ZX 1.9TD 1993 Engine overreving

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Paul Thomas
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ZX 1.9TD 1993 Engine overreving

Post by Paul Thomas »

When I dip the clutch to change gear (particularly when accelerating) the engine revs rise for a few seconds before dropping back down.
Has anyone any suggestions as to the cause ? Clutch ?
It has now done 108,000 miles on most of the original parts.
Thanks
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Post by VisaGTi16v »

Does it idle highly as well? What if being stationary on idle you rev it then take foot off the throttle? If it still stays high then, then its probably the throttle cable sticking somewhere or the linkage at the engine end. Ive had that before
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AndersDK
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Post by AndersDK »

Does'nt this engine type (turbo) has the vacuum hoses to the diesel roto-pump for fuelling ?
I think I remember a couple of postings about fuelling problems - where these vacuum hoses could be more or less clogged by oil.
My idea is that this could cause a delay in dropping the revs.
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Post by jeremy »

Anders - I think you are referring to the pipe from the intercooler to the extra fuel device on the pump. This pipe communicates the perssure in the intercooler to the extra fuel device, providing more fuel as the boost pressure increases. Its usual fault is dropping off, which of course instantly looses all benefit of the turbo.
The roto-diesel pump apparently use fuel as a hydraulic medium to operate the governing mechanism, and so air in the fuel can cause this system to malfunction which usually shows up as mysterious increases in speed - eventually becoming runaway.
I suppose this could be Paul's problem - the chain of events being: There is no separate lift pump on these engines so the whole of the fuel line is subject to suction. You accelerate - taking the engine to high revs, causing the fuel pump element of the injection pump to work harder, drawing air in. The runaway is masked by the load on the engine, but when the throttle is released and the clutch dipped it shows. As the engine uses no fuel the pump quickly restores adequate fuel in the pump and the revs fall.
Paul - if you have a Bosch pump - forget what I ahve said as the linkage is mechanical. If not examine the fuel pipes carefully - I found the connections to the filter were in fact push fit and no doubt others are as well. In particular those around the fuel heater are prone to leakage. You will not find any external leakage. If you can't find any problem easily replace the last piece of pipe to the pump with clear plastic and look at the bubbles - there shouldn't be any.
Hope its the throttle cable! - its not the clutch - this would slip under load - if the engine accelerates when you break the clutch - its working properly.
Jeremy.
Paul Thomas
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Post by Paul Thomas »

I will take a look when I have the opportunity.
I replaced the accelerator cable only 3 months ago with an aftermarket one after the other one frayed and snapped.
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Post by Paul Thomas »

I haven't had a chance to check it yet but in reply to one of the other questions:-
If you sit idling and then rev up the engine the revs quickly return to normal. It only seems to happen when you are accelerating up the gears. It's very annoying as it reaches up to 4000RPM before dropping back down. Sound like I have poor accelerator/clutch control ! !
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Post by Paul Thomas »

Ok, had a look at Lunch time. Can't see a make on what I take is the fuel pump. (To the left of the Fuel filter in front of the intercooler ?)
Ther is a pipe from the middle bottom front of the intercooler joining the top right side of the fuel pump. Where it joins the intercooler it is quite damp and dirty. I cleaned this off and took it for a spin. It was wet again when I got back.
There is also quite a lot of wetness above the 3rd fuel injector (from the left).
Perhaps I need to jet-wash the engine to see it re-appearing !
Is this wetness on the pipe likely to be part of the problem ?
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Post by Kowalski »

This is normal behaviour for a TD, it has a throttle damper which prevents the accelarator lever on the fuel pump from closing down as quickly as it otherwise might. My Xantia TD will gain revs if you put your foot on the clutch after taking your foot off the accelarator after hard accelaration, although it usually will only go up to about 1500 rpm and come down slowly from there.
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Post by Paul Thomas »

This problem has been gradually getting worse. Never happened in first 100K miles.
If I press accelerator pedal down and release when stationary and out of gear the revs qill quickly drop. If I then accelerate up through the gears when I dip the clutch the revs rise.
I also tried going up a hill at a steady 30 in 4th and then pushing the accelerator down hard and then dipping the clutch. The same thing happens the revs rise and then fall again.
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Post by Dave Burns »

From your discription it would seem that there is a Bosch pump fitted, look at the pump, if there is a gizmo that looks like a small shock absorber about 6 inches long, between the bottom of the pump at the rear and the accelerator lever on top of the pump, unbolt it and wang it in the bin, don't bother putting another one back on, you don't need it.
Dave
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Post by Kowalski »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Dave Burns</i>

From your discription it would seem that there is a Bosch pump fitted, look at the pump, if there is a gizmo that looks like a small shock absorber about 6 inches long, between the bottom of the pump at the rear and the accelerator lever on top of the pump, unbolt it and wang it in the bin, don't bother putting another one back on, you don't need it.
Dave
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Is that throttle damper there purely to reduce emissions? i.e. Stops you putting your foot hard on the accelarator before the turbo can get up to speed and keeps throttle there while the engine revs die etc. Possibly it will help with MOT smoke tests...
When I got my current Xantia it's throttle damper had been disconnected. I reconnected it, dunno whether I should have or not...
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Post by blueboy2001 »

The damper Dave mentioned may be the problem, but it could equally be the damper that the throttle arm closes against. This is found on the back of the pump, its got an orange/red rubber diaphragm on it, and a shaft coming out with a conical shaped plastic end which the throttle arm touches. Its held on with a small nut to the back of the pump.
Take it off and bin it as you don't need it either!
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Post by jeremy »

I'm just curious why dampers would be fitted in the first place. I suppose the theory is that by gently closing the throttle the turbo is kept spinning faster during a gear change and less lag is experienced? Interesting!
jeremy
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Post by blueboy2001 »

I thought it may be something to do with slowing/smoothing the throttle movements down to improve fuel economy and smoothness of the power delivery.
jeremy
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Post by jeremy »

Possibly to reduce the slight snatch these engines seem prone to on gear change?
Jeremy
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