Rev counter drops out on load

grahamrally · Post by **grahamrally** » Tue Mar 20, 2007 6:18 pm

I have the Megajolt hooked up on a Peugeot 205 rally car running carbs. I'm using a TPS to map it 3D and everytime i put more than half load the rev counter drops down to zero. The system itself all works fine and the rev counter revs up fine on a stand still. Any ideas?

Thanks,
Graham

Post by **brentp** » Wed Mar 21, 2007 4:53 am

Do you mean your tachometer? How is the tach receiving it's signal?

grahamrally · Post by **grahamrally** » Wed Mar 21, 2007 8:38 am

Yes I mean the tacho. It's connected to the megajolt output. In 2D mapping I didn't have the same problem.
Quite annoying!

Graham

grahamrally · Post by **grahamrally** » Wed Mar 21, 2007 9:06 pm

Ok the story continues. The tacho was the only problem initially with it all setup. I had noticed that the shift lights running of the jolt were flikering every now and again so I knew I need to get shielded cable for the PIP and SAW lines. Since then, I was driving the car down the road and the same load that the tacho drops out at and it started to splutter and pop and bang. On mild load it was ok. I then took it to my work-shop and proceeded to shield the PIP and Saw cable. And it was exactly the same! So I hooked up my laptop and found that the rpm reading was intermitent. We checked the VR sensor and it was too far away. However, when I unbolted it and held it closer the whole system ceased to work. We checked the VR was creating a AC which it was. There was 12v to the EDIS module a good earth and the coils had 12v on both sides but weren't being discharged when the VR was giving the EDIS the right readings.

Does this mean the EDIS was playing up from the start?

From all the symptoms it sounds like it to me, but I'm not sure whether it's the megajolt causing a problem WITH the EDIS after it's hooked up. All of this only really started happening when I attatched the TPS to the jolt. Could I have wired it incorrectly to cause any problems with the tacho out, or EDIS??

Thanks
Graham

Post by **brentp** » Wed Mar 21, 2007 9:09 pm

So the TACH output piggy-backs off of the SAW output going to the MJLJ. This SAW output pulse will vary a bit depending on the ignition advance set. Your Tach may be sensitive to this.

As a test, when the engine is idling, try changing the ignition advance to whatever it would be when the engine is at '1/2 load'. See if that re-creates the problem. If this is the problem it's first time I've seen it indeed. What brand is this tach?

An alternate approach is to drive the tach directly from the coil packs. The technique is documented here:

http://www.autosportlabs.net/index.php? ... tion_guide

Jenko · Post by **Jenko** » Tue Apr 17, 2007 10:54 am

Probably worth mentioning that I had a very similar problem which was cured with the new 3.2.1 Config S/W and firmware upgrade......the noise filter on the PIP has changed, and it really did sort me out ------ Same thing though, on mild load everything was fine, when under higher load, everything started spluttering, the shift lights came on, and the engine bogged down - works a treat now, and tickover is smoother..........