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JDM '94 gen3 turbo
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Discussion Starter · #21 ·
@benckj So you and @J.harris both would suspesct I have a non-stock boost gauge in my cab somewhere? I do have what appears to be the stock boost gauge in my dash. Is it possible that my car didn't have that gauge from the factory and the PO jerry-rig installed it? I don't think I have any guages anywhere in my cab, it appears to be a completely stock interior other than my passenger seat, steering wheel, and shift knob. i've got some hunting to do I guess. Or I guess maybe someone could have removed the guage sometime after installing?
 

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JDM '94 gen3 turbo
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Discussion Starter · #22 ·
@CADMAN @GreenGhost74 Alright. I'll definitely check the ecu then since thats three of you now who've pointed it out as a very likely culprit. Thank you. It is encouraging to at least hear about other scenarios that are were identical to mine.
 

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91t gen5
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Post a picture of your gauge cluster sometimes aftermarket gauges are integrated into the factory spot.
 

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My car was doing that and it was due to leaky capacitors in the ECM. Fortunately I had some spare computers to make the diagnosis quickly. The caps go bad on everything. Speedometer, tach, headlight retractor module, and ecm. I replaced the capacitors after testing with a ESR meter.
Out of curiousity, does that cause the speedo to just stop working or read too low? My speedo needle has started to act like a dying slug, I only know how fast I'm going because I'm so familiar with the engine notes and where the tach sits at different speeds.
 

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Out of curiousity, does that cause the speedo to just stop working or read too low? My speedo needle has started to act like a dying slug, I only know how fast I'm going because I'm so familiar with the engine notes and where the tach sits at different speeds.
What year model is your car? 91-92 won't be affected because they have a cable driven speedo. 93+ has an electronic speedo that is affected by the bad capacitor.
 

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JDM '94 gen3 turbo
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Discussion Starter · #29 ·
Just replaced my capacitors. ECU still works, so I didn't botch the job at least. The thing that wasn't super encouraging is that none of the caps looked particularly bad, and they measured reasonably close to spec when I tested them after removal. I THINK the idle feels a little better, but I'm not positive. I basically won't know until I drive the thing for a month and the issue doesn't show up.

In the mean time, I'm going to order some vaccum hose, and figure out where that rogue sensor and rogue vacuum tube go.
 

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JDM '94 gen3 turbo
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Discussion Starter · #30 ·
Forgot to post this when I removed the ECU.
It doesn't look horrific to me. But it also doesn't look promising.
I need to find a wiring diagram and figure out what exactly has been toyed with it seems.
74479
 

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oooh yeah...someone has been there before... and it looks like stuff has been spliced/tapped and wrapped with electrical tape.

I don't have a diagram on hand, but if you search around you can find the Gen3 ECU diagram, it might be buried in a thread on gen 3 EFI conversion on a gen 2. That diagram and a multimeter will hopefully help sort that out
 

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All those wire splices might be why you had a problem, electrical tape around a wire connection tells me the person who did it didn't know what they were doing. I have a gen3 diagram but it's in Japanese, I've never seen an English one.

74489
 

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What are the wire colours that have tape on them?
You can't install an FCD on a GEN3 as it uses the MAP sensor for fueling. GEN2, fine as it's just for the boost cut.

Once we know what works have been messed with we can determine what needs doing. Maybe nothing, maybe it is the problem.

Stock boost gauge runs off the MAP sensor and is electronic so no vacuum hose goes to the gauge.

Like others said, sort out the vacuum hoses to the MAP sensor too as having 2 branches off it going to who knows where is not going to help.
 

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JDM '94 gen3 turbo
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Discussion Starter · #34 ·
Thanks for the diagram. Google translate's app will hopefully let me use that reasonably well. It has actually worked very well for other things on the car. I was able to decently translate a Japanese service record with it.

This coming weekend I'm going to dig in and find where that tube and extra sensor go. Then I can hopefully combine that info with the diagram and my ECU to paint myself a rough picture of whats going on. I'll make a list of which wires have been cut, and which appear to be splices and throw it on this thread.
 

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Discussion Starter · #35 · (Edited)
Hmmmmmm...

