C124 E320 Flat Spot???

[mercboiuk]

Recently my 124 series E320 Coupe has developed an intermittent flat spot in all gears between 4,000 and 6,000 rpm.

I keep my foot planted, but when in that rev range, the engine feels as though it struggles, and it feels as though there's power/torque loss.

Unfortunately, that's the best way I can descibe it, and hopefully it'll sound familiar to the MBClub techy-bods out there

Any pointers as to what this could be would be greatly appreciated.

Thanks,

Darren

 

[jaymanek]

have you had the loom replaced yet?

 

[grober]

variable inlet length resonance not working properly due to flaps not working? Final change over point is a 3,800 rpm

 

[talbir]

I had a very similar problem on my silver 500e about two months ago....when reaching the upper rev band, there was a noticeable struggle and power loss.....started losing drag races to all kinds of crap cars !

After much searching in the engine bay, the problem lay underneath the car....the cats ! I could hear a slight rattle from them when lifting off after revving at a standstill. When i had them taken off, they were broken inside into hundreds of bits....they are designed to flow air through thousands of minute holes....when they break up, they block the flow causing huge backpressure on the engine.

Put straight pipes in as a temporary check and voila, full power and rev needle sweeping upto the limiting point ! Back racing 911's again !

Since then i give the exhausts on my cars alot more attention.

The blocked cats and the resultant back pressues also caused hot running...consistently running at 100degC+...on removal running temps went down spot on to the 90deg C. Some suggest that 500e's run hot, but it's a myth in my experience, both mine run at 90degC regardless of ambient temps.

Other things could be the MAF sensor, as well as bad dizzy cap/plugs, ignition coil breaking up and faulty EZL.

Bu i'd check the cat first if you have one, i suspect so since the e320 were mainly post 91 cars ?

 

[kth286]

mercboiuk

You are missing that kick you get on the 320 at around 4k ish when the variable inlet valve timing mechanism triggers.

You have felt that I guess - like a turbo kicking in - please confirm.

So, I would be investigating that cam solenoid under the front engine cover.

There is no dizzy on the 320 so do not look for that.

 

[mercboiuk]

have you had the loom replaced yet?

Yup that was replaced (about a year IIRC )

Darren

 

[mercboiuk]

Thanks for that Talbir. The way you've described it, is pretty much spot on to what I've been experiencing

My MAF sensor has also been replaced within the last couple of months.
My cat did come into question with this year's MOT because my emissions were way out. The emissions were corrected with a new lambda sensor and O2 sensor, I think. I'll have to double check.

Yes, the 3.2 24v straight six wasn't included in the '124 series line up until 1993, just before the facelift.

Exuse my technical ignorance, but what's an EZL?

Thanks,

Darren

 

[mercboiuk]

mercboiuk

You are missing that kick you get on the 320 at around 4k ish when the variable inlet valve timing mechanism triggers.

You have felt that I guess - like a turbo kicking in - please confirm.

So, I would be investigating that cam solenoid under the front engine cover.

There is no dizzy on the 320 so do not look for that.

That second burst of power has already kicked in when I experience my problem.
And yup, it was one of the first things I noticed when I bought the car

I was informed by my garage about the dizzy cap, when I asked them to check it as a source of another problem a couple of years ago

Cam solenoid, you say?
I'll certainly be forwarding all this potential items to my mechanic, so thank you very much, guys

Thanks again,

Darren

 

[grober]

Excuse my technical ignorance, but what's an EZL?

Thanks,

Darren

Its the small wing mounted unit which controls the ignition, separate from the engine ECU which controls fuelling. Later distributor-less systems integrated the 2 functions into one main ECU.

 

[Dieselman]

Once you reach the problem revs what happens, does it get better again, worse or just stays a bit flat?

 

[mercboiuk]

Once you reach the problem revs what happens, does it get better again, worse or just stays a bit flat?

Through the problem rev range there's (best I can describe what feels like) power loss, then the power kicks in and off again in quick succession. This is repeated until 6,000rpm.
It'll change gear and be fine until the problem rev range, when it happens again.
But this problem is intermittent.
The car's been absolutely fine in the 150 miles I've done today. Yet yesterday the problem was evident at times.

Sorry, that's the best I can describe

Darren

 

[Dieselman]

Possible fuel pressure issue maybe.