Random Engine Hesitation

[Mike_04GolfTDI]

Edit/Spoiler: Just to help anyone reading this in the future, the solution turned out to be a new crankshaft position sensor. In case you don’t want to read to post #75 to find that conclusion. Also see post #71 for how I confirmed that the crankshaft position sensor was occasionally giving a bad signal…

After 7 years of running perfectly, two days ago my wife's 2015 Golf TDI suddenly stalled while she was at a traffic light. It started right up and continued to run almost normally.

I say almost, because now it has an occasional hesitation that can happen while cruising steadily, or during light acceleration. During hard acceleration, there is no problem.

Things I have tried:

VCDS scan. No codes in any module. Also viewed various sensors such as fuel pressure. Didn't find anything out of the ordinary. I was thinking maybe the HPFP was wearing out, but the requested and actual fuel pressures were very nearly the same under various conditions. Cam and crank speed sensors give normal readings. Turbo output is normal.

I drove it around and tried some full throttle pulls, which were fine. No lack of power, which suggests it isn't a fuel starvation issue.

I thought maybe it was oil accumulated in the intake ducting, but a 30km highway drive at 120km/h didn't change anything. During that trip it had a couple seconds of hesitation, and was normal the rest of the time. The hesitation happened while cruising steadily on the highway and caused a slight reduction in speed until it recovered.

I thought about bad fuel, but this started happening towards the end of a tank. The car made it through 90% of a tank without issue, and then this started happening. It has since been refilled with new fuel from a different location, but the occasional hesitation persists.

I'm kind of running out of ideas. The car is due for an oil change, DSG fluid change, and fuel filter change, which I'm going to do this weekend. When performed at the proper intervals, I haven't known any of those things to have any effect on how the engine runs, so I'm not hopeful that will make any difference.

I thought about perhaps a sticking EGR valve, but that would probably cause a fault code. If there's anything that might cause a fault code, it has to be the EPA's precious EGR valve.

 

[Nuje]

Ok - definitely staying tuned for this.
As I read, I mentally was coming up with ideas to suggest, and then you'd knock it down in the next paragraph.

Genuinely curious.

 

[Mike_04GolfTDI]

I’m going to play around with it this weekend. Hopefully I can figure something out.

She says the hesitation happens at nearly the same place every day during her drive to work. It happens about 20 minutes into the trip. This has me thinking it’s the EGR valve trying to do something once the engine reaches a certain temperature. Like maybe it’s sticking open or closed. However, there are no codes and no check engine light, which I would kind of expect for an emissions related issue.

On longer trips, it just kind of happens once in a while, but on shorter trips when starting with a cold engine, it happens after the first twenty minutes. This suggests it has to be fully warmed up for the problem to occur. It might also just be a coincidence!

I suppose I could just unplug the wiring from the EGR valve and if the problem never happens while it’s unplugged, then there’s a good chance the valve is plugged up and/or not working properly for some reason. In that case we would take it to a dealer because that should still be covered by the extended Dieselgate warranty.

If that proves inconclusive (if the problem still happens with EGR unplugged) then I’ll try graphing a bunch of data with VCDS while she drives around so I can see what is actually happening during the periods of hesitation. For example, does fuel pressure drop, or boost pressure, etc?

 

[Mike_04GolfTDI]

Well I just spent almost an hour with VCDS testing everything I could conceivably test. I did all the “basic settings” routines which do tests of the turbo, EGR, MAF, etc…. All of them completed successfully.

However, about 20 minutes into my testing, the engine started having occasional stumbling, bucking, or hesitation while trying to perform the tests. I did some of the tests multiple times, and during this approximately one minute span of time, which occurred about 20 minutes after starting the engine, it ran poorly. VCDS still reported that the tests were performed successfully, even though it sure sounded like something was very wrong.

After it got through its “minute of trouble” it worked perfectly for the rest of the time I was doing tests.

There are no fault codes at all.

I graphed the MAF values this time as well, and the MAF sensor seems to be working perfectly. One of the “basic settings” tests was a “Mass Airflow Plausibility test” or something to that effect, and it completed successfully.

What is happening 20 minutes after starting the car, which makes it run like crap, but doesn’t cause any fault codes, and goes away after a minute?

