2.1 DJ idle/CO

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davidoft1
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Re: 2.1 DJ idle/CO

Post by davidoft1 »

Clean out your original ISV with carb cleaner , refit see if you have the same effect, idle speed and timing will effect the emissions, try slowing your idle speed a little more, see what happens to the timing , it’s possible the advance is kicking in, have you cleaned he throttle body ?

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scotttie
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Re: 2.1 DJ idle/CO

Post by scotttie »

davidoft1 wrote: 11 Jan 2021, 17:05 Clean out your original ISV with carb cleaner , refit see if you have the same effect, idle speed and timing will effect the emissions, try slowing your idle speed a little more, see what happens to the timing , it’s possible the advance is kicking in, have you cleaned he throttle body ?
Ok I'll give that a go. Yep removed the throttle body and cleaned it. Did the light test on the throttle body and it looked good.
 
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Re: 2.1 DJ idle/CO

Post by ajsimmo »

An additional 8° advance will increase your idle speed significantly, and affect your emissions! I'd try knocking it back to maybe 12-15°, rather than the stock 10° (as it runs well with more advance). Then see how your idle and mixture readings are.

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scotttie
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Re: 2.1 DJ idle/CO

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ajsimmo wrote: 11 Jan 2021, 19:18 An additional 8° advance will increase your idle speed significantly, and affect your emissions! I'd try knocking it back to maybe 12-15°, rather than the stock 10° (as it runs well with more advance). Then see how your idle and mixture readings are.

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Thanks ajsimmo. Would you be able to confirm if I have correctly understood the workshop manual for adjusting timing: DIS 3 pin plugs disconnected and bridged, yellow connector in front of DIS disconnected, and distributor retard vacuum hose removed and plugged. Note the advance vacuum hose is still attached.

Am I correct in thinking with the engine set up as above, the only things that can affect timing are rpm, mechanical advance or vacuum advance? And with the engine idling at ~800rpm, the mechanical or vacuum advance should not be active. If this is the case then I guess it leaves me with two options, either the timing is out, or the mechanical advance is kicking in earlier than it should as David suggested (I believe the mechanical advance should kick in around 1050rpm).

This has also got me thinking what the timing should read at idle when everything is connected back up. Mine reads bang on the timing notch on the pulley. I guess if I adjust it back in the set up process, it will result in less advance at idle under normal running conditions.
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scotttie
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Re: 2.1 DJ idle/CO

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To give me a bit more confidence in making adjustments to the timing, I've been trying to get my head around how the vacuum advance and retard works.

Image

With the engine idling the throttle valve is closed, so there is no vacuum going to the advance side of the distributor. As the retard vacuum hose is connected to the plenum chamber, there is max vacuum going to the retard side of the distributor with the throttle closed. This means that when setting timing following the workshop manual process to 10 degrees BTDC with the retard vacuum removed and plugged, once the retard hose is reattached, the timing at idle will be retarded back down to around TDC. From what I have read this is a mechanism to reduce emissions whilst idling. As soon as the throttle opens, the advance receives vacuum and the retard vacuum in the plenum chamber is increasingly diminished as the throttle opens further.

So, in my circumstance, with the retard vacuum hose disconnected and for timing adjustment, I am seeing  around 18 degrees BTDC. With everything plugged back in for normal running I see 10 degrees BTDC, so the vacuum retard is doing its job in pulling down the advance at idle. So with the vacuum hose disconnected, if I adjust the timing down to where it should be (10 degrees BTDC), then my timing at idle with everything connected back up will be around TDC.

Any DJ gurus out there who can confirm whether I've got this right? 

 
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Re: 2.1 DJ idle/CO

Post by silverbullet »

Just a thought: if the diaphragm in the breather tower has split/disintegrated, the engine will be breathing in oil vapours all the time.
If the engine is also getting a little wheezy (piston rings not sealing as well as they were) then crankcase pressures may well be higher than they should be and oily vapours will push the CO reading up.
Might be worth taking it off, removing the baffle (it should slide out) and taking a good look in there.

