2.8 Idle Air Control Valve
Discussion
I think I am going to have to ask you to clarify that a bit. The 2.8 uses K Jetronic injection and the 2.9 uses the L Jetronic based EFI system, there are few similarities.
Are you talking about the Auxiliary Air Device mounted on the plenum chamber which has a rotating valve varying air bypass as engine temperature changes?
Any chance of a picture so I know exactly what you are after?
Are you talking about the Auxiliary Air Device mounted on the plenum chamber which has a rotating valve varying air bypass as engine temperature changes?
Any chance of a picture so I know exactly what you are after?
I confess I am still puzzled. Have a look at this photo (not the best but it should do)
The 7th injector is the one towards the left of the picture with the connector in blue. The device is the cold start relay and injector.
To the right of the picture, and on the front of the plenum chamber is the auxiliary air device which has a black connector.
The pipe between them is an air pipe.
The auxiliary air device draws air from the air intake duct prior to the throttle valve. That air flow is controlled by how far the auxiliary air device rotates, which is dependent upon a bi metallic strip which in turn is affected by water temperature and an internal heating coil which in turn is switched by the thermotime switch. When hot the device is closed and the heating coil switched off. When cold, air is allowed through and gets into the plenum chamber via the cold start injector housing. That increases the idle speed.
The cold start relay may or may not come on at the same time dependent upon other sensors. If the engine sensors detect cold water and cold air then the cold start injector should open and spray petrol into the 'auxiliary' air, which makes the mixture richer until the engine is up to an adequate temperature.
Does all that make any sense to you???!!!!
Does that help you identify which part you need?
The 7th injector is the one towards the left of the picture with the connector in blue. The device is the cold start relay and injector.
To the right of the picture, and on the front of the plenum chamber is the auxiliary air device which has a black connector.
The pipe between them is an air pipe.
The auxiliary air device draws air from the air intake duct prior to the throttle valve. That air flow is controlled by how far the auxiliary air device rotates, which is dependent upon a bi metallic strip which in turn is affected by water temperature and an internal heating coil which in turn is switched by the thermotime switch. When hot the device is closed and the heating coil switched off. When cold, air is allowed through and gets into the plenum chamber via the cold start injector housing. That increases the idle speed.
The cold start relay may or may not come on at the same time dependent upon other sensors. If the engine sensors detect cold water and cold air then the cold start injector should open and spray petrol into the 'auxiliary' air, which makes the mixture richer until the engine is up to an adequate temperature.
Does all that make any sense to you???!!!!
Does that help you identify which part you need?
I'm very confused too.
Can you explain the symptoms of the problem?
The idle air control on the 2,8 is by the air bypass on the throttle unit (big screw underneath).
The 7th cold start injector is connected to the thermo time switch (which turns it on until around 40°)
The only relay connected to the cold start injector on my circuit diagram is the 'Hot Start Module' (which has bascially no effect anyway....)
There are images of all the important parts here:
http://www.zeepoort.nl/jetronic/K-Jetronic-trouble...
Can you explain the symptoms of the problem?
The idle air control on the 2,8 is by the air bypass on the throttle unit (big screw underneath).
The 7th cold start injector is connected to the thermo time switch (which turns it on until around 40°)
The only relay connected to the cold start injector on my circuit diagram is the 'Hot Start Module' (which has bascially no effect anyway....)
There are images of all the important parts here:
http://www.zeepoort.nl/jetronic/K-Jetronic-trouble...
Struggling, I thought I had a spare one but dont appear to. Any of you guys out there remember the name of the firm who re-condition K Jet units, I cannot find that either!
If we cannot find one that way the next thing I would do is contact the Capri Owners Club, lots of 2.8 Colognes there.
If we cannot find one that way the next thing I would do is contact the Capri Owners Club, lots of 2.8 Colognes there.
Just to be clear, the cold start injector is only activated 2 ways:
i) If the engine is cold (below 40°) the thermo time switch activates the injector.
ii) If the engine is hot and fails to fire in the first few seconds of turning over the hot start relay will operate and pulse the injector until the engine fires.
