MSefi.com read only forum (Jan.15,2018)

The TPS has a clear and proper reading with the key on 'run' position, engine off.

With the engine running on 'run' position the TPS reading on the signal seems to be reduced:
- small blips of the throttle are not seen on the display
- when the throttle is around 50% i will only see maybe 10% on the display.
- all other gauges work fine

Is there a setting or a formula i have missed? When the car is running the TPS signal is maybe reduced by a fraction of what is should be

using MS - 1
V 2.2
tuning with megatune

How have you grounded it? Best way is to run the ground wire back to the DB37.
My guess is with the engine stopped there is only a low current flow on your ground. With the engine running, this goes up with the injectors firing.

Anywhere specific the ground should go on the db37?
I have the TPS ground going to the relay board

what is db37 Chris i am sure i have grd from engine block to the controller there is no place to ground just the TPS by itself

vwsuperbug wrote:Anywhere specific the ground should go on the db37?
I have the TPS ground going to the relay board

If it's grounded as per the relay board diagram, it should be ok. I've no personal experience of that board.

2088bob wrote:what is db37 Chris i am sure i have grd from engine block to the controller there is no place to ground just the TPS by itself

What I find works best is to run all the sensor grounds back to the DB37 or close, group them together, then run one wire to a ground pin.

just to restate my point, there is no way to ground the tps switch physically and why would you, you have v-ref and your 2 feeds backs, tps is just a data reference point ,unless you are refering to grounding one of the feed back legs


i am the person that wired chris's car if i check the actual switch with a meter it gives us the resistive change as it should again because its been a while what is db37

TPS indicates perfectly with engine not running change comes about when engines runs and as discussed the big change there is that the injectors are now being driven i seem to smell a potential controller problem

The TPS isn't a switch - it's a potentiometer which gives a progressive voltage output according to throttle position. If the ground side is connected to say the engine block instead of being run back separately to the MS, strange things can happen. Since it appears to be ok with the engine stopped (MS drawing virtually no current) but gives problems with the engine running, when MS draws considerable current to operate the injectors, it's one possible reason.

The DB37 is the MS connector.

Measuring the resistance of the pot is one check - but it would be better to measure the output voltage, preferably with a 'scope, and make sure it is clean DC, with the engine running.

it was understood when i call the tps a switch one thinks of it as a potentiometer i did check the pot with a meter before i wired the switch and it appeared to be working correctly

chris i have somebody with a scope that might be able to come verify it for us

vref come from MS and both legs are tied back to MS

Trakkies, awesome, thanks for the info, we will work on the scope and check all the grounds.

So I should put all the grounds for the sensors and put them together to run to a single wire to a grounding post, the same post that is the ground for the MS controller?
Do the grounds still go to the other places as well, ie; the TPS ground would be bunched together with others, then also go to the relay board ground?

Thanks again, I think we may be able to solve this problem soon :):):):):):)

I'll let you know what we find, Chris

Think some explanation is needed. I did see it in the manual somewhere, but can't find it now, so here's the theory as I see it.

There will always be some voltage drop in a cable. You choose the cable size for the maximum current flow to minimise this effect. A few millivolts at 12 volts doesn't matter much. However, if you share that cable with a sensor which is resolving millivolts it becomes a serious error.
The way round this is to run separate grounds to as close to the processor as possible. In practice this means heavy ground wire(s) from the MS DB37 connector to the engine block. These carry the high currents of the injector loads.

The sensors are then grounded at the MS DB37 connector too via their own grounds. It doesn't much matter which ground pins you use in the DB37 as they are all close enough not to make any difference. Because the sensor grounds carry little current, for convenience I've found it ok to group them together just outside the DB37 case and run one wire to a ground pin.

This theory of keeping power and signal grounds separate except at one point is crucial with audio engineering which is more my field. But the reasons for doing so are similar.

Ok perfect, so far so good, if i use the main ground off the relay board to bring all the engine block grounds to, will this ground be sufficient to ground the relay board and megasquirt, the DB37 i have is the DIY autotune cable as I had trouble with my home made one.

When you are saying grounding to the db37, should the CABLE be spliced and run to a ground from the engine block as well as the relay board ground?

Thanks for all your help I think I may have solved this issue, just need to find out about this DB37 ground?

So as i see it here are my questions;
using a relay board, MS -1 V 2.2

1. Does the sensor wires need to be additionally grounded to the engine block and as well brought to the relay board terminal strip JP1?

2. Should the cable from pin 19 on the DB-37 cable be grounded to the engine block? ( the relay board main ground is grounded to the engine block and battery )

3. Should the MS relay board be grounded to the battery only or the engine block as well

4. refering to this quote below, "you will want a multiple ground wires at the DB37 (one pin is rated at a max of 5 Amps)," Does this mean run multiple wires from the ground (block) to the MS relay board main ground? Or can other grounds from the body and battery be used as well as multiple grounds?

from - http://www.megamanual.com/v22manual/mwire.htm

The MegaSquirt® EFI controller only draws a few hundred milliAmps (from its 12V supply). However it sinks much much more than this by grounding the injectors, coil (if used), Fast idle valve, etc. So the total amount sunk can easily be several Amps to a dozen or more, and ALL of that has to pass through the ground pins. So you will want a multiple ground wires at the DB37 (one pin is rated at a max of 5 Amps). Even if the MegaSquirt® EFI controller works, too small/few ground wires might create a bias in the ground level (where the voltage at the MegaSquirt® EFI controller's 'ground' is higher than at the battery), which can create all sort of mysterious problems. So grounds are very, very important, and should be made as good as you can make them.

Thanks
Chris