Low RPM Issues: Causes and Solutions

Since I shifted to a higher gear, not only has my driving style changed, but also the engine speed has changed dramatically. I now only need a little more than 2,000 RPM, and my tachometer rarely shows more than 3,000 RPM, while the speedometer next to it displays a healthy 180 km/h.

"In normal traffic flow, I average around 1,600 RPM. I initially assumed that, in addition to the car's characteristics, the fuel consumption would also adapt to the conditions. Unfortunately, things didn't quite go as planned. At first, I saw a savings of about 10 to 15%. However, it seems that some kind of residue is building up inside the engine, which leads to increased fuel consumption after a few tankfuls, rather than less. Only after I can use a stretch of open highway does my fuel consumption return to normal. However, those types of roads are not very common in my area."

The difference is approximately one liter.

What's the reason for that? What can I do about it, besides not using my sixth gear?

I'm experiencing a bit of the same thing, even though I try to drive it as hard as possible on my daily 20km commute. When I occasionally drive the longer 600km route near my home, I feel like the fuel consumption improves. Don't you think it might be related to the AGR (selective catalytic reduction) system or the catalytic converter?

You might be able to disable the EGR valve (if it hasn't been already). I don't know your specific engine code, but it should still work with that, right? However, with the lower engine speeds, it should actually be activated less often than before...

Okay, then there's the catalytic converter. It might eventually become clogged, perhaps by running it with a higher air excess/earlier pressure buildup (if it's programmable within the data set and if it's possible from a hardware perspective). If that's not possible, then remove the catalytic converter. However, I would feel guilty about that and would rather just refuel more often. Maybe just to test if it's really the cause.

My AGR (Abgasrückführung) is not working, nor is the catalytic converter, which was flooded with oil after the engine failure last summer .

By the way, I've already observed something similar with the automatic transmission. In both cases, the fuel consumption decreased after a highway drive.

I can't drive any faster on these country roads. 2,000 RPM is already 120 km/h, which is already a bit too much for roads with speed limits.

My engine: AHF with VP 37 and 110 hp, chipped for a little more...

Soot in the exhaust system/turbocharger, perhaps. Otherwise, I'm out of ideas. Could you temporarily increase the air excess slightly to see if it helps?

Otherwise, here's something completely speculative. Increased strain on the battery due to short distances. Maybe connect a charger overnight. But it could also be complete nonsense .

Herr Antje wrote:

Otherwise, here's something completely speculative. Higher strain on the Lima due to short distances...

Short distances or low RPMs?
I would rule out the latter, as the efficiency of a lithium-ion battery, as far as I know, is not (strongly) dependent on its speed of rotation.
-> With a constant load on the LIMa (linear induction motor), the driving torque will likely only increase to the point where the power consumption remains approximately constant as the rotational speed decreases.

At low speeds, the alternator fan scoops up less air, which actually results in slightly less engine power consumption.

Herr Antje wrote:

Could you temporarily increase the air excess a little bit?

I don't like that, because I already have a higher boost pressure due to the chip.

Herr Antje wrote:

Increased strain on the Lima due to short distances.

It's also not suitable because my typical routes are at least 25 miles long, and often much longer.

Soot in the exhaust? It's possible, but what should I do about it? I don't have excessive soot buildup, and it's only visible under full load, when I'm being overtaken.

Hello,
The engine will likely continue to produce low torque at low RPMs because the turbocharger is not engaged.
And if you want to accelerate in this area, you inevitably have to use a richer fuel mixture so that the engine can even reach a higher RPM.
You only see it under full load because the exhaust pressure isn't high enough to push it out of the exhaust pipe otherwise. Therefore, it accumulates in the exhaust pipe under low load conditions.

I'm reducing the throttle using the intermediate gas. In these areas, I'm even achieving a Lambda value less than 1 (!). Now the question is, how often does the software also enter this range, especially when driving at lower RPMs where full boost is rarely available?


I had the same experience in a previous job.
I often drive my Seat at lower RPMs to achieve a fuel consumption of less than 5 liters per 100 kilometers.
If I drive for too long at a very slow speed, the responsiveness also diminishes.
The turbocharger builds up boost pressure more slowly, and there is hardly any overshoot.
The fuel consumption is also slightly higher.

I believe that, contrary to popular opinion, even older software versions have a form of adaptation of the driving profile. When driving over longer distances with relatively constant loads, the engine control becomes less aggressive. However, this adaptation cannot be stored in the MSG and is recalculated each time the system is restarted.

Best regards, Jochen.

@ulf
Yes, short distances, not low RPM. Unfortunately, it's still failing.

@Uwe
I mean the LD (likely referring to a specific measurement or value) at low RPM and partial load, that's where your problem lies. Not the maximum LD at full load. But it could also be complete nonsense. I still think the "Russproblem" (likely a specific issue) is relevant. The exhaust is clearing/blowing itself at higher RPM. What about driving at higher RPM until the desired speed is reached, and then driving at a lower RPM (as suggested by Jochen)? Maybe you'll have less than 1 liter more fuel consumption. But I'm worried that only letting it "blow" on the highway or using a lower gear would be beneficial .

@Jochen
Even if the control unit reacts differently depending on the driving style, a slower regulation should not increase fuel consumption at partial load, right? I can't follow that logic.

