Hi

I have an error code on my 6N1 Polo - 00533 , and one of the possible causes is a faulty fuel pressure regulator.

It's showing some of the symptoms for this to be the case. Missing on idle, lag in the revs increasing when revving up and stalling.

I recently fitted a new fuel filter, which was long overdue. This cured the error code for a little while.

I just spoke to a former VW mechanic and he said that he'd never had a FPR problem or come across one.

Another source of information suggested that the FPR be changed every 5 years.

If I do change it, the manual says 2.5 bar and the listed Bosch replacement is 3 bar. Would that be a problem ?

Or could the issue be injectors ?

The car has done 174K miles.

There is also another error code - 01087 . I think this might mean the throttle body needs aligning.

The above symptoms were not present before the car had been standing for a week, the battery died and it's had a new Lambda and Cat. I cant see that's got anything to do with it, but worth a mention.

 

Had a good look at all the vacuum pipes and all seemed ok. The vac pipe for the FPR at the throttle end was not all the way on and seemed a bit flared at the end. I pushed it all the way on and that was the only thing that I needed to do.

It seemed to do the trick as far as running goes. It's back to normal, but after a reset, both error codes are still there.

Has this forum gone the way of many others ? In that very few are on them any more, in favour of such things as Face Book ?

If it's now running nicely I wouldn't worry about fault codes.

 

The reason for worrying about this, despite it running ok, (Well was. It started the missing etc again), is that it has recently failed the MOT on the emissions test. The Lambda reading was high.

I assumed that a high reading meant it was running rich. But no, just the opposite. Running lean.

Does a faulty fuel pressure regulator cause a lean reading ? Yes !  Apparently, it is the most likely cause.

So I borrowed a FPR off a Golf, popped it onto the Polo. It now runs fine again. Now got a new Bosch FPR ordered.

Cleared  the codes and 00533 code has now gone and stayed gone. Bloody hurrah !

Some very experienced mechanics told me that they had never known of a FPR playing up and thought it highly unlikely to be the cause.

But when they are stuck open, the fuel pressure cant build. This was the cause of my high Lambda (lean) reading.

 

I havnt dived around the rest of the forum, but is it dead on here now ?  I hope not.

11 hours ago, Polo3 said:

I havnt dived around the rest of the forum, but is it dead on here now ?

If you want to see most recent activity across the whole forum, just go here: All Activity - Club Polo

 

 

Well done for sorting it. Yes, lambda numbers are a bit unintuitive.

Thanks Pete.

I just discovered that although I've cleared the error code I havnt fixed the problem. Took it for an emissions check and the sky high Lambda reading is still there. So what can be causing it to run so lean ?

An air leak after the injectors is not likely. So I guess the injectors are not delivering enough fuel for some reason ?

The Lambda is a new Bosch one, the plug is clean and dry. I intend to check the continuity to the ECU.

I'm wondering if the fuel pressure is still low, maybe a dirty, clogged up fuel pump mesh/seive ? Or even a slightly weak fuel pump ?

Maybe the injectors ? Although they looked in good clean condition after a recent dose of Cataclean.

The other possibility is the ECU. Is that likely ?

I'm also thinking of doing a compression test, just to get an idea of that side of things.

Any suggestions as to other possible causes ? or courses of action to try and shed some light on what may causing the lean reading ?

 

I would have thought that a lean Lambda reading would have been acceptable from an emissions perspective as less fuel is being burnt.

Is there any other way to get the Lambda reading checked without all the logging in at the test station ?

Any help gratefully received.

An air leak in the exhaust (after any sensors) could be pulling in fresh air and diluting the tailpipe measurement,

A leaky vac hose in the engine bay, like the brake servo one might be giving false air.

Doubt it would be ECU.

Might be able to watch lambda sensor activity on VCDS to see if that appears to be switching sensibly rather than at one or other limit constantly?

 

Catalytic converters only do their job fully and only survive longterm when the mixture is maintained near stoiciometry, which is why tailpipe lambda must measure within tight limits for MOT. CO2 might be lower with leaner mixture, but NOx, HCs and particulates will probably go up instead. 

Cheers Pete.

I had a chat with a couple of good mechanics at the local VW garage and the suggestion of a leaky exhaust and how it would affect the Lambda reading was made.

Makes perfect sense once you understand what the Lambda reading is all about.

 

Thanks for explaining the importance of maintaining a tight Lambda reading for long Cat life.

Time to make sure the exhaust is completely gas tight. The system is in good condition, but some joints may need some attention.

I can understand how air could be sucked, venturi style, but I would have thought the pressure inside the pipe would have negated that. But I guess not.

 

There is a pipe connected to the inlet just by the throttle body and it seems to go to the charcoal canister. It has something wired in half way along the pipe, some sort of sensor or switch.

What is the charcoal canister for and could that part of that side of things possibly be responsible for too much air getting ?

I havnt got eyes on the charcoal canister yet as it looks to be somewhere in the inner wing.

If I block the pipe to see if it makes any difference to the Lambda reading, will it adversely affect the running ?

 

Have they made the emissions test more strict in the last 12 months ?  I think I may have a small leak in the exhaust at a joint or two, but nowhere near as bad as has been in the past when it's passed the test.

I will do my utmost to make double sure that the exhaust is sealed all the way along, but know it has past before with an advisory for blowing.

Edited 26 November, 20232 yr by Polo3

No recent change to emissions test that I know of. Must be something new with the car.

Purge valve is partway between charcoal canister and inlet. Function is containment and controlled 'disposal' of fuel tank vapours.

Any pipe connected to the inlet manifold is a potential source of air leakage if it is not intact, or has a valve or diaphragm that is leaking.

 

Brake servo vac line is another such pipe.

 

 

I've checked the servo pipe and all fine. All original and no perishing.

Found a good leak on the exhaust, as suspected at the joint between back box and mid section.