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1992 SW20 5sfe M/T 171k + Miles
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Discussion Starter · #1 ·
Hi everyone, first-time poster here! Need some opinions.

TLDR: Crank, no start. No power to fuel pump. Sometimes no spark either. New Circuit Opening Relay (cor) didn't fix it. Mechanic's technician put in a new COR and said it was fixed and that the one I got new from the dealership was bad. The problem didn't go away. Changed COR again, no dice. Did my own diagnosis and found the IE2 wire was bad. Ran a bypass and it starts/runs perfectly, even with the old "bad" COR. Does this bypass prove the relays have nothing to do with the problem and the mechanic was wrong? Should I ask him to replace the IE2 wire pro bono since the problem wasn't fixed after all I paid? (I know some people would use $300 as toilet paper, but that's a lot of money to my cheap broke self)



Long Version:
Bought my 1992 5sfe MT MR2 with a crank, no start problem. The problem was intermittent, so it was a crapshoot if it would ever start or not. When it did run it would sometimes stall under hard acceleration. Checked all the fuses, put in a brand new EFI relay and COR relay, and had no luck. Did some basic diagnostics and found fluctuating voltage at the EFI 15a fuse. Sometimes 11v, sometimes 9v, sometimes 2v, sometimes nothing. Totally random. Decided to save time instead of money and took it to my mechanic who I trust and have had a great time dealing with until this issue.
I told him everything I wrote above. The voltage at the fuse, the new COR, everything.
The technician said the issue was the COR was bad, even though it was brand new. Didn't say anything about the voltage at the EFI fuse or if he did a full functionality test of the COR. Charged me $150 for the diagnosis and $150 for the COR. I thought it was fishy, but he's a pro and I'm not so I went with it.
And then not only did the problem not go away, it got worse as the no-start issue became more and more frequent over the next week until it was dead as disco. Crank, no start... ever.
Thinking it must be burning out the COR, I try a new one again, but it doesn't change anything.
Still guessing the technician was right, I assume there must be a secondary problem and spend weeks checking everything else (money's too tight to afford a 2nd diagnosis). Battery, alternator, fuses, ignitor, ignition coil, distributor, high tension wires, ECU. I check all off it. Then I get this crazy idea that maybe the tech messed this one up...
So I pull up the wiring diagrams from the BGB, and take it from the top. Eventually, I find there's constant 12v at the IE2 Connection, but no voltage or continuity at the EFI fuse or terminal 5 for the Ignition Main Relay (IMR). (remember I mentioned voltage problems at the fuse, and they didn't say anything about solving that?)
So I work out a way to set up a hotwire that leaves the relays in play. It sends 12v straight to the EFI fuse terminal that leads to the EFI relay, and a wire that bends under and inside the IMR to send power straight to terminal 5, so no power is drawn from the battery until the relay is actuated. The bypass effectively replaces the IE2 wire. (unless I'm mistaken) Pictures Below.
AND PRESTO, It starts and runs perfectly! And the super cool news? Not only does the new COR work with this bypass, but so does the old "bad" COR. Interesting, huh?
So I call my mechanic and met up with him and the tech and spend a long time explaining this.

They're saying the IE2 wire is a separate issue and the COR really was bad. The tech is sure the problem was the COR getting burned out because sometimes it worked if he tapped on it... sounds legit (sarcasm).
My theory is the IE2 wire was the problem from the start and he didn't check that and called it a day after the car coincidentally started after he put a COR in without even running a bypass or doing an out-of-the-car functionality test on the relay to be sure. I mean, if the COR didn't work, it wouldn't work with this bypass, right? I've been running it on the "bad" COR for a couple of weeks now after all. Whatever's wrong with the IE2 wire must have been getting progressively worse and worse until it failed completely.

Here's a picture of the bypass and some highlighted versions of the diagrams explaining the setup.

What do you think?
Automotive tire Motor vehicle Automotive design Automotive fuel system Automotive exterior
Rectangle Schematic Font Slope Parallel
Rectangle Slope Schematic Font Parallel
 

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Sounds like the “mechanic” is a big dummy dingus and doesn’t know what or how o diagnose with a wiring diagram and a simple test light.
A relay test with a test kit or bench test would easily prove this plus testing all relay terminals on harness side.
 

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So the blue with red wire is misbehaving? Seems a lot of people don't quite follow wiring that we'll. It does take some time to fault find and pin point but it they didn't fix it then it sucks to have to pay for it.
 