 

[krook]

is this not a dieselgate affected car? if not already patched, the acoustic function would come to mind that was used for NOx cheating. does it have a DPF and adblue system?

 

[Mike_04GolfTDI]

It is a dieselgate car, but it has had the modification to “fix” it. It still has all emissions equipment intact.

 

[Mike_04GolfTDI]

So today it had its little stuttering episode 12 minutes into a drive, and then was normal again. Today the weather is warmer than it has been recently

I have to believe this problem is happening within a narrow temperature range. It happened sooner because of the warm weather.

 

[krook]

did you try to log fuel limiters when the hesitation happens? from there you could see what's holding it back

 

[pedroYUL]

It is a dieselgate car, but it has had the modification to “fix” it. It still has all emissions equipment intact.

Gotta talk to the person who "fixed" it for ya...like you say it does sound EGR related, do you have dynamic EGR?

 

[Nuje]

I assume @Mike_04GolfTDI meant that it's had VW's Phase 1 and Phase 2 emissions fixes done to it.

 

[Mike_04GolfTDI]

So today I did a DSG fluid and filter service, engine oil change, fuel filter, brake fluid flush, and cabin air filter. Only because these things were due, not because I thought it would have any effect.

Drove for half an hour after that and absolutely nothing strange happened. More driving will be needed to see if the problem has really gone away, but so far this is the longest it has gone without losing power and stuttering.

The ONLY thing that I think could have conceivably helped was having the battery disconnected for a little while during the DSG service. For those who don’t know, you have to remove the battery and the tray that it sits in to get to the DSG filter.

Maybe it’s a case turning it off and on again to fix a computer glitch.

 

[Mike_04GolfTDI]

Well, with a little more driving, the problem seems to still be happening. This is quite perplexing.

 

[Mike_04GolfTDI]

So, my wife did a DSG reset, and the car hasn’t had this weird hesitation problem since then.

I wonder if somehow the ECU was getting confusing info from the transmission, and was cutting power because of that?

Other than that, I don’t see why else it might help, but so far it’s back to normal.

 

[Nuje]

Kudos to your wife!
(And to you for having a spouse willing to help troubleshoot. )

 

[krook]

if you logged limiters, you would've seen if it was the DSG limiting the torque (fuel). i still don't think it's a bad idea to log fuel limiters just to be sure nothing is out of place!

 

[Mike_04GolfTDI]

if you logged limiters, you would've seen if it was the DSG limiting the torque (fuel). i still don't think it's a bad idea to log fuel limiters just to be sure nothing is out of place!

If the problem comes back, I will try that. Thanks.

 

[Mike_04GolfTDI]

The problem is not completely gone. There has been some very slight jerky shifting and now there are some fault codes stored in the transmission module. I suspect this is related to the random hesitation. The DSG reset procedure seemed to mask the problem for a while, but didn't eliminate it.

Here are the codes. If I clear the codes they come back, but not always the exact same codes. Seems like different codes each time, after a few minutes of driving. One that is not shown here is "Implausible RPM signal from ECU."

Saturday,28,May,2022,16:02:41:63957
VCDS Version: Release 22.3.1 Running on Windows 10 x86
www.Ross-Tech.com

Address 02: Auto Trans Labels: 0D9-927-770.clb
Control Module Part Number: 0D9 300 041 N HW: 02E 927 770 AQ
Component and/or Version: DQ250-6F MQB H52 4512
Software Coding: 0014
Work Shop Code: WSC 00066 790 00149
ASAM Dataset: EV_TCMDQ250021 001001 (VW37)
ROD: EV_TCMDQ250021.rod
VCID: 2313EAC11B5A6543F2D-8076
9 Faults Found:

21153 - Gear 1
P072C 00 [002] - Not Selectable
Intermittent - Not Confirmed - Tested Since Memory Clear

21154 - Gear 2
P072D 00 [002] - Not Selectable
Intermittent - Not Confirmed - Tested Since Memory Clear

21155 - Gear 3
P072E 00 [002] - Not Selectable
Intermittent - Not Confirmed - Tested Since Memory Clear

21156 - Gear 4
P072F 00 [002] - Not Selectable
Intermittent - Not Confirmed - Tested Since Memory Clear

