No power at low revs

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mark_weaving
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No power at low revs

Post by mark_weaving »

Hi guys, I wonder if someone can help me. I've just rebuilt my engine after a cambelt failure, very painfull ( note to self always,always change cambelt). The engine runs roughly at tickover and lacks power until about 3000 rpm after this it runs fine. I need at least 3k rpm just to pull away in 1st gear. Is there something I may of missed during re-assembly, the map sensor is connected. It feels like its running on 3 cyl but I don't know how to check this, in the old days i could just pull of the HT leads one at a time. The model is an R regd Xantia VSX 16v 72K miles. Many Thanks in advance for any advice.
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Post by jeremy »

If it feels as though its running on 3 it may be. It may even be running on 2 if you have reversed 2 ignition leads (may be impossible on your engine)

backtrack - till the belt fell off was it running Ok. What have you disturbed since? - did you come close to damaging something during the work? (dropped something, had what looks like a near miss with something?)

I'd meter the leads - (20Kohm) and see if there are any problems there, look for air leaks (even some dirt under the inlet maniflold joint) make sure everything is tight, look at any pipework going into the inlet maniflold - if its old it may be slack and need clipping, look at the injector seals - especially if they were taken out or something like the maniflold may have rested on them and broken the old perished seals.

I don't suppose you have a distributor cap - if you have worth having a look at it and any rotor arm.

I expect someone may say have a look at the coil pack/s - don't know much about them except apparently they do fail. plenty of info on here about them.
jeremy
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Post by rbruce1314 »

I hardly dare mention this after all your hard work, but I suppose you are SURE the cambelt is not one tooth out............
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Post by Peter.N. »

I was about to say the same, but you beat me to it!
mark_weaving
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Post by mark_weaving »

No i'm not sure, but if its one tooth out wouldn't that also be apparent at high revs. It is possible i've got it wrong, but with the pins in possition the belt won't fit any other way.
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Post by fastandfurryous »

My first guess would have been cambelt timing too... it can be very easy to get it a tooth out somewhere, and the engine will still run.

Either that, or the ignition timing is a week-and-a-half out. Sounds like it's either very retarded, or the vacuum advance is not connected (MAP sensor). Is it munching it's way through petrol rather quickly too?
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Post by Peter.N. »

Did you have the flywheel locked? You can sometimes get away with marking the sprocket but it can move when you tighten the belt. The ignition timing is much more critical at low engine speeds, I am not saying that is the problem, but its a possibility.
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Post by dnsey »

Did you 'fine tune' the cam timing using the slots in the pulleys? If the valve timing's just a bit out, it may well affect just the slow running (because of overlap, but I'm too tired to think it through at the moment!)
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Post by mark_weaving »

dnsey, I did fine tune the timing using the slots in the pulley, but i only followed the Haynes manual, i must admit i didn't understand it completly. one of cams is at the maximum of the slots, i rotated the engine a couple of times as instruced but it made no difference. Do i need to phycically move the cam until the bolts are in the center of the slots? Many Thanks for any help
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Post by mark_weaving »

I've now realigned the Crank and cams and refitted the belt 3 times and each time the problem is just the same, also the engine management light comes on during idle. I'd be grateful for any other suggestions you may have.
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Post by Dave Burns »

If you are not using a new crankshaft pulley to set the timing your efforts will be wasted.

The pulley is in two pieces and is held together by rubber, during use the two pieces can (and do) move relative to each other, the hub has the keyway in it and the outer part has the timing hole drilling in it, once they have moved you can't use the pulley for timing purposes.

Insert the timing peg and look where the keyway is, it should be at 9 o'clock, where 12 o'clock would be the vertical line of the bores, and not true vertical, don't forget the engine leans rearwards.




Dave
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