EGR (?) problem- petrol engine

[indars]

Good evening/night guys,

 

Kindly ask for help with my Mk1 Fabia (not tuned 1.4L 16V 74kW BBZ petrol engine, prod.02.2007, 225k km, manual gearbox).

 

Yesterday evening started car and went out to clean snow from it..

After few minutes engine stopped by itselves. Started again. After few min.- stopped again.

Decided to drive home- but after few meters engine started to jerk, Exhaust Warning Light (alias Check Engine = Engine symbol) went on, engine stopped. 2nd gear, engine started- and with jerking and keeping hard on accelerator returned to job.

Engine couldn’t be started no more- jerking on 200...300 rpm and stopping all the time.

 

Attached X-tool VAG401 scanner > only one error, 17848 „EGR valve N18 / open circuit”.

Tried to make „click” test for EGR valve- silence; throttle body, fuel pump relay etc.clicked normally.

Erased error, went home with work car.

 

Next morning, after -13*C windy night in yard, car started perfectly- and died again after ~14min.idle. Same symptoms, same one error.

!!!

Recognized that unplugging of EGR makes sense- engine can be started and seems, works ~ok. Except Check Engine light in dash and bonus error 17851 regarding EGR’s potentiometer G212.

When re-attached EGR plug to working engine, it stopped.

 

Dismantled EGR. Coil resistance ~8Ohm, valve inside perfectly clean and clicks when supplied with outside 12V. Pipe from EGR to throttle's flap lower side- clean. Throttle body- clean.

Attached EGR to plug, made a click test- clicks! Attached 5W bulb to plug’s pins 1+5 > light flashes.

Hmm.

Mounted everything back; car started normally and stopped again after few minutes of idle. EGR click test afterwards- not successful.

Engine couldn't be repeatedly started.

Only one, the same error 17848 „EGR valve N18 / open circuit”.

Disconnected EGR plug- can be started and is working.

 

Have feeling that it’s concerned somehow with excessive exhaust supply under throttle flap + looks like problems starts after some warm-up.

When EGR was dismounted, made a check: closed with plug EGR pipe’s bore in throttle body, started engine > it started/worked. When tried to pull closing plug out (i.e., add.air supply appeared under flap)- engine started to jerk and stopped.

 

Any ideas, guys, what could be the problem?

Is it SAFE FOR ENGINE to drive with EGR unplugged until some solution will be found? Am pushed to drive ~50km in working days...

 

Indars

 

P.S.

Sorry, haven’t and am not familiar with VCDS.

My good workmates have VCDS but they’re Audi „dieselheads” and are not quite familiar with „petrolhead’s” EGR problems and how to check them in VCDS...

[sepulchrave]

You need a new EGR valve.

[indars]

You need a new EGR valve.

 

...which means that EGR coil can kick out problems only when warm? I.e., resistance starts to change to infinity = open circuit starts :-) to appear?

What about possibly nasty coolant t* sender? Just idea...don't know if EGR circuit is affected by it too...

Edited 6 January, 2017 by indars

[Breezy_Pete]

I think there is a minimum coolant temperature below which your engine ECU doesn't try to operate the EGR valve. This may explain the temperature dependence of the fault.

Have you examined the valve wiring close to the connector?  If there's a wire almost, but not quite broken, that might also become incapable of working the coil at higher temperatures. 

Edited 6 January, 2017 by Wino

[indars]

I think there is a minimum coolant temperature below which your engine ECU doesn't try to operate the EGR valve. This may explain the temperature dependence of the fault.

 

I.e., coolant t* sender could be guilty too? Hmm, much cheaper than EGR ;-)

 

BTW, car was in yard whole night at -16*C. Didn't tried to start it yet.

Any idea what check today haha since car is freezed through? Start engine with disconnected EGR plug (or connected), clear code in advance, watch for t* indicator/watch at ~which t* cut-off starts?...

Interesting is nature of that cut-off: it's very smooth (feels like somebody slowly starts to brake engine at crankshaft, more and more, few seconds, and engine stops).

[indars]

I think there is a minimum coolant temperature below which your engine ECU doesn't try to operate the EGR valve. This may explain the temperature dependence of the fault.

Have you examined the valve wiring close to the connector?  If there's a wire almost, but not quite broken, that might also become incapable of working the coil at higher temperatures. 

 

At first rough look yesterday plug<>wiring looked ok. Today will take more close look. Agree, wires to that plug (BTW, for almost all plugs in engine bay!) are very short and bends when plugging in-out...

[Breezy_Pete]

I.e., coolant t* sender could be guilty too? Hmm, much cheaper than EGR ;-)

 

BTW, car was in yard whole night at -16*C. Didn't tried to start it yet.

Any idea what check today haha since car is freezed through? Start engine with disconnected EGR plug (or connected), clear code in advance, watch for t* indicator/watch at ~which t* cut-off starts?...

Interesting is nature of that cut-off: it's very smooth (feels like somebody slowly starts to brake engine at crankshaft, more and more, few seconds, and engine stops).

I could try to log EGR activity and coolant temperature on my way to work this morning, In about 1 hour. For comparison, and investigation of what this minimum coolant temperature may be.

[indars]

I could try to log EGR activity and coolant temperature on my way to work this morning, In about 1 hour. For comparison, and investigation of what this minimum coolant temperature may be.

 

Thks Wino! In evening, after job, will try to measure EGR's coil resistance too, when cut-off starts. If normal ~8 Ohms will rise up to some huge digit then EGR could be gone. If no- then additional issue about what to think in weekend.

[Breezy_Pete]

I now have a ten minute log which I will upload in a while. No EGR activity (column E in log) seen below 57 52°C coolant temperature (column N).