21157 - Gear 5
P073A 00 [002] - Not Selectable
Intermittent - Not Confirmed - Tested Since Memory Clear

21158 - Gear 6
P073B 00 [002] - Not Selectable
Intermittent - Not Confirmed - Tested Since Memory Clear

10731 - Valve 3 in Transmission Part 1
P174A 00 [002] - Electrical malfunction
Intermittent - Not Confirmed - Tested Since Memory Clear

10732 - Valve 3 in Transmission Part 2
P174E 00 [002] - Electrical malfunction
Intermittent - Not Confirmed - Tested Since Memory Clear

10906 - Cooling Oil Valve
P179D 00 [002] - Electrical Malfunction
Intermittent - Not Confirmed - Tested Since Memory Clear

 

[Mike_04GolfTDI]

With a little more googling, I found that apparently you should not scan the DSG transmission while the engine is running because you will get lots of false codes, like what I’ve posted above.

Since learning this, I cleared the DSG codes before starting the engine, drove around much of the day, and rescanned later with the engine off. No codes at all. So DSG appears to be fine.

There was only one time today when the engine kind of seemed to hesitate, but it could just as easily been a weird or poorly timed up shift when just starting out. Maybe the DSG is still learning since the reset. I don’t know how long that takes…

 

[Mike_04GolfTDI]

Well, it’s still doing it. Now I’m thinking it’s the crankshaft position sensor.

I used VCDS to graph engine RPM and it appears to be working perfectly, but there is a fault code stored in the transmission that says “10657 - RPM Signal from ECU P0726 00 [002] - Implausible Signal, Intermittent - Not Confirmed - Tested Since Memory Clear”

Engine reports no fault codes.

I have read elsewhere that the symptoms of a failing crankshaft position sensor are random stalling or stuttering when starting out, and occasional engine hesitation while driving. Also, heat affects the sensor, so problems may occur only when hot. Sure sounds like the same problem this car is having.

Since this may be covered by the extended warranty due to the emissions scandal, the car is going to the dealer to be looked at. I’ll have to read the terms of that warranty again, but I think it mentioned sensors…

 

[pedroYUL]

OP: ever replaced the lift pump (in-tank)?

I am positive my CVCA Passat has a dying lift pump, some of the symptoms are: random long cranks, slight bucking (hesitation) almost always at the same distance in the drive, noise that gets worse with lower tank fill level.

Now, this also got me thinking about my wife's GSW CRUA, no noise, same random long cranks (there is a sticky about that), and the same hesitation that my Passat is doing, but at a different distance in the drive.

I have opened the variable cam system (both) and there's no gunk to be found there, nice liquidy oil, so that is no suspect for me. Both have new batteries, and new timing belts...no codes at all.

I should get my CVCA pump tomorrow, and I have a CRUA pump ordered. Let you know if that solves those weird symptoms....as I said, Passat has an almost dead pump, and GSW could be just weak and flakey.

 

[adjat84th]

Stock cat still on the car? Maybe it's getting plugged up, how many miles on it?

 

[Mike_04GolfTDI]

Thanks for the suggestions. Anything fuel system related will be under the extended warranty so hopefully the dealer will figure it out and replace the right parts. I don’t want to start replacing suspect parts at great expense when we can get them for free.

The car only has 120,000km on it, or 74,000 miles. At that mileage, nothing should be wrong, but it is a Rube Goldberg machine of emissions parts, so I’m not surprised that it’s unreliable. Meanwhile my 2004 TDI which I gave to a friend is still running like new with 320,000km on it. All sensors are original. The only things that have ever been replaced are wear items. Actually, not quite true. I did replace a coolant temperature sensor on it once, but that didn’t affect how the engine ran.

My wife keeps watching online car reviews of new Toyotas and Hondas…. I don’t think her first German car has made a very good impression. First it turns out the entire company is run by criminals, some of whom went to prison (but she did get $7000 back), and then it starts stalling on her in random places in busy traffic. Meanwhile, her previous car, a 2006 Honda Civic which she sold to her brother, is still working perfectly and has never needed anything repaired.

Anyway, I hope the dealer can fix it so I can have my Golf R back.

