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91 SW20 Turbo won't start, flickering dash engine warning lights.

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WHITCHY
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2015/07/26 16:09:07 (permalink)
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91 SW20 Turbo won't start, flickering dash engine warning lights.

Hi guys, 
 
I am trying to troubleshoot another starting issue with my 91 SW20 Turbo. It has been flaky for a few weeks, after cutting out while driving the other day I managed to get it started again and home, now it won't start.
 
This all seems to have happened after I had to unbolt and move my engine bay fuse box around to replace my washer bottle.
 
I am noticing that the check engine, battery and exhaust temp lights do not come on most of the time, then when they do they will flicker as if there is a bad connection.
 
I am digging through the wiring diagram here I think I may have found an issue with the power to the ignition main relay, but I'd love some advice if I'm even on the right track?
 
When I remove the ignition main relay and check for power on pin 5 with the ignition off it bounces between 11.8v and 11.6v.
When I turn the ignition on this drops and bounces between 3.7v and 4.8v. If I switch the probes around I see the same results in negative.
With ignition still one if I then put the negative prove in pin 5 and the positive into one of the powered terminals (pin 3) it bounces between 6.8v and 7.8v? How can it act as both a +ve and -ve?? Its doing my head in?
With the ignition on, +ve probe in P5 and using a strut bolt for -ve if I remove the EFI Main Relay the readings go up from 3.7v and bounce between 11.4 and 11.5
 
From the wiring diagram I can see the power into P5 of the ignition main relay comes from the battery, through 40A AM2 (confirmed 12. in the frunk fuse box, through II1 in the right kick panel, through IE2 in the left kick panel, through 15A EFI fuse right next to Ignition Main Relay then into P5.
 
If I pull the 15A fuse and stick the +ve probe in the side closest to the IG Main relay it reads 12.49V stable with ignition off.
If I check P5 with the fuse out it also reads 12.49v stable.
If I keep the probe in P5 while I put the 15A fuse back in it reads 12.39v and begins to slowly discharge by .01v then it starts bouncing around between 12.38 and 12.32v
 
I've checked my multimeter isn't toast by using the strut bolt as earth and checking voltage at the main power cable coming into the fuse box, it reads 12.2 stable with ignition on and 12.45 stable with ignition off.
 
Sorry for the long post, thanks in advance for any advice on my issue.
Cheers.
 
-Whitchy-
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3 Replies Related Threads
    WHITCHY
    MR2 Aficionado
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    Re: 91 SW20 Turbo won't start, flickering dash engine warning lights. 2015/08/05 18:45:57 (permalink)
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    Finally found the issue! After my last round of troubleshooting I couldn't even get the check engine dash lights to come back on. On the advise of old_mr2 I started stripping back the loom looking for a short. I figured it would be in the power wire leading into the 15A EFI fuse so I traced that back to a factory splice near where the cable splits out for the engine lid temp sensor. As soon as I went to unwrap the tape around the splice the two wires running up to the fuse box just fell into my hand.

    It looks like moisture had been getting into the loom whenever it spilled out of the filler neck. I checked to confirm it hasn't penetrated any other splice points.
    I had a spare gen 3 loom so I decided it would be better to cut the required cable from that loom and remove the pins from the spare fuse box, seal the factory splice as well as possible with some self amalgamating electrical tape and a squirt of plasti dip then plug them into the existing fuse box and solder the joint further down.
     
    This is how it should have looked under that tape

     
    Wrapped nice and tight with self amalgamating tape then coated with plastidip, that should prevent this re-occuring.

     
    Its all back together now, the loom is wrapped tightly with self amalgamating tape, split tubing then more tape so there won't be any water getting in there again.
     
    I noticed when I was dismantling the Gen3 loom that it is sealed up much better than the Gen 2 loom, it had a layer of white tape then a layer of black.
     
    Cheers.
    #2
    Fast Eddie
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    Re: 91 SW20 Turbo won't start, flickering dash engine warning lights. 2015/08/05 19:07:22 (permalink)
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    Good fault finding and repair, you sorted that problem out once and for all.
    #3

    robk
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    Re: 91 SW20 Turbo won't start, flickering dash engine warning lights. 2015/08/05 19:25:23 (permalink)
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    Good work, what a relief hey!

    There is an extensive build thread for my car here: http://www.mr2australia.com/mr2play/tm.aspx?m=18316
    #4
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