Loss of power low mpg, after 20 miles of driving

Chat about your 9n Polo (inc GT and Fun)
Post Reply
dizzypolo
New
Posts: 20
Joined: Sun Jan 27, 2019 1:24 am
Drives: 9N 1.4 2004 petrol
Location: Nottinghamshire

Loss of power low mpg, after 20 miles of driving

Post by dizzypolo »

Hi

Please can someone help shed some light on this, as I am now starting to feel throwing in the towell. I am having an ongoing issue where as its only noticeable when on longer journeys and motorway driving. The car appears fine, until I have driven 20-25 miles then all of a sudden the is a loss of power. The car then feels gutless, the car is also using loads of fuel. Last night I drove from nottingham to skegness on the a46 and a158 covering 80 miles, and I almost used half a tank! The car prevoiusly showed up with a p0171 error, running lean. All basic things have been done, including recent service, filters, plugs, new coils, the garage thought it was an MAP sensor prevoiusly and that was changed to no luck, last week it went back in, they re aligned the throttle body cleaned the plugs as they were all carbed up, (after 3000 Miles!) and said that the car needed to get a bloody good blastthough! They have said that if its still doing the same, it is likely to either be a bad CAT, or bad pre cat, or post CAT o2 sensor. They explained that the readings from both sensors were not correct.

Has anyone come across this before and able to comment on these symptoms. Its fustrating as I need the car for my main commute. Its starting to feel like I am just chucking money at it. Its also odd, that if I dont do long distances its fine. its only happends after 20 miles of use. Everything else seems fine, it idles nicely at 700rpm, there is no smoke, although i did notice that the tip of the exhust had loads of carb. I have also tried using different fuels including redex and putting in super unleaded, which made no difference at all. The car is a 2003, with a BBY engine and has 76K on the clock

my next step is replacing the sensors before the cat, I have seen there are cheap aftermarket ones, are these a bad idea, The garage have said to me its best a VAG one from salvage yard, rather then aftermarket, they have said an NGK OEM one is £122, to be honest ill probably bite the bullet and go with this, the back one isnt so bad at around £60. Next step to this will be changing the CAT.
RUM4MO
Bling Bling Diamond Member
Posts: 5859
Joined: Sat Dec 30, 2006 9:12 pm
Drives: B8 S4 & 6R/6C1 1.2TSI 110
Location: Mid Lothian

Re: Loss of power low mpg, after 20 miles of driving

Post by RUM4MO »

I'd guess if it thinks that its running lean but is in reality running far too rich, the pre cat Lambda probe which is the basic mixture "regulator/measurer" is where I'd start, I also agree that if you want to take a chance and save money, getting a genuine NTK (NGK brand for these probes) as fitted by VW Group used from a scrappy is a better idea that buying a cheap "fit anything or nothing" brand.

Have you tried finding out the VW part number and NTK part number and used that info to find one online? Many years ago when my wife's 2002 Polo had a "failed heater" fault code logged, I tried to source one online, but quickly discovered that buying from my local VW dealer was the same price when postage is taken into account - though as these cars have been out of production for many years and maybe that probe is no longer used in new cars, things might have changed quite a bit pricewise for a non VW supplied NTK genuine probe.
bvs
Silver Member
Posts: 271
Joined: Sat Feb 13, 2016 7:56 am
Drives: 02 1.4s 16v
Location: perth

Re: Loss of power low mpg, after 20 miles of driving

Post by bvs »

Might also be an idea to take a look at all the vacuum hoses in the engine bay for any obvious splits/age deterioration.
bvs
Silver Member
Posts: 271
Joined: Sat Feb 13, 2016 7:56 am
Drives: 02 1.4s 16v
Location: perth

Re: Loss of power low mpg, after 20 miles of driving

Post by bvs »

Also perhaps check for binding brakes ?
dizzypolo
New
Posts: 20
Joined: Sun Jan 27, 2019 1:24 am
Drives: 9N 1.4 2004 petrol
Location: Nottinghamshire

Re: Loss of power low mpg, after 20 miles of driving

Post by dizzypolo »

The garage said it was running rich, i can confirm this as the exhuast tip is black has loads of soat on it, and the plugs were coated even after the short mileage.

In addition to the last post, one other things I have noticed is if I drive for 20 miles, the fault occurs, i stop let the car cool down, then drive again very soon, i seem to be ok again for a bit, it just seems weird.

I have done some digging around ECP supply a o2 sensor part number 710443935, for £87.99. I dont want to take chances on a cheapo one. Guess this will be the next course of action and seem how things go

The problem is I do not have a great deal of knowledge where it comes to diagnostics, I kinda learn as I go, and a little bit of knowledge can be a bad thing. Your help is appreciated.
dizzypolo
New
Posts: 20
Joined: Sun Jan 27, 2019 1:24 am
Drives: 9N 1.4 2004 petrol
Location: Nottinghamshire

Re: Loss of power low mpg, after 20 miles of driving

Post by dizzypolo »

bvs wrote: Sat Apr 06, 2019 10:19 am Also perhaps check for binding brakes ?
This has all been checked. No vacuum leaks
bvs
Silver Member
Posts: 271
Joined: Sat Feb 13, 2016 7:56 am
Drives: 02 1.4s 16v
Location: perth

Re: Loss of power low mpg, after 20 miles of driving

Post by bvs »

