Car jerking at constant rpm

spetz · Post by **spetz** » Fri Oct 27, 2006 1:24 am

This is a problem I had since fitting the 6A12 into my car

At constant rpm in the lower range (under 3000rpm) it jerks as if the engine switches off suddenly and then back on
It happens in most gears but usually 1st and 2nd as it only happens at extremely light throttle

I am not going to get it fixed as the engine is coming out but just wondering what it is?
I assume TPS sensor or something?
Maybe some fuel issue?

Hobbsie · Post by **Hobbsie** » Fri Oct 27, 2006 7:59 am

sounds more like a clutch/gearbox problem or something..

my work car has started doing this too recently, since i drive it like its stolen.. dont even use clutch when i change gears half the time etc haha

umm · Post by **umm** » Fri Oct 27, 2006 2:09 pm

Yeah i have that too. Exactly the same symptoms. Mine is caused by the stepper motor starting to fail. Its been doin it for a while and haven't got around to fixing it yet.
Search for a guide to test if you stepper is the problem. There is a guide that shows how to test the resistance in the coils.

Post by **Bennoz** » Fri Oct 27, 2006 5:08 pm

http://lightning.prohosting.com/~v8mate/mitsux.html

spetz · Post by **spetz** » Fri Oct 27, 2006 8:24 pm

Yeah I thought it would be something like the stepper motor

Where is that located? on the TB?
I got a Magna TB with all the gear on it so I assume I can just use that one couldn't I?

Post by **Bennoz** » Fri Oct 27, 2006 11:00 pm

Yeah its on the TB just below the inlet. Unsure if you can use the Magna one, I believe they are different internally. I have a spare FTO one I could post down to you if you want to test the theory...

spetz · Post by **spetz** » Sat Oct 28, 2006 1:41 am

Well I already have another FTO TB with the gear on it but if that doesn't work I'll shoot you a line

payaya · Post by **payaya** » Sat Oct 28, 2006 7:31 pm

is your problem more like your disengaging the clutch??

So when you apply light throttle the rpms are were they are meant to be at a certain speed, but when you release the throttle the rpms drop to almost near idle???

Liquidity · Post by **Liquidity** » Sat Oct 28, 2006 7:59 pm

I experienced this in a different car once, but only on cornering. Problem was a badly designed fuel tank meant at low fuel levels, on a hard left turn the car would just cut out.

Felt like the engine had been switched off, or you'd tapped the brakes on fairly hard. Car would cut in again after a moment.

So maybe a fuel regulation issue? Your using a piggyback, right? Does it have injector control? Are you using "stock" injectors/pump etc?

spetz · Post by **spetz** » Sun Oct 29, 2006 10:39 pm

Its not through corners that it happens

And at the moment this is still the old engine and everything is stock on it. piggyback is at zero state doing nothing

I think it is TPS or something like that
But yeah it's kinda like the engine switches off then back on again

Quite annoying at parking lots etc

Liquidity · Post by **Liquidity** » Mon Oct 30, 2006 1:53 am

I know its not through corners that it happens, i'm just saying i experienced something similair, and the problem was fuel starvation, so maybe look at that system.

spetz · Post by **spetz** » Mon Oct 30, 2006 3:33 am

Fuel issues was the first thing that came to mind but I quickly dismissed it as I know everything SHOULD be good (ie, pump, filter, regulator, injectors not sure though)
But, considering it is fine at what and high rpm, and other people experience this with the TPS or stepper etc I think fuel should be ok

At the same time as you know this engine isn't staying in there long so I am just curious rather than trying to fix it