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1992 SW20 5sfe M/T 171k + Miles
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Discussion Starter · #5 ·
Sounds like the “mechanic” is a big dummy dingus and doesn’t know what or how o diagnose with a wiring diagram and a simple test light.
A relay test with a test kit or bench test would easily prove this plus testing all
My understanding is my mechanic had his technician work on the car, so I guess the technician is the dingus and my mechanic is just taking his word for it. I did do a bench test to be sure the relays are functioning properly once I figured out what was going on.
 

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1992 SW20 5sfe M/T 171k + Miles
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Discussion Starter · #6 · (Edited)
Yeah bypass those fuses that sounds like a good idea!
I did bypass the 15a EFI fuse to test the bypass, which is what I took a picture of, but I now have the 15a fuse spliced into the bypass wire.

edit: I should mention the picture was also taken before I noticed I put the 20a fuse where the 7.5 fuse goes, and vice versa. The vent fuse doesn't do anything since it's a 5sfe, so it's just there for storage. And according to the wiring diagram the ECU-IG fuse is still in play. Appreciate the concern though!
 

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1992 SW20 5sfe M/T 171k + Miles
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Discussion Starter · #7 ·
So the blue with red wire is misbehaving? Seems a lot of people don't quite follow wiring that we'll. It does take some time to fault find and pin point but it they didn't fix it then it sucks to have to pay for it.
It's a black wire with a red stripe, but yeah. Took me forever to find where the color abbreviations are explained in the BGB, lol. Still not sure if the problem is with the wire itself, or if it just needs re-soldered to its connectors. Electrical stuff is always such a pain, which is why I took it to the shop in the first place. I'm hoping I can show this thread to him so he'll realize his technician really did make a mistake on this job.🤞
 

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Well there you go you figured it out then.
These oem Toyota/denso relays rarely go bad I can tell you that they’re quality built from many years of experience, unless corrosion gets to them first of course.
Like you said more than likely that black-red power wire corroded over time, ive seen them corrode starting at the terminals inside the fuse box in engine compartment so will definitely cause high resistance issues.
I’d say go and show this to you’re “mechanic” and show him how the old relay still operates normally on your car and get your money back, I would if I were in your situation because it’s just not right, why would you give them money if he didn’t even fix the problem you signed over to them on the repair order?
 

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Hold up, but you didn’t start/crank the engine with the 20A fuse in the wrong position where the 7.5 ECU-IG goes right?
Maybe you fried overloaded heated the black-red wire no?
 

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It's a black wire with a red stripe, but yeah. Took me forever to find where the color abbreviations are explained in the BGB, lol. Still not sure if the problem is with the wire itself, or if it just needs re-soldered to its connectors. Electrical stuff is always such a pain, which is why I took it to the shop in the first place. I'm hoping I can show this thread to him so he'll realize his technician really did make a mistake on this job.🤞
Sorry. Black with Red. Got my colour coding wrong. B is black, BR is brown and L is blue.
 

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Why not take the fuse box out and repair the messed up wire the right way?


But yes, the mechanic who worked on your car sounds like he shouldn't even be installing car radios if he just slapped a new relay in a spot for an intermittent low voltage issue.
 

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1992 SW20 5sfe M/T 171k + Miles
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Discussion Starter · #12 ·
Why not take the fuse box out and repair the messed up wire the right way?


But yes, the mechanic who worked on your car sounds like he shouldn't even be installing car radios if he just slapped a new relay in a spot for an intermittent low voltage issue.
That's basically what I'm trying to get my mechanic (or more specifically the tech who works with my mechanic) to do since I already paid them to fix it. I just needed the car running for now and the bypass proved it was the IE2 wire and not the relays as well.
 

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Discussion Starter · #13 ·
Hold up, but you didn’t start/crank the engine with the 20A fuse in the wrong position where the 7.5 ECU-IG goes right?
Maybe you fried overloaded heated the black-red wire no?
No, the fuses were in the right place before the bypass + while I was diagnosing it. I put the bypass in and took the picture, then noticed and put them back before cranking, and the 7.5a fuse isn't blowing, so I don't think that's what killed the wire. The problem started with the previous owner (which I knew about) so who knows if he did something that burnt it out. I should have taken a new picture but it was late (hence the flash) and my back was sore from literally bending over backwards to inspect the IE2 connection so I just wanted to lie down asap, lol.
Here's a pic of the bypass at the moment:
Trunk Electrical wiring Audio equipment Gadget Cable
 
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