Hello All
Another problem has surfaced with my recently acquired 1998 Xantia 1.9 TD. A flat spot/hesitation appeared yesterday when accelerating from low revs, say after slowing and turning. while its not serious enough to cause a stall its spoiling my enjoyment of the car. I think its related to the tickover which I noticed has altered. Previously it was a constant 900 rpm according to the on-board tacho yesterday it reduced itself to a base 850 rpm but would also drift lower to about 820. the problem was exacerbated if I ran the air-con and it dropped about another 10 rpm. When starting the car the tickover was only just above 800 until the throttle was blipped and then it would return to 850. My car is the one with the part managed engine. The only thing I can think of is that the outside air temperature is warmer than it has been previously and I've been running with the air-con on, I've also noticed that the cooling fans have been running at full tilt as well although the engine temperature has remained at around 70 degrees. Any advice will be gratefully received.
mark_sp
xantia TD flat spot
Moderator: RichardW
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Dave Burns
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The fans run while the aircon is active to maintain air flow over the condenser, this is regardless of vehicle speed or ambient temperature.
The engines idle speed is increased when the aircon is active and is achieved by the same method used to increase idles speed at cold start, this being via vacuum diaphragm and electrovalve, the valve(s) is to the left of the LHM reservoir, the other being for the EGR system.
If you rev the cold engine you should firstly see the cable going to the fast idle lever on the injection pump being released, and then pulled again as the engine returns to idle.
With a hot engine at idle the cable should be released when the aircon is switched on, thus raising the idle speed.
Because these valves are energised most of the time the engine is running its not uncommon for them to fail, when they do fail however they are in the closed to vacuum state and idle speed remains at the set maximum.
You probably still have both throttle lever dampers fitted to your pump, my advice is remove them both and discard them, then if the electrovalve and vacuum tract are as they should be, and air and fuel filters clean, simply set the idle speed to spec. or to your liking.
Dave
The engines idle speed is increased when the aircon is active and is achieved by the same method used to increase idles speed at cold start, this being via vacuum diaphragm and electrovalve, the valve(s) is to the left of the LHM reservoir, the other being for the EGR system.
If you rev the cold engine you should firstly see the cable going to the fast idle lever on the injection pump being released, and then pulled again as the engine returns to idle.
With a hot engine at idle the cable should be released when the aircon is switched on, thus raising the idle speed.
Because these valves are energised most of the time the engine is running its not uncommon for them to fail, when they do fail however they are in the closed to vacuum state and idle speed remains at the set maximum.
You probably still have both throttle lever dampers fitted to your pump, my advice is remove them both and discard them, then if the electrovalve and vacuum tract are as they should be, and air and fuel filters clean, simply set the idle speed to spec. or to your liking.
Dave
Dave
Thanks, In response to each point:
fans run all the time the air-con is on - didn't realise this/hadn't noticed it before but at least this is working correctly then.
higher tickover on air-con cars - I knew the air-con was powered by the engine and that the idle speed on an air-con car was approximately 50 rpm higher to compensate so I had expected an 850 rpm tickover instead of an 800 rpm tickover. I've had the car for 2 months and until yesterday it had a 900 rpm tickover which I always thought was a little high but the car performed well.
fast idle mechanism - the fast idle cancel mechanism does nothing on my car, it never has. I noticed very soon after purchase that the cable adjustment was so loose as to be ineffective. I did some basic tests and 2 things were revealed. The cable is not pulled by the system which I believe to be down to a lack of vacuum and even if it were the pump end lever appears to be unmovable, I couldnt move it in any direction when I pushed it with a screwdriver. It looks as if the idle and fast idle screws have 'locked' it in position if that's possible. I put this to the specialist that I use and he said that it wasn't unusual as the idle speed is controlled by the ECU, he even let me look at his own car [which was inconclusive unfortunately]. Anyway apart from the fact that I don't think I've enough vacuum and presumably the EGR isn't functioning proprly either the main point is that that the car has been like this since I bought it but only just started to play up.
Throttle leaver dampers - I'm only able to identify one but yes it's still there. It's behind the pump, where is the other likely to be ?
The car is still exibiting the problem and I've noticed that it actually hits at about 1800 rpm.
One other point that I hesitated to mention yesterday because I thought it was my imagination but which I think is real now, the car appears to have become more powerfull.