Jochen_145 wrote:

You only see it under full load, because the exhaust pressure isn't high enough otherwise to push it out of the exhaust. Therefore, it accumulates in the exhaust under low load conditions.

Okay, I see. Apparently, the only solution is a different driving style, which unfortunately isn't feasible for me, as I mostly drive on country roads. I already tend to accelerate more on inclines, not just for fun, but also to clear out my exhaust system. It seems that's not enough.

Are there any alternatives?

As mentioned above, avoid using the turbo within the rev range where it's not active during acceleration. Rev higher with less throttle (of course, don't overdo it) until you reach the desired speed. Then, you can shift to a lower gear and drive at a lower RPM.

If your vehicle has been "blown free" (presumably referring to a cleaning or modification), you can try it out. It would be good to know if it then consumes more fuel. Don't just consider that one liter; also factor in the fuel consumption you had *before* the "blowing free" process. It won't last forever, but I suspect it will last significantly longer than before.

Herr Antje wrote:

Rev the engine higher with less gas (of course, don't overdo it) until you reach the desired speed. Then, only after that, reduce the engine speed.

That's quite a Catch-22 situation. If I use only moderate throttle at engine speeds suitable for turbocharging, the turbo pressure decreases again, which also reduces the amount of exhaust gases. If I let it run wild, I quickly reach a speed that's incompatible with driving on country roads. I already use inclines to allow for moderate exhaust flow. But even here, I quickly exceed the permissible and drivable at full throttle and have to either ease off the gas or shift to a higher gear.

The distances are too short to effectively remove the exhaust fumes. Even short sections of autobahn are not long enough to achieve a noticeable fuel-saving effect. It would require many kilometers.

Is there a technical solution? Perhaps increasing the boost pressure in the partial load range to reduce blurring?

@Jochen
Even if the control unit reacts differently depending on the driving style, a slower regulation should not increase fuel consumption at partial load, right? I can't follow that logic.

However, to a certain extent, yes.
If you've ever looked at those 'fuel-saving' courses, you'll probably remember that they always teach you to briefly accelerate to full speed and then coast without using any gas. This is supposed to reduce fuel consumption.

If the system is sluggish, you cannot briefly accelerate with full power and then use the thrust cutoff while rolling.
So, you accelerate for longer periods of time at partial load to achieve the same speed, which ultimately leads to an increase in fuel consumption (or can lead to it).
You are correct that the power consumption doesn't really increase at partial load, but later, during the shut-off phase, it ultimately amounts to the same thing.

In my opinion, the fuel efficiency advantage of the 110 hp TDI engine compared to the 90 hp TDI engine in the Seat Leon lies in this area.

Best regards, Jochen.

Quote:

In my opinion, for example, the fuel consumption advantage of the 110PS TDI compared to the 90PS TDI in the Seat Leon

is as follows.

When it comes to the 90 horsepower Leon, you need to check whether it's an AGR (wastegate) or ALH (variable turbine geometry) TDI engine.

It's clear that the "Waster" version consumes more fuel. That's why the G3 with 90 horsepower consumes more than its 110 horsepower counterparts (in the G3, the 90 horsepower version was always considered the "Waster" version).

m;

Jochen_145 wrote:

But to a certain extent, yes. If you have ever looked at these "fuel-saving" courses, you will certainly remember that they always teach that you should briefly accelerate to full throttle and then coast without using any gas. This is supposed to reduce fuel consumption.

This applies to gasoline engines that use a throttle valve.

Uwe wrote:

Herr Antje wrote: Rev the engine higher with less gas (of course, don't overdo it) until you reach the desired speed. Then, only after that, reduce the engine speed. "That's a classic Catch-22. If you use a gentle throttle with a turbocharger designed for higher boost pressures, the boost pressure decreases, which in turn reduces the amount of exhaust gas." The distances are too short to effectively remove the exhaust fumes. Even short sections of autobahn are not long enough to achieve a noticeable fuel-saving effect. It would require many kilometers. 2) Is there a technical solution? Perhaps more boost pressure in the partial load range to reduce blurring?

1) Therefore

Quote:

If your vehicle is free of debris, you can try this

. This is not for cleaning, but rather to minimize dirt buildup during acceleration.
Therefore, it also delays the "congestion problem" significantly, which means you might automatically be back on the highway and not have to specifically drive to that area.

2) My explanation regarding the LD increase:

Quote:

I mean the LD (load) at low RPM and partial load, that's where your problem lies. Not the maximum LD at full load.

However, even that would be an attempt and not a guarantee, since the main cause of fouling is usually acceleration at low RPM.

EDIT
@Jochen
wegen die Verbrauchsenkung, siehe Antwort von Roger, so kenne ich das auch eher. And because of:

Jochen_145 wrote:

If the system is sluggish, you cannot briefly accelerate with full power and then use the thrust cutoff while rolling.

The regulations aren't going to change quickly, are they? And even if they do, we're still talking about fractions of a second, right?

The regulation is definitely not that slow. Otherwise, you wouldn't be able to accelerate spontaneously .

The fuel-saving effect of accelerating to full throttle also exists with diesel engines, although it is less pronounced. This is because the higher load results in better efficiency. The subsequent driving with coasting enabled is fuel-efficiency neutral and, therefore, results in the greatest overall fuel savings.