My 2.3 ltr. fuel injected sedan runs rough on overrun and on overrun and low throttle, however, it goes well under full power. It has new plugs, points, spark plugs and leads and condenser. I have changed the throttle valve switch and the timing is O.K. I would be happy for any input to get me running smoothly. Thanks in anticipation.
1974 ‘D’ Citroen. Help wanted
- Thread starter Buckle
- Start date
Mmmmm, I'm no expert on these things, my '72 DS21 ie has some similar hesitations and backfiring when starting to apply power after overrun. It runs well the rest of the time....... similarly I have attended to the normal things, but it seems that somewhere there is a valve or sensor that is not happy.
I guess we have to expect some things like this on 50 year old electronic stuff.
I guess we have to expect some things like this on 50 year old electronic stuff.
Many thanks, will look into this
This post would be better in the Citroen forum. With that said, have a look at all the vacuum lines to make sure there are no cracks or holes in any of them. Don’t forget the rubber couplings between the inlet manifold and the inlet runners.
Next is to check that fuel pressure is holding steady at 28psi both at idle and full throttle.
Check the ignition timing so set properly and the leads, coil and condenser are in good order.
Your 23 will have a deceleration valve in the air line between the air filter and throttle body. If it’s not working properly I think it will cause the problem you have. Dirty contacts in the throttle switch can also cause strange problems particularly if the idle contacts are dirty.
Next is to check that fuel pressure is holding steady at 28psi both at idle and full throttle.
Check the ignition timing so set properly and the leads, coil and condenser are in good order.
Your 23 will have a deceleration valve in the air line between the air filter and throttle body. If it’s not working properly I think it will cause the problem you have. Dirty contacts in the throttle switch can also cause strange problems particularly if the idle contacts are dirty.
sounds like vacuum leaks to me .... the more you open the throttle, the less vacuum leaks matter... I wonder if the cold start "thing" could be a huge vacuum leak when it dies. a pinhole in the diaphragm of the manifold pressure sensor could also be a problem......
Oh ... I've just seen faulksys reply. I didn't know about the deceleration valve. I'm going to see if my old car has one of them next time I'm near it.
Oh ... I've just seen faulksys reply. I didn't know about the deceleration valve. I'm going to see if my old car has one of them next time I'm near it.
Thank you both for the suggestions. I sure persistence will pay off eventually.
A huge amount of information about D-Jetronic is here ... https://jetronic.org/en/
Check all you vacuum and air hoses and that everything is connected properly. The full load switch is the UFO shaped thing on the firewall and it's an on/off device you can test easily enough. D= Druck = Pressure and the heart of the system is the pressure sensor capsule, which can crack internally, so it is worth testing it carefully. Make sure it is the correct one for the car by the Bosch number on it. 21 and 23 are different and there are many similar looking versions out there. It has a plug covering the adjuster, but can be adjusted if absolutely necessary. The early-1970's version of emission tampering I'd guess.
Check all you vacuum and air hoses and that everything is connected properly. The full load switch is the UFO shaped thing on the firewall and it's an on/off device you can test easily enough. D= Druck = Pressure and the heart of the system is the pressure sensor capsule, which can crack internally, so it is worth testing it carefully. Make sure it is the correct one for the car by the Bosch number on it. 21 and 23 are different and there are many similar looking versions out there. It has a plug covering the adjuster, but can be adjusted if absolutely necessary. The early-1970's version of emission tampering I'd guess.
Thank you David for your input. I will check out the website.
There are 4 golden rules when trouble shooting D-jetronic.
1. Check the ignition system is in perfect working order
2. Check there are no vacuum leaks in hoses and inlet manifold
3. Check the fuel pressure
4. Never adjust the MAP sensor
The MAP sensor was preset at the factory and resetting it once you have messed with it is complicated to say the least. Bosch never published data on them so there are no reference values to aim for. The only thing that you can easily measure about them is the resistance of the coils but that only tells you if the unit has internal shorts or not.
A more likely culprit is the throttle position sensor or the trigger points as they both wear over time causing odd behaviour and rough running.
1. Check the ignition system is in perfect working order
2. Check there are no vacuum leaks in hoses and inlet manifold
3. Check the fuel pressure
4. Never adjust the MAP sensor
The MAP sensor was preset at the factory and resetting it once you have messed with it is complicated to say the least. Bosch never published data on them so there are no reference values to aim for. The only thing that you can easily measure about them is the resistance of the coils but that only tells you if the unit has internal shorts or not.
A more likely culprit is the throttle position sensor or the trigger points as they both wear over time causing odd behaviour and rough running.
Trigger points?
Do you mean the contacts in the dizzy?
Mine has 123 ignition fitted by the previous owner. Seems to work well.
I doubt he paid attention to the trigger points at the time.
The accelerating stagger it gets is very similar to a carby with non functioning accelerating pump......
Are the trigger points involved with that aspect of control?
Do you mean the contacts in the dizzy?
