Hunting down FR 150 TDI surge issues

[iammooks]

Just in case, 1.9 TDI FR 150, ARL engine, 54 plate.

As a few of you know, I've been having an issue lately where if I hold the car at steady revs, I get a surging or lurching feeling - like the car is pogoing. As time's gone on, it's got worse and is both more noticeable and affects other gears - it used to be just second and third but now I can feel it in fifth too.

I'd pretty much decided it was a boost leak, but after changing the intercooler pipe on both sides, the problem hasn't gone away. Replaced some gaskets and o-rings but nothing noticeable changed.

There are no codes on VCDS Lite.

New fuel filter in the past couple of months, which I filled with Forté injector cleaner. No effect.

Turbo seems healthy. When I did the Mr Muscle clean I checked for play and there's none at all.

I'm also getting grey/black smoke out the back if I accelerate hard after holding the car at steady revs. Sorry to the people who have been driving behind me. It's less obvious in daylight but I could definitely see it when it got dark and people had their lights on.

After installing the boost gauge, I had my first long drive in a good while and it gave me a chance to test the gauge out.

Really interesting journey.

No loss of boost on acceleration and it seems to hold boost well - around 15-18psi - but when I was on partial throttle - anything from 1,500rpm and 2,500rpm - the surging was often followed by a surge in boost as well, but I haven't noticed any fluctuation or significant drop in boost pressure. The surge isn't accompanied by a surge in revs though.

Going by the gauge, it doesn't look like I have a boost leak - unless there's something else - so am starting to look elsewhere.

On some other sites, some people have suggested their issue was caused by the N75 valve, which I'm happy to replace, but as I'm reaching the end of my knowledge, I wanted to throw it out there to see what anyone else thought. I feel like I'm running out of things it could be and don't want to start replacing things that don't need replacing.

I know a lot of people have had issues with their N75, so even if you don't have a diesel, any thoughts would be welcome.


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[Russ220]

Any time I've had similar issues on previous diesels it's been the EGR causing it.

 

[iammooks]

Any time I've had similar issues on previous diesels it's been the EGR causing it.

Thanks for this - EGR has always been an issue for me over the past few years, but it's pretty clean at the moment - but I'm going to give it the once over to make sure it's doing what it should. Might get myself a vacuum pump to see if it opens and closes fully under vacuum. Half of the 'plunger' that you can see running from top to bottom when you look through it is clean, but I don't know if the whole thing is supposed to be clean, so will spray that with a bit of penetrating lube and see what difference that makes. I've cleaned the EGR pipes that run off the bottom too, but they've always been pretty clean.

The one thing I keep coming back to is the TIP. I took it off a few months ago when I was trying to take the intake manifold off to clean it (and failed) and the surging issues really became apparent after putting everything back together. I'm wondering if it's not seated absolutely perfectly and it's allowing either air to escape or extra air to come in. Either way it could be confusing the MAF sensor and could be causing the drop in fuel economy. From what I gather, it's easier to do from under the car so I'll put it on axle stands and refit it. Before I was doing it from the top and I was never 100% that it was on properly. I was just too lazy to jack the car up and take the undertray off.

At least those two things are cheap to do and I don't have to worry about buying a new N75 just yet, and I'll be taking the elbow boost pipe off the EGR to get more light on the TIP and get the mounting bolts off to be able to wiggle it around, which will give me access to the inside of the EGR.


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[Gokiwi64]

Our Kia Sportage does/did the same thing, as with Russ was the EGR valve however I fitted a generic non oem unit from Euro's - lasted a year , put genuine oem on and 2 years on still going strong with no issues.

I should add its not the mechanical part of the EGR valve but the solenoid itself , being electrical time and heat kill them.

 

[iammooks]

Our Kia Sportage does/did the same thing, as with Russ was the EGR valve however I fitted a generic non oem unit from Euro's - lasted a year , put genuine oem on and 2 years on still going strong with no issues.

I should add its not the mechanical part of the EGR valve but the solenoid itself , being electrical time and heat kill them.

That could be it - I cleaned the EGR in January 2020 I think and it's possible when I rinsed it that some water or cleaner got into the diaphragm. Given I've not driven it much during the pandemic, that could have caused some issues, like degradation or rust or something, just from sitting for months on end.

