I have a 92 300e that occasionally stalls at idle after about a 10-minute warm-up. It will refuse to restart for approximately 20 minutes. Then it will restart fine but hesitates off idle and runs fine when RPMs get above idle speed. No dash lights are illuminated when the car is stumbling off idle and there are no trouble codes. After about another 15 minutes of driving it runs perfectly with no hesitation. So it runs fine when cold and runs fine after fully warmed up. Seems to happen if the car has been sitting for a couple of days. Last week it on a freeway off-ramp and had to get a push to the side to wait 20 minutes. I can definetly do without that experience again.

I've removed and resoldered the OVP, no difference. It is Hungarian and the larger internal coil heats up. That seems abnormal to me. I also checked on my 300te (which runs fine) and the OVP seems warm also.

What does the idle switch do? I connected a multimeter to the idle air valve (read 8v when cold, went down as the car warmed up) and watched as I activated the idle switch. I also removed the plug to the switch and directly bridged it. Nothing seemed to happen at the idle air valve, in other words the voltage didn't deviate. Is that right?

What's the best way to measure fuel pressure (I have two 300e's, so I'm fine with purchasing tools that are reasonably priced)?

Thanks,
Robert

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89 300te 222,222
92 300e 190,000

*bump*

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89 300te 222,222
92 300e 190,000

I just copied the last thread post to this;
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03-21-2005 09:38 PM
trants4md The good news is I have found the main problem, sort of! All you who assisted and said vacuum leak were correct. But where the leak is caught me off guard.

In tracking every vac line I came to the large line connector to the left of the throttle body air intake that goes into the intake manifold. Upon pulling the line and plugging the tap into the manifold my idle immediately smoothed out. The motor purred again! By this time the engine was warmed up.

Tracing down hose from there looking for a vac leak I tested every hose and connector under vac pressure. Every hose OK. Not a bad hose in the entire system. Then I reconnected it one section at a time. When the C4020-13554 Warn up regulator was reconnected it went ruff again and I had major engine hesitation on acceleration.

It appears that I have a vacuum leak internal in the warm up regulator diaphragm.

Does anyone know if a rebuild kit is available, or will I have to build my own diaphragm parts?

I am certain I can do something as the regulator is not staked together, but it never hurts to get a kit if possible!

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A medium rubber vacuum plug (1/4") lets you run this quick test to see if it responds!

The origianl thread is here!
http://www.peachparts.com/shopforum/showthread.php?p=846283#post846283

trants4md
______________
85 500SEL
80 Leland TR7 Convertible
And Some American Stuff
94 Dodge Ram
93 Chev Lumina APV
79-81-83 Forzda

I'll try shooting some ether on the hoses and inspect them vacuum leaks. Do I have a warm-up regulator on a '92 M103?

Thanks,
Robert

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89 300te 222,222
92 300e 190,000

Read what Benzmac has to say in this thread.

http://www.peachparts.com/shopforum/showthread.php?t=81404&highlight=ovp

__________________
'91 300-SEL

Robert,

Don't know the answer but am sure interested if you solve it. Have been a fellow suffering for 2+ years and although I've tried various remedies it's still not fixed. The symptoms you describe are so close to mine I already feel a bond between us . In particular the problems being only seen in that period post cold start but before fully warmed up, and most significantly, that 2+ days of inactivity cause the problem to be more acute, and never any trouble codes.

A couple of things to note though: (1) our cars are not quite identical – mine is ’92 but has the 104 engine which uses the KE-Jetronic injection system (CIS-E/EZL). (2) my problems are slightly milder than yours with a rough (hiccupy) idle being the norm, with an escalation to complete stall/20 min wait only occurring every 6 month or so.

Think I've read all the warm engine misfire/hesitation/stall posts on all the main MBZ forums, and have tried most of the proposed solutions - thus I have new plugs, leads, dizzy cap, crankshaft position sensor, OVP relay, fuel filter and air filter. I've also checked for air leaks, cleaned out the Throttle Body and Idle Control Valve (ICV), tested both the O2 and engine temp sensors and tried injection cleaner fuel additive.

There are more things on the list of people’s suggestions to try such as replacing the: coil, EHA, injectors, ICV, CIS-E, EZL, MAS, etc. but have been holding back mainly due to the expense. The thing that seems particular to me (now hopefully us) is the seemingly intermittent nature of the problem (car can run fine for several weeks) but that 2+ days of non-use consistently exacerbates the problem. My understanding is that these subtleties in our symptoms should let us rule out most of the proposed remedies.

