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Old 07-31-2001, 02:26 AM   #1
Scooby Newbie
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1988 323 GTX

Default TEC-II install question

Well, nobody seems to be over at the Vishnu Performance Board so I'll try here too.

I'm installing the TEC-II with 550cc injectors this weekend, and I need to have a bung welded on for either the EGT probe or the O2 sensor. Right now I've got the EGT probe mounted about 4" before the turbo on the up-pipe. It seems like alot of people have the EGT mounted about 3" under #3. So my question is, should I just move the EGT to the location under #3 and put the 02 in the spot where the EGT was or...?
Thanks for the help!

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Old 07-31-2001, 03:19 AM   #2

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Sounds like a plan to me. IIRC, Autometer stated in their instructions to mount the probe 3-4" from the head on the exhaust manifold.

The real question to pose is... cyl #3 (pass rear), or cyl #4 (driver rear). Ready for a theory-filled post?

Ok, well everyone has suggested in the past that #3 is at the end of the fuel rail and therefore the injectors before it were using up most of the pressure and/or flow, so #3 will run the leanest.

However, it has recently come to my attention that a rash of people blowing motors in their RS-T's ended up blowing up #4. This leads me to believe that possibly the flow is what we're concentrating on more here...

See, my theory is that the flow creates the pressure most accurately nearest the FPR, as the rest of the line is using fuel between it and the FPR. Taking that into consideration, the pressure drops more and more down the fuel rail (3, 1, 2, 4) until #4 is getting the least fuel pressure.

I believe most people will disagree at first, however you have to take into consideration that the pressure along the rail is being interrupted by the injectors spraying the fuel, causing it to draw more through from before that.

Take for example a channel in which water is running through at a high rate. At the end of this channel we have a wall which builds up the "pressure" upstream of the wall. Well, remove a plug from a hole (assuming this hole is rather small compared to the flow) just before the wall - the flow keeps going, but the pressure before it drops. Open another hole, and another, and another.

Think about what type of flow that first hole is getting - basically it'll have very little pressure to draw from since the first 3 holes are drawing water through to make the pressure before each more and more, until finally the desired pressure is reached just before the wall, after the last hole.

People have reported much better fueling when they have rerouted their fueling system to a parallel system between each side rather then having both sides in series. I think this just provides a bit more info that the fuel system 1.) sucks as it sits for high-power applications, and 2.) must be reworked to provide adequate fueling all around.

Any comments? I'm by far not a professional, trained fluid-engineer, however I do understand the concepts of fluid dynamics and our current fueling system setups.
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Old 07-31-2001, 05:29 AM   #3
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Sorry to blow your theory 8 but I blew my #3.

It was by FAR the leanest running in my setup. YMMV

I would put the probe in the headers about 3" from the block. When I moved mine there I was amazed by the quick response I was getting.

As far as the O2 sensor, I thought with the Tec-II you would install that in the place of one of the stock O2 sensors (not sure which one).

You could just plug the other exsisting hole from your EGT probe I suppose.

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Old 07-31-2001, 11:40 AM   #4
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I thought its better to have the O2 sensor closer to the "action" and puting it in the stock location makes it much more removed, no?
Just searching for the answers.

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Old 07-31-2001, 08:13 PM   #5
Joe Hogan
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The O2 is best placed just after the Turbo according the Corkey Bell [a well known turbo guy]
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Old 08-02-2001, 02:23 AM   #6
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Yesh, the O2 sensor is best placed behind the turbo, unless you conveniently have a spot in the turbo's up-pipe where the EGT you just moved used to reside...

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