W140 Intermittent starting issues

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STAO305
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W140 Intermittent starting issues

Post by STAO305 » Tue 12 Feb, 2013 8:40 pm

I have a pretty good idea of what this issue may be but i thought i would put it to the forum for advice before i start replacing things. My 92 400SEL recently has developed an intermittent starting issue. It tends to backfire slightly when trying to kick over, and if it is left for a couple of hours it will generally start and run fine before stalling and failing to start again. I replaced the fuel filter and the car ran fine but the next day has failed to start again. I am starting to think the fuel pump may be the issue but was thinking the fuel pump relay should be replaced first beforehand, where abouts is the relay located? Any advice would be great
~1992 W140 400SEL white 270,000km
~1986 Mercedes O305 MK4 Ex STA (NSW) Citybus 416,000km (showing lol)
~1978 300D beige 592,000km

http://www.hcva.org.au - Committed to Commercial Vehicle Preservation & Restoration since 1964

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STAO305
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Re: W140 Intermittent starting issues

Post by STAO305 » Fri 03 May, 2013 7:34 pm

Hi everyone, this problem appears to have developed into a runs fine until operating temperature (80C), coughs splutters & stalls. I have replaced the older fuel pump of the two, fuel pump relay, fuel filter and am starting to think it could be a sensor. If anyone has any pointers as to the cause of these symptoms that would be appreciated :)
~1992 W140 400SEL white 270,000km
~1986 Mercedes O305 MK4 Ex STA (NSW) Citybus 416,000km (showing lol)
~1978 300D beige 592,000km

http://www.hcva.org.au - Committed to Commercial Vehicle Preservation & Restoration since 1964

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Ivanerrol
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Re: W140 Intermittent starting issues

Post by Ivanerrol » Fri 03 May, 2013 9:04 pm

Does the ASR light come up occasionally?

Does it go away if you reset the ECU?

Hope your throttle body control unit hasn't started to go faulty...... :whistle:

You may need the car to be put onto a code reader to sort this out.
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My Mercedes Benz
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Re: W140 Intermittent starting issues

Post by My Mercedes Benz » Wed 29 May, 2013 9:52 pm

Hi there,

I also have a 92 400 SEL.

I seem to be having the same issue, and now when the car has warmed up it stutters and misses and doesnt seem to have power.

I have had a new wiring loom installed, fuel pump, radiator and they are still telling me I shouldnt be driving it, have you got your fixed and if so have you got any ideas as to how to get it going?

Hope you can help, thanks heaps.

KimB
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Re: W140 Intermittent starting issues

Post by KimB » Thu 30 May, 2013 9:54 am

My Mercedes Benz wrote:Hi there,

I also have a 92 400 SEL.

I seem to be having the same issue, and now when the car has warmed up it stutters and misses and doesnt seem to have power.

I have had a new wiring loom installed, fuel pump, radiator and they are still telling me I shouldnt be driving it, have you got your fixed and if so have you got any ideas as to how to get it going?

Hope you can help, thanks heaps.
Dizzy cap?
W126 86 300SE Champagne
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My Mercedes Benz
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Re: W140 Intermittent starting issues

Post by My Mercedes Benz » Fri 31 May, 2013 6:44 am

Thanks for that, Ill get it looked at, is it a big job?

Will it stuff the car if I drive it in the mean time?

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STAO305
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Re: W140 Intermittent starting issues

Post by STAO305 » Wed 14 Aug, 2013 11:40 am

KimB you were right on the money, both of my dissy caps were cracked & warped, when the car reached operating temperature it would make the casing expand and the crack get bigger causing the misfiring and stalling. I ordered parts online (Bosch) two new rotor buttons & two new dissy caps incl freight were $260AUD from rockauto.com. It is relatively simple to install them yourself with an allen key set
~1992 W140 400SEL white 270,000km
~1986 Mercedes O305 MK4 Ex STA (NSW) Citybus 416,000km (showing lol)
~1978 300D beige 592,000km

http://www.hcva.org.au - Committed to Commercial Vehicle Preservation & Restoration since 1964

KimB
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Re: W140 Intermittent starting issues

Post by KimB » Wed 14 Aug, 2013 12:34 pm

STAO305 wrote:KimB you were right on the money, both of my dissy caps were cracked & warped, when the car reached operating temperature it would make the casing expand and the crack get bigger causing the misfiring and stalling. I ordered parts online (Bosch) two new rotor buttons & two new dissy caps incl freight were $260AUD from rockauto.com. It is relatively simple to install them yourself with an allen key set
Great news!
W126 86 300SE Champagne
W126 84 380SEC Signal Red

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STAO305
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Re: W140 Intermittent starting issues

Post by STAO305 » Fri 01 Nov, 2013 6:55 pm

Hmmm seems I have came to the end of the road with this issue - after replacing both distributors & rotor buttons the car worked fine for a couple of months before it randomly developed a constant misfire. I subsequently replaced the leads & both coils to which It was reduced to a slight bump at idle. This lasted about 70km before the car stalled and refuses to start again. The coils have power but do not appear to be providing spark, it would appear this was the underlying issue all along. Before the car stalled the ASR light appeared. Any hints as to what this may be would be appreciated before I get it towed to a code scanner next week :P
~1992 W140 400SEL white 270,000km
~1986 Mercedes O305 MK4 Ex STA (NSW) Citybus 416,000km (showing lol)
~1978 300D beige 592,000km

http://www.hcva.org.au - Committed to Commercial Vehicle Preservation & Restoration since 1964

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Ivanerrol
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Re: W140 Intermittent starting issues

Post by Ivanerrol » Fri 15 Nov, 2013 8:11 am

The dreaded bio-degradable wiring issue.