Mark_sp
Thanks, In response to each point:
fans run all the time the air-con is on - didn't realise this/hadn't noticed it before but at least this is working correctly then.
higher tickover on air-con cars - I knew the air-con was powered by the engine and that the idle speed on an air-con car was approximately 50 rpm higher to compensate so I had expected an 850 rpm tickover instead of an 800 rpm tickover. I've had the car for 2 months and until yesterday it had a 900 rpm tickover which I always thought was a little high but the car performed well.
fast idle mechanism - the fast idle cancel mechanism does nothing on my car, it never has. I noticed very soon after purchase that the cable adjustment was so loose as to be ineffective. I did some basic tests and 2 things were revealed. The cable is not pulled by the system which I believe to be down to a lack of vacuum and even if it were the pump end lever appears to be unmovable, I couldnt move it in any direction when I pushed it with a screwdriver. It looks as if the idle and fast idle screws have 'locked' it in position if that's possible. I put this to the specialist that I use and he said that it wasn't unusual as the idle speed is controlled by the ECU, he even let me look at his own car [which was inconclusive unfortunately]. Anyway apart from the fact that I don't think I've enough vacuum and presumably the EGR isn't functioning proprly either the main point is that that the car has been like this since I bought it but only just started to play up.
Throttle leaver dampers - I'm only able to identify one but yes it's still there. It's behind the pump, where is the other likely to be ?
The car is still exibiting the problem and I've noticed that it actually hits at about 1800 rpm.
One other point that I hesitated to mention yesterday because I thought it was my imagination but which I think is real now, the car appears to have become more powerfull.
Mark_sp
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Dave Burns
- Posts: 1915
- Joined: 14 May 2001, 05:30
- Location: United Kingdom
- My Cars:
- x 2
I don't take any notice of the spec. for idle speed I simply set it to my liking, which is the lowest point obtained without intrusive engine vibration, thats about 900 in my case, set any lower in my experience and they can be somewhat unpleasant to sit in while stationary, but depends on the individual engine of course.
Before condeming the vacuum pump, press the clip and pull the pipe off it to test the amount of suction, there should be plenty, these things are much more long lived than a solenoid winding that can't dissipate its heat because of being housed in plastic.
The only control over engine idle speed by the ECU is via the vacuum diaphragm, cable and electrovalve setup, if it had any other method of control there simply would be no need for the setup that exists, find yourself a specialist that knows what he's talking about, if you bought the car from him he's bull****ting you, screwing the idle speed down like this is just a way of doing it manualy without going to the expense of doing it properly.
In short, the route most garages will take when selling a used car, leaving the punter to pay for correcting it later when he becomes familiar with his purchase and finds out what is wrong.
The ECU does however have some control over injection timing, pull the brown conector on the pump while the engine is running and you should hear the "diesel knock" become much more pronounced and metalic like as the timing swings toward advance, plug it back in and the ECU will readjust the injection point to the previous setting.
The damper behind the pump damps the last few degrees of lever return, I've seen them with a tit left on them from the injection moulding process which causes eratic operation, cars I have removed them from including mine operate just fine with no Ill effect.
The other one is like a very small shock absorber on the front of the pump and works throughout the levers entire range, this is also best got rid of and sounds like its allready been removed from your car.
Dave
Before condeming the vacuum pump, press the clip and pull the pipe off it to test the amount of suction, there should be plenty, these things are much more long lived than a solenoid winding that can't dissipate its heat because of being housed in plastic.
The only control over engine idle speed by the ECU is via the vacuum diaphragm, cable and electrovalve setup, if it had any other method of control there simply would be no need for the setup that exists, find yourself a specialist that knows what he's talking about, if you bought the car from him he's bull****ting you, screwing the idle speed down like this is just a way of doing it manualy without going to the expense of doing it properly.
In short, the route most garages will take when selling a used car, leaving the punter to pay for correcting it later when he becomes familiar with his purchase and finds out what is wrong.
The ECU does however have some control over injection timing, pull the brown conector on the pump while the engine is running and you should hear the "diesel knock" become much more pronounced and metalic like as the timing swings toward advance, plug it back in and the ECU will readjust the injection point to the previous setting.
