Minor Performance Issues M104
 

1997 E320, 165,000 miles. This car is new to me. I've noticed a couple very minor issues and have done a search - nothing seems to match up. So here goes.

First of all, acceleration doesn't seem linear when flooring the gas. I don't know what other way to describe it. When accelerating lightly or moderately, everything seems fine. But when flooring the gas, such as when passing or entering an on-ramp, it seems like the rise in engine RPMs just isn't very smooth, almost like it's choking very slightly. And I can never get it quite to redline like with my M103; this one just seems to struggle to get way up there. Air and fuel filters are recent, so I don't suspect them.

The car starts every time, but not always easily. When cold, it starts up almost instantaneously. However, when it's hot, it can take 2 or 3 long (5 seconds or more) cranks to get it going. And I think I can smell gas when this is occuring. Could it be a temp sensor? The Check Engine light is not illuminated, and it runs fine once started, so I'm a bit confused.

Overall it runs great, but I know this isn't how it's supposed to be. And I'm hoping the two issues are related. I'm new to the M104 and have not yet learned all the ins and outs.

The acceleration thing sounds normal for an M104. The engine has variable timing on the intake camshaft and also resonance flaps inside the intake manifold. As these gadgets are adjusted while accelerating the changes in torque produced can be felt as fits & starts in the acceleration rate. I certainly notice this in my M104 engined 124 car, and also recall mention of it in some auto magazine reviews from back when.

Long crank is a tougher diagnosis over the internet. One common service item on the M104 is the fuel pressure regulator. Quick & dirty test is to pull the vacuum line from it and check for presence of gasoline and/or strong odor of fuel.

- JimY

Thanks for the info - I'll do a search on the regulator.

As for the acceleration - what you describe seems to fit my description pretty accurately. All I can say is YUCK! Heavy acceleration is not very smooth at all, nothing like my M103. I had no idea there would be such a night-and-day difference between the two engines. My M103 will sing all the way to redline, whereas the M104 sounds like a blender under the hood and won't hang out in the upper RPMs for very long. And this is improvement?

Well, it does have 50HP more than the M103...

Yes, I knew in advance there was 50 more HP, and I eagerly anticipated it. I guess I just wish there was a smooth-revving M103 out there with the extra 50 horses. Maybe I should keep the 300E and do a turbo kit?

The more I compare the two cars, I am beginning to wonder if the W210 shouldn't be the one to get sold...

Not so with my '97 E320...
 

it will willingly go to the red line smoothl yat any time. Particularly likes to do it on this one little curvy hill leading from a four-way stop I traverse frequently. Great sound effects too! I'd say the car's fuel-air mixture may not be regulated properly. Maybe the mass air sensor is suspect? My car has 102K miles on it.

No, I don't think any of those are suspect. There are no codes of any sort and the vehicle recently passed inspection with flying colors. The differences I am observing are in comparison to an M103. Jcyuhn pretty much described it aptly - the irregularity is very subtle, but for someone who has driven thousands of miles in an M103 it is very apparent to me.

Have you driven an M103 over the same course? What basis of comparison are you using?

Have not driven M103....
 

but the only thing I have ever had that would wind up like the E320 was a 1993 Ford SHO.

Puegot 605 Turbo Diesel
 

until it grenaded, it would wind up and sound like a
P-51 right up until the moment of failure..then it sounded like a wood chipper trying to eat a steel ingot.

I had a 1989 Taurus SHO. Really interesting, unique, and fun car. Only available with a standard transmission until 1993. Kept it as my daily driver until 1998.

- JimY

Sorry, I would have to disagree with the post on non-linear acceleration being the norm on an M104. If you are getting a slight "choke" or "miss" under hard acceleration, there is a problem somewhere.

Trouble is, there are so many systems to diagnose, and a combination of issues can also contribute. Old vacuum hoses, a cracked intake, wiring harness, plug wires, fuel distributor...the list goes on. It's too expensive to parts swap at this juncture either.

My W124 suffered from some of what you experienced, and it took a top-end rebuild (it was head gasket time anyway) to cure it. I experience none of that anymore when I tromp on the gas pedal!

My M104 was as smooth as glass accelerating up to the redline.

Something doesn't sound right.

I replaced my MAF and the M104 now appears to be working properly. No flat spot or hesitation anymore! However, I should add that it is still a bit notchy and less linear in acceleration vs. the M103. In particular around 3000 RPM it appears there is a marked burst of power. Sort of reminds me of very mild turbolag. I still think the M103 is smoother, but let's face it - time to move on. At least with this M104 working properly now it is much more enjoyable!

I experience similar behavior in my 94 E320. Just dropped in new plugs and it still has a 'non-linear' feel. How much was the MAF and did you pop it in yourself? The m104 definetly starts putting out the power around 3400 rpm- from there it rockets to the redline.

That is the point where your variable length intake runners/valve timing kicks over to the higher RPM setting.

Exactly....my W124 E320 had a slight bump when this happened, sort of like a turbo kicking in.

The M104 in my friends S320 is smooth as butter to redline.

Your plugs are probably dirty or something.

On a 104 HFM/SFI , if you DON'T feel the Runners change length and the cam advance , THEN there is something WRONG..this is a Performance power-plant, and when Engine Management calls for the power/load intake runner matching and cam valve advance mapping , it is a noticable change ...don't compare the power/torque range habits of a 104 to a 103 .... 104 HFM/SFI is a full electronic, distributorless, high performance engine and has nothing in common with a 103 engine.
They are light years apart.

Thanks Arthur, I feel much better. Like I said, it is smooth as glass now. It just seems to have a performance notch around 3000 RPM where a sort of turbo boost kicks in. After researching more of the technical aspects of the M104, this now makes sense. However, though primitive in comparison, I still love the M103. You are correct, though - they are light years apart.

gmercoleza-

Is this the part you are referring to as the MAF? AKA mass air meter? Thanks, J

Yes, that's it. Technically, I believe it is actually an Air Mass Meter, or AMM. I should also report that, after installing a new AMM and fuel pressure regulator, the car runs wonderfully smooth, all the way up to redline. It still has that turbo boost effect at 3500 RPM, but I understand now this is normal, and it has grown on me.

Did the MAF fix your starting problem? My ' 94 E320 had the same kind of problem, only without the hesitation under acceleration. My car had 206K miles and would still pull right up to redline very smoothly. It was a blast to drive. Now I'm driving a ' 99 S420 which I love, but sort of miss the E.

I have no starting issues whatsoever, just the slight feeling of hesitation. I haven't gotten around to changing the air mass meter yet, but I feel like it is getting worse so it will be time soon. Just have to cough up the couple hundred bucks for the part..