The thermo time unit is a bi-metallic switch that also incorporates a heating coil which limits the activation time to less than 10 seconds.
i) If the engine is cold (below 40°) the thermo time switch activates the injector.
ii) If the engine is hot and fails to fire in the first few seconds of turning over the hot start relay will operate and pulse the injector until the engine fires.
The thermo time unit is a bi-metallic switch that also incorporates a heating coil which limits the activation time to less than 10 seconds.
greymrj said:
LeTVR, I think the word 'relay' may be confusing you.
Better resign my IEEE membership then....Le TVR said:
Better resign my IEEE membership then....
I am not sure where MIMechE stands me in such august company 
To be completely accurate with the descriptions of components;
When the engine is cold the thermotime SWITCH detects this and makes an electrical connection to the Kalt RELAY which sends current to operate the SOLENOID in the cold start injector, which opens the injector and allows a constant stream of fuel into the plenum chamber.
(as I understand it there is no hot start relay or pulsing of this injector, pulsing didnt come in until electronic control was possible. Hot starting is however influenced by the function of the warm up regulator which controls fuel pressure to the injectors. The large screw under the throttle body, although referred to as an idle adjuster, isnt really. It does effect air bypass of the throttle valve but not in the same simple way or for the same function as say an SU idle adjust screw. )
David,
I am not sure what issue you had with the cold start injector but when you have the new one there is a test you can try. Get a jam jar or similar with a lid, make a hole in the lid and insert the injector unit from under the lid, then replace the lid. The injector should not now be able to come out of the jar. Connect the injector blue terminal. Hold this jar right way up close to the plenum then ask an assistant to turn the engine over. You should see a continuous fine conical shaped mist from the injector. If it dribbles out rapidly, jets out or is off to one side, the injector isnt working as it should. If no fluid or small dribble then the solenoid isnt opening the injector properly.
There is an inherent fault in the K Jet system which can give rise to problems. The temperature sensor and the thermotime switch itself can be a bit inaccurate, causing the cold start injector to open when the engine or air is warm enough for the engine to start normally. That happens briefly but can easily be enough to over richen the mixture and effectively 'flood' the engine. So if the engine has been starting normally but fails to start after standing for a bit, DONT keep trying to start it. Disconnect the blue connector and then see if it starts, if it does then the cold start injector has opened unnecesarily.
This is a reasonably common issue on the 2.8 K Jet in the S and I believe in the Wedge.
Some people leave the blue connector off until they need a cold start. The alternative is to introduce a switch into the circuit so the cold start cannot operate until needed.
While you have the injector off, pull back the blue cover on the connector and make sure all is well. The electrical joints are a bit fragile and there could be a continuity fault there. New connectors are available, I would have to check to remind myself of the supplier.
Good luck and let's know how you get on.
I am not sure what issue you had with the cold start injector but when you have the new one there is a test you can try. Get a jam jar or similar with a lid, make a hole in the lid and insert the injector unit from under the lid, then replace the lid. The injector should not now be able to come out of the jar. Connect the injector blue terminal. Hold this jar right way up close to the plenum then ask an assistant to turn the engine over. You should see a continuous fine conical shaped mist from the injector. If it dribbles out rapidly, jets out or is off to one side, the injector isnt working as it should. If no fluid or small dribble then the solenoid isnt opening the injector properly.
There is an inherent fault in the K Jet system which can give rise to problems. The temperature sensor and the thermotime switch itself can be a bit inaccurate, causing the cold start injector to open when the engine or air is warm enough for the engine to start normally. That happens briefly but can easily be enough to over richen the mixture and effectively 'flood' the engine. So if the engine has been starting normally but fails to start after standing for a bit, DONT keep trying to start it. Disconnect the blue connector and then see if it starts, if it does then the cold start injector has opened unnecesarily.
This is a reasonably common issue on the 2.8 K Jet in the S and I believe in the Wedge.
Some people leave the blue connector off until they need a cold start. The alternative is to introduce a switch into the circuit so the cold start cannot operate until needed.
