Hello, 

I'm reaching out for some assistance with a perplexing issue I'm experiencing with my 2016 Skoda Superb 2.0 TDI SE L (engine code CRLB). I've been dealing with engine RPM and voltage fluctuations that have been challenging to diagnose and resolve.

 

**Description of the Problem:**
- The problem occurs rather regularly and is characterized by constant up and down fluctuations in engine RPM when engine is hot. 
- Voltage behavior is also a concern. It briefly shows 14.5V before dropping to 12.9v straight after engine start. 

- after starting the engine it keeps voltage on lvl. 13.1v but it's steady below 60 degrees 
- The issue is particularly noticeable once the engine reaches around 60 degrees Celsius.
- The fluctuations persist and the voltage continuously varies after the engine reaches this temperature threshold.

- engine goes stable (fluctuating a lot less) when additional electrical load is applied. Like heated seats. Voltage jumps to 14.5v and seems to be stable. As soon as electrical load is off, drops to 12.9v and start fluctuating constantly. 

 

**Modifications and Recent Maintenance:**

- I've replaced the battery, which was a factory-fitted 7-year-old unit. For new Yuasa Start stop EFB battery (coded in). 
- The alternator and voltage regulator have been replaced (Lukas) 
- removed the DPF and EGR systems, including an ECU remap. But ECU still seeing oil ash on 68.8grams, differential pressure sensors are not readible anymore 

 

**Additional Information:**

- There are no parasitic drains on the battery when car is parked. Battery keeps the charge and not going down. 
- The battery tested as "good as new."
- Intermittent fault code U1406 static current too high. 
- I've installed a brand new oxygen sensor.
- All glow plugs have been replaced.
- All injectors seem to be functioning well, with most maintaining close to 0mg per stroke. The one on cylinder 2 shows variations around 2mg per stroke when idling but falls to close to 0mg per stroke while driving.

 

 

I'm hoping the experienced members of this forum can provide some insights or guidance on what might be causing these fluctuations and how to resolve them. Your input is highly appreciated, especially if you've encountered a similar issue or have expertise in diagnosing these kinds of problems.

Thank you in advance for your help!

 

Edited 25 October, 20232 yr by gicu

I can also add that sometimes I can see the headlights are flickering while driving. 

 

I would suspect grounding issue but once heavy load is applied like heated seats, voltage and rpms seem to be stable. Keeps nice and steady 14. 5v constantly. 

 

As soon as I switch off electrical load, and engine is hot, it drops to 12.9v and rpms starts to float. 

Variable output voltage from the alternator is a normal situation with charging systems for EFB/AGM batteries in recent VW group cars, this isn't the problem.

 

14 minutes ago, gicu said:

removed the DPF and EGR systems, including an ECU remap.

This sounds like the source of the trouble.  Your engine was designed to work with both of these systems. If the remapped engine is not working well, you should probably return it to the place that remapped the ECU and ask them to fix their mapping. It's also illegal to remove these systems, but I expect you already new that.

Yes, I will ask them to fix the ECU map then. This was also suspicious for me. They refuse this as a source of the problem but will force them to look into it as it occurred directly after the process mentioned... 

 

Regarding the legality of DPF removal... 

- Looking at the thousands of electric cars burning worldwide,

- how poluttant are battery factories, - disposing perfectly good cars because of silly Ulez, 

- Regenerating DPF with tons of chemicals once in a while

- Producing new and disposing old used DPF... 

 

Everything is contributing to false Eco world so I couldn't care less about legality of DPF removal. 

4 minutes ago, gicu said:

Yes, I will ask them to fix the ECU map then. This was also suspicious for me. They refuse this as a source of the problem but will force them to look into it as it occurred directly after the process mentioned... 

 

Regarding the legality of DPF removal... 

- Looking at the thousands of electric cars burning worldwide,

- how poluttant are battery factories, - disposing perfectly good cars because of silly Ulez, 

- Regenerating DPF with tons of chemicals once in a while

- Producing new and disposing old used DPF... 

 

Everything is contributing to false Eco world so I couldn't care less about legality of DPF removal. 

The real problem here is that when your car is due for its annual MOT test, it will fail as the required pollution control elements are not there.

11 minutes ago, Graham Butcher said:

The real problem here is that when your car is due for its annual MOT test, it will fail as the required pollution control elements are not there.

I already checked these. Won't fail as DPF is present. And the check is only by a "torch". 

Emissions are still way below the fail threshold. 

Edited 25 October, 20232 yr by gicu

One thing you could try, to prove that the alternator voltage is unrelated, is to disconnect the battery monitor control unit connection at the battery negative post. One of the wires (violet/white, LIN) tells the alternator what is required of it, and if that is disconnected, the alternator should revert to a constant voltage output.  See what, if anything changes when you try this. 

I think that may fix the flickering headlights, which could be a consequence of the alternator trying to keep a particular output voltage whilst the engine rpm is fluctuating in an uncontrolled way.