The surge tends to happen while the car is at anything under 2,500rpm, and it just so happens that in lower gears and in town driving, this is when the EGR valve is doing most of its work, I think.

I'm going to try to do some runs while VCDS is plugged in too to see if I can see anything amiss there.


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[MoToJoJo]

Drive at higher RPMS, problem solved

 

[iammooks]

Funnily enough, keeping the car at higher RPMs does seem to solve the surge issue, but it's probably not the best in the long term.

Went it today to see if I could have a look at the plunger that's activated by the diaphragm.

When I replaced the o-ring a month or so back, I noticed the plunger part was only half clean and the lower part is covered in soot. You can see the lower half in this photo.

Does anyone know if it's supposed to look like that, or is it only supposed to go up half way like that?

I'm going to change the vacuum line for the butterfly valve today or tomorrow to see if that does anything. I can also get a new Wahler EGR valve fairly cheaply, but if it doesn't look like there's anything wrong with it, I can give it a miss for now.


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[iammooks]

I wanted to update this thread as I hate it when I do a search for something on Google and the only sites I find are ones where the thread dies off after a little while and I never know if the person gets their problem sorted.

Got under the car today to check the TIP was seated properly and that the turbo actuator wasn't seized. The TIP I had managed to convince myself wasn't put back on properly when I took it off last August, and the best way to check is from underneath. Both of those are absolutely fine, so I sprayed the turbo actuator with a little penetrating lube just to make sure it stayed healthy.

While I was under the car I noticed that my intercooler boost pipe (turbo side) had come half off, so I re-seated that and also cut away some of the undertray side panel so it didn't constrict the pipe like it was doing before. All good so far.

Them I replaced the vacuum line for the butterfly valve on the EGR valve body and took it for a test drive.

When the engine was cold, I didn't get any of the surging issues I'd had before and was feeling hopeful, but when the engine was warmed up, it came back. It was nowhere near as strong as before, but still noticeable.

The fuel economy seems a bit better now too, with no noticeable black smoke, but I'll need to do a motorway drive to see if it's back up to 54mpg like it was getting before.

It's not an injector or fueling issue so far as I can tell because if I rev when the engine isn't under load (in neutral) I don't get the same issue with hesitation/stuttering at steady revs.

That makes me think I might still have a boost leak somewhere else, so I'm wondering about the pancake pipe or the turbo to pancake hose. The boost gauge shows that the engine holds boost much better now, with the readings much more steady at all rev ranges. I don't have many pipes to replace now though, with those two being the only ones I haven't touched. The elbow pipe to EGR is fine.

I'm also working my way through all of the vacuum hoses. I've noticed when the passenger window is cracked open, I can hear a hiss coming from the left side of the car on acceleration that I can't hear from the driver's side, that goes away when I lift off. I have no idea if that's normal on the PD150 because it's been so long since I knew what normal is with this car, but various sites (not SEAT specific) say it's either normal, a vacuum leak or a boost leak - or a combination.

I'm waiting to see if the vacuum line replacement makes a difference before I put a new EGR in, as the lines cost less than a tenner while the EGR cost about £50. I might also just get a new turbo to pancake hose as it looked quite oily on the turbo side. Still not worried about the turbo though as Darkside say on one of their blogs that oil will seep out of the connector if the lugs are rounding off.

So there we are for the moment. Doing the cheap fixes first to see if that makes a difference before getting more drastic. I'll spend some of tomorrow doing the vacuum lines and will report back after doing that.


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[iammooks]

We might be getting somewhere...

I was going to start replacing more of the vacuum lines today and was eyeing up the vacuum ball hoses, given that's ultimately what controls the turbo (I think?). It's probably a good thing I didn't replace that line, as it's long and I understand there are connectors that are prone to snapping, but it's good I was thinking about it, as I might not have noticed something else...

There's a hole in the accordion pipe from the airbox/MAF to TIP. It's bigger than a pin-***** and if I can see it without looking too hard, I reckon it's definitely going to be having an effect. Given that it's after the MAF, if there's enough air to be able to hear it, that's bound to be having an effect on AFR and might explain the drop in MPG and the black smoke from the exhaust.

The part number for the accordion pipe is 1J0129684AG and I can get hold of one of those fairly easily, but wouldn't mind replacing it with a silicone one, so I can be a bit of a tart.