While you have the injector off, pull back the blue cover on the connector and make sure all is well. The electrical joints are a bit fragile and there could be a continuity fault there. New connectors are available, I would have to check to remind myself of the supplier.
Good luck and let's know how you get on.
Amazing the knowledge that is present on this site. The car is running rich and holding a an RPM OF 1500 even when warmed up. Checked for all the usual air leaks however hit a brick wall as we didn't fully understand how the K Jet worked. Going to check the injector over the next couple of days as it feels like the most likely culprit.
OT but mine does have an impulse relay for hot starts. Put a 'scope on it years ago to try and work out what it was doing which was as described. Its the TVR 'build standard' again.
My K-Jetronic service notes give the following:
Idle too high: Injection control pressure too high/Auxiliary air device not closing/airflow meter not closing
Too rich : Control pressure wrong/base setting wrong/vacuum leak/cold injector leak
Has anyone touched the base setting (CO) on the airflow meter?
greymrj said:
I am not sure where MIMechE stands me in such august company
Touché My K-Jetronic service notes give the following:
Idle too high: Injection control pressure too high/Auxiliary air device not closing/airflow meter not closing
Too rich : Control pressure wrong/base setting wrong/vacuum leak/cold injector leak
Has anyone touched the base setting (CO) on the airflow meter?
Hmmm the plot thickens. Nothing has been adjusted. A full day of exploration is required. The idle has always been iffy on the car and it went through period hot start issues last year which somehow cured themselves! The aim was to have the car running for next weekend however I can see this being a long painful process.
Might be a wild thought, but well worth a look. Take the air filter cover and air filter out, easily done. In the evening get a mate to shine a torch inside the inner part of the air box and see if you can see any light. You will see a plate fixed to the back of the airbox with alloy pop rivets, these corrode and fail. That allows air in on the downstream side of the filter which effects the way the large air sensor valve lifts. Furthermore it allows dust into the intake. That air sensor valve is VERY sensitive, a coating of dust will be enough to effect it. It is fairly easy to take the black cover off the top of the air sensor valve. Do NOT press the valve down to see if it is working, it has to move up. Check first to see if the top of the air sensor plate is level with or very slightly below (under 0.5mm) below the top of the annular section.
If it is dirty or not in the correct position you will never sort the K Jet out. This has to be right. Dont even think of adjusting the allen screw in the fuel distributor head before checking this. The air sensor has to be right FIRST. If it isnt right then I am afraid adjusting it is a job for an expert.
Another thought, if the idle is high but steady when at normal temperature, try squeezing the pipe from the auxiliary air control device to the throttle body. If the revs drop then the aux air device isnt closing properly, a reasonably common problem especially if a car has been laid up. Take it off and clean it as best you can, a bit of corrosion may be the problem. Shine a light through, there is a disc section which should be open when closed then rotate to closed when hot. You can, with care, put 12v across the terminals and it should gradually close completely. Take the voltage off and it should gradually open again. If it doesnt move, or doesnt complete its movement then I am afraid it cannot be repaired. Cleaning was enough to get mine working properly and the car had been unused for at least 4 years when I got it.
If it is dirty or not in the correct position you will never sort the K Jet out. This has to be right. Dont even think of adjusting the allen screw in the fuel distributor head before checking this. The air sensor has to be right FIRST. If it isnt right then I am afraid adjusting it is a job for an expert.
Another thought, if the idle is high but steady when at normal temperature, try squeezing the pipe from the auxiliary air control device to the throttle body. If the revs drop then the aux air device isnt closing properly, a reasonably common problem especially if a car has been laid up. Take it off and clean it as best you can, a bit of corrosion may be the problem. Shine a light through, there is a disc section which should be open when closed then rotate to closed when hot. You can, with care, put 12v across the terminals and it should gradually close completely. Take the voltage off and it should gradually open again. If it doesnt move, or doesnt complete its movement then I am afraid it cannot be repaired. Cleaning was enough to get mine working properly and the car had been unused for at least 4 years when I got it.
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