losing tps when engine is running

General Topics for configuring, operating and tuning the Megajolt. Also see the <a href="http://www.autosportlabs.net/MJLJ_V4_Operation_Guide">Operation Guide</a>

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st3v3nw
Posts: 5
Joined: Wed May 21, 2008 12:34 pm

losing tps when engine is running

Post by st3v3nw »

Just installed my mjlj and calibrated the tps with the engine off but mjlj on.

it works fine when the engine isn't running and shows a healthy range of movement.

As soon as i start the engine the tps goes. The rev reading shows on the computer but not when it is connected to my digi dash

any ideas?

MartinM
Posts: 433
Joined: Sat Aug 27, 2005 12:08 pm

Re: losing tps when engine is running

Post by MartinM »

st3v3nw wrote:As soon as i start the engine the tps goes
Don't really know what you mean :(
Goes where? On the Configurator? To 0%? To 100%? To something else?
st3v3nw wrote:The rev reading shows on the computer but not when it is connected to my digi dash
Don't really know what you mean :(
You mean that the rpm reading on the Configurator continues to accurately reflect the rpm?
What's your "digi dash"?

More than happy to help, but my crystal ball is a bit cloudy today ;), so any further info would be good...

PS Welcome to the Forum!

st3v3nw
Posts: 5
Joined: Wed May 21, 2008 12:34 pm

Post by st3v3nw »

Hi Martin.

Sorry for the vagueness.

Try this:

When mjlj is powered up but engine is not running, I get a tps reading on the configurator software. (this can be calibrated and seems to function correctly.)

If i now start the engine, the software shows the tps position at 0% no matter where the throttle is. Occasionally it flutters to 6-7% if i pump the throttle peddle.

The next bit may be coincided so i added it too, but could be a separate subject altogether:

The config software (v3.2.1) shows an RPM reading when the engine is running which changes in relation to engine speed. (normal)

But: I have an ETB components digi dash lite. it is configured to receive a tach input but doesn't show anything when connected to the tach out of the mjlj. If i do not have an oscilloscope can i test this output with a multimeter

MartinM
Posts: 433
Joined: Sat Aug 27, 2005 12:08 pm

Post by MartinM »

For the second problem, try connecting the digi dash to the PIP signal that goes from EDIS to MJLJ. Nothing will come to any harm and it might well solve the problem ;)

If that doesn't work, you might need to go to the "diode circuit", but a quick Google turned up the ETB install manual that seems to indicate it is quite happy with a typical ECU voltage level tach signal

For the first problem....errr... don't know. If you have a multimeter and can break into the TPS<->MJLJ connections you should be seeing:
...+5v at one end of the TPS
...GND at the other end
...an about 0-5v voltage at the centre of the TPS, depending on the rotation.

Report back....

st3v3nw
Posts: 5
Joined: Wed May 21, 2008 12:34 pm

Post by st3v3nw »

tach out of the mjlj is at permanant 12v dc. that doesnt seem right at all.

Just reversed over my multimeter so will have to report back further tomorrow on that one!!!
:roll:

Thanks for the help. and btw are you martin millener? if so you built my mjlj!!

brentp
Site Admin
Posts: 5986
Joined: Wed Jan 24, 2007 6:36 am

Post by brentp »

Hello,

For the TPS, you may want to check the TPS input with your meter while the engine is running- see if the readings change compared to when the engine is off. Also, you should check to ensure you have the proper 5v VRef signal going to one side of your TPS, and ground on the other side- repeat the test with and without the engine running. See if it correlates with the reading in the software.

Let us know what you find out!
Brent Picasso
CEO and Founder, Autosport Labs
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st3v3nw
Posts: 5
Joined: Wed May 21, 2008 12:34 pm

Post by st3v3nw »

Ok this is what readings i get.

First, with ignition on and engine NOT running.

TPS> brown wire 0v and 0ohms to chassis (ground)
TPS> yellow wire 4.99v (+5vDC)
TPS> white wire ranges from 0.6v to 3.9v when opening and closing the throttle. (vRef)

Now with the engine running

TPS> brown wire 0v and 0ohms to chassis (ground)
TPS> yellow wire 4.99v (+5vDC)
TPS> White wire 0.6v , no change in voltage with movement of throttle. (TPS is moving through its range)

I tried reversing the polarity of the TPS and the config software told me I had it wired the wrong way round so i definitely know it is right.

Quite baffling this one.

david jenkins
Posts: 204
Joined: Tue Feb 14, 2006 2:14 pm
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Post by david jenkins »

It's not something as basic as a loose connector, or a dry joint? Perhaps engine vibration is causing a disconnection.

Try waggling the wires and connectors while measuring the voltage on the TPS wiper (white wire).

Also check the Molex connector, as they can cause problems if the pins aren't crimped correctly.

HTH,

David

st3v3nw
Posts: 5
Joined: Wed May 21, 2008 12:34 pm

Post by st3v3nw »

Not a loose connector.
I think i may have sorted it.

It seems that when i have the engine running my peddle goes nowhere near flat out as it redlines at half throttle, but the butterfly valves in the carbs are only half open. It does seem very rich so this may sort itself a bit when i get it tuned.

Also there was a little bit of play in the adaptor from the carb to the TPS. This meant that it wasn't moving the TPS until about a quarter throttle. And as i didn't really want to take it over 6000 rpm yet i wasn't getting much of a reading from the tps.

I have now sorted the play by filling the gap with araldite as a temp measure until i get something machined to be a better fit.

I'll report back with my findings once it has all set.

MartinM
Posts: 433
Joined: Sat Aug 27, 2005 12:08 pm

Post by MartinM »

Sounds good...let us all know when it's working perfectly!

Martin

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