Might be worth checking the Hot Air Flap in the Engine Cover,controlled by a waxstat - they tend to fail 'Open' which would give permanent Hot Intake Air,we took our AUB engine 1.4 16v (almost identical to BBY) and monitored the Intake temperature on the 'Torque' APP - even with our Air Flap manually locked in 'Cold' and on a cool day of 9 deg c - the intake temp eventually got up to over 40 Deg within 14 miles.I am not saying it is causing your problem but might be aggravating it.
To quote my own post.
Tried out my new 'Torque' app/OBD dongle thingy today and we went for a short (14 mile) drive to get some real time engine parameters - Engine Intake Temp started off at +9 deg c (agreeing with ambient) but was up to + 35 deg c at the halfway point - by the time we got back into town it was reading +42 deg c - so even with the Intake Flap closed - the engine is still getting hot air LOL.
This is a pic looking forward inside the Engine Cover with the air filter removed,the brass disc is the rear of the waxstat,it is being held forward (closed) by a woodscrew.

Image
Attachments
Air Intake Flap fix.JPG
RUM4MO
Bling Bling Diamond Member
Posts: 5859
Joined: Sat Dec 30, 2006 9:12 pm
Drives: B8 S4 & 6R/6C1 1.2TSI 110
Location: Mid Lothian

Re: Loss of power low mpg, after 20 miles of driving

Post by RUM4MO »

dizzypolo wrote: Sat Apr 06, 2019 10:42 am The garage said it was running rich, i can confirm this as the exhuast tip is black has loads of soat on it, and the plugs were coated even after the short mileage.

In addition to the last post, one other things I have noticed is if I drive for 20 miles, the fault occurs, i stop let the car cool down, then drive again very soon, i seem to be ok again for a bit, it just seems weird.

I have done some digging around ECP supply a o2 sensor part number 710443935, for £87.99. I dont want to take chances on a cheapo one. Guess this will be the next course of action and seem how things go

The problem is I do not have a great deal of knowledge where it comes to diagnostics, I kinda learn as I go, and a little bit of knowledge can be a bad thing. Your help is appreciated.
Unless that you know something that I don't, that Lambda sensor that you mentioned above is described by ECP as the "after cat" sensor, the most obvious one you should be considering is the "before cat" sensor as that controls/sets the basic fuel mixture - the after cat sensor is only there to monitor the exhaust after its passed through the cat, it does not control anything so should not be influencing the over rich basic mixture.
dizzypolo
New
Posts: 20
Joined: Sun Jan 27, 2019 1:24 am
Drives: 9N 1.4 2004 petrol
Location: Nottinghamshire

Re: Loss of power low mpg, after 20 miles of driving

Post by dizzypolo »

Air box seems A ok thanks.

Thanks for all the advise so far, i will make sure the correct sensor is replaced if needed. However this afternoon, I did have a play about with things and decided to disconnect the EGR. Car chucked out loads of carbon onto the drive, after 10 minutes of running it even left a huge black stain on the drive. I did a 10 mile run and the car now drives 100% better, prevoiusly around 1500-2000rpm, it felt lumpy when applying very low idle at these rpms, and now there is no hesistation. I have a drive from Skegness to Nottingham tommorow so the moment of truth will be answered.

My thought process for disconnecting the EGR is that it does not always throw up an error code, and there was no light on the dash. Why did the garage, not pick this up last week?

If it is the EGR, and its the root cause is it just worth blanking it off, I dont really feel like cleaning it just for it to clog up again the future, and Ive read that they dont really impact performance at all, nor will it effect the Mpg a great deal, or is it worth replacing it?
RUM4MO
Bling Bling Diamond Member
Posts: 5859
Joined: Sat Dec 30, 2006 9:12 pm
Drives: B8 S4 & 6R/6C1 1.2TSI 110
Location: Mid Lothian

Re: Loss of power low mpg, after 20 miles of driving

Post by RUM4MO »

To be honest, if that EGR valve assembly is choked or coked up it will only be because that engine has been left running far to rich for too long so that has messed up the EGR valve.
In my (limited) experience of petrol engines with EGR valves, they should always run clean if the engine is running okay, TDI engines do tend to coke up their EGR valves and so people feel that limiting the exhaust gases passing or blanking it off is the best way to go, I've never heard of anyone blanking off a petrol engine's EGR valve.
Typically the only failures that occur with these Pierburg EGR valves is the stem seizing due to contaminants or the plug/Welsh washer being blown out or otherwise leaking - that plug just seals up the valve after it has been assembled in the Pierburg factory.
I, in desperation, when nothing else so far had worked, replaced the EGR valve on my wife's previous 2002 Polo 1.4 16V 75PS - the old one at around 10 miles and 90K miles was "as good as new" and fitting the new one did not change anything, you can test if that valve is still being able to move through its full range of travel using VCDS and any other scan tool that allows activation of certain parts.

When you disconnected the EGR valve, what exactly did you do?
User avatar
alexperkins
Site Admin
Posts: 14866
Joined: Sat Nov 11, 2006 5:29 pm
Drives: 91 Golf GTI, 01 TT 225, 54 T5 174
Location: Poole, Dorset, UK.
Contact:

Re: Loss of power low mpg, after 20 miles of driving

Post by alexperkins »

I’ve cleaned many FSI egr valves that are terribly gunked up. It’s a different kind of coking to diesel, less sticky. Equally just as troublesome
Post Reply