10 minutes ago, Breezy_Pete said:

One thing you could try, to prove that the alternator voltage is unrelated, is to disconnect the battery monitor control unit connection at the battery negative post. One of the wires (violet/white, LIN) tells the alternator what is required of it, and if that is disconnected, the alternator should revert to a constant voltage output.  See what, if anything changes when you try this. 

I think that may fix the flickering headlights, which could be a consequence of the alternator trying to keep a particular output voltage whilst the engine rpm is fluctuating in an uncontrolled way.

Alright. Will try that! Thanks a lot. 

Doing this will also inhibit the start/stop function I think, but I guess you maybe don't care about that either?

 

6 minutes ago, Breezy_Pete said:

Doing this will also inhibit the start/stop function I think, but I guess you maybe don't care about that either?

 

Indeed. I have disabled start stop permanently anyways. 

2 hours ago, gicu said:

Yes, I will ask them to fix the ECU map then. This was also suspicious for me. They refuse this as a source of the problem but will force them to look into it as it occurred directly after the process mentioned... 

 

QED

3 hours ago, gicu said:

I already checked these. Won't fail as DPF is present. And the check is only by a "torch". 

Emissions are still way below the fail threshold. 

OK, now I'm confused, you said in the first post that you had removed the DPF and EGR systems, so does that mean you have refitted them, or have you left them in placed but taken the working parts out so they are only the shells left behind in order to give the appearance of being there?

1 hour ago, Graham Butcher said:

OK, now I'm confused, you said in the first post that you had removed the DPF and EGR systems, so does that mean you have refitted them, or have you left them in placed but taken the working parts out so they are only the shells left behind in order to give the appearance of being there?

Yes. All internals out. Shell is in place. 

1 hour ago, gicu said:

Yes. All internals out. Shell is in place. 

They insert a tube up the tail pipe and analyse the fumes, so how do you know that your emissions are low enough to pass? 

1 hour ago, Graham Butcher said:

They insert a tube up the tail pipe and analyse the fumes, so how do you know that your emissions are low enough to pass? 

They checked it right away. Using the fumes analyzer you mentioned. Also there's no smoke coming out when idling or revving but only after some aggressive acceleration while driving.

 

I saw the cars that emit **** load of smoke and they keep passing MOT so there's no reason to be worried at all as I said before... fail threshold is really high and engine needs to be really destroyed to fail it.

3 hours ago, Graham Butcher said:

They insert a tube up the tail pipe and analyse the fumes, so how do you know that your emissions are low enough to pass? 

As far as I know the MOT emissions test equipment is relatively basic, so I would have though its unlikely pick up the difference (significantly enough anyway) if an engine was running okay.

 

@gicu I appreciate this isn't helping you with your question, what led you to have the DPF removed?  Had it filled up and reached the end of its service life?

41 minutes ago, MrRich said:

As far as I know the MOT emissions test equipment is relatively basic, so I would have though its unlikely pick up the difference (significantly enough anyway) if an engine was running okay.

 

@gicu I appreciate this isn't helping you with your question, what led you to have the DPF removed?  Had it filled up and reached the end of its service life?

My garage advised me to do this so I don't waste money on cleaning it few times £300 plus ultimately replacement £1000+labour on the end. 

17 minutes ago, gicu said:

My garage advised me to do this so I don't waste money on cleaning it few times £300 plus ultimately replacement £1000+labour on the end. 

Hmm, I've had loads of diesels and I have never had any issues with the DPF, my current car has over 140,000 miles on the clock and again no issues with the DPF, no warning light in the instrument cluster and zero error messages on the ECU's and I do run a regular scan for error codes using my VCDS, So what is the current mileage of your car I wonder and what sort of drives are you doing i it?

Edited 25 October, 20232 yr by Graham Butcher

4 hours ago, gicu said:

They checked it right away. Using the fumes analyzer you mentioned. Also there's no smoke coming out when idling or revving but only after some aggressive acceleration while driving.

 

I saw the cars that emit **** load of smoke and they keep passing MOT so there's no reason to be worried at all as I said before... fail threshold is really high and engine needs to be really destroyed to fail it.

modern diesel engines  like the tdi only rev to 2500 rpm or so before the revs cut off

they use to rev the engine to max 6 times during the mot test, but they obviously cant do this now, 

the only problem you might have is  if in the future if the mot  test gets stricter 

 

if manufacturers would make  emissions equipment more reliable or lower cost to replace,  most people would'nt need to gut / disconnect etc

but they keep making them ever more complex, 

adblue systems on some engines are even more unreliable than  dpf and egr valves but there's an easy fix for that  😄

8 hours ago, Graham Butcher said:

Hmm, I've had loads of diesels and I have never had any issues with the DPF, my current car has over 140,000 miles on the clock and again no issues with the DPF, no warning light in the instrument cluster and zero error messages on the ECU's and I do run a regular scan for error codes using my VCDS, So what is the current mileage of your car I wonder and what sort of drives are you doing i it?

Purchased with 136000 miles and had almost full DPF. Constant regenerations etc. So I decided to take care of it. DPF out, new oil with ceratec. New glow plugs etc etc. Couple new sensors. 