Edited 6 January, 2017 by Wino

[sepulchrave]

You can drive the car perfectly safely with the EGR disconnected, you could try re-adapting the existing valve but I think it's probably toast.

[Breezy_Pete]

Here's the log: link. I don't have time to plot anything just now, but help yourself to anything that's useful.  Correction to previous post - No EGR activity (column E in log) seen below 57 52°C coolant temperature (column N).

 

I agree with sepulchrave above. The thing that I'm failing to understand is that the diagnostic error code suggests that it's failing open circuit; which I would expect to mean fully closed. So why's the engine stopping?

Edited 6 January, 2017 by Wino

[indars]

You can drive the car perfectly safely with the EGR disconnected, you could try re-adapting the existing valve but I think it's probably toast.

^ very good ;-)

MOT is only after month- think, will sort it due this time.

And in MOT Nx amount isn't measured anyway; but who knows- maybe Limp Mode with EGR disconnected can rise CHx and CO, too...

Edited 6 January, 2017 by indars

[indars]

Here's the log: link. I don't have time to plot anything just now, but help yourself to anything that's useful.  Correction to previous post - No EGR activity (column E in log) seen below 57 52°C coolant temperature (column N).

 

I agree with sepulchrave above. The thing that I'm failing to understand is that the diagnostic error code suggests that it's failing open circuit; which I would expect to mean fully closed. So why's the engine stopping?

 

Yep, strange. With open circuit, valve must shut bore = no extra air under throttle flap, hmmm.

[sepulchrave]

Yep, strange. With open circuit, valve must shut bore = no extra air under throttle flap, hmmm.

 

It's not air remember, it's inert gas, It won't tick over so it stalls and is impossible to start because the ECU ignores your pedal input when the engine is started, I had this with my 1.4 16V AUB engine, drove me absolutely mad. It was the EGR valve solenoid breaking down at high temperature. These engines are designed to rely on the EGR valve for mixture regulation once they're warm, the only other way to get it to run would be to map out the EGR which would be very tricky to do indeed since the ECU is not programmable.

[indars]

It's not air remember, it's inert gas, It won't tick over so it stalls and is impossible to start because the ECU ignores your pedal input when the engine is started, I had this with my 1.4 16V AUB engine, drove me absolutely mad. It was the EGR valve solenoid breaking down at high temperature. These engines are designed to rely on the EGR valve for mixture regulation once they're warm, the only other way to get it to run would be to map out the EGR which would be very tricky to do indeed since the ECU is not programmable.

 

 

Yes, for me too that EGR valve looks "unstable"...

Was prepared yesterday to catch EGR coil infinity... plugged EGR back, cleaned error, nicely started engine (after 24H standing in -13...-16*C).

It idled fine for 30min, then made some "handbrake joy" for few minutes in snowy yard hehe, then left it idle.

Nice, no shut-downs.

When driving home, after half a minute again- jerking, EML, shut-down...but engine was starting normally afterwards / click test ok / = no need to check coil's Ohms...

Same error 17848 „EGR valve N18 / open circuit”- but "sporadic" now.

 

Erased it, started engine- and with no problems arrived home (22km/1H through city).

 

Let's see how it will be next week.

Price for new EGR (Pierburg) already checked.

If replacement will be needed- will kindly ask / push :-))) my job mates make adaptation with VCDS.

 

At this moment- thank you sepulchrave and Wino for advises/help!

[Breezy_Pete]

:thumbup:

 

I still haven't got round to plotting any useful graphs from that log I did, but I did have a little look last night and it appears EGR is not used at all while the engine is idling.

[sepulchrave]

:thumbup:

 

I still haven't got round to plotting any useful graphs from that log I did, but I did have a little look last night and it appears EGR is not used at all while the engine is idling.

 

That doesn't make any sense, any time the throttle butterfly is almost shut is when EGR is used the most to offset the parasitic loss due to manifold vacuum on engine efficiency.

[Breezy_Pete]

Check it on your car.

No need to optimise efficiency when idling, and the rarefied charge would easily fail to ignite/misfire if you made it less flammable, no?

[sepulchrave]

Check it on your car.

No need to optimise efficiency when idling, and the rarefied charge would easily fail to ignite/misfire if you made it less flammable, no?

 

My 2.0 doesn't have EGR, it's an old school lean burn conversion of an ancient donk with secondary air injection to help clean up the exhaust before it hits the cat.

The addition of inert gas doesn't make the mixture 'less flammable', it simply aids cylinder filling to reduce parasitic loss, it means less fuel is needed because there is less oxygen to go with it and it is considered essential to reduce emissions and increase economy in stop/start traffic driving conditions.

[Breezy_Pete]

Just look at the log. When engine is mostly idling, in a queue of traffic approaching a roundabout for a chunk in the middle of the journey, EGR is mostly fully shut.

You don't have your AUB any more? End of an era!

Edited 7 January, 2017 by Wino

[sepulchrave]

Just look at the log. When engine is mostly idling, in a queue of traffic approaching a roundabout for a chunk in the middle of the journey, EGR is mostly fully shut.

You don't have your AUB any more? End of an era!

 

Loaned it to the ex-wife, better than it sitting on the drive, it's in daily use and passed another MOT easily.

[Breezy_Pete]

Here's a plot of the data from that log, few things scaled to fit all on the same y-axis.  Time in seconds along the x-axis.

Far as I can see, below 52°C, no EGR use, and most time revs are below about 1250, EGR flatlines.  (EGR pot voltage should say x1000, not 100)

 

Edited 9 January, 2017 by Wino

[indars]

Update:

EGR valve replaced & adapted / errors cleaned 10 days ago > so far everything works nice ;-)

Again- thank you guys for help!