Just recently in a post I received from a UK forum someone pointed me towards the charcoal canister that forms part of the EVAP system which was a completely new area to me. Reading up about this has lead me to look at the switchover valve and purge valve in the system – the interesting thing about them being that they only come into play when the engine warms up, intermittently cause air (fuel vapour) to be added at the intake manifold, and they are controlled by a vacuum (that I presume could dissipate over time – e.g. 2+ days!).

Not sure if I’m putting 2 + 2 together and getting 5, but on reading “trants4md”’s post to you I did start to get excited – not that I’ve a warm-up regulator either, but could I/we be suffering from a minor vacuum leak internal to one of the valves?

Going to have a good look tonight then the car will be left unused for 4 days over Easter. Will keep you posted if I find anything….

Regards,
Neil
Car: '92 300 CE-24 (LHD) cabrio

Thanks for your consolation Neil!

I've been out of town the last few days and haven't been near a computer...

I have two 300e's , one is a 92 and the other is an 89 (both M103). Now that the car has been sitting for a few days I'm going to pull out a bunch of parts from the *working* car, drive around until the problem manifests, and start swapping things. I worked in an auto parts store for a few years back in highschool and saw people spending lots of money parts they didn't need. I just can't get into that rythm with this car, especially since the dist cap is pricey. People would get new batteries, remanufactured starters and alternators and return their cores. We had a bench tester and probably 50% of the cores were in perfect working conditions. Dist caps can last a long time, so can wires and plugs (besides, I just can't see those causing this problem).. I might throw a new rotor in there, and maybe a fuel filter.

I do believe it is a fuel starvation issue, but not positive. I just received a digital mutlimeter (DMM) with an interface to my laptop. I'm going to connect the DMM to the idle control valve, temperature, EHA, and CIS-E diagnostic port and observe/record the various values and see how they change when the problem appears. The next diagnostic I'll be after is fuel pressure, though not sure of the best approach there...

Should take a few days to find the time and get the diagnostics set up.

Robert

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89 300te 222,222
92 300e 190,000

The car sat for several days. I just took it out and experienced the same syndrome - runs good cold, stalls when warm and refuses to run, after 20 minutes of sitting it finally starts and runs rough for a few minutes, then runs perfectly.

When the car stalled I sprayed ether into the throttle body and cranked the engine. This did nothing. I tried various amounts of ether and various amounts of gas pedal. Seemed to make no difference. Wouldn't the engine at least kick a couple times on ether alone?

I connected a timing strobe to the #1 plug wire and cranked the key. The timing light erratically came on, and occasionally blinked as would be expected. I wasn't sure if a timing strobe would illuminate when cranking so I disconnected the #1 plug wire and observed the spark as the engine was cranked. The spark fired regularly and was brite white. Will a timing stobe correctly diagnose a no-spark condition when cranking the engine?

I removed the OVP relay and tried to start the car; did nothing. I also bypassed the OVP with a piece of wire and this still did nothing. I disconnected the ICV and attempted to start the car. This did nothing except activate the "Check Engine" light. I also checked the battery voltage; it was 12.7 volts

When the car finally started I tested the voltage at the ICV and it ranged between 5 and 6 volts. I also checked the voltage at the battery; it was 13.7 volts.

Does this seem like the problem is on the fuel side or the spark side?

*help*

Thanks,
Robert

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89 300te 222,222
92 300e 190,000

I purchased a DMM with duty cycle and connected it to pins 2 and 3 on the X11 connector. The duty cycles were all over the place, but mostly around 97%. What does this mean?

Thanks,
Robert

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89 300te 222,222
92 300e 190,000

Hey Neil,

I had all my tools available and let the car sit for a couple of days, then warmed it up and experienced the full stall effect. There are two small solenoids that activate what looks like valves to vacuum tubes. These are on the passenger fender and click when the engine dies. Not sure if they are related at all to the charcoal canister you mention. I disconnected the wires to these solenoids and found it makes no difference. I have the unfriendly service CD and will try to look up how fuel vapor system works.

