D-Jet AAV

[cassell]

Question: The Bosch auxilliary air valve on my B20E 1800ES seized in the partially open/closed position a long time ago, this appears to be a common problem. The resultant problem is that tickover is far too high and can't be adjusted down.

My understanding is that as the AAV operates as a 'choke' mechanism to aid cold starting it can be blocked-off and although cold start idling may be affected until the engine is warm, normal running isn't affected.

I have now noticed however that the car is running 'rich' and the spark plugs are powdery black when I remove them for checking and gap setting. Is this because I've blocked off the upper port of the AAV completely with a tight fitting rubber plug, does the system still require a limited amount of air to be drawn through the AAV under normal driving, and mine is being starved of that airflow which is affecting the fuel/air mixture?

Any thoughts would be welcome.

Paul

[Ron Kwas]

Paul;

Your understanding of function of AAV is correct...it by-passes throttle and only allows additional air when cold and thereby raises Idle (other sensors of D-Jet assure correct amount of fuel is injected under this condition)...once warm and closed off it does not affect running...if yours is stuck partially open, I'd block it of completely and tickle the idle up manually during warm-up...I very much expect your rich mixture is a result of something else (check Cold-Start Injector for leakage!)...link to good D-Jet troubleshooting guide can be found here: http://www.sw-em.com/bosch_d-jetronic_injection.htm

"does the system still require a limited amount of air to be drawn through the AAV under normal driving" NO...after warm-up, aux air path is fully closed off and AAV is out of the picture.

I am currently compiling notes on the AAV assembly with the goal of possibly refurbishing these NLA gems...info is not yet live and on-line...you are welcome to contact me directly (preferably not through forum which is cumbersome and does not allow me to keep a running thread in the manner I prefer)...I recall a thread on this forum also dealing with AAV: https://www.volvoforums.org.uk/showt...=279071&page=2

Cheers

[amazon69]

I managed to free my 25 year freezed AAV with a cycle of extreme heat (blowtorch) and extreme cold (freezer) over a week, with loads of penetrating oil. Might be worth a go.

[cassell]

Originally Posted by Ron Kwas

Paul;

Your understanding of function of AAV is correct...it by-passes throttle and only allows additional air when cold and thereby raises Idle (other sensors of D-Jet assure correct amount of fuel is injected under this condition)...once warm and closed off it does not affect running...if yours is stuck partially open, I'd block it of completely and tickle the idle up manually during warm-up...I very much expect your rich mixture is a result of something else (check Cold-Start Injector for leakage!)...link to good D-Jet troubleshooting guide can be found here: http://www.sw-em.com/bosch_d-jetronic_injection.htm

"does the system still require a limited amount of air to be drawn through the AAV under normal driving" NO...after warm-up, aux air path is fully closed off and AAV is out of the picture.

I am currently compiling notes on the AAV assembly with the goal of possibly refurbishing these NLA gems...info is not yet live and on-line...you are welcome to contact me directly (preferably not through forum which is cumbersome and does not allow me to keep a running thread in the manner I prefer)...I recall a thread on this forum also dealing with AAV: https://www.volvoforums.org.uk/showt...=279071&page=2

Cheers

Thanks for your detailed reply Ron and a grateful thanks for confirming that I was correct in my understanding of the AAV function!

I'll leave mine well and truly sealed off and turn my attention to the cold start injector which may be dribbling fuel and causing a too-rich mixture.
I understand that the cold start injector is under constant fuel feed pressure and opens/operates via a signal from the thermal timer? Presumably just unplugging the electrical connection will not detect a nozzle leak and so the fuel supply pipe to it needs to be disconnected and blanked off to verify a leak?

Thanks again for your help.

Paul

[Ron Kwas]

Paul;

"cold start injector which may be dribbling fuel and causing a too-rich mixture." ...that's the typical failure mode (but any Injector can exhibit this failure).

"I understand that the cold start injector is under constant fuel feed pressure and opens/operates via a signal from the thermal timer?" ...Correct

"Presumably just unplugging the electrical connection will not detect a nozzle leak and so the fuel supply pipe to it needs to be disconnected and blanked off to verify a leak?" Also correct, since leak is of the mechanical part, and not under electrical control...ideally, remove Cold Start Injector from Manifold while Fuelfeed-Rail is under pressure but engine is warm so no flow should occur...

