Gen3 turbo (swap), rev limit dropped to 6800rpm. - why????? - MR2 Owners Club Message Board
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post #1 of 16 (permalink) Old May 12th, 2019, 16:27 Thread Starter
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Hello, last year my car for some reason has stopped revving to 7200rpm normal rev3 redline and now will not rev past 6800rpm.

It definitely used to rev to 7200 I can confirm with Dyno graph, and I've double checked that the tacho is reading accurately.

Has anybody experienced this in the past?

Possible causes I've considered:
Coil: I've removed it and tested it and it meets Toyota spec (also only 2 years old).
TPS: A similar problem on a different car forum turned out to be tps related and Broken valve spring: the one I really don't want it to be (running hks springs), car performs totally normally up to that point though so seems unlikely to be a mechanical issue.

Going to swap the coil anyway, got a sprint next week and don't want to drive the car to its limits without knowing what is wrong

Any other similar experiences you can share would be helpful!
Thanks
Dan


Car is a jdm rev 2 turbo with rev 3 conversion running rev3 standard ECU, hks 264 cams hks valve springs
Running rev3 ignitor

Last edited by Danbob; May 13th, 2019 at 00:44. Reason: Adding detail about ignitor
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post #2 of 16 (permalink) Old May 12th, 2019, 16:48
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One thought on JDM ECU's. From memory they have a lower RPM restriction if the speed sensor is disconnected or malfunctioning. This was due to a Japanese speed restriction law.

No way around this one I'm afraid unless you can repair speed senor feedback to ECU or go standalone.
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post #3 of 16 (permalink) Old May 13th, 2019, 00:43 Thread Starter
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That's an interesting lead, I'll look into that and check the wiring in case something a been knocked.

Do you have any more information on this lower rpm limit? I've not seen it mentioned before.


Thanks
Dan
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post #4 of 16 (permalink) Old May 13th, 2019, 01:19 Thread Starter
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Found some good info on speed signal topic here:

http://www.mr2.com/forums/archive/in...p/t-78473.html

Looks like that problem will impose a 6000rpm rev limit and also will raise a check engine lamp and code 42

Unfortunately I have no code and the limit is definitely above 6k, around 6800.

You might ask why I'm bothered about the last 400rpm, but this car is only ever used on track for time trials and my power is made right at the top end so it makes a difference, and I want to know why it's happening so I know if it's safe to keep driving the car

Thanks
Dan
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post #5 of 16 (permalink) Old May 13th, 2019, 13:58 Thread Starter
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Anyone else had a similar problem?
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post #6 of 16 (permalink) Old May 13th, 2019, 15:26
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What does the engine do when you hit that limit? Same as hitting the normal limit?
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post #7 of 16 (permalink) Old May 13th, 2019, 15:39 Thread Starter
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Yes very similar to hitting the normal limit. It will bounce off of the 6800 rev limit like a factory limiter, it doesn't rise up and settle there, but it's also not a really harsh jerk like a fuel cut.
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post #8 of 16 (permalink) Old May 13th, 2019, 16:40
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I'd suspect ECU as the unknown for limiting rev limiting. Possibily the failing caps are the cause for the change? Any chance you can try another as not having stored codes is a sign of internal software issues.

One reason I bring this up is I had a friend in a similar circumstance. He runs a gen 3 car for track use but is a Frankenstein of parts. Think his reduced rev limiter was from using a gen 2 speedo or harness connected to the gen 3 ECU. Never really got to the bottom of the issue as he eventually switched to an aftermarket EMS and problem disappeared.
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post #9 of 16 (permalink) Old May 13th, 2019, 16:51 Thread Starter
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That's another good point, my car is also a Frankenstein of gen 2 and 3 so also runs gen 2 speed sensor and Speedo, but neither have been a problem until now. I do also have a spare ECU somewhere so I will add that to the list of parts to swap!

Cheers
Dan
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post #10 of 16 (permalink) Old May 13th, 2019, 17:43
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I don't know if this is a thing with the GEN3 3SGTE ECU but I know some Toyota have soft cut and hard cut limits. My mums 2000 Corolla with a 4AFE has this and at higher speeds you can feel the soft cut come in. There isn't enough power to push through the soft cut to hit hard cut before you change gears. Hard cut really only happens in 1st or 2nd when you are in those rev ranges. Not that your car has any issues pushing through especially with those cams.

Not that this helps figure out why it's doing what it's doing where it didn't used to.
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post #11 of 16 (permalink) Old May 15th, 2019, 18:23
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I thought I had a problem with my 91 MR2 rev limiter, but as it turned out it was actually the tach that was wrong and I was just trying to over rev the engine. Just check to make sure you have an engine problem and not an instrumentation problem.
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post #12 of 16 (permalink) Old May 16th, 2019, 00:52 Thread Starter
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Hi, yeah I have confirmed the tacho is correct using an external tacho on the HT lead, it's fine.

I think it could be a bad earth on the ignitor as I've learned the ignitor earth's through the bracket and the bracket was painted, and the 12v side of the coil earth's through the ignitor.

Hopefully I'll have time to fix and test that this weekend and might have it solved
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post #13 of 16 (permalink) Old May 19th, 2019, 15:09 Thread Starter
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UPDATE:
Swapped the coil pack for a new one, removed paint from Coil/Igniter bracket and made sure igniter has a really good earth, took it out to test and now won't rev past 6300!!
It's gotten worse by 500rpm since last test.

Engine and oil up to temp,. No fault codes, car otherwise behaves normally!
AFR shows its running rich (9.5) up to that point then looks like it's cutting fuel bouncing between 6300 and 6200, could still be cutting spark as the wideband would read the unburnt fuel as lean anyway,

Any new ideas?

Will swap ECU for a spare one next
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post #14 of 16 (permalink) Old May 19th, 2019, 17:40
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Time to swap in another ECU.
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post #15 of 16 (permalink) Old May 19th, 2019, 21:41
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I know you have cross checked it with another tacho but what RPM do you get when travelling at 60mph in 5th? This should be 2750rpm right? If it's dropping then it still could be the tacho.
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post #16 of 16 (permalink) Old May 20th, 2019, 00:48 Thread Starter
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Good point, I could reconfirm using rpm in known speeds/gears, wish I'd recorded it when I was testing yesterday!

Unfortunately I'm not on stock tyre sizes so I'd have to work that part out
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