Eratic reading from TPS and aux input when engine is running

Patriq · Post by **Patriq** » Mon Jun 28, 2010 12:27 pm

I was going over my set-up and was recalibrating my TPS axis.

Dial shows a nice steady increase when I use the throttle. But....

when I start the engine, it suddenly is very eratic. This was only with car standing still mind you (the only lap-top I have has a non-working battery, so needs to be supplied from an outlet), but still the TPS only reads 0 all time, but bounces upp to 11% at times. This is with throttle that would give up to 30-40 % with engine not running. Same with aux-input (water temperature in my case). It is steady when engine is not running. At idle the aux gauge starts to bounce, and with increasing rpm it bounces up and down from 20-80 dgs within the split of a second.

Has anyone got any pointers as to why the rpm suddenly would affect these readings ?

NITROPIXIE · Post by **NITROPIXIE** » Mon Jun 28, 2010 9:40 pm

It could be noise being induced across the tps and aux in wires form the ht leads or the voltage stabilisation part of the meagjolt circuit has reduced and is causing an intermittent fault by electrical noise from your alternator.

Try unplugging your alternator and run the engine again and see if there is any difference. Your ignition circuit does not use a vast amount of power so a good 12v battery should be able to power it for a very sufficent amount of time to test.

Post by **brentp** » Mon Jun 28, 2010 9:49 pm

This is a good suggestion. Also check the ground connection for the EDIS module and Megajolt. Both should be grounded to the same point on the chassis.

Patriq · Post by **Patriq** » Tue Jun 29, 2010 7:08 am

Thanks, I'll try that and see. Battery is sound and new(ly charged)
Ground is common for both MJLJ and EDIS.
Is was thinking that the only common point both TPS and water-temp has is ground. Although sensor is grounded to engine and TPS to same ground as EDIS and MJLJ, I was reasoning that that would be the only source of influence.

I'll get back with my findings.

Noggy · Post by **Noggy** » Sat Jul 31, 2010 8:19 pm

Did you ever resolve this? After a fresh install this afternoon mine is doing exactly the same, but I did not have enough time at the workshop to start troubleshooting and now it is bugging me like mad!
Just to flesh out my problem the TPS reads fine with engine off but is erratic and only reads to 10 or 15% with engine running. Car has no alternator.
Otherwise the MJLJ is working fine on 2D/engine speed.

Does the TPS cable need to be shielded, currently it's not. Also MJLJ is mounted about 400mm away from the coil, but shielded by a steel bulkhead.

Finally I'd just like to say what a fantastic and user friendly device the MJLJ is. Top marks guys.

Cheers.

Patriq · Post by **Patriq** » Mon Aug 02, 2010 8:18 am

Yes, it fixed it self.... sort of. I think it was because I had washed the car and there was some how water somewhere around.

Sorry for not posting back, I completely forgot to.

TPS sensor is not shielded. At least not on my installation, and trying to recall - I don't think it is ever mentioned in the installation guide either.

Sorry I can't help any more.

Noggy · Post by **Noggy** » Mon Aug 02, 2010 1:03 pm

Hi

Thanks for the reply.

I posted on your thread because the symptoms you described are exactly the same as what mine is doing, and thought I'd save some diagnostic time.

Just had a look back and you are correct, there is no mention in the instructions about needing a shielded cable for the pot. At least I know that is not an area I need to be looking in.

I haven't had chance to get to the car again yet, but hoping it will be something simple. Maybe I'll start a fresh thread to try for some pre-emptive advice.

Cheers,

N.