Beware: Extreme caution is called for when disconnecting fuel-feed from CSI, as even with engine OFF, Fuelfeed-Rail will hold operating pressure for some time after shut-down (obviously less time if any Injectors are allowing it to leak down), but opening the Fuelfeed-Rail will possibly result in a spray-mist of fuel just looking to ignite...be ready to catch and manage this spray, not to get a face full, and observe Ignition of Fuel Vapor Safety Precautions!!

A69; Thermal sensor which drives the AAV is not a bimetalic element which wouldn't be bothered by a flame based heatsource as much as the wax-filled pellet of the AAV (similar to a Thermostat)...any flame based heat-source to try to get it moving is not doing it any good!

Good Hunting!

[Pigeon]

Hehe, I remember having an injector hose spring a leak and 3-4 gallons of petrol being pumped out under the bonnet. Thought the fuel gauge was dropping a bit quickly, but didn't realise what was up until petrol got into the channels at the side of the bonnet and started being blown onto the windscreen. Had a look... puddles of petrol on the webs of the inlet manifold and anywhere else there was a depression, and the honk of the vapour fair knocked me back. I was nearly home by then, so I decided that if it hadn't gone up in the last 10 miles it wasn't going to go up in the last few hundred yards, shut the bonnet and carried on.

Anyway...

The fault description sounds as if the rich running started coincident with fiddling with the aux air valve... is this correct? If so, probably worth checking the connection to the engine temperature sensor is clean, tight, and hasn't been knocked into a position where it makes bad contact or is off altogether. It's quite easy to bash that without realising it while guddling around the valve.

[cassell]

Originally Posted by Ron Kwas

Paul;

"cold start injector which may be dribbling fuel and causing a too-rich mixture." ...that's the typical failure mode (but any Injector can exhibit this failure).

"I understand that the cold start injector is under constant fuel feed pressure and opens/operates via a signal from the thermal timer?" ...Correct

"Presumably just unplugging the electrical connection will not detect a nozzle leak and so the fuel supply pipe to it needs to be disconnected and blanked off to verify a leak?" Also correct, since leak is of the mechanical part, and not under electrical control...ideally, remove Cold Start Injector from Manifold while Fuelfeed-Rail is under pressure but engine is warm so no flow should occur...

Beware: Extreme caution is called for when disconnecting fuel-feed from CSI, as even with engine OFF, Fuelfeed-Rail will hold operating pressure for some time after shut-down (obviously less time if any Injectors are allowing it to leak down), but opening the Fuelfeed-Rail will possibly result in a spray-mist of fuel just looking to ignite...be ready to catch and manage this spray, not to get a face full, and observe Ignition of Fuel Vapor Safety Precautions!!

A69; Thermal sensor which drives the AAV is not a bimetalic element which wouldn't be bothered by a flame based heatsource as much as the wax-filled pellet of the AAV (similar to a Thermostat)...any flame based heat-source to try to get it moving is not doing it any good!

Good Hunting!

Thanks for the confirmation that my knowledge is yet again correct in terms of the cold start injector, much appreciated. I promise not to turn my ES and myself into a fireball during my investigation!!

[cassell]

Thanks Pigeon, all good in that area, the temperature sensor in the head adjacent to the AAV solely provides a signal to the temperature gauge and not the D-jet system.

[c1800]

Originally Posted by cassell

Thanks Pigeon, all good in that area, the temperature sensor in the head adjacent to the AAV solely provides a signal to the temperature gauge and not the D-jet system.

Just to clarify. The temp sensor in the head adjacent to the AAV DOES supply the signal to the ECU. The sensor for the gauge is at the back of the head.

Also, if the temp sensor at the front of the head, or the one in the air intake has failed then they can cause Djet to run rich.

[cassell]

Thanks c1800, my mistake, you are correct of course, I was confusing myself with the thermal timer sensor at the back of the engine block!