What Factors Affect Relationship Between Accelerator Depression and Acceleration? - PeachParts Mercedes-Benz Forum

shertex · #1 04-22-2011, 08:03 AM

Two essentially identical cars: 91 300D and 92 300D. Downside is that I notice small differences. The 92 seems to have a quicker response to the depression of the accelerator. With the 91, it seems that I have to depress the accelerator further for the boost to kick in (but not so far that the kickdown solenoid is activated....KS on both cars work fine). But, as long as the accelerator is sufficiently depressed, the acceleration is just fine. It just somehow FEELS less responsive because I have to push more.

So I'm curious: what governs the relationship between how far the pedal is pushed and quickly the car moves? Is there something that can be adjusted, or do I just chalk this up to idiosyncratic differences between the cars?

If it matters....the 91 has three pressure converters, the 92 has two (the updated design); I have replaced the pressure converters on the 92.

Thanks.

woodboat3 · #2 04-22-2011, 09:19 AM

There are all sorts of things that can be different but I want to point out one that plagued me for weeks before I figured it out. I had a small crack in the stainless expansion collar on the two piece manifold. It was bleeding energy before the turbo making the car sluggish

scottmcphee · #3 04-22-2011, 09:35 AM

Car to car variance is what gives them personalities. Drive the "slow" car when you're feeling relaxed. And drive the "fast" car when you want to get there in a hurry. You're lucky to have different vehicles for your various needs, in same superb Mercedes body type.

shertex · #4 04-22-2011, 09:39 AM

Quote:

Originally Posted by scottmcphee

Car to car variance is what gives them personalities. Drive the "slow" car when you're feeling relaxed. And drive the "fast" car when you want to get there in a hurry. You're lucky to have different vehicles for your various needs, in same superb Mercedes body type.

That's a great perspective for me to adopt! I guess my tendency is to get curious about inconsequential things when I'm between repairs....if only these periods of idle curiosity could last longer....

pj67coll · #5 04-22-2011, 10:18 AM

Does the 124 have the engine bay "firewall thingy" like the 123? That might be a factor.

- Peter.

scottmcphee · #6 04-22-2011, 10:30 AM

Quote:

Originally Posted by pj67coll

Does the 124 have the engine bay "firewall thingy" like the 123? That might be a factor.

- Peter.

yes, both cars are fitted with a firewall, thankfully

(and fuel pedal linkage passes through each)

shertex · #7 04-22-2011, 10:43 AM

FWIW I oberved the movement of the throttle cable while depressing the accelerator on both cars; seems to be exactly the same.

vstech · #8 04-22-2011, 10:18 AM

Quote:

Originally Posted by shertex

Two essentially identical cars: 91 300D and 92 300D. Downside is that I notice small differences. The 92 seems to have a quicker response to the depression of the accelerator. With the 91, it seems that I have to depress the accelerator further for the boost to kick in (but not so far that the kickdown solenoid is activated....KS on both cars work fine). But, as long as the accelerator is sufficiently depressed, the acceleration is just fine. It just somehow FEELS less responsive because I have to push more.

So I'm curious: what governs the relationship between how far the pedal is pushed and quickly the car moves? Is there something that can be adjusted, or do I just chalk this up to idiosyncratic differences between the cars?

If it matters....the 91 has three pressure converters, the 92 has two (the updated design); I have replaced the pressure converters on the 92.

Thanks.

"response to the accelerator" is related to two different conditions. first is the linkage, if it's worn/rusty (most linkage is plastic on the 124...) or the bushings are damaged, it will take more pedal pushing before the linkage actually moves the accelerator rod on the IP to give it fuel.
second, the IP itself has an aneroid for controlling the amount of fuel before boost kicks in, if it's out of adjustment, it'll affect the acceleration of the car.

babymog · #9 04-22-2011, 11:18 PM

ALDA. Every 60x enigine I've had needed an ALDA adjust, it's in the FSM for weak acceleration below 2500rpm as a fix, is fairly simple and yields excellent results.

Problem is, once you adjust the ALDA in the weaker car, you'll need to do it on the other car.

Skid Row Joe · #10 04-23-2011, 12:09 AM

Just looking at the 'brass?' linkage on my '83 300SD, did something primal to me.

What a magnificent set of mechanical artistry to admire.

shertex · #11 04-23-2011, 01:11 PM

Quote:

Originally Posted by babymog

ALDA. Every 60x enigine I've had needed an ALDA adjust, it's in the FSM for weak acceleration below 2500rpm as a fix, is fairly simple and yields excellent results.

Problem is, once you adjust the ALDA in the weaker car, you'll need to do it on the other car.

What section of the FSM?

woodboat3 · #12 04-23-2011, 12:33 AM

Is the slow car slow through the entire rpm band? My car was dead, badly, right in the middle of the power band like 2000-3500 RPM. If the slow car is dead all the way through matters. Below 2000, from what I have read, the ALDA will help. My crack was nearly invisible, and made no noise per say. Only way I found it was I noticed soot and investigated. Now the car feels like a gasser and pulls hills without downshifting.

scottmcphee · #13 04-23-2011, 09:39 AM

Quote:

Originally Posted by woodboat3

Is the slow car slow through the entire rpm band? My car was dead, badly, right in the middle of the power band like 2000-3500 RPM. If the slow car is dead all the way through matters. Below 2000, from what I have read, the ALDA will help. My crack was nearly invisible, and made no noise per say. Only way I found it was I noticed soot and investigated. Now the car feels like a gasser and pulls hills without downshifting.

crack in what was barely visible?

shertex · #14 04-23-2011, 09:43 AM

Quote:

Originally Posted by woodboat3

Is the slow car slow through the entire rpm band? My car was dead, badly, right in the middle of the power band like 2000-3500 RPM. If the slow car is dead all the way through matters. Below 2000, from what I have read, the ALDA will help. My crack was nearly invisible, and made no noise per say. Only way I found it was I noticed soot and investigated. Now the car feels like a gasser and pulls hills without downshifting.

My sluggishness is not at its most noticeable from a dead stop. It's most obvious when I'm traveling at highway speeds and then accelerate. Again, I ultimately have no difficulty accelerating....it's just that the pedal has to be depressed further for the acceleration to kick in. As compared to my 92, this is what creates the impression of a lack of responsiveness.