Soft Rev limiter

[steer_rally]

How do I set/change the soft rev limit? Not sure which version of MJLJ I have, but it's at least a year old now, but assuming it does have a soft limit, where and how do I access it to change it? I'm running a Pinto in my Mk2 escort and it won't rev much over 4.5K.

[capri_turbo]

Is there not a function in the tuning software to alter this? I havn't got up and running yet and I'm still learning myself, but in the tuning software I have, it has a rev limit setting under the "programmable outputs" tab.

I'm currently fitting MJLJ V3 to my Capri (2.1 pinto). What map are you running? I have finally got the crank trigger etc sorted out. I'd be interested to know how you have set yours up?

I can be contacted on: colin@ford-capri.fsnet.co.uk

Col

[rmaddock]

As I understand it, the programmable output "rev limit" is just a switch which can be used to turn off/on a relay which in turn supplies the power to the coil - I think this is considered a "hard" rev limit.

When people talk about soft rev limits they mean that the advance map severely retards the engine beyond the rev limit, thus causing it the cease to pull beyond that.

[steer_rally]

Hi colin
I always assumed that the rev limit setting you refer to was for a "hard" limiter, i.e. one of the physical outputs from the megajolt itself as opposed to incorporated in the software/map.
Anyway, I'll have a look tonight.
As I mentioned in my original post, I'm not even sure what version of the hardware I have, or if I'm running the latest software. Maybe My system doesn't have a soft limiter, although it seems as though this is what's happening. It revs like an animal up to around 4.5k an then just sits there and won't go any higher. Very frustrating.

[capri_turbo]

So I could use this function with a rely to cut the power to coil pack as a "hard" rev limit...

My learning curve is quite steep at the moment.

[Magnolia]

Since there is no soft limiter, it sounds suspiciously like you are running at the default 10 degrees which is inadequate for the rpm bandwidth. 1) Did you verify advance with a timing light? 2) If so and your static is 10 deg and it is advancing, what is the timing at 4500? 3) Did the engine rev > 4500 before MJLJ?

[steer_rally]

To be honest, I haven't checked the advance with a timing light. I connected everything together, she started first attempt, I tried a few maps for pintos that I found on this site, chose the one that worked best and have not really messed around with it since. I'm more than happy with the performance of the car, I'm pretty sure it's not running at default 10 degrees (limp home mode?) as acceleration is excellent, idle is smooth, it just won't rev high enough.
I will however check the advance with a light as soon as I can.
I never had a distributor for the engine, so don't know whether it reved > 4500 or not.

[4600cc]

100 rpms before the set hard rev limit, advance goes to 0. Just upload the latest firmware there.

[DannyP]

As I understand it, a hard limit is like a switch, on or off. A soft limit is proportionate to some extent, you pick what rpm to start retarding the timing and at what rate it is retarded. Of course I would leave the hard cutoff as a failsafe.

[MartinM]

The "Rev Limiter" setting in Programmable Outputs in the Configurator is the value at which the Rev Limiter output (pin 13 on MJLJ V3) pin switches. It can therefore be used to power an external circuit to either, say:
- power a relay to cut coil power so that there are physically no sparks occurring - ie a hard rev limit
- power a light on the dashboard so that you know the engine is at the "Rev Limit"

The MJLJ does NOT do a hard rev limit at all - in fact it cannot, since the only thing it can do is stop sending commands to the EDIS, in which case the EDIS goes to limp home mode and the timing goes to 10 BTDC.

However, the MJLJ does set the timing to 0 degrees 100rpm before whatever the "Rev Limiter" value is - the so called soft rev limit. So 100rpm before the "Rev Limiter" value, the timing goes way too retarded for the engine which has some effect of limiting the rpm. Note that you still get sparks during the soft rev limit - they're just later than the engine needs.

You can experiment with the soft rev limiter on a working installation by setting it to say 3000 rpm and increasing the throttle. On my install, there is definitely a big effect when under load (ie actually driving) but it's interesting that when stationary I can get the rpm appreciably higher than the soft rev limit - my engine is obviously reasonably happy with 0 BTDC timing!

Note that is a debatable thing to power a relay from the Rev Limit programmable output to cut the supply to the coil - search for "rev limiter" in this forum and see the views


...and back to the original problem, if the engine won't rev over 4500 but is fine up to 4500 then it could well be the Rev Limiter value. However, I would suggest the following tests:
- look at the timing with a light (you really shouldn't be attemting an install without using a timing light to verify operation) - does it generally increase with rpm?
- disconnect the MJLJ completely - does it make any difference?
- ...then look at the configuration of the programmable outputs

[steer_rally]

It was indeed the rev limiter output, which I hadn't realised also retarded the timing to 0. I assumed it only worked as programmable output. I've now increased the limit to 6.2k and shaved 30secs off my time at my local track. Many thanks to all for clearing this up for me.

[MartinM]

Must be a long track - or you've now got a humungous increase in power!

Nice to see all the theory working out....

[steer_rally]

but now got my time down to 5.20, the difference is amazing. Just wish I'd sorted it out sooner. Still, better late than never!