74578


Looks like whoever had an aftermarket boost gauge before me decided to remove it. I'm actually working on the car now, still need to figure out where that 2nd map sensor wiring is going, but I thought this image was too funny in the moment not to share.
 

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Discussion Starter · #36 ·
Alright, after a good session with the MR2 today. I feel far more informed about my car.
74579
74580

I followed the unknown vacuum tube and 2nd map sensor wiring back into my cabin, and found the following wiring, which was plugged into.... nothing at all. It looks like you guys were right and at one point, there was a boost gauge and controller hooked up somewhere in my car. One of these connectors went all the way to glovebox, and the other ended just behind/next to the drivers seat.

The map sensor and etc were all plugged in and hooked together using long pieces of the red and black wire, but when I followed that red and black wire, it actually doubled back into the engine bay. You can see from the 2nd picture though, that it also was just cut off in the engine bay.

My guess is that someone was done with this car, took out their aftermarket equipment, and returned the car to "stock", but they did it as fast as possible, and cut some corners.

The thing I found that is STILL in my vehicle, is the boost control valve. Though, it was connected to the wiring above, and thus is not electrically plugged into anything. I assume that when not plugged in, the valve would just be open and my boost would be unaffected. Is that correct? I plan on just removing it regardless, but haven't done so yet because I want to do it properly.
74581


For now, I have removed all the wiring, as none of it was hooked up to anything anyways. I also removed all the extra vacuum tube lines, and replaced the 5 way intersection hell with some of the vacuum tube that was in my cabin (it looks to be in good condition). The vacuum tube going to the cabin had some really janky extension joins in it, not to mention the screw which was capping it, so at a minimum I wouldn't be surprised if there was a vacuum leak.

The below photos just follow my (now solo) vacuum tube straight from the stock map sensor, to the manifold. I'm going to throw some fasteners on those to squeeze them at the connection points.

74583
74584
74582


At this point, I can probably safely say those most of those cut red and black wires were going to the ECU. which is why the ECU looks to have had surgery. I definitely need to confirm that the wiring is correct because someone may not have properly returned the wiring to stock when they removed the aftermarket gear.
 

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Interesting find. I guess now you'll need to look at the APEXi boost control solenoid and return the vacuum hoses back to stock so the engine ECU can control it again with the stock T-VSV.
 

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Discussion Starter · #38 ·
Just an update. I dug into the wiring on the ECU, and it appears that no wires have been completely changed, its just that 6 wires had extra connections spliced off them. 4 of them probably went to the black and red wires in the engine bay that I removed as those are the colors of the spliced pieces of wire.

I can see at least that all the wire colors match from before and after where the splices occurred. One of the connections was sketchy, so I'm going to fix it properly, and that should be that.
74731
74732
74733
74734



With this being the case:
I've replaced ECU caps.
Checked/Fixed ECU wiring.
Removed the non-stock MAP sensor and vacuum hosing additions.

If none of these things I've done solve the problem, then I think issue is either the stock map sensor is intermittent, or
some of the other vacuum hoses could be bad.

I'm gonna fix the wiring and remove solenoid today/tomorrow, and then try to daily it again for a week or two and see if the problem still occurs.
 

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Discussion Starter · #39 ·
So, I officially risked it and drove the car to Pittsburgh for Easter. (4.5 hr drive) and then back. I've also been dailying the car since then and haven't had the problem occur since I fixed the vaccuum tube, wiring, and replaced the ECU caps. One of those must have fixed it. (My guess is the caps).

Thanks for the help everyone.
 

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Good to hear! All those splices makes me think there was an S-AFC (or something similar to control air and fuel) in the car at one point too. Didn't look at the wire colors specifically but when going back to the ECU to splice, you're looking for RPM signal, MAP signal, Speed sensor, etc all in one place.
S-AFC faked the air sensor to add or remove fuel at various speed and rpm ranges. Proved to be bad for the stock ECU as it would compensate and pull timing to the point of popping motors if left long enough.
On Gen2 there was also a VPC from HKS to remove the AFM but you're Gen3 so not an item you'd have in there.
 
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