ZX Diesel (non-turbo) pump timing and fuel economy

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srx600
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ZX Diesel (non-turbo) pump timing and fuel economy

Post by srx600 »

As with most people I have become more conscious of the cost of fuel and consequently my fuel economy. I recently checked the economy over one tank (not ideal I know) and found it to be 46mpg. Whilst this is ok its not as good as I had expected, since a) I was driving carefully b) My previous ZX (200,000 miles), which also has a Lucas pump, returned 50mpg+ without me having to try.
Looking around at various sites, diesel pump timing is mentioned as a possible cause. The car starts fine, does not chuck out smoke and always goes through the MOT smoke test with flying colours. Performance is not great and I'm sure my old ZX was much crisper.
I recently removed the pump to fix a seal, I scribed a line around the pump before removal and I'm confident it went back in the same position. Ive not noticed a significant difference in performance.
When replacing the belt it was quite difficult to get the belt to engage correctly between the pump and the camshaft pulleys, with two timing location bolts in the pump pulley and one in the camshaft it was impossible to get the teeth aligned. Eventually I removed one of the pump pulley timing location bolts which allowed a degree or so of rotation allowing the belt to fit. I tried fitting the belt loose with two the two location bolts in the pump, when I did this and tensioned the belt, the timing was clearly out (I didnt run the engine just did a static check). I also remember this being the case when I changed the belt shortly after getting the car.
So in summary I think my pump timing could be out. There seems to be two approaches
a) Purchase the correct tools, this will cost me between £100 and £150.
b) Looking through previous posts, one approach seems to be trial and error, the timing is adjusted untill it clatters at tickover then backed off slightly. How accurate is this approach ? I dont fancy tweaking the pump location with the engine running, so can I assume the adjustment is done incrementally without the engine running, and then the engine started up and checked. How much should you adjust each time ?
For those that have read this far, apologies for the length of this posting
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CitroJim
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Post by CitroJim »

You don't specifically state which car this is and if it's the fully mechanical Lucas pump fitted. I'll assume it's a ZX and the pump is fully mechanical.

Timing on these is quite easy to set up carefully and a lot easier than a Bosch. All you need is a special probe (which can be turned up on a lathe easily and a Dial Test Indicator (DTI). The BoL for the XUD Diesel Engine describes the process very well.

Timing on a diesel is very critical and if you are after the last mpg, doing it by ear will not give full satisfaction. It has to be done using a DTI.

I'd be feeling that timing is not fully the issue though, although it is worth a check to eliminate it. You may be well advised to have your injectors cleaned and recalibrated.

One thing to bear in mind that after adjusting timing it is important to loosen off the injector pipes and retighten them in order to releaive any stresses that might have built up in them in being moved to a different position.
Jim

Runner, cyclist, time triallist, duathlete, Citroen AX fan and the CCC Citroenian 'From A to Z' Columnist...
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Post by Peter.N. »

From what you say the timing sounds about right. Over advanced it will knock and sound noisy, retarded it will be sluggish, smokey and difficult to start.

Was you previous car a turbo? They have the potential to give a better fuel consumption driven carefully as the extra air provides a weaker mixture and they are usually higheer geared.

46mpg sounds quite good to me, my wife has a turbo estate which only manages about 45, wheras my 2.1 XM is capable of over 55!

If the timing belt was a tooth out I am sure you would notice the diffefence. The secret of good fuel consumption is to keep the revs below 2000 whenever possible, but you probably already know that. The reason for the frugality of the 2.1 engine is that it produces tremendous tourque below 2000 rpm permitting very low average engine speed.
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Post by Peter.N. »

You beat me again :wink:
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