PS if the dissy diaphragm has failed, then you wont be getting any vac advance at idle, but that usually goes with a noticeable drop in mpg
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scotttie
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Re: 2.1 DJ idle/CO

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silverbullet wrote: 12 Jan 2021, 19:20 Just a thought: if the diaphragm in the breather tower has split/disintegrated, the engine will be breathing in oil vapours all the time.
If the engine is also getting a little wheezy (piston rings not sealing as well as they were) then crankcase pressures may well be higher than they should be and oily vapours will push the CO reading up.
Might be worth taking it off, removing the baffle (it should slide out) and taking a good look in there.
Hi Ian, For measuring the CO I disconnected the breather tower and plugged the hose (air intake side) as per the workshop manual for this reason, but it is still high. I will take a look at it though and make sure it's functioning properly.
silverbullet wrote: 12 Jan 2021, 19:20 PS if the dissy diaphragm has failed, then you wont be getting any vac advance at idle, but that usually goes with a noticeable drop in mpg
This is what I am trying to get a handle on. Is there any vacuum advance at idle? I believe the vacuum advance hole in the throttle body is located on the AFM side of the throttle valve, so when the throttle is closed the hole isn't getting any vacuum.
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Re: 2.1 DJ idle/CO

Post by scotttie »

After a bit more reading of the workshop manual I think I'm on the right track with this:

1. DIS unit disconnected and connections bridged, yellow connection in front of DIS disconnected, disconnect and plug vacuum retard hose
4. adjust timing to 10 degrees BTDC (idle at 800 +/- 50)
5. with engine still running, reconnect vacuum retard hose to distributor. The timing will now drop down to around TDC (This is where I got to above) and rpm will drop.
6. However, I didn't consider the DIS unit! With the engine still running reconnect the DIS unit and if all is well the timing at idle should advance back up and rpm should increase.
7. switch off engine and reconnect yellow connection in front of DIS.
8. restart engine and idle timing should fluctuate between 5 and 15 degrees BTDC. This is what the idle timing should be under normal running and confirms the DIS unit is working.

Sorry if this is already common knowledge for some (and for waffling on), but I thought I'd share in case it's of use to others. Hoping my timing currently being at 18 instead of 10 is the cause of my idle/CO adjustment issue. Now I just have to wait for the weekend to test it.

 
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davidoft1
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Re: 2.1 DJ idle/CO

Post by davidoft1 »

scotttie wrote: 12 Jan 2021, 23:18 After a bit more reading of the workshop manual I think I'm on the right track with this:

1. DIS unit disconnected and connections bridged, yellow connection in front of DIS disconnected, disconnect and plug vacuum retard hose
4. adjust timing to 10 degrees BTDC (idle at 800 +/- 50)
5. with engine still running, reconnect vacuum retard hose to distributor. The timing will now drop down to around TDC (This is where I got to above) and rpm will drop.
6. However, I didn't consider the DIS unit! With the engine still running reconnect the DIS unit and if all is well the timing at idle should advance back up and rpm should increase.
7. switch off engine and reconnect yellow connection in front of DIS.
8. restart engine and idle timing should fluctuate between 5 and 15 degrees BTDC. This is what the idle timing should be under normal running and confirms the DIS unit is working.

Sorry if this is already common knowledge for some (and for waffling on), but I thought I'd share in case it's of use to others. Hoping my timing currently being at 18 instead of 10 is the cause of my idle/CO adjustment issue. Now I just have to wait for the weekend to test it.

 


Sounds about right, I had an idea it was an ignition timing / advance issue. I think
You should now get a slower idle that you will need to speed up which should bring your 2 adjustment screws into somewhere part way up the adjustment

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Re: 2.1 DJ idle/CO

Post by Aidan »

Just a FYI the CO screw in the AFM has a o-ring seal on it, if this has failed or is damaged then air can be drawn down the threads

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scotttie
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Re: 2.1 DJ idle/CO

Post by scotttie »

Aidan wrote: 13 Jan 2021, 20:58 Just a FYI the CO screw in the AFM has a o-ring seal on it, if this has failed or is damaged then air can be drawn down the threads

Thanks Aidan I’ll check that.

I have a spare AFM I tried but the problem remained. Off topic but what I did notice is my current AFM is made in France and my space is made in Germany. Both Bosch and both the same part number. Though on the german one the AFM screw could be unscrewed and removed whereas the french one seemed to hit a point where it wouldn’t unscrew any further. Could be gunk stopping it but it felt like if I tried to force it something would break. Not sure how that would be possible though as the bottom of the AFM appears cast so the screw must have got in there somehow!
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scotttie
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Re: 2.1 DJ idle/CO

Post by scotttie »

Successful day today. Adjusted the timing down to 10 degrees BTDC, which then gave me room to play with the idle/CO settings. After timing adjustment I was able to confirm vacuum retard is working (connected timing retards to ~TDC), and the DIS unit is working (connected timing advances back to fluctuating 5-15 degrees BTDC at idle). With idle at 800rpm the CO reading was ~2% on the Gunson gas tester. This was with the AFM screw about half a turn from the top, so not much room to reduce the CO % further if I ever needed to. Pleased to have the timing and CO within spec now, and it's nice to gain a bit more knowledge on how the Digijet system works! 

Cheers,
Scott
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