rotor arm, spark plugs and wires. Now my 18 year old 190 has the smoothes idle and acceleration you can imagine.

Tip #1 - check the EHA current, and go from there.

you can read some of my previous mosts on hesitation about how to do this, just look for "Hesitation - History" yes I had a lot of time to come up with that one

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Old 05-03-2003, 08:53 PM
Walter Ebner
Posts: n/a
Some additional observations:

Loosening the connection to either the fuel distributor or the fuel injector on cylinders 1, 5, or 6 caused an immediate effect on the engine performance -- loss of rpm's and rough idling. However, doing the same for cylinders 2, 3, or 4 had no effect on the engine performance. In fact, the lines could be completely removed and there was no detectable change in engine performance. Connections for cylinders 2,3, and 4 are on one side of the fuel distributor while those for cylinders 1, 5, and 6 are on the other side. Would this observation imply that there is a probem with the fuel distributor? NOte, however, that when the connections for cylinders 2, 3, and 4 are loosened, gas does flow out, so at least some gas is being pumped to these lines.

I live near Bristol Connecticut. Does anyone know of any good shops in this area?


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Old 05-04-2003, 12:00 AM
Registered User
Join Date: Dec 2001
Posts: 565
Re: Severe hesitation in 1987 300E

"The problem started a few weeks after the fuel pumps and fuel filter were replaced."

I always first ask if it's applicable, "what's changed"? You mentioned this started after fuel pumps and filter were changed.

I wouldn't bother with plugs, wires, ign. of any kind. I'd look into any and everything related to the work that apparently brought on this problem.
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Old 05-04-2003, 11:36 AM
Registered User
Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
You need to have the fuel distributor flow tested to make sure you have proper fuel delivery to all cylinder.

Do check the mixture, too -- if the fuel pressure was low due to dirty filters and a weak pump, and the mixture was set under those conditions, it will now be off from higher pressure and better flow. The EHA can go bad, too, resulting in a small fuel leak and unstable idle.

Also, I would check the condition of the idle control valve hoses -- when they get old, they leak and cause all sorts of mixture problems. You will only chase your tail until you have any vac leaks fixed.

Check the spark plug wires, too -- if they are old, they will fail and you get no spark to some cylinders. Expensive, but the car won't run properly with bad spark plug wires.

1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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