Mine has 123 ignition fitted by the previous owner. Seems to work well.
I doubt he paid attention to the trigger points at the time.
The accelerating stagger it gets is very similar to a carby with non functioning accelerating pump......
Are the trigger points involved with that aspect of control?
The injected DS's have a second set of points in the base of the distributor to trigger the injection pulses. Its a pair of contacts. Generally easy to diagnose as the car will drop a pair of cylinders if one of the contacts plays up.
On trigger points, a dual set, this may be of interest ... https://www.aussiefrogs.com/forum/index.php?threads/wtb-d-jetronic-bits.141914/
If they were faulty, it probably would show up in poor general performance across the power range. 123 ignition does away with them and gives a better idle and better ignition, so worth considering that as an upgrade.
If they were faulty, it probably would show up in poor general performance across the power range. 123 ignition does away with them and gives a better idle and better ignition, so worth considering that as an upgrade.
The trigger points are used by the ECU to open the injectors and provide a tach signal for engine speed. As the cam followers wear it throws the injection pulse timing out for each pair of injectors but not necessarily by the same amount. The net result is rough running and poor fuel economy. They can be adjusted by bending the contacts closer together.
If one of the trigger points fails completely then the engine will drop two cylinders. Either 1&3 or 2&4. If you lose 1&4 or 2&3 then you have a different problem somewhere else.
The 0280100011 ECU on the 21 had an over run cutoff circuit. When engine speed is above a threshold and the idle contact is closed, the ECU shuts down the fuel injectors and the engine coasts. The transition to/from cutoff can be a bit rough depending on a number of other factors. That could be part of your problem Bob. I’m not sure if the feature was carried through to the 0280100023 and 0280100048 ECUs in the 23s
There are different revisions of each ECU denoted by coloured stickers on the casing and they aren’t all necessarily interchangeable. That said, any combination of ECU and MAP should get the car running although possibly not as well as it could.
If one of the trigger points fails completely then the engine will drop two cylinders. Either 1&3 or 2&4. If you lose 1&4 or 2&3 then you have a different problem somewhere else.
The 0280100011 ECU on the 21 had an over run cutoff circuit. When engine speed is above a threshold and the idle contact is closed, the ECU shuts down the fuel injectors and the engine coasts. The transition to/from cutoff can be a bit rough depending on a number of other factors. That could be part of your problem Bob. I’m not sure if the feature was carried through to the 0280100023 and 0280100048 ECUs in the 23s
There are different revisions of each ECU denoted by coloured stickers on the casing and they aren’t all necessarily interchangeable. That said, any combination of ECU and MAP should get the car running although possibly not as well as it could.
Thanks Faulksy, it is during overrun and the following desire to accelerate that it misbehaves. It staggers and gives a cautious backfire, then is willing to go.
Otherwise it runs smoothly, and has good top end power.
Is that overrun cutoff something that can be tinkered with, or is it an ECU thing involving whizzing electrons......
Boy, do I hate whizzing electrons!
Otherwise it runs smoothly, and has good top end power.
Is that overrun cutoff something that can be tinkered with, or is it an ECU thing involving whizzing electrons......
Boy, do I hate whizzing electrons!
You can't easily compensate for a worn out cam on the distributor with three sets of points in the one distributor. This is why 123 ignition is such a worthwhile improvement on the EFI cars, as it means the angular firing position of both the ignition and injector timing is always consistent. The first thing you notice is that the idle is more consistent.
I should also point out that I was not advocating random fiddling with the adjuster under the sealing plug on the pressure sensor. Not a good idea, but be aware it may have happened if that plug is missing. At nearly 50 years old, the factory setting could be a bit off by now. The site I linked to has very useful information on this device.
Most importantly ... regularly check for hose leaks and don't ignore any cracks in hoses or fuel smells. Use a good quality EFI hose like Gates and proper injection hose clips - e.g. by Norma - not water hose worm clips.
The other sensor on the throttle butterfly acts as an accelerator pump and as the throttle is opened, it adds some extra injection pulses to put more fuel into the engine. There are a series of flaps in the mechanism so that these pulses are only added as the throttle is being opened and not when the throttle is being closed. If this is not working, it will be like not have an accelerator pump on a carby, the engine will not respond immediately to throttle opening with more power.
Cheers, Ken
Cheers, Ken
That sounds like my situation.
Is this a mechanical thing..... which I can look at, understand and restore physically?
OR is it an invisible whizzing electron thing that I could never understand, nor do anything about?
Its a physical switch inside the throttle position sensor. There are two of them, one tells the ECU the car is idling when the throttle is closed and the other does as Ken describes. You might also find that the first half of the circuit board trace is worn as that section get the most use.
You could buy new circuit boards for the flappy ladder switch on ebay from the europe.
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Is there an idle switch in there? I thought that was later injection system (full load and idle switches on the spindle). I thought DJet just produced a square wave output when the throttle was moving. I'd never realised there was an idle switch in there too!