The damper behind the pump damps the last few degrees of lever return, I've seen them with a tit left on them from the injection moulding process which causes eratic operation, cars I have removed them from including mine operate just fine with no Ill effect.
The other one is like a very small shock absorber on the front of the pump and works throughout the levers entire range, this is also best got rid of and sounds like its allready been removed from your car.
Dave
ECU? ARGH, please tell me your kidding,and at what age these got brought in and ANYTHING else that could be usefull to know (such as where the ECU is located). I have never heard any mention of an ECU on a 1.9TD, but now im scared, it all seems like normal sensors on the one im looking at (p-reg on 46k)
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Dave Burns
- Posts: 1915
- Joined: 14 May 2001, 05:30
- Location: United Kingdom
- My Cars:
- x 2
Just my two-penny worth but I have a 1998 Xantia 1.9TD Estate which I bought new. Normally it runs faultlessly but if I run the air-con then there is a 'flat spot' somewhere about 2000 rpm. The idle speed does increase when the air-con is running and the flat spot has been there from new.
I thought that it was normal!
Richard Green
I thought that it was normal!
Richard Green
Dave
Thanks, a lot of information to digest, right:
Idle speed, car is now starting with an idle speed of about 790 and is purring in fact the opposite appears to be true that the faster the idle speed the more noticable, 900 is definately more obtrusive.
specialist - he must have been having a bad day, I've a lot of faith in him as he has twice sorted a problem very quickly that the main dealers had not got a clue on. Once on an XM and once on a BX, he also has a thriving business, have to book in well in advance. Didn't buy the car from him simply got him to look it over after, wish I'd had him look it over before.
Brown connector on pump - pulled it when engine warm and idling and it did what you said it would.
Pump dampers - front one already removed, rear one still intact, looks okay to me but I'm not sure I know what I'm looking at these days. No 'tits' or hollows and doesn't appear to act until throttle nearly closed.
Vacuum pump - stuck my finger over the outlet at tickover and could feel suck but not a lot, don't have a vacuum guage so have to use rule of thumb sorry finger [perhaps humour isn't my strong point] anyway how should it feel, should it hurt ? Presumably this is irrelevant until the winter anyway ?
Yesterday went out in the daytime, air temp hot, car displayed fault at every opportunity. Had to go out in the early hours of this morning when air temp was quite cool, car performed faultlessly ?
Back to fundamentals, I made the assumption that a reduced tick-over could cause the problem I'm experiencing, this may be be a little late but Dave could it ?
If you think yes then I'll take your advice and adjust the tickover back to 900.
Vanny
I believe the part managed 1.9 TD came into being in 1997. My car is a 1998 and has a mechanical pump and an [injection ?] ECU. I'm more confused than ever over what the ECU actually conytrolls now]. My car also has a catalictic converter which I suspect is why there is an ECU, control of emissions. My car also has EGR. In a nutshell my personal view is that the post 96 cars are not only more complicated but also more difficult to work on due to the extra underbonnet pipework and cabling. As you look at the engine the ECU is under a cover parallel to the left hand wing.
Mark_sp
Thanks, a lot of information to digest, right:
Idle speed, car is now starting with an idle speed of about 790 and is purring in fact the opposite appears to be true that the faster the idle speed the more noticable, 900 is definately more obtrusive.
specialist - he must have been having a bad day, I've a lot of faith in him as he has twice sorted a problem very quickly that the main dealers had not got a clue on. Once on an XM and once on a BX, he also has a thriving business, have to book in well in advance. Didn't buy the car from him simply got him to look it over after, wish I'd had him look it over before.
Brown connector on pump - pulled it when engine warm and idling and it did what you said it would.
Pump dampers - front one already removed, rear one still intact, looks okay to me but I'm not sure I know what I'm looking at these days. No 'tits' or hollows and doesn't appear to act until throttle nearly closed.
Vacuum pump - stuck my finger over the outlet at tickover and could feel suck but not a lot, don't have a vacuum guage so have to use rule of thumb sorry finger [perhaps humour isn't my strong point] anyway how should it feel, should it hurt ? Presumably this is irrelevant until the winter anyway ?
Yesterday went out in the daytime, air temp hot, car displayed fault at every opportunity. Had to go out in the early hours of this morning when air temp was quite cool, car performed faultlessly ?
Back to fundamentals, I made the assumption that a reduced tick-over could cause the problem I'm experiencing, this may be be a little late but Dave could it ?
