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Trying to diagnose a low power issue

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Old Aug 2nd, 2020, 14:10   #1
Sidonas
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Default Trying to diagnose a low power issue

Good day,

I have a Euro3 2004 Volvo S40 with a 2.0D engine. It's supposed to be a 100 kW unit but it quite clearly is weaker thant that. Every single diesel that I've driven that's 80+ kW has much more torque than mine. Other than it being low on power, the engine runs fine, starts up easily, doesn't stall or lose power completely, has normal fuel economy, there are no weird sounds coming out of it, the RPM sits where it should sit, etc. There are also no errors on VIDA/DICE. It doesn't have a DPF and I've blanked and plugged out the EGR.

Since everything is supposedly running fine, I was wondering whether the real time graphing of different sensors that's provided by VIDA/DICE could help me find the culprit of the low performance problem? If so, what things should I graph to be looked at? If not, any ideas what it could be?

Thank you for your time.
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Old Aug 8th, 2020, 21:29   #2
Sidonas
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I think I have found an issue with the car but I'm not sure what could be the cause of it. While graphing the desired and actual boost values during a pedal to the metal run I've noticed that pretty much every time the car manages to boost to the desired value, it overboosts (actual value goes above desired). It then goes into some sort of fail-safe and lowers the boost pressure. After this happens, it does not boost back up to the desired value. I am suspecting a faulty TCV but it is fairly expensive to just replace it, so I'm looking for a second opinion.

The first graph also shows whatever the TCV is doing during a similar run but I find it hard to interpret.

Graph:
https://imgur.com/a/LcDQUa3

Last edited by Sidonas; Aug 8th, 2020 at 21:36.
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Old Aug 18th, 2020, 09:59   #3
Sidonas
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I've made some progress since and have a request, so I've decided to update the thread. It's going to be a long one but someone might find it useful in the future.

As I wrote earlier, my first suspicion was a bad TCV (the brown solenoid valve on the right side of the engine when viewed from the front). I took it out and did a quick test on it, as per this video: [YOUTUBE]https://www.youtube.com/watch?v=lKnE0RDVXBU&t=492s[/YOUTUBE].
Since it behaved like a faulty one, I decided to swap it out for a new one - no change in performance. The next step wasto figure out whether all the vacuum hoses that control the geometry of the turbine were intact. Since I couldn't get my hand on a vacuum meter, I bought a 60 ml syringe for that.

For someone that might go through the same procedure, it would make sense to get familiar with the anatomy of the vacuum system. Someone on this forum has already drawn it out for the Euro4-5 (twin throttle body) engines: https://i.imgur.com/apNRBEJ.jpg. Euro3 (single throttle body) engines don't have the "C" valve and all of its connections, other than that it's the same.

I then disconnected each hose on both ends, plugged one side and used the syringe to both vacuum and pressure test it - all of them were intact. My next suspicion was the second TCV (tagged as "B" in the drawing). It is responsible for controlling the anti-shudder valve but shares the same vacuum source as the TCV, thus a failure there could cause a vacuum loss in the whole system. I took it out and tried the test shown in the video. However, even without any electrical or mechanical input, it couldn't hold any vacuum and was basically a straight connection to the atmosphere for the vacuum system. It got replaced as well.

After I fixed the vacuum system, the car is now more predictable and requested vs actual boost stays fairly close up until 3k RPM at which point the actual boost value starts to go down. This is of little consequence in longer gears (3rd and up), however, in 1st and 2nd gears, as soon as I get to feel the boost, it starts to go down (see graph - https://imgur.com/a/opFONbf).

At this point, there are two problems:
1) Turbo lag is too high (doesn't boost up to the "desired" value until ~2.3k RPM;
2) Loss of boost past 3k RPM.

Taken together, the car is only really working to its full capacity in a narrow 2.3 - 3k RPM range. I will get the car tested by a specialist on Thursday and update you on the topic.

Now to the request, I'd like to ask someone who has a normally behaving 2.0D and a VIDA/DICE to record a wide open throttle run from 1st to 4th, switching gears no sooner than 3.5k RPM, so I could see what I should be aiming for with this car in terms of turbo lag and boost control.
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Old Aug 26th, 2020, 16:40   #4
Sidonas
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Last update:

The specialist couldn't help me in any way, other than "you can leave the car with us and we will fix it but I'm not sure how much it will cost you". With that not being an option, I bought myself a vacuum meter to see what's the car doing when accelerating.

By using a T-shaped tube, I put it in between the vacuum pump and the TCV - 26 inHg delivered throughout the RPM range. I then put it between the TCV and the Actuator - it was jumping around a lot and I couldn't make out much except for the vacuum dropping to ~3inHg past 3.1k RPM. I also went for a ride with a disconnected TCV with ~6 inHg of vacuum applied to the actuator - the idea was to find out whether it is possible to get the turbo to boost to the desired value at 3000+ RPM. The turbo lag was horrible, however, at 4200 RPM it hit the desired value. This confirmed that the turbo is functional and can generate boost past 3000 RPM but the turbo control mechanism is out of order.

Then I wanted to test the actuator, so using the same T-shaped tube I connected it to a syringe and started applying vacuum. It started to move as soon as I applied even 1 inHg (i believe the spec is ~4 inHg) and hit the stop screw at ~16 inHg (spec 19-24 inHg). Since I had already replaced the TCVs and was sure that there are no vacuum leaks, this led me to believe that the problem lies in the actuator. However, there is very little space to work with, thus replacing and setting it up properly would require at least specialist tools if not a removal of the whole turbocharger.

Now the actuator is made out of two elements: a metal can with an arm that retracts while applying vacuum to it and an electronic turbo position sensor that tells the ECU how far down the actuator arm is retracted. I thought that perhaps it wasn't spooling up properly in the low end because the turbo position sensor was telling it that it is already 100% retracted when it was not. To move the sensor a little bit further back, I removed it and then replaced it in using a 1 mm gasket. This didn't change the low-end in any way, however, for some reason it fixed the high RPM boost drop-off (to confirm that this was not a coincidence, I also tried to remove the gasket and the car started to drop boost once again).

To test whether the turbo lag issue was indeed caused by the turbo control mechanism, I bypassed the TCV by connecting the actuator directly to the vacuum reservoir of the car (26 inHg stable). There was a very slight improvement in turbo lag but it might have even been a placebo. Additionally, yesterday I got to drive a well-working V50 with the same engine and noticed that is was way more powerful in the 1000-1600 RPM range. I now think that perhaps there is some other thing wrong with my engine and it just isn't generating enough exhaust gas to spool the turbo up at low RPM.
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Old Mar 13th, 2021, 14:43   #5
Jorrit
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Default I know how you feel

Hello sir,

I exactly or nearly have the same problem on my 2.0D volvo v50 2005. There is a lot of power loss going on and I can't seem to find the cause. I checked the vacuum schematics and mine is slightly different.

Have you checked your throttlebody? I found out that one of my gas valves was broken. For me it did help a little. My dealer also could not find any error codes.
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Old Mar 14th, 2021, 10:39   #6
Sidonas
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Hello,

On Diesel engines the valves that are near the throttle body are called the anti shudder valves. Their function is to cut the air supply when you stop the engine, thus reduce the shudder of the engine switching off.

I also played around with the length of the actuator rod and found that it was too long. Shortening it by half a circle did the trick in removing the drop off in boost at high RPM. However, the low end power still isn't there. Additionally, it can also be shortened too much, in that case the car doesn't build any boost until it hits certain RPM, after which it just kicks fully in.
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