Strange timing issue ?

[totta Crolla]

Cam timing correct 16v blue top. 260 /266 cams
If I set the ignition timing to 10 degrees with diagnostic shorted the engine has no power below 5000 rpm and gets very hot.
To get the engine 'crisp' it needs 29 degrees advance at tickover
Is the engine losing power with this much advance ?

[jondee86]

How did you set the cam timing ? According to the stock pulley dimples
and marks on the backing plate, or by degreeing to the cam card ?

Cheers... jondee86

[Bean]

have you checked if the timing advances if you remove the lead to get it out of diagnostic mode?

[totta Crolla]

I have set the cam timing 3 different ways.
To original marks
With timing disc and piston stop
Valve lift at TDC
At the moment it is set at 108 degrees on both cams. and as specified.
The timing does advance a little from the 29 degrees, I guess it is about a further 10 degrees and that, I think, is about right t 40 degrees.
But if I'm starting at 29 the actual increase is only11 or so degrees.
Can you tell me what the ecu uses to work out the advance curve ?

[totta Crolla]

Please shed some light on this development guys.
With the engine running at around 1000rpm I moved the TPS back and forth, at full extent clockwise the idle settled nicely and the timing magically reduced to about 17 degrees. Great
However....
I now have a code 7 (tps)
I did adjust it as per the manual beforehand

[totta Crolla]

Problem solved.
Throttle position sensor incorrectly set so no 'idle map' could be selected by the ecu.
School boy error by me then !

[jondee86]

Some known facts... the ECU has pre-programmed fuel and ignition maps
that control the injector duration and ignition timing according to a
combination of rpm and MAP. The TPS tells the ECU how far open the
throttle is, and how fast the throttle position is changing.

Some speculation... the ECU will also have some preprogrammed "trim
tables" that add or subtract fuel/timing under certain circumstances. One
of those circumstances will be idling. To ensure a stable idle and on and
off throttle transitions, the ECU will switch from a RUN map to an IDLE
map. The idle map will probably have reduced advance and increased fuel.

The ECU knows to switch to the IDLE map when the IDL switch in the TPS
is open (= closed throttle), and the engine rpm's are below some set
figure. So, one explanation for the odd behavior of your ignition, would be
that the throttle was closed, but the ECU was still on the RUN map i.e. it
was not receiving a closed throttle signal from the IDL switch in the TPS.

The only flaw in this theory is that the ECU should not go into diagnostic
mode if the IDL switch is closed (= throttle slightly open). Maybe you
have some wiring defect in your TPS circuits ? Anyways, the above is
the best I can do on short notice

Cheers... jondee86

[totta Crolla]

Jondee you are spot on, even at short notice :wink:
I have since discovered that the ecu was not going into diagnostic mode due to the tps being incorrectly set, the ecu thought the throttle was open.
Now when I short it out the revs drop significantly.
Thanks so much fellah.
mot test 2pm today

[totta Crolla]

Passed mot no problem
Engine fooked
Noticed oil dripping from the air intake so I took off the breather pipe, smoking nicely out of that.
Compression test tells the whole story:
1 & 2 210psi
3 65 psi
4 180 psi
Head off tomorrow then

[jondee86]

Autoshop101 has this to say...



I don't know if you would have been running with excessive advance. It
more or less would depend what you did with the dissy when you were
moving it around. There was a time when, by error, my engine was idling
at around 30 deg advance, and I drove it like that for a while with no
apparent ill effects.

Anyways, tough luck to lose the engine. But, out of curiosity, I would like
to know what you find when you get the head off.

Cheers... jondee86