 

If that was me who drive the car before DPF would still be OK. 

Doing 12 miles one way to my workplace x2. 

I had previous Superb 2013 and it was totally fine with all DPF etc. Never had any issues, same as you. So yeah. Not very lucky when purchased this one. 

3 hours ago, gicu said:

Purchased with 136000 miles and had almost full DPF. Constant regenerations etc. So I decided to take care of it. DPF out, new oil with ceratec. New glow plugs etc etc. Couple new sensors. 

 

If that was me who drive the car before DPF would still be OK. 

Doing 12 miles one way to my workplace x2. 

I had previous Superb 2013 and it was totally fine with all DPF etc. Never had any issues, same as you. So yeah. Not very lucky when purchased this one. 

Do the seats look worn at all? If so I wonder if it had been a taxi with it's previous owner and thus doing a lot of short trips? I had similar concerns when I purchased my current car in June, it 137,000 miles on the clock the last 2 MOTs showed it had done 40,000 miles a year with it's 2nd owner. However, my seats do not show any signs of excess wear and the rest of car seemed to be in good order. The old car was like yours, a 2013 model which I had new and only done 78,000 miles in 9.5 years so was like new still. 

 

My local Skoda service dept recently looked over my car and declared it to be a good car, despite it's high mileage, it has been well looked after and everything has done when needed. 

That's interesting. I thought it may be the case. 

According to mot history, first owner made 80k miles in first 3 years... 

Well...driver's seat is bit worn. But all passenger ones are like "new". Especially on the back of the car. Literally look brand new. 

@gicu Looking at my MOT history, I can see the original owner did 40k in the 4 years that they had it for and the second owner did 42k in his first year, 42.5k in his second year and then 13k in the next 6 months before he sold it and I got it from the dealer at 137.5k, and it had the cam belt and water pump done, new brake pads and discs, brake fluid change and had the DSG oil changed, new N/S headlight (running light failed), new N/S rear light, lens was cracked, done before they would sell it to me. The high mileage that the second owner done, did make me think it might have been used as an airport taxi car, but the overall condition makes that seem unlikely. Now my regular garage who looked after my other car for almost 10 years has seen the car and is happy with it, I feel much more relaxed about the mileages as I know that if things are done at the right time, these cars are pretty much bulletproof. 

 

I can tell you that in the 2 months after my other one was written off, I did well over 2,000 miles trying to find another L&K in similar condition to my old car, and I saw plenty of dogs being offered at inflated prices for their condition, and it seemed that when one became available, if it was any good, they were snapped up within a couple of days. One car I saw in May at a dealer near Heathrow was trying to flog me an old dog of a car, all chrome trim round back windows, missing, huge crack in the windscreen, loads of small dents everywhere, tailgate was very noisy, engine rattled badly, would not do any work on the car to fix the problems or do the cam belt and water pump change etc, it was not even an L&K, over 130,000 miles and they still have that car for sale at almost £11k, more than I paid for my L&K with all of its extra toys. So yes, I had to put the leg work into finding a car that was a worthy successor but it was worth it.

Additional electrical load puts also an additional mechanical load on the engine and therefore ecu rises the idle rpm to compensate.

Not all "tuners" perform a correct de-dpf and de-egr procedure, more to that - many of them even don't do the actual ecu dump calibration, they just read it out and in best case send it to outsourced guy or company. Worst case - they just download an already pre-done file somewhere. On the internet you can actually get a dpf_egr_off.exe that "does" everything for you. You would be very surprised how many of them are actually working in this manner.

 

Oil ash should be read out as a volumetric unit. For 2.0 diesel the max threshold is ~0.18l. Oil ash amount can't be measured, instead it's a counter built into the software and actually has no direct correlation with physical condition of the dpf. Differential pressure and soot amounts are that tells you something. Although there are few things that can be extrapolated from the oil ash amount - and those are the approx. actual mileage or condition of the engine. For correctly working engine it refers to 250+k km (depending on driving conditions) and at max oil ash volume the dpf can still be very much alive and fit to duty. Other option is too frequent regenerations, which usually are the consequences of some problem, that invokes increased amount of soot production.

 

Counter can be easily reset via vcds or obd11 by activating the dpf replacement basic setting.

Edited 26 October, 20232 yr by CJXA

It's somewhat surprising how many of the "garages" are disabling the EGR for no particular reason. There is a widespread misconception of sole purpose of the EGR system as such - the EGR re-routs exhaust gasses to be burned again.

In fact the EGR is used for two main reasons that may seem to contradict to each other - to help heat up the engine during warmup process and to reduce the combustion chamber temperature during normal operation. The second is the most important one. With lowering the combustion temperature, soot and NOX emissions are also significantly decreased. Therefore it makes completely no sense to rip out a fully operational EGR system even though the DPF has been removed.

 

But if you remove the EGR, then you must remove the DPF as well because it will simply be overloaded and clogged soon enough due to reasons explained above.