Diesel Won't Max Out? Troubleshooting Tips!

Hello!
I found this forum through Google and mostly found posts related to VAG vehicles, but I hope the forum is also open to vehicles of other brands.

Okay, I've been driving a 1-year-old Corsa DTI with a 1.7L engine and 75 horsepower (55 kW) for the past 3 days. It has 20,000 kilometers on the odometer.

My problem:
It's registered with a top speed of 170 km/h, but the speedometer only shows 162 km/h. It reaches 165 km/h going slightly downhill, then drops back to 162 km/h on a straight section. I drove the entire 10 km in both directions to rule out headwinds. Normally, the speedometer should show 175-180 km/h, which would correspond to a real speed of around 170 km/h.

Um gegenüber des Opelhändlers was in der Hand zu haben bin ich zum ADAC auf den Bosch Rollenleistungsprüfstand gefahren(25€). Das Result:

47 kW at the shaft + 12 kW power loss = 59 kW / 80 hp at approximately 4000 RPM.

Measured speedometer deviation at 140 km/h = 7-8 km/h.

So, it only reaches a real speed of 155 km/h instead of 170 km/h, even though it's producing more than its full power output!
The tires are winter tires of the standard size, the tire pressure is correct, the air conditioning is turned off, and there are no other aerodynamic modifications to the vehicle.

Does anyone have any idea what might be causing this? Could the car be performing poorly even though it seems to have enough power?

Thank you & best regards,
André.

"Well, that's quite an interesting phenomenon. I can't entirely agree with your theory about the engine being poorly tuned ("limp mode"), as it completely contradicts the diagnostic results. What was the maximum speed you were able to achieve? At what RPM was that reached? How much potential does he still have in terms of RPM? In VAG vehicles, the stated top speed is generally achievable."
How does it look? Are there any error messages? Is the air filter okay? Does it produce smoke? Is the diesel particulate filter clogged? Is the mass airflow sensor (MAF) working properly...? Please provide more information about the vehicle.

Currently, with a real top speed of 155 km/h (or 162 km/h on the speedometer), it's running at exactly 4000 RPM. According to the documentation, it should produce 55 kW / 75 PS at 4400 RPM, so there's definitely still room for improvement in terms of engine speed.
I think the air filters should be okay because, four days before I bought it, the car had its first (one-year) inspection at the Opel dealership.

So far, I haven't been able to detect any smoke in the rearview mirror, neither when the engine was cold, nor during acceleration, nor under full throttle on the highway.

According to two people on the Motor-Talk forum who own the same vehicles, their cars show a speedometer reading of 180 km/h, which would correspond to a real speed of 170 km/h. However, those individuals clearly have no technical knowledge whatsoever.

Okay, then it really seems like something isn't right. However, you always have to be careful because many people exaggerate the top speed of their car. Alright, so you're at 4000 RPM. I'm quite sure that the Opel diesel engine will also regulate somewhere between 4400 and 4500 RPM. So, if there's nothing in the error memory and you've definitely ruled out the possibilities mentioned above, then I don't know what else to suggest.

Are the brakes okay? I know there was a problem with the rear brakes on an Astra before...

Hello Andre,

Could it be that your transmission is no longer the original one?

'165 km/h and 4000 RPM is quite a lot, although I'm not familiar with Opel cars.'
I would like to ask the people on the 'Motortalk' forum at what RPMs the 180 km/h speed was measured.

Good luck, Rainer.

Are the gear ratios listed in the instruction manual?
Then you can calculate it.

Unfortunately, Opel only has the PDF for the CDTI engine (75 kW) available online, and its transmission is different.
Otherwise, I only found the axle ratio (3.55). By itself, that's quite informative... marketing jargon versus real life.

With the transmission from the 1.3 CDTI engine (51 kW), you can reach 165 km/h at 4000 RPM and 181 km/h at 4400 RPM.
Tire size: 175/65/14, according to technical specifications.

CU Gremlin.

Hi everyone.

My colleague is having the same problem.

After the timing belt replacement and air conditioning repair, there is a loss of 15 km/h in top speed.
The mystery is deepening because a performance test was conducted both when the car was purchased and again recently, and now the car even has 6 kW more power than it did at the time of purchase.

The catalytic converter has already been replaced, and for safety's sake, the mass airflow sensor was also replaced, even though it was new. We also provided the car dealership with the instructions for adjusting the diesel fuel pump.

Anyone have any more ideas?

Hi,

Here are two thoughts:
a) Fuel supply: When driving at full throttle on the highway, a clogged fuel tank vent or an old, clogged diesel filter have a much greater impact than "fuel starvation," especially compared to short bursts of high RPMs during a dyno test.
b) Adjusted valve timing (camshaft). It's possible that the engine now runs slightly better in the lower RPM range, but it lacks power at higher RPMs. -> Check this!
c) clogged exhaust systems, kinks or dents in exhaust pipes, catalytic converters...