Robert

__________________
89 300te 222,222
92 300e 190,000

Hi, I have a 300E and had experienced the same symptoms for the past 3 weeks until last sunday when the car would not start @ all. I towed to the shop where I worked and checked spark, which was good. then I checked the pumps, no power was getting supplied to them. I pulled out the Fuel pump relay shook it and put it back on and the car started. I left it there for a day and then the problem recurred: the car would start and run for a few minutes and it would die. I pulled out the fuel pump relay and jumped the connector holes #7 and #8. The car started right away. I then test drove it with the jump and no problems. Ive ordered a Fuel pump relay and got it today. I will install it tomorrow and let you know what happened.

Mazinger4@yahoo.com

Hi Robert,

Have been away for a few day........ here's the latest:

Thought I was on to something with my switchover/purge valve theory….. Just before Easter I swapped the switchover valve for another one (both had the same part number: 001 540 86 97) as the original appeared to be cracked on top – initially this seemed to make a difference. Went away for 4 days over Easter leaving the Merc behind, returning last Tuesday evening full of enthusiasm, convinced I was finally making progress…… Then:

Car started perfectly Wednesday morning after its holiday and drove for 5 minutes to a shop. Parked it for 5 minutes. On returning and restarting, idle was really rough, revs in ‘P’ fluctuated between 600 and 800, soon as I put it into ‘D’ revs fell to zero and it stalled. Restarted it twice, rev’d it to 1500 to smooth out the idle before putting it in ‘D’, but again both times once in gear the revs dropped to a point where it stalled. From then on, car would crank but refuse to fire….. Waited the customary 20 mins and ‘bingo’ - successfully started it, and while at low revs it was certainly not well, if I put my foot down and got the revs over 1500 it ran perfectly. Drove straight home (5 mins), parked up leaving engine running, idle was still rough with a ‘hiccup’ every 10 secs or so, opened bonnet, removed air filter housing and started to investigate….

1) Could activate the switchover and purge valves as expected (pulled the throttle cable so revs up around 800 and decal switch disengaged) – could hear/feel them pulsating
2) Didn’t seem to be any correlation between activating the purge valve and the idle hiccups – I think thus ruining my thoughts of this being the root cause of my problems
3) Disconnected the ICV wires – idle revs went from 600 to 1000 (I think as expected)
4) Pulled a few vacuum lines, blocked them off (as proposed by “trants4md”), but nothing seem to make a difference

After about 10 mins the idle ‘hiccups’ started to become less frequent until finally the engine idled perfectly smooth. Put air filter back on and took it for a spin - all was fine. Parked it with engine off for 10 mins, restarted and took it for another spin – again perfect. Also since then no problems what-so-ever!

As I mentioned before this stalling/20 min wait is the exception for me with the norm being my hesitant/hiccup’y idle. For me it could be that leaving the car for 2-3 days gives a rough idle while 4+ days leads to stalling.

Car’s going to be left for 5 days again soon so shall see if the same behaviour results. If so at least I’ll know (hopefully!) that the way to avoid the dreaded stall is simply to leave it idling for 20 mins before taking it out for the first time. If that works though it’s still baffling as to what is actually degrading over time (‘n’ days in-activity) to cause the problems to occur, but then can cure itself over time (20+ mins idling).


Robert,

One thing I did read about recently is a ‘Safety Switch’ feature on the fuel pump relay. What I found says: “There are two safety switches, one in the accelerator pedal position sensor and one in the actuator. These two switches, in combination with a switching transistor using circuit 15 to control power to the fuel pumps via the fuel pump relay or Engine System Control Unit (MAS). The purpose of these switches is to shut off power to the fuel pumps (thus stopping the engine) if the throttle setting is higher than idle while the accelerator setting is idle. Thus, if a malfunction occurs where the driver has his foot off the accelerator pedal (thus requesting the engine to idle) but the actuator output shaft is not at idle, the engine shuts off.”

Could it be that our fuel pumps are being shut down deliberately by the FP relay because some kind of malfunction has been correctly/incorrectly detected? Note, I’m presuming that our cars have this feature and that once ‘tripped’, if left for some time (20mins?) everything get reset….. Just a thought.

Let me know of any progress.

Cheers,
Neil

Mazinger4: I don't have a separate fuel pump relay, in my car it is embedded in the MAS. I need to figure out how to run direct power to the pump to see if that's a problem. I think the fuel pumps/pressure are suspect. Thanks for the tip!

Neil: We have the exact same symptoms. I have a fuel pressure guage on order and am going out of town this weekend. The car will sit for a few days. Then I am going to connect the fuel pressure guage with a "T" and test it. I am sure it will stall, I just want to see what the fuel pressure is like when it stalls vs when it is fully warmed up. Last weekend it sat, and I loaded up the tools and let it stall. I sprayed varying amounts of ether (quick-start) into the throttle body and nothing happened. That somewhat tells me that the ignition system could be the culprit.

