marcjagman
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| posted on 13/5/11 at 07:11 AM |
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V6 2.9 problem
Okay chaps and chapesses heres little problem I hope someone can help me with. I have a 1990 XR4x4 2.9 V6 NON cat. Past it's MOT 3 weeks ago.
It's a little lumpy on tick over but passed emmisions on MOT, Co 0.65% HCC 73PPM so very low. Here's the problem, once driving the car is
fine EXCEPT between 40-46mph where it's a bit jerky, like it's mis firing. Car goes like stink when floored, has new plugs, HT leads,
dizzy cap and rotor arm. I have set the tappets but did notice that one side was worn and still rattles a bit. Could it be then worn rocker shaft that
is causing the mis fire? seems at bit strange how it only does it at a certain engine speed. All help welcome.
Andy.
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adithorp
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| posted on 13/5/11 at 07:38 AM |
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If it's got a vane type air flow meter (think they did from memory) it could be that. They used to wear away the track at points where they
often sat like idle and light load steady running. Tappets too tight is more likely to be a problem than slightly noisey.
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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SeaBass
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| posted on 13/5/11 at 08:25 AM |
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If it's the Bosch vane or flap type like Adithorp mentions then I had an almost identical issue when I bought my 944.
There is an air bypass adjustment on the sensor which effectively enriches/leans the mixture across the board. I added about 1/2 turn richer and it
now runs perfectly at light load when cruising. Before is was stuttering but was fine at WOT just like you mention.
JC
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marcjagman
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| posted on 13/5/11 at 08:33 AM |
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Will have a look at that as it is burning lean going by the emissions read out.
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marcjagman
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| posted on 13/5/11 at 08:46 AM |
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quote:
Originally posted by SeaBass
If it's the Bosch vane or flap type like Adithorp mentions then I had an almost identical issue when I bought my 944.
There is an air bypass adjustment on the sensor which effectively enriches/leans the mixture across the board. I added about 1/2 turn richer and it
now runs perfectly at light load when cruising. Before is was stuttering but was fine at WOT just like you mention.
JC
Can't find the bypass, which sensor should I be looking at?
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stevec
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| posted on 13/5/11 at 01:14 PM |
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Those engines suffer from inlet manifold gasket creep then they have an air leak that may effect emissions.
Steve
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Chippy
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| posted on 13/5/11 at 01:34 PM |
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quote:
Can't find the bypass, which sensor should I be looking at?
[img]
 
V6 Air flow metter
[/img]
From memory the adjusting screw is in the bottom of the Air Inlet Vane Do Da, will see if I can find a picture of one and stick it on this post. I had
one of these engines in my special untill I changed for the BOA. Cheers Ray
Edit to add picture. You should adjust the front AFM first and only adjust the rear one if you run out of adjustment on the front one. HTH Ray
[Edited on 13-5-11 by Chippy]
To make a car go faster, just add lightness. Colin Chapman - OR - fit a bigger engine. Chippy
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marcjagman
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| posted on 13/5/11 at 02:26 PM |
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quote:
Originally posted by Chippy
quote:
Can't find the bypass, which sensor should I be looking at?
[img]
V6 Air flow metter
[/img]
From memory the adjusting screw is in the bottom of the Air Inlet Vane Do Da, will see if I can find a picture of one and stick it on this post. I had
one of these engines in my special untill I changed for the BOA. Cheers Ray
Edit to add picture. You should adjust the front AFM first and only adjust the rear one if you run out of adjustment on the front one. HTH Ray
[Edited on 13-5-11 by Chippy]
Read that in the haynes BUT, it says that only affects tick over, so it's lying to me, again.
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Chippy
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| posted on 13/5/11 at 10:23 PM |
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Hi mate, Oh! yes does a lot more than affect tick over, it will affect the fueling across the whole range. Cheers Ray
To make a car go faster, just add lightness. Colin Chapman - OR - fit a bigger engine. Chippy
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