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Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 20385
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Misfire onMercedes 230 slk compressor over 4000rpm

Customer Question

misfire on
Mercedes 230 slk compressor over 4000rpm
Submitted: 9 months ago.
Category: Mercedes
Expert:  Shantal-Mod replied 9 months ago.
I'm Shantal and I'm a moderator for this topic.
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Expert:  Matt replied 9 months ago.
You can also try spraying some water on the coil pack/s with the engine running. It is possible the coil is faulty and causing the misfire. If you see sparks arcing with the water, then replace the coil.
I'd check the condition of the injector plugs / connections as this could be a lean misfire if an injector isn't firing properly - the best way to check this is with a 'noid' light
Then check all the connections to the engine sensors one at a time, remove each one and examine for signs of corrosion or damage and a squirt of contact cleaner ( not WD40) will also help.
This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and leans the engine out causing rough running.
Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.
The best way to locate a leak is to have the engine running and warm and then spray lighter gas around each joint in turn. If the engine rev's up you've found your leak.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.
It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine
Expert:  Matt replied 9 months ago.
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