Hi Guys,
I have been working on my Matiz for a few weeks now and I have cleaned up the mess left by a chronic rich fuel mix. Now I am trying to figure out why the long term (-100) and short term (-12) fuel trims are so negative.
All the plugs were very sooty so it?s a universal problem.
I replaced an EGR valve that was faulty and I hoped that this was the reason but thinking about it more it probably would account for a small enrichment and not this mega one.
No codes showing not even P0172
Air filter; fine, and no blockages in the throttle body or the inlet manifold.
Throttle position sensor (TPS ), fine; Manifold Absolute Pressure (MAP) sensor, fine; engine temp sensor, fine; idle air control valve, fine and finally PCV not blocked.
I have not changed the fuel filter but I would have thought a blockage would cause a lean condition.
The fuel return is fine so no blockages.
I took the fuel rail off and connected it to the fuel pump to see if the injectors were leaking; they were fine.
Fuel pressure not an issue, I swaped over a fuel pump from a Matiz that is running without fault and that did not cure the LTFT.
Next stop is a Chevy garage, unless anybody has an ideas.
Many thanks for your thoughts.
Eddie
Edited by Dynamic Dave on 25/04/2008 at 22:28
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Eddie
Interesting... You seem to have thought of most of the mixture-controlling factors that might be causing the ECU to have to go so far out to keep the oxygen sensor happy.
That's my first thought - the oxygen sensor. Is it tired and reading low? Have you ever had it on a 4-gas to confirm the actual gas readings against the oxy sensor's?
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Thanks for the post.
I forgot to say that I replaced both the O2 sensors (Gendan) as they were black with soot.
I might pop into Kwik fit and ask them to stick it on their exhaust gas analyser.
I am sure the problem is getting worse as the short term fuel trims are getting increasingly negative. So something is deteriorating.
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What are the O2 sensors reading at hot idle? Soot would suggest massive overfuelling or an EGR issue.
What's the MAP reading at idle? Does that match-up with a vacuum gauge?
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how about a small hair line crack in the manifold (exhaust) pre lambda sucking air fooling the lamda probe into thinking its weak, and does this vehice have two probes if so what is the other probe doing is it switching or is it stuck telling the ecu that the cats knackered or had you already thought of this !!!
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Both sensors are fine precat switching nicely and post cat showing normal activity. Cat diagnostic is fine Map sensor and vacuum don?t read the identical (after doing the conversion) but that?s happened on a couple of cars that I tried.
My car has pulls a steady 18 inches of Hg, and the blip test looks goods i.e. big fall in Hg and then a small overshoot.
Interestingly on high revs the vacuum does not hold but falls by a good 5 inches of Hg and the revs are not stable "hunting". On a good car the increase in revs caused a sustained increase in vacuum by about two inches.
So the car has all the symptoms of a partially blocked exhaust. What do you think ?
I think the EGR valve was failing (and eventually failed), causing a rich condition this flooded the combustion chambers causing oil to be burnt and fouling up the inlet manifold (via the EGR) further enriching the mix generating lots of soot and a bunged up exhaust. I can see the soot from the tail pipe I just did not think of a blocked exhaust.
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Hi,
I think I have the same issue. Do you any symptoms like cold rough idle and really poor performance when cold?
Thanks!
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Given the age of the thread, I expect the Matiz has gone to car heaven by now. Or possibly hell?
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Possibly to hell :P but I would like to know if the problem was solved!
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