check engine light

[wkpaul]

hello everyone,

i recently purchased a 2001 1.4 16v Lupo .

when i got it the previous owner said the had a small problem but had changed the egr valve and everything was sweet, on the test drive it drove great .

2 weeks later the check engine light came on , garage replaced one of the lambda sondes and the light was gone, 

A week later the light was back on , they changed the petrol filter as it was done , checked for vacuum leaks, cleaned out the pcr vale ,checked the injectors , plugs and leads, cleaned out the throttle bodies and light went out .

2 days later light back on , they changed the MAP sensor and again seemed to fix it but 2 days later its back on .

it shows fault code 17559 long term trim additive bank 1system too lean .

any ideas what it could be or where to start looking?

I have seen lots of posts where people have experienced the same issue but no solutions?

thanks in advance

[mk2]

Sounds like an air leak. Check the brake vacuum pipe, as they often let air in.

Late edit- just re-read your post. It also could be the fuel pressure regulator? I also remember reading something about the sump gas pipe/pcr thing...

And welcome to club lupo!

pics of car?

Edited November 15, 2023 by mk2

[wkpaul]

Thanks for the quick reply ,

I love the car ,can’t wait to work out the issues .

will check the brake vacuum pipe in the morning .

is there a separate fuel pressure regulator or is it in the tank with the fuel pump?

I will post pics tomorrow 

[wkpaul]

So I went to get the fault code read and it shows the EGR valve isn’t working , the previous owner had replaced it with a used one , looks like it’s faulty .

they were talking about bypassing it ,

is that a good idea?

[mk2]

You can block off the EGR feed, which might clear that fault code. But the ECU will know and give you a different code!  

Worth an experiment

If you get two codes, then you know it is not the EGR...

 

[wkpaul]

At the moment there are 2 codes ,the original long term lean trim and now EGR,

can the EGR be causing the lean running fault?

[mk2]

It is possible.

If you remove it and have a look at the sealing valve (the part that opens to allow exhaust gas into the inlet manifold), does it look like it fully closes? And is the mounting seal ok? The fault will probably only happen at idling, not when normal driving. So when you are in traffic, once warmed up, that is when the inlet air leak is detected.

The fault is basically too much air is in the mixture, meaning that the engine is running too lean. The ECU knows this because it can see the gas result on the O2 sensor. It tries to fix the problem by closing the throttle at idle and increasing fuel. But when it reaches the limit, it can't add any more fuel or close the throttle any further, so it gives up and turns the light on. It can also be caused by low fuel pressure, blocked fuel filter, bad injector(s) or coolant temp sensor. The most common reason is that is an air leak in the inlet manifold. There is an old trick to find a leak, but it's a bit dangerous... get a small low pressure propane or butane pipe and while the engine is idling, blow propane around various parts of the engine. When the revs pick up a bit, propane is being sucked in to make the fuel mix stronger, and so the revs get a but faster. But sometimes the ECU notices the RPM goes up, so closes the throttle valve a bit to keep the RPM constant. You need to watch the O2 sensor reading while experimenting

 @Rich @Skezza @Silver! @Blue Loop what do you think?

Edited November 16, 2023 by mk2

[wkpaul]

Thanks for the great tips,

the EGR valve was pretty dirty so it’s Ben cleaned ,

found a bodjed joint in the vacuum hose from the master cylinder ,it’s now sealed .

all faults reset , let’s see if it fixed 🤞🏻

[wkpaul]

[mk2]

Nice! 👍🏻

[wkpaul]

So my euphoria was short lived ,on my way to work this morning ,the Lupo started stuttering and I’m pretty sure it’s only running in 3 cylinders now 

[wkpaul]

So I bought an obd reader and here the following codes:

P0304 misfire on cylinder 4

P0407 exhaust gas recirculation sensor B circuit low

P0403 exhaust gas recirculation control circuit.

and of course the original 17559

not a good day

[mk2]

Ok, so egr stuff sounds like short circuit. Check each wire to the solenoid to see what you get. Shouldn't be earth.

what colour is the plug in 4?

