2.9 engine ignition timing for octane rating

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simmit
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Re: 2.9 engine ignition timing for octane rating

Post by simmit » Thu Apr 13, 2017 6:07 pm

peter freeman wrote:If you send me your email address I will forward on to you the emission set up document - its 2megs so too big to send otherwise. The wiring mods are there to retard the ignition for poorer than 97 Ron fuel so I think the engine is designed for 97 anyway and the timing will not need to be touched - it seems to run ok on 95 as well not that I have done it very often - only when 97 is not available in such as Morrisons and they have given me a 10p per litre off coupon.
Thanks Peter, I've sent PM with email address.

I do believe the engine was designed for 97 RON fuel and the Octane plug only comes into play where lower grade fuel is used (whereby through changed wiring connections it instructs the ECU to retard the timing somewhat). It is quite possible a previous owner set the plug to run on lower grade fuel (I simply can't tell) so I need to know which way round the wires go in order to check.

It has been suggested I use a strobe to check the timing. That's fine ............ if I had one.

As an aside, I'm advised timing ought not be adjusted by turning the distributor as that may upset the ECU, timing ought be set by dialling in the ECU. I'm strictly clockwork and find all this electrical gimmickry confusing. Big spanners and bigger hammers is more my scene.



simmit
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Re: 2.9 engine ignition timing for octane rating

Post by simmit » Fri Apr 14, 2017 7:01 pm

peter freeman wrote:If you send me your email address I will forward on to you the emission set up document - its 2megs so too big to send otherwise. The wiring mods are there to retard the ignition for poorer than 97 Ron fuel so I think the engine is designed for 97 anyway and the timing will not need to be touched - it seems to run ok on 95 as well not that I have done it very often - only when 97 is not available in such as Morrisons and they have given me a 10p per litre off coupon.
Hi Peter.
Many thanks for the excellent set-up article/ document received. It shows photo of the Octane socket so at least I know what I'm looking for (and it's nearby the ignition coil on MB50).
The article states there are three wires from the Octane Service Socket, Red, Blue and yellow. Goes on to say that if we cut the blue wire it will retard the timing by 2 degrees, cut the red wire for 4 degrees and cut both for 6 degrees retardation.
All good stuff until I look under my bonnet to find ................ blue and yellow wires are both cut! This is completely at odds with the article so where does that leave my timing to be?
The remaining red wire is connected to the ignition coil mounting bracket (earth connection) where where I suppose the blue and yellow wires were also originally connected.
It would seem then, that in order to return the ignition timing to it's factory setting (to run on 97 RON fuel) I ought reconnect the blue and yellow wires together with the red to earth.
But as the engine seems to be running OK and I don't want to upset the ECU, the question is, should I? From sad experience I know ECU's can be awkward little buggers if tormented.

To get a wider audience I'll post my Octane socket issue on the General Technical Forum.



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