Yaris hesitation when cold
Stu
Engine code 1NZ-FE
The car suffers from a hesitation when first pulling away after a cold
start, and occasionaly when changing up a gear. It misfires and feels like
it will stall, but never does. Once the engine has a slight warmth, the
problem disappears and the car runs perfectly. This takes about a mile,
perhaps less, and it revs freely right from the word go, the problem is
only apparent as one transfers load to the engine. The symptom is very much
like the way a cold carb fed engine would perform with insufficient choke.
This problem first started when I replaced the OEM Denso plugs with NGKs:
Denso chart recommendation: K16R-U gapped at 0.8mm (that is straight from
their website. Autodata contradicts this and says to use K16R-U11 with
1.1mm gap. The car was fitted with K16R-U when I acquired it.)
NGK recommendation: BKR5EY-11 gapped at 1.1mm
So, since they appeared to cause the prob, I removed the NGKs and got a new
set of Densos, gapped them at 0.8mm, fitted them and the problem
disappeared. For about 2k miles. Now, it has returned, yet the plugs are
still like brand new and the gaps are still correct. Deposits are the
normal light grey, with no fouling or evidence of poor combustion.
Could it be that the plugs are a red herring and the car has some other
problem? Checks I have done so far are:
- Checked for intake air leaks using soapy water. Found none.
- Measured coil resistances, all four are between 21 and 23K
- Checked readout from CTS via OBD scan. Reads normally, i.e. around
ambient temp when cold, rising to 80-90deg warmed up.
- Checked intake air temp readout as above. Reads ambient temp with a cold
engine.
- Checked for any stored DTCs. None present.
- Measured TPS voltage: 0.54V closed, rising to 3.87V at WOT. No dead
spots.
Any other ideas, please? It's a very small issue but doesn't seem right for
an EFi car.
Duncan Wood
Plug leads?
Duncan Wood
Or more relevantly, try looking under the hood in the dark & seeif you can
see any tracking from the coils
Mrcheerful
you cannot check for inlet leaks with soapy water, the leak will be sucking,
not blowing, check for inlet leaks using a flammable liquid or gas, carb.
cleaner is convenient with the engine running, any leaks that you spray over
will cause a speed variation.
running the larger gap may have caused a tracking issue, which may have
damaged one or more coils.
Colin Wilson
> > start, and occasionaly when changing up a gear. It misfires and feels
> > like it will stall, but never does.
I finally got around to replacing my plug leads last week, after
putting up with my ageing Hyundai Accent doing exactly the same thing
for a few months.
Changing the leads appears to have sorted it :-)
Mrcheerful
I have an idea that the Yaris does not have any plug leads, but ICBW
Duncan Wood
wrote:
I think it's coil on plug, but they track as well.
--
Duncan Wood
Stu
news:AsYIm.2302$Ym4...@text.news.virginmedia.com:
> you cannot check for inlet leaks with soapy water, the leak will be
> sucking, not blowing, check for inlet leaks using a flammable liquid
> or gas, carb. cleaner is convenient with the engine running, any leaks
> that you spray over will cause a speed variation.
>
> running the larger gap may have caused a tracking issue, which may
> have damaged one or more coils.
>
>
under cover of darkness in a couple of days (working nights right now)and
look for any evidence of tracking. At the same time, I'll also check again
for air leaks with whatever flammable spray I can lay my hands on. ;-)
Stu
news:0vednX1xHqnkhWjX...@brightview.co.uk:
Update
Checked under the bonnet in darkness and nothing is glowing. Done another
check for leaks with a flammable spray and nothing happened. The only idea
I have left is to disable the fuel pump and try the coils on a spare plug,
looking for a weak spark. Any other theories?
Mrcheerful
it is extremely difficult to see a tracking spark on 'coil on plug'
vehicles, and in any case if the misfire only occurs when the engine is
loaded (ie not when ticking over then there will be nothing to see in any
case.)
I would try a scrupulous clean of each coil pack and spray it well with
wd40, clean the outsides of the plugs well too, and then try it, if there is
an improvement then you are on the right track (no pun intended) the other
problem is that the coil may be tracking internally like mondeo ones do and
then the only way is to substitute with a known good pack.
there is also the possibility that the fault lies somewhere else completely,
such as a tdc sensor.
Stu
wrote:
>it is extremely difficult to see a tracking spark on 'coil on plug'
>vehicles, and in any case if the misfire only occurs when the engine is
>loaded (ie not when ticking over then there will be nothing to see in any
>case.)
>
>I would try a scrupulous clean of each coil pack and spray it well with
>wd40, clean the outsides of the plugs well too, and then try it, if there is
>an improvement then you are on the right track (no pun intended) the other
>problem is that the coil may be tracking internally like mondeo ones do and
>then the only way is to substitute with a known good pack.
>
>there is also the possibility that the fault lies somewhere else completely,
>such as a tdc sensor.
>
Thanks, Mr Cheerful
I'll do as you suggest and see if I can get any noticable improvement.
Failing that, I don't think it's worth getting into advanced
diagnostics to try and solve a very small driveability issue that only
affects a completely cold engine. I'll wait and see what develops. ;-)
Cheers,
Stu
Scionxa
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