Rpm gauge needle bounce and dosen’t match engine. Help!!!

G_Péji

New Member
Mar 9, 2022
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Hello all,
I really need help. I recently notice that my rpm gauge dosen’t follow all time the engine and bounce and act weirdly. I thought at first that the rpm modul was defect so I replace it with an other I had in stock. Dosen’t change at all still doing it. I don’t know where to look or what diagnosis to do.

thank you for the help.
I have made a video to show the exact problem.

The car is a 1990 original turbo with a 1JZ vvti swap. Ecu is a megasquirt.

 

supra90turbo

shaeff is FTMFW!
Mar 30, 2005
6,150
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MA, 01440
Looks like a possible loose connection causing the signal to drop out and then quickly try to catch up. Have you checked connections in the harness?
Also, does that car really have 76k on it?
 

G_Péji

New Member
Mar 9, 2022
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Looks like a possible loose connection causing the signal to drop out and then quickly try to catch up. Have you checked connections in the harness?
Also, does that car really have 76k on it?
Ok you think it could be in the cluster harness a loose connection ? I didn’t check that. Will check all screw and wire. Thank for pointing out.

And yes a true 76000km car. Born in Montreal Canada and still there. I am the 2nd owner :)
 

figgie

Supramania Contributor
Mar 30, 2005
5,209
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The RPM signal is getting sent from the Megasquirt... So you either have a lose connection or there is something telling the megasquirt that it is climbing that much since in most all standalones, RPM is based on physical crank RPM measurement (12 tooth wheel, 36-1, 60-2 etc).

FYI, I am hearing a miss fire in your engine. It is slight but it is definitely there. You might have something interfering with the Crank signal. I would check within the megasquirt (assuming it has an oscope function) that the RPM signal is solid.
 

G_Péji

New Member
Mar 9, 2022
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Yes true. There is slight missfire for sure and when I let the gas off, the engine goes on and off by itself. I have an appointment with a tuner to verify the tune. I have bought the car as is in the last October.

He already check the tune and adjust some parameters. He explained me too that the signal come from the megasquirt. So either I got 2 bad tach module or a problem with the wiring or the rpm tell me that there something wrong in the tune but too subtle to hear or feel via the engine.

I just don’t understand either.

Thank you for the help and I will keep you updated.

I don’t know if it worth it to put it on a dyno since I want to change the 1JZ vvti by a 2jz gte.
 

figgie

Supramania Contributor
Mar 30, 2005
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so... my initial guess would be that you have interference going to your RPM signal...not much but it is there. It might be tied to the missfire you are having.
 

G_Péji

New Member
Mar 9, 2022
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Hello guys, So today was my dyno session day with my tuner and everything went smooth and we corrected some points in the tune and overall the car run near perfect! I don't know if there was something via the megasquirt, but now it dosent do the bounce thing but my rpm needle is off by 200rpm from what we see on the Tunerstudio. I wish the previous owner never touch the cluster needle.. Its so useless as mod and give me only trouble. I am about to just ditch this cluster and just buy a new/old one in good condition.
 

Zazzn

l33t M0derat0r (On some other forum) n00blet here
Apr 1, 2005
958
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Toronto/SF Bay area
I think the resistors are off for a JZ swap tach. My tach was never quite on par with what the logs said. Always off by a few hundred RPM. I just don't think anyone has ever really said anything, and it's off as you go up in RPM at idle, the difference is minimal. BTW the tach jumping around is generally something with timing. I had a section from 2000-3000 that my tach jumps around when cold, so the signal from my CPS could be not great or something I don't know, but I'm on an ms3 pro pnp myself and never figured it out.
 

G_Péji

New Member
Mar 9, 2022
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Exactly, im off by 300 rpm. Idle is at 850 in the tunerstudio and tach show 1100rpm. But as soon as i pass 2500rpm is near on point with the tunerstudio. Like you said must be a resistor thing. My tach signal comes directly from the MS3 pro pnp. I just remember seeing somewhere that painting the needle would trigger the cluster operation... Anyway, since I updated the firmware in the ms3, my tach never bounced again.. i don't know... im a bit pissed by that. IM just tampted to put a stock cluster in and fuck the dimming needle