I know this probably needs to be in the EFI section but thought I would try here...

So I'm troubleshooting a rough running bike. If you didn't know there is such a thing as a 5 volt sensor reference used by our sensors (09 bike anyway) to communicate back to the ECM to make EFI adjustments etc.
Thing is when I measure at any of the sensors on this bike the voltage always reads 2.9 volts. I'm thinking it should be 5 volts (reference) right?

I've unplugged all the sensors and taken a measurement at the ECM and at "5v sensor power 1" and "5v sensor power 2" all I get is 2.9 volts. Yes there are two of the little devils!

I've had all sensors plugged in and at the sensor still getting 2.9 volts.

So....

Anyone willing to put a sewing needle or something on pins 5 (5 volts) and pins 1 (ground) of their TCA (Throttle Control Actuator) since it's so easy to reach and let me know if they see 5 volts or only 2.9 or something.

TCA plug can be plugged in or off - doesn't matter.
Bike needs to have ignition on.

Be careful. Don't cross the streams! Don't touch the two pins together.

OR has anyone ever battled the same thing and can tell me for certain that I should be reading 5 volts feed to the sensors?

I appreciate any help guys... kinda sucks not having a reference point to work with. If you find 5 volts it pretty much means I need a new ECM... $$$

Thanks!

lp

 

Are you sure your meter is good? They have been known to be off and with small voltages like 5 v that could be the case. Does your manual say you should read 5 V? in most sensors 5v might be full scale and 2.9 might be where it's actually reading?

 

Is the Throttle Body clean ? Reason I ask is I have found a gunk buildup in the throat of the my Throttle Body . I would eliminate all the easy stuff first . I have used Carb cleaner a number of times and it always helps the idle .

 

The meter is good unfortunately (I mean fortunately - its an expensive Fluke)

I'm reading the 5 volt feed to each sensor. The sensor return values are on other pins and vary depending on whatever the sensor reads.

Sucks man... I'm thinking to should read 5 volts always unless someone tells me different. (Pin 50+ to Pin 61- and Pin 68+ to Pin 62-) Each feed has an isolated ground just for it. It's crazy. lol

lp

 

Thanks Keybear. Yeah I'm all past that stuff now. Everything clean, new intake seals, clean injectors, good compression, battery, BRAND NEW sensors and all. Just the ECM left...

lp

 

pin 5 to ground= 5.01 VDC

09 flhtc/ Fluke md88, ign on, motor not running

i'd suggest only that you isolate the ecm from all loads ...maybe a bad sensor or acuator loading it down.


costwise, maybe a thundermax would be a good ecm replacement option

mike

 

Man I was really afraid of that... Yeah I have already removed every sensor from the circuits and I still get 2.9. Also chased all system grounds and such and reseated everything - 2.9...

Even rang out all wires from the ECM to all the sensors. Nothing grounded, full continuity where needed - all good.

Well this pretty much sucks. Guess I'm going to look into a thundermax.

Mike, since I know you are around these bikes a lot, ever seen this before? I mean I guess the ECM is just not making the full 5 volts... crazy.

lp

 

no, i'm only guessing

and you get same low voltage on both ECM pin 50 and pin 68 ?

anything that could have pooched the ecm? a tuner etc?

the voltage being 1/2 of reference make me wonder if 1 of a pair of dropping resistors has gone...finding it would be tough...replacing a resistor would be easy.

almost wondering if it would be possible to pull those 2 leads from the ecm and supply 5VDC with a transformer, or a resistor network.


I'd be interested in how you make out and how much it dings you.

mike

 

I see a thundermax on the classifieds today, priced kinda high, maybe the seller has room to move.

Mike

 

I'll check it out thanks!

I'm going to get another meter and check this thing front to back again.
I've been looking all over and have not found one instance of "low voltage" problems online. A few of No voltage only.
Maybe my Fluke 77/bn has finally let me down or something.

You'd think low voltage would set off all kinds of Codes but I'm getting nothing so I'm beginning to wonder if my test setup is accurate.

lp