I also purchased a DMM with duty cycles. At idle, when the car is acting up and when it is running perfectly, the duty cycles are all over the place. Over 2500 RPM they stabilize at around 35%. This tells me that I might have a vacuum leak. I started another thread on hunting down vacuum leaks, and people have contributed some excellent advice there. I pulled up the carpet on the passenger side and checked the volts coming from the O2 sensor. They ranged from .01 to .9 volts. So that seems to be okay.

I checked the ignition with a strobe light and got unusual results. This also tells me that perhaps the EZL is the culprit. The wires, cap, and rotor are all pretty old, but I dislike the idea of throwing a couple hundred dollars on a guess. My car should be somewhat easier to trouble shoot because sometimes the rough idle progresses to a complete "refuse to start" syndrome. When this next happens I am going to connect the six spark leads to a set of six spark plugs that are arranged in firing sequence in a strip of aluminum bar stock that is grounded to the chassis. This way when I am cranking the car over I can verify that the plugs are firing consistently, brightly, and in the correct sequence. I'll post some pics of the rig when I'm done assembling it.

Regarding the switchover valve - thanks for checking that system. We now know that's probably not involved and you've saved me time there!

Regarding the fuel pump safety switches - I remember seeing somewhere that there's a way to interrogate the MAS, I think it is on pin 14 of the X11/4 plug but I'll need to go back to the CD there. I would have thought that this would cause a complete shutdown instead of rough idle/occasional stall, although I have heard of these symptoms caused by bad relays and pumps. I think this, possible vacuum leaks, and the EZL are where I'm going to focus. The fuel pressure guages should tell the story on the complete fuel supply system. I'll know alot more when I get back on Sunday afternoon and do another phase of testing.

Good luck and thanks for the tips! I'll keep things posted.

-Robert

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89 300te 222,222
92 300e 190,000

If you have a MAS, Remove it. Dial knob on top is turned CC to loosen, then you simply pull it up to get it off.

Jumper #1 and #2. You should hear fuel pump turn on. Start car. If it runs continuosly, you have a bad FPR circuit in the MAS. Been there. Good luck.

__________________
'91 300-SEL

Robert,

Sounds like you’re going to be busy.

Have also had the passenger carpet up and checked out the varying signal from the O2 sensor which I too took to mean all was okay there.

Like you my fuel pump relay is within the MAS. Just checked on the 'AllDataDiy' site and it is pin #14 of the X11/4 plug. The only codes that look like they might apply are:

2 – ‘fuel pump relay not functioning’
15 – ‘short circuit detected in fuel pump circuit’

Did check pin #14 on mine straight after the last incident but no codes where found. Also checked #3 (CIS-E) which showed no codes, and #8 (EZL) which did give code 17 (crankshaft position sensor defective (L5) ). Tend to ignore this code 17 though as 6 months ago I had the thing replaced (cost £150+) and it made no difference, also through this forum was subsequently advised that the recurrence of this code is a known problem and not to worry about…..

While at AllDataDiy I was just reading up about the location/workings of the fuel pump when I came across a MBZ Technical Service Bulletin entitled “Engine hesitates, cuts-out or is difficult to start at times” (#N7, AF07.32-U-3701A, issued on 05/05/97). This is the link:

http://www.alldatadiy.com/alldata/AFI~V4623745~C10264~R0~OD~N/0/34870055/56621118/56621127/56621128/34853741/34857029/34858641/34859192/34859264/82240627

but you probably need a login to really see what it says. Amongst other things this bulletin does mention are:

o All gasoline engines with rpm controlled fuel pump relay – The engine rpm signal (circuit TD) to the fuel pump relay may be short-circuited to ground or otherwise disturbed by one of the following components which utilise this signal: A/C compressor unit; Fuel pump replay; CIS-E control unit; Idle speed control unit; Tachometer.

o Further possible causes (CIS-E related): Loose ground terminal screw at intake manifold; Loose connectors for CIS-E wiring harness; Loose connectors (ground) in trunk for fuel pump; Loose connection at plug (X36) of fuel pump wiring harness.

Should get some time towards the end of this week to look at some of these things. As always, keep the correspondence coming.

Best regards,
Neil