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The mkiv Supra Owners Club

Idle and start problem with tt auto conversion


Woggle1993

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Hi there,

 

So to start off with I had a supra tt auto engine from a 93. I also had a n/a auto aerotop 93.

 

The tt engine ran smoothly in the other car with no problems.

 

So my mechanic did the full conversion to the specs on forums and everything. He changed engine, harness, brakes, ecu, suspension, clocks, dash.... Everything that was on the tt car that needed to be changed over to the n/a to make it as genuine as possible has been changed.

 

I have the a problem with the idle but my mechanic says next step is to change spark plugs. He also said that coil packs and ignitor can be troublesome? I don't know if people would agree with this. However everything ran smoothly in the other car so it doesn't make sense?

 

I have a few other issues I don't know if people can help with. I'm new to this and this is my first post so bare with me please.

 

The other problems are these (I will try and describe them as best I can)

 

If I Go from P to N.. Rev counter goes to 4k then drops.... But engine doesn't rev at all just the needle moves?? Any ideas?

 

Also, if I get the car running... Put into D.... Engine cuts off..... Keep cranking and when she starts up she runs on 2 cylinders and then you can hear each individual cylinder kick in until she runs smoothly on all 6. She then idles low.

 

I'm not a mechanic and as I've said earlier, don't really know what I'm doing on here, so if someone could help that would be awesome.

 

Just a bit more info on the car.... Full decat.... Boost controller.... Hybrid turbos....

 

But this was all on the engine when it was running before the conversion so I can't see any of this causing a problem.

 

Thank you

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Sounds like a wire loom/connector issue , maybe on the gearbox loom , trapped or cut etc - you will have to con check each wire on the effected system neutral switch , crank signal , rpm signal and so on also it’s not mix and match is it - ie a partial loom swap

- lots of time needed on wiring diagrams and fluke meter

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I had a brief look at the wiring diagrams and there are some differences NA to TT such as NA has 1 EFI relay and the TT has 2 , so things like the relay box and fuse box needs swapping as well , I dont know exactly what was done in the swap over , the tach signal comes from the no1 ignitor , but it also feeds elsewhere in the combination meter and does share a supply feed with the gear selection indicator , one bad earth or missing earth can cause all sorts of problems ,and without knowing what was done and how carefully the loom instal was done its very hard to trace possible defects unless you con check every loom wire

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The trac cont is probably different - signals go to trac and then on to the ECU - you could easily have the sub throttle not opening so no air to the engine despite opening the main throttle - it also uses things like the brake switch which in turn is used by the gearbox control

Gear indication wise I would start with the gearbox plug .

I’m trying to avoid going through the wiring diagrams as it takes ages !!

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First things first, check all connectors are into the relevant ECUs and the connectors are correctly in the AUTO box gearshift unit. Then I would get him to check if he has missed an earth connection somewhere, the one under the inlet manifold is easy to miss but wouldn't cause all these issues IMO. As mentioned, the auto box wiring plugs to check.

Then take to someone who knows supras could be a good plan. Changing plugs etc is unlikely to be the fix if it ran fine in the other car and all parts were swapped. Has he swapped the looms over? If so, and he hasn't gone through them all with a fine tooth comb and replaced anything suspect, the issue could lie there as 20 year old wiring looms don't like being moved, I know this as I ended up redoing large parts of mine in mil spec wiring to eliminate possible issues

Edited by and1c (see edit history)
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