W202 C200 (m111) exhibiting hesitation under load

[Rudy7831]

Hello, my dependable W202 2.0 petrol vehicle has begun to exhibit hesitation while under load.

I presume the issue pertains to the plugs, coil(s), or injector(s)?


I will begin by replacing the spark plugs, since I neglected to remember they had been in place for almost 50,000 miles.

It is likely that diagnostics should be addressed by a local individual in Surrey with STAR expertise.

As the vehicle is 25 years old, I am eager to do the repairs myself.

[MidnightMarauder]

Is there a PMS unit located under the washer bottle reservoir?

[Rudy7831]

I briefly examined it: no, it does not.

[SD1too]

I often use the strategy of prioritizing the least expensive tasks, therefore beginning with the plugs is a prudent choice.

I am also inquiring about the potential for fuel starvation—when was the fuel line filter last replaced? If partly obstructed, this may limit gasoline flow at peak demand, therefore producing the symptoms you describe. There exists a strainer in the tank and an inline filter near the fuel pump(s). Some vehicles are equipped with a single fuel pump, while others have two; a malfunctioning pump might also be a contributing factor.


Replacing plugs is straightforward; using a set of ramps facilitates the process. Additionally, it is rather simple to deplete your fuel tank to a minimal level before replacing the gasoline filters independently, following the drainage of sediment from the tank by detaching one of the pipes and collecting the residue in an appropriate container.

I would like to do these actions prior to investing in more costly items; neither plugs nor filters can cause any harm. Fuel pumps are rather pricier, although on a 25-year-old vehicle, they may be nearing the end of their efficacy, thus warranting consideration.

[Rudy7831]

Thank you; I performed the filters when the tank was removed for welding around six years ago.

I suspected fuel starvation, since after a significant pause, it seemed to operate on three cylinders until I pulled over and restarted the engine. During that period, my Arduino MPG gauge, which receives input from the VSS and a single injector, ceased displaying fuel data, as if the injector was inactive.

[SD1too]

There may still be a gasoline supply issue, perhaps due to a clog in the fuel line, a malfunctioning pump, or an obstruction in the fuel distributor.

One method involves detaching the fuel line beneath the hood from the fuel distributor and directing it into an appropriate receptacle. Subsequently, request an assistant to briefly activate the ignition; a robust surge of fuel should be observed. While specifications for flow rate may exist, a discernible, vigorous discharge of fuel indicates that issues at the rear can likely be ruled out. Given that you have removed the tank and replaced the filters, you can likely exclude these components, leaving the fuel pump or the fuel pump relay as potential issues.


While there may not necessarily be a fuel issue, refrain from examining the injectors, which may cost around £400 apiece, until you have confirmed a reliable fuel supply to the engine. A new fuel pump, costing a few hundred dollars, is a more economical choice than replacing four injectors.

Search for postings by a user named Optimusprime, who has just replaced gasoline pumps on his W124 due to fueling problems.

[SD1too]

https://www.ebay.co.uk/sch/i.html?_nkw=fuel pumps&campid=5338181132&customid=2518X1570512X129eed78a7da8db844f92fac7c1d89ba&mkcid=1&mkrid=710-53481-19255-0&subId2=15&toolid=10001

[Rudy7831]

Thank you; I will examine those options.

I must clarify that I was likely not very explicit in the original post (which I am unable to amend) when I said "hesitating under load."


The vehicle exhibits hesitation or stalling when I accelerate significantly in a high gear at low RPM, almost causing the engine to stop.

[Doncaster34]

It seems to be a malfunctioning M.A.F, since I had a similar issue with my M111, which I used and maintained for twelve years.

[Doncaster34]

😊😇😊