[wkpaul]

So the EGR stuff turned out to be me (blonde moment),I unplugged the EGR to see if it would run smoother ,

it didn’t so I plugged it back in ,

I tried to swap the leads but they were too short, but when I tried to start it again it ran smoothly but after a 5 minute drive light came back on and started running like a bucket of bolts.

i will pull the plugs in the morning and have ordered new leads

[wkpaul]

So todays juicy update

i pulled the plugs and the 1st surprise was there were 2 the same and 2 random

plug 4 is definitely darker than the rest.

I remembered that I had bought a compression tester for a previous project but never used it ,so did a compression test

cylinders 1-3 are all right on 180 cylinder 4 is Alitalia less at 170 ish

so definitely replacing the plugs as well ,leads should have arrived today but won’t be here until tomorrow,

suspense is killing me 

[mk2]

Compression looks fine. Within 10% is ok.

Did you by remote chance buy this car off a pikey...? 3 types of plugs. That's a first for me! Not seen that before. Technically it shouldn't make any difference if they're all the same heat rating, gap, depth and resistance.

The third one (snow white insulator) might be the problem cylinder. That plug looks awfully clean; Running too lean.

[wkpaul]

Yeah I’m beginning to wonder if I bought off of del boy,

its the classic from an old lady 1 owner car "………….

never seen it before and remarkably the garage said they checked the plugs but never found it weird?

it was showing misfire on cylinder 4.

what could be causing cylinder 3 to be lean ? Injector?

[wkpaul]

Which plugs should I get?

 

[wkpaul]

So , todays adventure.

new set of NGK plugs and leads and it’s running like a dream,

lets see how long it lasts 🤞🏻

 

[wkpaul]

So after 2 weeks of no issues , on the way back from work today the dreaded check engine light came on,

its the 1st time I was stuck in traffic not sure that makes a difference?

car is still running fine at this point but code is my favorite 0171 too lean on bank 1.

what i did notice , not sure if it’s connected, the temp gauge sits around 70 until I put the heater on then it drops of the scale as if it isn’t working , could the temp sensor be the culprit?

[mk2]

Yep. But a low reading should make it run rich... It is a dual sensor (i think on this model). One runs the instruments, the other the ECU.

You might have a stuck thermostat too. They're cheap to swap over at the same time as doing the temp sensor.

[wkpaul]

So I just swapped the temp sensor , seemed ok ran it for a while stationary,went for a drive ran great.

when I got back let it run stationary temp got to around 80/90 then the light came on again same code p0171.

if I had any hair I would be pulling it out 

[mk2]

So drives fine and when idling once warmed up throws a code. Yeah, i'm still convinced that it's a plenum/inlet manifold leak. A tiny air leak will only affect the idling once warmed up. Not when cold.

You could move around injectors, but i don't think that'll move the fault. The O2 sensor reading via VCDS will tell you what's going on. Too lean or just right as the engine warms up, and while being driven.

Late edit- just thought- ignore the fault for the minute and just drive the car normally for a couple of weeks. Then pull the plugs and analyse the colour.

Edited December 5, 2023 by mk2
Idea

[wkpaul]

So this afternoon I drove to work ,25km the 1st 20km was motorway and the temp stayed low .

after a couple of km of city driving the temp went up to 70 and the light came back on .

will monitor it again on the way home .

good idea to check the plugs ,I will keep resetting for a couple of weeks then pull the plugs ,

cheers 

[wkpaul]

Diary of a madman

drove home last night temp stayed low no light on 👍

drove to work today temp came up to 70+ no issues no light on 👍

drove home tonight temp stayed low but guess what drove in the driveway and bingo !light came on.

serms like there’s no rhyme or reason to this 🙈