1990 300E 2.6 Stalling and Fuel Pressure Questions - Mercedes-Benz Forum
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#1 (permalink) Old 03-23-2012, 01:26 PM
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Unhappy 1990 300E 2.6 Stalling and Fuel Pressure Questions

Hi all,

Car has 255,000 km (155,000 miles)

Problem: stalls when engine gets to op temp (80deg), can't restart until cools down below 60deg. When cold starts right up and idles smoothly. Once gets hot, idle starts surging up and down until a complete stall.

Replaced the following parts (thru-out last 2 years):

- fuel pumps, fuel accumulator, fuel regulator
- fuel injectors
- spark plugs, wires, rotor, cap, coil
- CPS sensor, temperature sensor, Oxygen sensor
- OVP, EHA
- air flow meter and fuel distributor (used parts)

First time this happened about a year ago, adjusted the mixture and that seemed to fix it but not for long. Discovered the potentiometer in the air flow meter had a bad spot (worn out) just off idle position, replaced the whole meter assembly and fuel distributor, adjusted mixture and car ran great for another 200-300 km.
Now I am back to a square one with the problem repeating itself again and again

I decided to re-check the fuel pressure and followed Mercedes procedure:
Operating pressure: 5.35 bar
Lower chamber pressure: 4.95 bar
But once re-attaching the electrical connector onto EHA the lower pressure was dropping to 4.7 bar (on hot engine), which is different from manual statement which says pressure should not change when plugging the connector.
Has somebody else experienced that? This electrical signal to EHA is coming from the Injection Computer so perhaps all my problems are coming from the computer?

Any ideas???

Thanks,
Ivan
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#2 (permalink) Old 03-23-2012, 01:34 PM
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Sounds like a bad OVP relay. Was the one you replaced Bosch or KEA? If not, then that is the likely culprit. You may also want to remove and inspect your distributor cap and rotor.

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#3 (permalink) Old 03-23-2012, 02:00 PM
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Hi Jayare,

OVP has been replaced, it is made by Kaehler (KAE).
But frankly I don't think it matters much in 1990 as fuel pump current does not go thru OVP on this model year, it has MAS unit which has a built-in fuel pump relay which by-passes the OVP.

I will remove and inspect the distributor cap and rotor, but again I don't think they are faulty as I replaced them twice, first time with Bosch, second time with Bremi.

Any other ideas?

Thanks,
Ivan
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#4 (permalink) Old 03-24-2012, 01:34 AM
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Originally Posted by ivpr View Post
second time with Bremi.

Any other ideas?

Thanks,
Ivan
Bremi rotor failed for me after less than 18 months. I replaced it with an MB original and all's fine.

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#5 (permalink) Old 03-24-2012, 02:53 AM
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How about the cold start valve and/or hard and cracked hoses? Often neglected because the hoses especially are obscured and not easy to get at.

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#6 (permalink) Old 03-25-2012, 06:30 AM
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Same symptoms. Did everything. Ovp, Pump relay, plugs, wires, distributor and rotor... It improved for a day, then back to the stalling. While trying to detail the engine, I discovered cracks on both hoses leading to and from the idle control valve. Replaced the idle valve hoses..... Yes, it is a chore but there's a link somewhere here that describes how to remove the hoses.

Doodleing with the af mixture will not help.... As the cracks expand when the engine gets hot. Check all vacuum hoses too.... I improvised my hoses by replacing the rubber portions with small diameter fuel lines. So far so good.....
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#7 (permalink) Old 03-25-2012, 05:55 PM
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I am jumping in on this because at cold start my engine doesn't start or it coughs before turning over. When I turn to third position second time. Turns over. No problem. I have new spark plugs and OVP. I am thinking it's distributor cap and rotor. Any thoughts.
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#8 (permalink) Old 03-25-2012, 08:06 PM
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Originally Posted by giocamoto View Post
Same symptoms. Did everything. Ovp, Pump relay, plugs, wires, distributor and rotor... It improved for a day, then back to the stalling. While trying to detail the engine, I discovered cracks on both hoses leading to and from the idle control valve. Replaced the idle valve hoses..... Yes, it is a chore but there's a link somewhere here that describes how to remove the hoses.

Doodleing with the af mixture will not help.... As the cracks expand when the engine gets hot. Check all vacuum hoses too.... I improvised my hoses by replacing the rubber portions with small diameter fuel lines. So far so good.....

I did replace all the rubber hoses and vacuum hoses including both hoses to/from idle control valve...
Engine starts and runs great when cold, but as soon as it gets to operating temperature it's like somebody turns a switch and it starts stalling. RPM are surging up and down, when adding gas it stumbles but then runs fine above 2000rpm, when back to idle it stalls. At this point I can't restart it until it cools down.
I am thinking the problem is electrical in nature, perhaps computer sending wrong EHA signals???

Has anybody done a fuel pressure check per Mercedes procedure, I still can't figure out why I have the lower chamber pressure dropping when I plug the electrical connector to EHA, it clearly says that pressure should not change...
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#9 (permalink) Old 03-26-2012, 03:34 AM
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What is your air/fuel ratio reading at full operating temp?

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#10 (permalink) Old 03-26-2012, 08:23 AM
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What is your air/fuel ratio reading at full operating temp?

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The actual meter reading is at 70% at 2500rpm, and 70-80% at idle.
So the actual (1-x) duty cycles must be 30% at 2500rpm and 30-20% at idle.
I had no luck getting them close to 50% - engine won't run at all.
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