Darkside do one, but that costs £50. If it solves my surging issues then I've half a mind just to do it, but if there are any cheaper options out there, that'd be really helpful.


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[Rich.T]

If it has a hole, it obviously needs replacing. Have you tried taping the hole to see if it makes any difference?

 

[iammooks]

If it has a hole, it obviously needs replacing. Have you tried taping the hole to see if it makes any difference?

Of course now I've taken it off the car and cleaned it up, I can't find the hole again. It's going to be pretty annoying (and embarrassing) if it turns out it was just dirt.

At least it'll be a chance for me to clean the MAF.


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[Rich.T]

Found the hole yet?

 

[MoToJoJo]

Found the hole yet?

I hate that question

 

[iammooks]

I hate that question

Just roll her in flour...

No, wait...

I was convinced there was a hole and now it's nowhere to be seen. I feel like a proper idiot - you can tell how excited I was - thought I'd done some proper detective work and solved what I thought was a complex problem with a proper 'ah ha!' moment.

At least the new EGR is arriving tomorrow. Will do the vacuum lines and clean the MAF before putting that in to see if there's any difference.

It's just weird - it only happens under load and only at a certain rev range, and is more obvious when the engine is warm... It's a head scratcher.


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[iammooks]

So now I know what a clean EGR valve looks like... Haven't taken it out of the packet in case I need to send it back, but it's clean as a whistle.

While I'm going to keep replacing vacuum lines, I'm thinking more and more about the intake manifold and that one of the ports might be blocked, leading to the 'miss'. I'll be calling a diesel specialist later to see what they say.

I think the plan right now though is to get the lines changed, put it through the MoT and then if it fails, try the new EGR and then get biblical with the intake manifold.


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[iammooks]

Finished replacing the rats' nest that is the vacuum lines yesterday. That was fun. I was going to stop at doing the main ones but when it comes down to it, you can't do half a job on them if there's a leak somewhere and it's having an effect somewhere else in the system. When you get the vacuum controllers away from the firewall, you see that there are all different connectors and the lines are interlinked in some shape or form, so even if you change the turbo actuator or the vacuum reservoir line, they're still connected in a way.

I also cleaned the MAF sensor as well as I could. You can only take the actual MAF out with a five-point security bit that I don't have. I've got all the other ones except this, it seems. I just sprayed contact cleaner in as best as I could.

I needed to get some cat food, so took the car out for a run. The hissing sound from the engine bay was less pronounced, so that was good, and the surge when it did come was much less aggressive and only really felt obvious when I was really searching for it - keeping the car in gear when I should have shifted up, that kind of thing. There's definitely still something there, but I don't know how much effort I'm prepared to go to to get rid of it.

One thing I did notice is that changing the vacuum lines seems to have improved brake performance, and the acceleration felt smoother than before. It could just be in my head though. I'm thinking I'll probably change the brake booster/servo vacuum line eventually and see if that helps the brakes a bit more, and it's possible it'll help the engine if there's actually a leak in one of the bigger I/D lines, so will change those as well.

Next step is to book the car in for its MoT and see if it passes on emissions and then get down to ironing everything out.

 

[smutts]

You might be on the right track with vacuum leaks.
The plastic servo vacuum tube has a habit of splitting at the joints and letting in air.
This buggers the braking & the turbo boost control.
Wrapping the connectors with insulating tape sorted mine.
The brakes then worked & I got a good bit of extra mpg too.

 

[smutts]

My mate did have a TDI passat with weird surges & drops of power, we finally tracked it down to a misbehaving brake switch.
VW sensibly cuts the engine power if you press the stop & go pedals at the same time.
Peugeot stupidly don't,
So any electrical noise on the sense wire from brake switch to the engine management can cause weird hiccups.
The power cuts instantly, and returns gently over three seconds, once the braking signal has gone.

 

[MoToJoJo]

Meh, need to disable that on my car so I can left foot brake

 

[iammooks]

It’s one of the things I love and hate about this car in equal measure - so many mysteries hidden inside it, but all of them things you’d never have a hope of tracking down yourself if someone hadn’t said anything first. I mean, how the hell do you work out that an engine surge is caused by a dodgy brake switch?

A garage I spoke to the other day said it could be a faulty ABS sensor kicking in, or the traction control reducing the engine speed momentarily.

It’s all mad.


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