If you think yes then I'll take your advice and adjust the tickover back to 900.
Vanny
I believe the part managed 1.9 TD came into being in 1997. My car is a 1998 and has a mechanical pump and an [injection ?] ECU. I'm more confused than ever over what the ECU actually conytrolls now]. My car also has a catalictic converter which I suspect is why there is an ECU, control of emissions. My car also has EGR. In a nutshell my personal view is that the post 96 cars are not only more complicated but also more difficult to work on due to the extra underbonnet pipework and cabling. As you look at the engine the ECU is under a cover parallel to the left hand wing.
Mark_sp
RichG
Just seen your response after I posted my reply. Interesting, I only got the car at the end of March. I've used the air-con regularly since that date, to dehumidify in the colder damper weather [in parallel with the heater]and to cool in the recent hot spell. The problem only surfaced in the hot spell and it appeared to coincide with a drop of about 50 rpm in the tickover [air-con running or not]. I wonder if the air-con has more work to do in hotter weather and draws more power from the engine ? Anyway thanks for your response and I hope it isn't actually a feature.
Mark_sp
Just seen your response after I posted my reply. Interesting, I only got the car at the end of March. I've used the air-con regularly since that date, to dehumidify in the colder damper weather [in parallel with the heater]and to cool in the recent hot spell. The problem only surfaced in the hot spell and it appeared to coincide with a drop of about 50 rpm in the tickover [air-con running or not]. I wonder if the air-con has more work to do in hotter weather and draws more power from the engine ? Anyway thanks for your response and I hope it isn't actually a feature.
Mark_sp
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Dave Burns
- Posts: 1915
- Joined: 14 May 2001, 05:30
- Location: United Kingdom
- My Cars:
- x 2
A diesel runs better in cold damp air than hot air because the cold damp air is denser and expands more and its effect is so noticable because of the high compression ratio.
I don't think the ambient temperature makes any difference to the power drawn from the engine, but I'm not sure, maybe the compressor does cut in and out during use but can't say I've ever noticed.
The idle speed as adjusted by the ECU and vacuum gubbins is achieved by altering the injection timing slightly and not the amount of fuel, when the fast idle lever is moved it turns the roller ring inside the pump which advances the injection point by around 2.5 degrees (camshaft).
It then seems likely that mal adjustment here could contribute to such running problems.
On top of that the actual engine speed is maintained by the govoner in the pump, one thing that this means is that during overrun where the engine is being driven by the wheels, the govoner (though purely mechanical) perceves this to be engine overspeed and cuts back the fuel accordingly, in the extreme it can cut the fuel completely until the engine speed drops back to within fueling range.
What I don't know is wether or not fueling comes back on the moment you press the pedal, going from overrun to power in a very short time, (bearing in mind its all levers, springs and flyweights)I would think so, but with other adjustments being incorrect might they have a knock on effect of sorts?
Dave
I don't think the ambient temperature makes any difference to the power drawn from the engine, but I'm not sure, maybe the compressor does cut in and out during use but can't say I've ever noticed.
The idle speed as adjusted by the ECU and vacuum gubbins is achieved by altering the injection timing slightly and not the amount of fuel, when the fast idle lever is moved it turns the roller ring inside the pump which advances the injection point by around 2.5 degrees (camshaft).
It then seems likely that mal adjustment here could contribute to such running problems.
On top of that the actual engine speed is maintained by the govoner in the pump, one thing that this means is that during overrun where the engine is being driven by the wheels, the govoner (though purely mechanical) perceves this to be engine overspeed and cuts back the fuel accordingly, in the extreme it can cut the fuel completely until the engine speed drops back to within fueling range.
What I don't know is wether or not fueling comes back on the moment you press the pedal, going from overrun to power in a very short time, (bearing in mind its all levers, springs and flyweights)I would think so, but with other adjustments being incorrect might they have a knock on effect of sorts?
Dave
DaveB -
From memory driving my n/a BX19RD, there seems to be no trouble with a soft taking up of power - when from engine overrun at moderate speed - pressing the pedal again.
it seems to be a kind of override mechanism then - on the accelerator input axle.
That was the thrill driving my RD - it was such a nice creature - very much like my former BX14 - but with better torque - and somewhat more noisy of course (but surprisingly not much).
