Rev limiter cutting in early?

nickt · Post by **nickt** » Sat Jul 30, 2011 10:18 am

I have had the hard cut rev limiter installed for a few months now. Sometimes, usually when the engine is quite cold, it's as if the limiter is cutting in early. The car loses power for a moment then it returns along with a loud backfire (just like hitting the limiter). It can happen at any point in the rev range and usually the power returns after a moment or so but on my way home from a friends last night, shortly after leaving it popped banged and died and I had to stop, but then it fired up without a problem and got me home fine. It seems like a fault with the rev limiter due to its nature. It doesn't happen every time I use the car and seems to be quite random. My only other guess was that it could be the coilpack on its way out but I understand the EDIS coilpacks don't fail very often and I don't know if these symptoms are typical of a coilpack failing. Anyone have any ideas or similar problems?
Thanks in advance!

Post by **brentp** » Mon Aug 01, 2011 3:55 pm

Hi Nickt,

what RPM set point do you have the Rev Limiter at?

Also, you might want to check it with the rev limiter bypassed- i.e. move the coil pack power supply to fixed +12v. Does the problem still occur?

nickt · Post by **nickt** » Mon Aug 01, 2011 5:52 pm

I have the limiter set at 7,100rpm.
I have not tried moving the coil power, I suppose that will rule out the coil pack. Though it never occured before I fitted the hard cut limiter. I will try moving the coil power over the next couple of days and report back.
Thanks
Nick

910esprit · Post by **910esprit** » Sun Aug 14, 2011 8:11 pm

I had a similar problem a few years back.. it turned out to be a broken wire from the crank sensor..
Under hard acceleration as engine moved on mounts the connection broke then as the engine moved the other way it made contact again and everything was fine. occasionally it would die completely and not start for a few minutes then all would be ok again.. It took ages to find and the wire was broke in the sheathing so not very obvious.
Good luck

nickt · Post by **nickt** » Mon Aug 22, 2011 5:16 pm

Thanks for the replies. Took a bit longer than planned (the car isn't my daily driver and I've been busy) but I have eventually managed to swap coil power back to swithed 12v as it was before the hard cut limiter was intalled. I have only driven about 30 miles since doing so but the problem has not occured and it was getting worse up untill I moved the coil power. So it would seem that the limiter has a fault. I removed the pcb from the mj case and checked the connections which looked fine. Also none of the resistors looked burnt out.
Any more suggestions?
Thanks
Nick

Post by **brentp** » Tue Aug 23, 2011 9:44 pm

The rev limiter cutting in early might be caused by RPM spikes due to noise on the PIP line coming into the Megajolt. If noise exists, it could intermittently trigger the rev limiter.

One way to verify this is monitor the data using the configuration software while the car is driving. See if you can observe any erratic RPM readings.

Also, it could be a good idea to just drive without the rev limiter for some period of time (100 miles or so) to verify everything is running rock-solid.

Let us know what you find out!

nickt · Post by **nickt** » Wed Aug 24, 2011 9:16 am

If the rpm was spiking wouldn't that still have an affect without the hard cut limiter? The megajolt itself retards timing as means of limiting doesn't it? So would that not still be noticable though obvoiously not as much so and with no backfires?
I'll try and put some more miles in this weekend and see how it is.
Thanks again.
Nick

Post by **brentp** » Wed Aug 24, 2011 3:59 pm

It depends on your engine- it might not be nearly as noticeable as a full engine cut.

Let us know what you find out!

Autosport Labs

Rev limiter cutting in early?

Rev limiter cutting in early?

Re: Rev limiter cutting in early?