 

[turbobrick240]

Could be any number of things like the CP sensor, but my first thought was a dpf issue. My tdi used to exhibit a very minor hesitation/stutter when a regen was initiating.

 

[Mike_04GolfTDI]

Could be any number of things like the CP sensor, but my first thought was a dpf issue. My tdi used to exhibit a very minor hesitation/stutter when a regen was initiating.

The most recent time it had a problem it actually stalled in traffic and she couldn’t restart it for a minute. Took many attempts to get it running again. No codes found with VCDS after that incident.

When it does run, it runs perfectly. So weird.

 

[adjat84th]

The crank sensor is a great thing to check, the wiring loom for it runs RIGHT by the oil filter housing and if not careful when spinning that back on with the new filter during a change, you can easily pinch the wires for the crank sensor (ask how I know)! It's right at the edge of the block where the gearbox mates up, and can be changed without gearbox removal. Worth a good check to see if it looks like the wire loom has even been crimped by the filter housing.

 

[pedroYUL]

$147.29 (tax in) for the Passat lift pump with eEuroparts...oh boy, what a difference.

Noise is obviously gone (that was the clear tell for failure), hesitation is gone, random long cranks too soon to tell, but the biggest difference is POWER. Now this Passat can pull good to the red line and chirp the tires in 2nd, before felt like a boat, specially compared to the GSW or even my '04 jetta wagon with mild tune.

I'll report back once the new pump is in the GWS, but my logic is like this: yes, this lift pump should be covered in the dieselgate warranty, but it has to fail, which means getting stranded, possibly destroying the HPFP. Also, as this pump gets weak, the HPFP has to do more work, and this could be a factor in premature fails of CP4 pumps.

 

[Mike_04GolfTDI]

This car has no problem with power, and the pump seems to work when performing tests. After changing the fuel filter, it primed the system very quickly as expected, by running the pump with VCDS.

I have no worries about any further damage that the pump may cause, because that would also be covered by the warranty. The car is not being driven anyway. My wife is driving my Golf R until the dealer has a chance to fix the TDI, Her appointment is for this Monday. (She’s afraid of the TDI leaving her stranded).

I sincerely hope the dealer can figure this out. Since there are no fault codes, and you can often drive the car for long distances without anything happening, I won’t be surprised if they say nothing is wrong. However, they do have access to more diagnostic equipment than I do, and they can do things like software updates, so there is a glimmer of hope.

 

[adjat84th]

CPS wiring is absolutely worth a check IMO

 

[Mike_04GolfTDI]

CPS wiring is absolutely worth a check IMO

I grabbed it and tugged on it and wiggled it around. Didn’t make it worse. I wouldn’t say there’s a loose connection or anything like that.

I also used VCDS to make a graph of engine rpm, and transmission input rpm, which were both identical. The sample rate was about 16 times per second and at any RPM both lines were right on top of each other. For ten minutes I just varied the throttle input and watched the lines on the graph perfectly follow the engine RPM. There were no spikes, drops, or anything to suggest any problem with engine speed as read by the crank position sensor.

If the car wasn’t under warranty I would probably replace the crank position sensor just to see if it helped, but it is under warranty, so it’s Volkswagen’s problem to figure out. Appointment is on Monday.

 

[Mike_04GolfTDI]

Noticed an interesting thing today. While driving, the hesitation occurred and I happened to notice the tachometer drop like a rock at that moment. I think that usually points to a bad crank position sensor.

It’s difficult to be sure because this event lasted only two or three seconds. I was accelerating away from a stop and it just kind of hesitated and jerked a bit around 30 or 40km/h on the way up to the speed limit of 50km/h. I just happened to be looking at the tachometer at that moment and saw the needle drop for a second.

So of course we’ll let the dealer know, as I believe a crank position sensor will be covered by the extended TDI emissions cheating warranty. I’ve read what is covered and “all sensors and actuators” is among the items listed.

Edit: Just wanted to add, this morning I disconnected the fuel line that goes from the fuel filter to the high pressure fuel pump and used VCDS to run the electric fuel pump. There was a good healthy stream of fuel. It only took a few seconds to fill a one litre container. So I don’t think there’s anything wrong with the in-tank fuel pump.