Short circuits in the harness can cause the ECU/Ignition module to fail and cause exactly your prognosis.

Carefully check the harness for signs of insulation breakdown and short circuiting.
W211 - E240
W204 - C280
Departed
W202 - C200, C180, C180
W126 - 380SE , 380SE (Ex SA Import), 560SEL
W124 - 300e, 260e (ex Japan)
W111 220s (Indonesia) 4 speed manual column shift
W123 230
W116 450SEL
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W210 E240, E240
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Greg in Oz
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Re: W140 Intermittent starting issues

Post by Greg in Oz » Fri 15 Nov, 2013 9:34 pm

Being a '92 model I was wondering if there was a remote possibility it may have been built before the biodegradable wiring harness era. Maybe not?
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STAO305
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Re: W140 Intermittent starting issues

Post by STAO305 » Thu 28 Nov, 2013 3:34 pm

Thanks for your responses, yeah I was fearing it may be the wiring harness :( It has a build date of Dec 91 so it is a really early 400SEL. It is still at the repairers so I will keep everyone updated on what the ultimate solution was.
~1992 W140 400SEL white 270,000km
~1986 Mercedes O305 MK4 Ex STA (NSW) Citybus 416,000km (showing lol)
~1978 300D beige 592,000km

http://www.hcva.org.au - Committed to Commercial Vehicle Preservation & Restoration since 1964

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Ivanerrol
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Re: W140 Intermittent starting issues

Post by Ivanerrol » Thu 28 Nov, 2013 11:43 pm

Greg in Oz wrote:Being a '92 model I was wondering if there was a remote possibility it may have been built before the biodegradable wiring harness era. Maybe not?
All early W140's got the bio degradable wiring.
W211 - E240
W204 - C280
Departed
W202 - C200, C180, C180
W126 - 380SE , 380SE (Ex SA Import), 560SEL
W124 - 300e, 260e (ex Japan)
W111 220s (Indonesia) 4 speed manual column shift
W123 230
W116 450SEL
W140 420SEL
W210 E240, E240
W209 CLK 240
W201 190e 2.6 (ex U.K.)

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STAO305
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Re: W140 Intermittent starting issues

Post by STAO305 » Tue 14 Jan, 2014 2:03 am

Wiring harness.jpg
Well after some time trying to diagnose issues with the car it seems my harness had turned to dust. Now replaced at great expense with a new one (I did not want to bother trying to get one rebuilt) the car runs like a dream. But as with all 140s you put one spot fire out and another appears lol. Now when give the car a bit of hard acceleration the throttle alternates a few times before eventually bogging down and stalling the car. Restarting the car and driving normally solves the issue - I take it this is probably the throttle position sensor?
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~1992 W140 400SEL white 270,000km
~1986 Mercedes O305 MK4 Ex STA (NSW) Citybus 416,000km (showing lol)
~1978 300D beige 592,000km

http://www.hcva.org.au - Committed to Commercial Vehicle Preservation & Restoration since 1964

User avatar
Ivanerrol
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Re: W140 Intermittent starting issues

Post by Ivanerrol » Tue 14 Jan, 2014 12:23 pm

Throttle body controller also suffers from the dreaded wiring issue.
T.P.S. also can be suspect.
You nay need to get someone with a code reader to check the issue.

Another issue that causes these problems is the brake switch.
Dirty ABS sensors.
W211 - E240
W204 - C280
Departed
W202 - C200, C180, C180
W126 - 380SE , 380SE (Ex SA Import), 560SEL
W124 - 300e, 260e (ex Japan)
W111 220s (Indonesia) 4 speed manual column shift
W123 230
W116 450SEL
W140 420SEL
W210 E240, E240
W209 CLK 240
W201 190e 2.6 (ex U.K.)

marks
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Re: W140 Intermittent starting issues

Post by marks » Mon 19 Jan, 2015 12:36 am

Apologies for re-opening an old thread.
Did the TPS get changed? Was that the issue?

In the recent Qld heat, I'm seeing a miss developing at low rpms which goes away above 3000 rpm. It is a 93 500SEC

Had to get it towed to the mechanic the other weekend. Nothing showed up on the scan as fault or fault log.
He did replace the crankshaft sensor. The wiring was corroded and oxidised near the sensor and the car seemed to running better than ever after it was changed.

But another hot day and another repeat performance. The car starts to miss at low revs and wants to stall. Mid to high revs was fine. Kept it in a low gear to keep the revs high and get home.

The coils, leads & Dizzy caps where fine when it was inspected. New spark plugs during the recent service. The engine harness has been replaced a few years ago (not sure if it was the top or bottom one) and the MAF sensor about 12mths ago.

The ASR light doesn't come on if it happens.

Is this a symptom of a faulty TPS?
Is there a test I can do, to check when it occurs again? As it is intermittent, it doesn't always show.

Cheers.
1993 500SEC

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