TPS interference problems

[rjwoods77]

We are having severe problems with our tps. It is a 518 sensor from MoTec. It work like it is supposed to when we don't have the engine on but when the engine is running we are having issues with the signal jumping around and in some cases dropping out completely. Our twin does vibrate and we are shoring up the intake assembly some but there is talk of the stator ring in the flywheel causing crazy interference. We are trying to shield the sensor wires but it doesn't seem to be working well. Has anyone had any problems like this before? It is extremely frustrating since we have all of the other engine issues such as fuel, spark,etc all working great.

[rjwoods77]

We are having severe problems with our tps. It is a 518 sensor from MoTec. It work like it is supposed to when we don't have the engine on but when the engine is running we are having issues with the signal jumping around and in some cases dropping out completely. Our twin does vibrate and we are shoring up the intake assembly some but there is talk of the stator ring in the flywheel causing crazy interference. We are trying to shield the sensor wires but it doesn't seem to be working well. Has anyone had any problems like this before? It is extremely frustrating since we have all of the other engine issues such as fuel, spark,etc all working great.

[Dan G]

Rob, are you running "resistor" spark plugs? They're standard on any EFI motor, but the briggs came with non-resistive plugs. Look for an R in the part number of the plug.

[rjwoods77]

NGK R5671A-7.

Did you run into problems with you stator kicking out a field? I dont know if that is what it is but it has been suggested. Also how much vibration did you really get out of your motor? Our is probably about 50 percent more than a baja engine.

[raska]

How is the power and ground to the sensor when this is occurring? Are those rock solid and just the signal is jumping?

[John Stimpson]

2 thoughts:

1: You can wire a TPS wrong, such that on the motec, you still get a signal, but you'll only get about 20% of the resolution you should have after you set the low/high limits on the TPS with the motec. This will produce a very jumpy signal, because resolution is so low and a small change in voltage will show up as a big change in throttle position. On the motec, you're low and high "values" for the TPS should be at least 50 units apart... When I miswired mine, I had only 10 units of separation, and got a super jumpy signal. Solution: Rewire

2. Because you're motor vibrates a lot, the wiper on the TPS pot is worn and changing the resitance of the pot. I used to think TPS's basically never went bad, but that is dead wrong, a shaky motor can wear one out pretty quick.... Solution: New TPS.

I've had both problems before!

[Scott Borg]

We had some weird injector opening times that were eventually tracked down to an oscillating TPS signal. The ECU was using acceleration enrichment and decel lean parameters, and it made things run very rough.

Using the ECU's time-plotting function, we saw that the TPS signal was oscillating. A new TPS fixed everything. We're using the OEM Suzuki TPS, running a 4-cylinder engine.



-s-

[rjwoods77]

We hardly have much time on it at all. We checked the wiring and we are getting between 3 and 19 unit on our MoTec M4. This isnt enough from what you are saying. Opinion?

[John Stimpson]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Rob Woods:
We hardly have much time on it at all. We checked the wiring and we are getting between 3 and 19 unit on our MoTec M4. This isnt enough from what you are saying. Opinion? </div></BLOCKQUOTE>

I don't think so. Using an OEM Ford TPS (green, orange, black) wired improperly, we were getting between 3 and maybe 15 or thereabouts. We were also having trouble attaining the minimum of 3 that motec requires for the lower limit. We had to clock the shit out of the TPS to achieve that. Then our TPS signal was super shaky and crappy. I wish I remember *how* we had it wired then.

The CORRECT wiring for our TPS is:

Orange (top wire) : 5V in from ECU
Green (middle) : signal out, ~.5V - ~4.5V
Black (bottom) : Ground

Once wired properly, our lower limit was about 15Mo (Mo = "motec unit"), and the upper about 85Mo.

This is on a Motec M800, but I think it oughtta be the same deal.

John