"Smelly" exhaust, slight popping on overrun

[silverbullet]

I am pretty sure that I know the cause, but just for the sake of a bit of chat:

The SA (5 cylinder, motronic efi not k-jet) has developed a pungent (not petrol smelling) exhaust at idle and a fondness for a soft sporty *poppoppop* on the overrun.
I don't mind a bit of overrun crackle but the exhaust is a bit "ripe" and the smell really gets into ones clothes in no time, its a bit antisocial in traffic.

My diagnosis is a vacuum system leak or inlet manifold/injectors not sealing properly, making it go lean at idle. IACV hoses ok. Brakes seem ok but... the SA uses a syncro style vacuum reservior behind the grille just for the demist flap vacuum solenoid.
These reservoirs are known for leaking where the hose plugs into a special grommet on syncros.
I have also capped off the vacuum pipes for the old lpg system/flashlube, just in case they are leaking air.

Anyone else got good any ideas?

Ich fahre einen Bulli. Ich hilfe mir selbst...meistens!

[silverbullet]

No-one offering a diagnosis? It's only an open-loop batch-fire efi, no different to a DJ but without an AFM (it has a MAP sensor) and no vacuum advance/retard on the distributor, the ecu does it all.

I am wondering if the IACV is a bit sticky and making it go lean at idle...

[MGP]

I'm not well versed with the SA setup but I know the early motronic system.
Have you checked the fuel pressure? Have had a few fpr's go wonky before.
Temp sensor I'm assuming is a single wire brass body type? Normally bullet proof but worth cleaning the terminal up, if it's the later blue 2 pin or worse 4 pin just change them.
Is the map sensor in the ecu? If so I would assume there is a length of hose inside, never come across one fail but might be worth a look.
Assuming it's not got obd but does it have the vag 2+2 diagnostic plugs if so it should have some live data capability.
If you can post up some more details of the ecu I may be able to dig up some pin out data.

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[silverbullet]

Now I do have a pair of small mystery plugs under the back seat near the ecu...
The ecu is a Bosch "made in south africa" with a 22S part number. The map sensor is outboard, same part as Audi 1Z diesel!
Fuel rail and injectors like nothing I have ever seen, they are German made Bosch but large diameter with what look like 4 hole "fogger" nozzles and connected by copper busbar cables in a plastic housing, with the fuel rail and regulator integral.
Temp sensor is a 4-wire affair that plugs into a housing on the head between cylinders 1 & 2.

Ich fahre einen Bulli. Ich hilfe mir selbst...meistens!

[silverbullet]

Had a tipoff to check th inlet manifold for air leaks. It was removed a couple of years ago to sort an exhaust leak (2-piece manifold) and I did re-use the gaskets...

Ich fahre einen Bulli. Ich hilfe mir selbst...meistens!

[MGP]

How is the hot starting? The 4 pin combined gauge and ecu temp sensors are known for causing problems.
Do the 2 mystery plugs look like they will plug into these?
[img]//uploads.tapatalk-cdn.com/2016062 ... 7f0740.jpg[/img]

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[silverbullet]

I'll have to view that later. Tapatalk no longer displays on desktop

No starting problems whatsoever, hot or cold. Reliable as a reliable thing.

[silverbullet]

http://i1103.photobucket.com/albums/g47 ... 3zsl34.jpg" onclick="window.open(this.href);return false;
Wires are L to R: grey/brown, grey, white, white/red but plugs not obviously handed. One is a little "distressed"
http://i1103.photobucket.com/albums/g47 ... fw47xz.jpg" onclick="window.open(this.href);return false;
Wires on the temp sensor have seen better days but are intact.
Can't see a part number on the sensor but "made in Belgium"
http://i1103.photobucket.com/albums/g47 ... nvbhnr.jpg" onclick="window.open(this.href);return false;


Ich fahre einen Bulli. Ich hilfe mir selbst...meistens!

[silverbullet]

Tapatalk pics


Ich fahre einen Bulli. Ich hilfe mir selbst...meistens!

[MGP]

Those plugs look to speaker connections? They are certainly the correct style not 100% on the wiring colours tho.
I can't see the wires causing too many problems to be honest, although it might be worth trying a new sensor.
Another thought you say it's popping on overrun, I would assume that the ecu would fuel cut when you let off, is there a closed throttle switch?


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[silverbullet]

They arent the diagnostics. The SA Motronic has a 6-way plug in the engine bay. I cant find that oair anywhere on my 2.6 wiring diagrams so who knows?
The throttle pot is a Golf 3 part, I renewed that with a genuine one a few years ago.
New temp sender now ordered, its still a current part 6U0919501B (previously 357919501B) and under a fiver so I will give that a go first.

Ich fahre einen Bulli. Ich hilfe mir selbst...meistens!

[silverbullet]

Just swapped the dual temp sender, engine not dead cold but definitely a lot cleaner smelling.
Now to see if it also cures the slight tendancy toward kangarooing on a light throttle that it recently developed.
I am confident...

Ich fahre einen Bulli. Ich hilfe mir selbst...meistens!

[silverbullet]

Happy days. Weekly shopping run, exhaust is sweet and it drives nicely once again.
Generally less loud pedal required so it was going lean, mileage should pick up a little too.
Now to see how long the generic sender lasts, the OEM one I removed was dated '03

Ich fahre einen Bulli. Ich hilfe mir selbst...meistens!

[silverbullet]

...and it's slid back to how it was before. Temp sender must have been iffy because it's now better on fuel and the gauge reads slightly lower (unless that reflects correct mixture, quite possible)
Defo inclined to kangaroo on a trailing or light throttle when hot i.e. when returning home from CamperJam and hitting the traffic queues
I'll replace the inlet manifold gasket next and change the fuel filter, plus some new plug leads. The latter were pattern ones five years ago, won't do it any harm.

[silverbullet]

...except that it wasnt. Backing off the timing made its performance a bit "flat" but didnt cure the overrun near-backfiring so I went looking again.

The popping was never present when cold, only one the engine had warmed up a bit, then I found the culprit: the vacuum hose for the fuel regulator was a bit "easy" on its spigot and worse when warm, barely hanging on in fact. So I reckon the regulator wasnt seeing full vacuum and throwing the mixture out.

All for a bit of 3mm hose! I had some semi-pliable nylon pipe so replace them all with that. Normal service has been resumed.

Re-time at 10 degrees btdc, no Octane plug (SA thing) and 99 Octane when I fill up at Tescos

PS before finding the vaccum hose, I prised the metal shrouds off the spark plug leads, curing a slight misfire.