Hello all,

 

Recently, my BBZ engined Fabia developed hesitation, loss of power and unstable idle. While servicing (belts and tensioners change) a quick VCDS scan revealed something in the vicinity of a 17961 fault code, MAP intermittent signal or so. Changing the MAP for one of a nearby car solved the issue, but it was only a test since it was from another customer's car. A new sensor had to be ordered since it wasn't in stock in the city.

 

Well, I ordered a new sensor, installed it... And nothing. The symptoms still persist. I have no access to a scanner for the time being and the shop is closed, because, you know, coronavirus and such, not to mention it's 100 miles far from where I am. For the symptoms I believe the same fault code will pop if scanned.

 

Am I missing something? I disconnected the battery to sort of reset the ECU just in case. Nothing.

 

So, I'm wondering if the new sensor is faulty, or I need to actively clear the codes through VCDS and do a rescan to see any change, or, God forbid -gasp- is it a wiring issue? 

 

Have at it and pardon my french. Thanks in advance.

The wiring looks like this:

 

D141 is a 5V supply from the engine ECU pin 98.

 

220 is an earth connection in the engine wiring loom.

 

Could also be...an air/vac leak, an EGR fault, an EVAP purge valve fault or a throttle valve fault. 17961 fault code is defined as "manifold pressure signal - implausible ratio" on a BBZ.

 

Starting with a wiring inspection/test seems wise though, as there has been work done in that area recently.

Excellent, Wino. Vacuum leaks, split pipes, actuators, EGR and sensors were ruled out while the car was in the shop. Readiness values were fine, tests were OK. Only thing out of place was the oil cap seal, the one that goes between the oil filler neck and the valve cover, it was changed. To be clear, the fault developed before the belt service. 

 

Is it possible to test the MAP sensor itself and the connection from the wiring loom with a voltmeter, and what values should I be looking for, just in case? I'm not too electrically minded, if that's not apparent already. There is a possibility that the sensor itself is at fault, being a cheap Chinese unit. In my defense, apparently there are no better options available, and the other sensor that worked was one of those, so I ordered it. Getting a proper one from abroad leaves me stuck for approximately two months and that's while the world isn't on lockdown.

Edited 2 April, 20206 yr by juanse_2691

I'll have to think about that. Not too sure what sort of output the MAP sensor produces. I probably have some info somewhere that'll tell me. Or the www will. 

MAP sensor is like a strain gauge, a diaphragm attached to a piezo element, output will be a very small variable voltage.

Can you take the map sensor out and check the resistance of it with a multimeter or ohmmeter to rule out a duff sensor? 

1 hour ago, Wino said:

I'll have to think about that. Not too sure what sort of output the MAP sensor produces. I probably have some info somewhere that'll tell me. Or the www will. 

 

Something makes me think most sensors on a car use a pulse output rather than a voltage or current output

Edited 2 April, 20206 yr by SuperbTWM

18 minutes ago, SuperbTWM said:

 

Something makes me think most sensors on a car use a pulse output rather than a voltage or current output

 

Modern tackle use a digital MAP sensor with a variable frequency output, Fabia is an analogue MAP since its PCM is from the 90's.

 

21 minutes ago, jars said:

Can you take the map sensor out and check the resistance of it with a multimeter or ohmmeter to rule out a duff sensor? 

 

No.

Edited 2 April, 20206 yr by sepulchrave

Went to have another look around the engine. Checked and disconnected EVAP valve, EGR, ran the engine like that and symptoms didn't change, poked around the lines going to the throttle body, all seem healthy. Cleaned and reconnected everything, no change. Idle with no load whatsoever feels decent enough, turn the A/C on and hell breaks loose.

Disconnecting the purge valve and EGR wouldn't necessarily change anything if either was stuck partly open; but if that was the situation, the 'borrowed' MAP sensor should not have made any difference. What's the part number of the original MAP sensor?

036906051. 

I think I maybe saw one of those an hour or two ago while tidying one of my sheds...

Will check tomorrow and perhaps if it is that number, try running it in my car. It's not new, but it may work just fine.

Thank you as always. 

Here's the engine properly warmed up, at idle with the air-conditioning running. Hopefully you'll be able to see how it dips, stumbles and then surges, so much that some of the vibration is transferred to the camera. 

 

 

Edited 3 April, 20206 yr by juanse_2691

Got ahold of a FAE unit while a genuine one comes from abroad. Disconnected the negative battery post while changing the sensor, got everything back together but I notice no change. Is clearing the code through VCDS the only way for the ECU to 'learn' that a new sensor is installed? Should I look for anything else? 

It won't be the MAP sensor anyway, I'd be looking for an air leak, switching on the aircon simply tells the ECU to increase the idle to compensate for the additional parasitic load which is done with the throttle body servo motor plus additional fuel injected. I think yours is leaning off excessively.

Good, thanks for your input @sepulchrave. I couldn't find any air or vacuum leaks in the usual places but now that you say that, removing cabin fuse #10 (10 amp "lambda probe" fuse) seems to alleviate most of the symptoms. At least power is restored. I guess because as you said, the readings lead to over leaning, maybe? With the fuse in place the engine stumbles quite badly and barely moves out of its own way. Would a dodgy O2 sensor cause this as well?

 

 

I'll have to go to the garage in the next few days to see what the readings say, hopefully we're going to finally solve this issue.

Should've put fuse #9, sorry.

Yes, a bad lambda probe would do it and wouldn't give you a code either.

Thank you very much.

"You have to find the problem before you can fix it". 

 

 

It's been an interesting day. I went to the garage to get the car sorted. I was just arriving, parking the car, couldn't even get out of the car when my mechanic passed by, put his ear by the exhaust and greeted me with "Welcome. You have a bad coil"

 

Plugged in VCDS, lo and behold, misfire in cylinder #4. 

 

Anyway, he wanted to check the condition of the spark plugs. This is what we found. Iridium plugs have only 30k km on them. 

 

New Beru coil, new spark plugs and an oil change later, the car came back to life. MAP sensor is fine as I changed it earlier, and the O2 sensor was doing its job flawlessly.

 

Also put Cupra console bushes and new bushes and tyres all around while I was there.

 

Thank you everyone, the issue seems to be gone.

 

Next thing to service: valve stem seals.

Those gaps look huge; have you measured to see what they currently are? 

Don't  think I'll be rushing out to buy any plugs like those.  What's the part number? BKR6EIX?

 

Great to hear you've finally got it running better. 

 

 

They're good plugs, it's bad fuel that ruins good plugs, so much electrode erosion that pinking is a certainty, you should only be using super unleaded with that engine.

2 minutes ago, sepulchrave said:

so much electrode erosion that pinking is a certainty

I guess you mean pinking has caused the electrode erosion, rather than the other way round?

 

12 minutes ago, Wino said:

Those gaps look huge; have you measured to see what they currently are? 

Don't  think I'll be rushing out to buy any plugs like those.  What's the part number? BKR6EIX?

 

Great to hear you've finally got it running better. 

 

 

@Wino gap is huge indeed. Gap was fine when I fitted them new 2 years ago (it's even documented in the forum on another thread of mine). 

 

I don't blame the plugs themselves. These are NGK BKR6EIX-11, honestly one of the best plugs you can ever get for this engine, but remember the car has spent all its life using subpar 91 "premium" octane fuel, only until recently 95 octane started to appear in pumps across the country replacing 91, and there's even parts of the country where you can only get the regular 84 octane (!). With so much pinging due to subpar fuel it was only a matter of time, I guess. 

 

 

Basically what @sepulchrave said.

Edited 12 August, 20205 yr by juanse_2691