Best regards, Rainer.

Okay, I've been looking at the Opel Combo 1.7 DTi with 55 kW, which is based on the Corsa.

According to the calculations, the translations should match.
Dann sind wir bei 4000UPM bei echten 150km/h, das paßt zuzüglich Tachotoleranz genau meinen Abgelesenen ~4000UPM bei ca.160km/h lt. TI think so.

Unfortunately, the performance graph was taken in 4th gear because the inspector couldn't keep the car steady above 150 km/h even with the handbrake applied. It only shows horsepower (KW) and speed (km/h), not RPM.
I've now converted it to the 5th gear and added a direct drive shaft.

I saved the whole thing under http://home.arcor.de/avesen/images/corsadti.gif.

Axis: 3.74
4th gear, 0.95.
5th gear, 0.76.
MaxUPM is at 5100-5300 RPM, maximum power output is at 4400 RPM, and the maximum torque of 165 Nm occurs between 1800 and 3000 RPM.


Actually, there's nothing inherently wrong with power loss; perhaps the amount of power being lost is simply too high.

Hello AndreV,

"Increase the tire pressure on your winter tires by about 0.3-0.4 bar. The maximum pressure they can handle is usually indicated in PSI (PSI/14 is approximately 1 bar) after the DOT number. Then, find a relatively straight and empty section of highway and drive for 2 km at top speed, using the speedometer to measure your speed. The small blue signs are located every 500 meters on the right side of the road. That way, you'll know exactly how fast you were going. After driving about 100 km with full throttle, the engine should be reasonably warm."
When it comes to absolute values, you can pretty much disregard readings from a dynamometer test bench. With all those correction factors, you can easily manipulate the results to make them look better.

Best regards,
Christian.

Okay, I dropped the car off at the workshop on Saturday, and they just called me (tomorrow morning) to say it's ready.

The LMM was defective.

Thankfully, it's free because the car still has a full factory warranty until the end of 2004.

I'll pick up the car tonight after work and then, after 8 PM, I'll take it for a spin on the A555 highway between Cologne and Bonn to see if it makes any difference.

Regards,
AndréV
For sale: Ford KA, manufactured in 2000, 60 horsepower, first owner, 85,000 km, accident-free, asking price €4400. If anyone is still looking for a 'cutie' car for their wife or something like that.

'I have to say, this forum is absolutely top-notch when it comes to expertise on turbodiesel engines.'
Habe fast 10 Stunden lang von Seite 1-99 interessante Themen zu Leistungsverlust und Leistungssteigerung etc. gelesen. RESPECT!!!

Unfortunately, this is limited to 98% VAG engines, and I drive an Opel.
'Does anyone know of any popular Opel forums where 'DTI' owners aren't alone and where there's also good technical expertise? I'm not looking for a forum full of immature teenagers who are just visually modifying their old Corsa Bs with things like 57i kits and ATU exhaust systems, trying to be faster than everyone else with their 50 or 60 horsepower cars *lol*.'

Regards,
André.

However, the question arises for me as to why it supposedly delivers more power in that particular role. Either the measurement result is incorrect, or it wasn't due to the LMM (lambda sensor). If the LMM is faulty, shouldn't the engine also be running below its full potential?

Hello Andre,

I once knew a website with the address containing "C20LET"; it was quite an interesting forum dedicated to the 2-liter turbo engines from Opel. Just try searching for "c20let" and "forum" on Google.

@joergs: That was probably a smile-testing station.
He is called that because then the owners of lowered, cleaned, and equipped-with-a-roof-rack (KuN) 60 horsepower Polo/Corsa cars will finally get a smile on their faces, even if it's not due to the acceleration that pulls the corners of their mouths upwards...
"Measurements from testing rigs are often intentionally tweaked upwards because customers then smile with satisfaction (no joke). And who wants unhappy customers?"

Best regards, Rainer.

@rainer

I already understand that! But what are those smirking test benches for? They're just there to mock and deceive the 'seeker.' I wanted to post 'lmm swap' at the beginning of the thread, but I was discouraged by the results.

The place I went to was a Bosch rolling road test center. It was located at ADAC Luxemburger Str. in Cologne.

If it was indeed the mass airflow sensor (MAF) and the car is now running as it should, it would be interesting to test it again. Let's see, maybe I'll invest those 25 euros again.
Then it would be better to use a different testing setup that also records the engine speed (RPM) and thus the torque, rather than just measuring the brake horsepower during acceleration and the power loss at idle while coasting, and simply adding those numbers together.
The 162 km/h I achieved would actually be a good match for the 47 kW (63 hp) of pulling power, which was consistently maintained between 3000 and 4000 RPM.

I'm looking for a C20LE engine, thanks.
I also found opelforum.de, but *well*, it's not great.

Thank you and best regards,
André.