Difficulty Setting TPS to Specification

[Tennessee T]

1997 150 EFI, serial number 0G478627

I have recently removed the idle stabilizer module from my engine and have been going through the required sync and link procedure since the removal. I am having trouble setting the TPS to the specified 0.240 - 0.260 volts DC that the service manual specifies. I do have and am using the recommended test harness, part number 91-816085. My problems are that I have a very difficult time zeroing in on the middle of the specified ranged, 0.250 volts DC, because an ever so slight adjustment of the sensor makes a huge difference in the voltage reading. Furthermore, the adjustment that I set it to does not stay consistent. For example, when I set it to 0.250 volts, and move the throttle lever through the full range of idle speed to full throttle several times, then return the lever to idle, my sensor will not return to the voltage that I set it to. I have also noticed that sometimes, but not always, after getting the adjustment where I want it, the voltage will change while just sitting there, with no movement of the throttle lever.

I have tested the sensor, as the manual recommends, by moving the throttle lever through it's full range of motion, and I do see a steady increase and decrease of voltage output. However, the maximum output, at full throttle is only reaching 7.10 - 7.20 volts DC, which is a tad shy of the approximate 7.46 volts that the manual says I should see. There is some obvious damage to the insulation of the wires coming from the TPS but the copper wires themselves do not appear, emphasis on appear, to be damaged. See the picture below. I have been hesitant to immediately jump to replace the sensor because the replacement cost is over $500.

Based on the information and picture that I have provided, do you think my sensor is bad?

[EuropeanAM]

Tommy- those bared-spots are a problem, as they can permit moisture to enter the wires (and quite possibly the sensor itself).

It's been my experience that you need to "snap" the throttle roller back to the idle position in order to see if you reach a consistent position/reading. "Easing" it back may not seat the linkage on the set screw firmly, resulting in a different reading.

Most commonly you'll end up with .26 or .28 VDC (consistently). If you can't get that, there may be a problem.

As for the WOT voltage- have you checked to make sure that the maximum throttle position screw on the BLOCK is set properly (permitting you to reach the HORIZONTAL POSITION at the throttle butterflies)?

[JOE54]

looks like somebody set it with a hammer one time

[Tennessee T]

Don, thanks for your reply. I took your suggestion of "snapping" the throttle roller/cam follower against the throttle cam while adjusting the TPS and was able to attain a much more consistent voltage output of 0.267 - 0.271 VDC. Thank you very much for that suggestion!!

As for the WOT voltage, I did check to make sure that the maximum throttle position screw on the block is allowing me to reach what sure appears to me to be the horizontal position at the throttle butterflies while maintaining the ever so slightest gap between the arm of the throttle shaft and the stop on the induction box. I even went so far as to push (with my finger) the throttle roller/cam follower up as far as it would go, to where the arm of the throttle shaft was coming to rest against the stop on the induction box, and was still only able to attain 7.12 VDC, which is exactly the reading I get with moving the throttle lever to WOT against the stop screw on the block.

I will be fishing a tournament on Saturday, and assuming I am satisfied with the performance of the engine with my now confident TPS setting at idle position, I will probably not replace the TPS. I am the type of guy that if I have the slightest doubt in my equipment, I will always repair/replace the problem. But at $500+ for a new TPS, I am either going to make every effort I can to make my TPS work, or become 100% sure it is defective. However, if you, or anyone else, has another idea as to how I can get closer to the 7.46 VDC that the manual calls for at WOT, please let me know.

[Tennessee T]

looks like somebody set it with a hammer one time

Wow Joe, I can't slip anything past you guys! As I was struggling to reach an adjustment that I was confident in, and given that the ever so slightest adjustment that I made gave me a huge difference in voltage output, I resorted to tightening the screws and using a screwdriver and very lightweight hammer to very lightly bump the TPS in hopes of making very slight adjustments, thus causing the "wounds" that you see to the plates. Very good detective work on your part!!

[EuropeanAM]

You might glance around for a used sensor... as much as I hate saying that, the new one is pretty cost-prohibitive.

If it weren't for the battle-wounds, I wouldn't be overly concerned with the .33 VDC variance at WOT.

[JOE54]

Wow Joe, I can't slip anything past you guys! As I was struggling to reach an adjustment that I was confident in, and given that the ever so slightest adjustment that I made gave me a huge difference in voltage output, I resorted to tightening the screws and using a screwdriver and very lightweight hammer to very lightly bump the TPS in hopes of making very slight adjustments, thus causing the "wounds" that you see to the plates. Very good detective work on your part!!

i can help it i ment no disrespect, may can find some liquid neophrene and seal it for a while, as DON said kind normal not to return dead on .250 and vari at wot

[kls2020]

Looks to me like previous owner ? cut the insulation to read the TPI setting voltage with no test cable . Tan wire = "zero" end of pot , Lt Blue wire = pot "wiper " , and Orange wire is "100% "end of of pot .I read somewhere that the TPI affects fuel delivery from "idle" to "midrange" but has no effect on "WOT" fuel delivery . Set for .250V @ idle and take what you get for WOT.As already mentioned probably best to seal with some "Liquid electrical tape " or some other brush on insulation .