From memory driving my n/a BX19RD, there seems to be no trouble with a soft taking up of power - when from engine overrun at moderate speed - pressing the pedal again.
it seems to be a kind of override mechanism then - on the accelerator input axle.
That was the thrill driving my RD - it was such a nice creature - very much like my former BX14 - but with better torque - and somewhat more noisy of course (but surprisingly not much).
Dave
Thanks again. As you say the last couple of days have been cooler and damper and I've not run the air-con. The result is that the tickover has restored itself to 900rpm and the flat spot has been nowhere in sight. I've decided to leave well alone for the time being and put up with the flat spot when I run the air-con as permanently adjusting the tickover to compensate will affect the non air-con usage [although I'm tempted to temporarily up it just to see if it has the desired effect]. Just one last point - the fast idle mechanism, I know its a tricky one with me not having access to a vacuum guage but how much suck should be coming off the pump ?
Cheers
Mark_sp
Thanks again. As you say the last couple of days have been cooler and damper and I've not run the air-con. The result is that the tickover has restored itself to 900rpm and the flat spot has been nowhere in sight. I've decided to leave well alone for the time being and put up with the flat spot when I run the air-con as permanently adjusting the tickover to compensate will affect the non air-con usage [although I'm tempted to temporarily up it just to see if it has the desired effect]. Just one last point - the fast idle mechanism, I know its a tricky one with me not having access to a vacuum guage but how much suck should be coming off the pump ?
Cheers
Mark_sp
Just a note to mention that the A/C on the Xantia TD consumes a hideous 10-12 h.p, which is the reason you're experiencing a flat spot at low revs. That flat spot is actually there all the time, its just that without the extra load of the A/C you accelerate through it without noticing it. It's very noticable on my '93 XM TD12 with the larger version of the XUD engine - it's always been i little hesitant below 1900 revs where the turbo comes in, but with the A/C on i feels like my fathers ZX D auto until it gets up to about 2200 revs.
//NiSk
//NiSk
Hello there, great forum!
My xantia TD '98 seems to have a similar issue, idle does not increase when airco on, stays at about 800 and with this warm weather the engine cuts off when the clutch is in for corner or traffic light. It also takes 8 or 9 turns before starting when warm. also a flat spot but not alwys at same rpm. Normal power. With aircon off while warm idle stays a bit low. Now my dealer suggests to take the fuel tank down as there seems to be a filter (which normally does not need servicing) he wants to clean. He hasn't mentioned checked things under the hood first!! Does this make sense to you?
My xantia TD '98 seems to have a similar issue, idle does not increase when airco on, stays at about 800 and with this warm weather the engine cuts off when the clutch is in for corner or traffic light. It also takes 8 or 9 turns before starting when warm. also a flat spot but not alwys at same rpm. Normal power. With aircon off while warm idle stays a bit low. Now my dealer suggests to take the fuel tank down as there seems to be a filter (which normally does not need servicing) he wants to clean. He hasn't mentioned checked things under the hood first!! Does this make sense to you?
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Dave Burns
- Posts: 1915
- Joined: 14 May 2001, 05:30
- Location: United Kingdom
- My Cars:
- x 2
I suspect the flat spot that all are refering to here is not infact a flat spot at all, but simply the aircon compressor cutting in and out, when the aircon is on the compressor will be disconnected and re-connected to its drive as the pressure in the system fluctuates, the compressor can't run non stop.
Then you feel a slight jolt as it cuts in, and when accelerating if it cuts out there can be a slight surge of extra power being mistaken for a flat spot, I doubt anyone is experiencing anything worse than that.
Check the idle speed electrovalve windings and that the vacuum system is intact first, even if there is a filter there that needs cleaning or replacing its hardly going to affect the difference in idle speed, and if it did you would hardly get the car to move at all, such would be the level of fuel starvation.
Dave
Then you feel a slight jolt as it cuts in, and when accelerating if it cuts out there can be a slight surge of extra power being mistaken for a flat spot, I doubt anyone is experiencing anything worse than that.
Check the idle speed electrovalve windings and that the vacuum system is intact first, even if there is a filter there that needs cleaning or replacing its hardly going to affect the difference in idle speed, and if it did you would hardly get the car to move at all, such would be the level of fuel starvation.
Dave