Optimax TPI Problem

[Red70]

1998 Mariner 150 OPTI #0G655960. Last June was getting alarm and no power. Connected to MEDS diagnostics and showed TPI codes about 90 times each. Both would sweep but while idling, the #2 TPI would jump about a volt. I ordered both TPIs and one did not arrive until Oct. I installed both and cleared codes and all seemed ok running in tank. No more fluctuations and codes not resetting. Boat sit from then til Feb and first time out was doing same thing. Checked codes again and had same TPI codes. While monitoring guage sweeps the #1 will stay on about 5 volts and never move and #2 will move from about.48 volts to about 5 volts. I checked wiring and terminal A is ground, B goes to ECU and C is 5 volts and when I unplug sensor it goes to 0 on guage so I assumed it was a bad #1 TPI. Installed a new one is still same. Something else strange is it will store an active TPI 2 code even though that sensor appears to be operting correctly. I have Mercury manuals but they do not show what I should be seeing at connectors or terminals. Is there a manual for Optimax diagnostics that might help me. I only saw a 90-889525 that says for 2000 model year and up. I think 1998 and 1999 might be only years with dual TPIs. Thanks for any info.

[lpugh]

inspect pcm and tps connectors very carefully for damage or loose pin fit, use a lab scope or dso to monitor voltage at the pcm, could even be an internal problem with pcm. Keep in mind the pcm is checking the the tps circuit which includes sensor, connectors, wiring and pcm. PCM is a very low probiability for this fault

[EuropeanAM]

Also- don't overlook the very remote possibility of a brand new (but no good) sensor. It does happen...

[Red70]

Also- don't overlook the very remote possibility of a brand new (but no good) sensor. It does happen...

Yes I keep thinking that but it is doing exactly same thing as old one. When I check voltage at TPI connectors(disconnected) # 2 has 5 volts on 2 terminals and GRD on other terminal. #1 has 5 volts one one terminal and GRD on other and no voltage on other terminal. I cant find any info that shows what I am supposed to read at each terminal so I dont know if I am loosing something at sensor or out of ECU.

[EuropeanAM]

One sensor returns INCREASING voltage, the other sensor returns DECREASING voltage.

At 50% throttle position they should both be approximately 2.5V.

[Red70]

Yes. #1 stays at 5 volts and never moves. You can unplug sensor and it goes to 0. #2 is at 0 and ramps to 5 volts when throttle moved to wide open

[EuropeanAM]

Yes. #1 stays at 5 volts and never moves. You can unplug sensor and it goes to 0. #2 is at 0 and ramps to 5 volts when throttle moved to wide open

Verify that the connector is not damaged- if not, connect the ORIGINAL TPI and see if it varies like it should.

Not impossible that you have a faulty (new) sensor.

[Red70]

The connector terminals have good tension on them at the sensor and ecu, not pushed out,spread or corroded. Connected to original and does same thing. I come from the auto repair profession so yes I know about defective new parts but its a little strange that 3 sensors would be doing the exact same thing. If I just had a schematic that shows what signal or voltage or resistance I should have at each terminal I could figure it out . Thanks for your help. Its beginning to eat on me a bit because it looks like such a simple circuit if I just knew what I was looking for.

[EuropeanAM]

I would pin out the three (3) leads (well actually two... you already know you have 5V power). Manual should have wiring diagram in it.

[lpugh]

..................sensor output...........
grd... 0v ...........l............ 5 volt ref
.^^^^^^^^^^^^^^^^^^^.

very simple sensor: the resistor has a fixed voltage at any given point from 0 to 5 volts. Sensor return voltage will be dependent on the wiper position
first test voltage between sensor grd and referance (not battery ground or block) Then check sensor output return

[Red70]

Thanks Leon, that is exactly what I was looking for. I get no voltage change on sensor output wire on TPI1. TPI2 varies voltage on sensor output wire as supposed to. I can plug sensor 1 connector into sensor 2 and get a sweep on MEDS display although it is backward. I guess this proves it is just a defective sensor. Just been having a hard time beleiving I would get 2 defective sensors doing same thing. Now to hopefully make dealer understand and get it replaced. Thanks for everyones help. I will post after I get a replacement installed

[EuropeanAM]

I can plug sensor 1 connector into sensor 2 and get a sweep on MEDS display although it is backward. I guess this proves it is just a defective sensor.

Yes, it does sound like you have a DOA sensor in the TPI-1 position.

[Red70]

Got a new sensor and didnt fix problem. Only thing I can assume is maybe the ECU.

[lpugh]

Got a new sensor and didnt fix problem. Only thing I can assume is maybe the ECU.

Lets start over:
verifie the the sensor is actually being moved when throttle is opened
test the sensor with it off in your hand with harness connected

ground= black/orange
5 volt ref = purple/yellow
sensor output = gray/white

key on harness connected
check voltage between the sensor ground wire and the 5 volt referance?
check voltage between the sensor ground wire and the sensor output? closed throttle & open throttle
do not us anything for ground for these test other than the black/orange wire

Caution: do not jump anything to these wires (power or grounds and use only a 10 mega ohm impedance meter)
as PCM can be damaged by doing so
DO NOT ohm test any computer circuit with PCM connected, possible PCM damage as well
OHM meters induce a small voltage to test resistance

pcm harness disconected from pcm
TPS harness disconected key off, one lead connected to a good ground the other conected to the gray white wire on the connector, how much resistance? (should be open circuit)
If it has continuity the harness has a short

Now I am going against recomended proceedure because I am sure you do not have correct adaptors and pin removal tools for the next test:
cut the sensor output wire
reconect the pcm and tps
key on
check the voltage of the cut wire from the sensor, if normall now you have a short in the pcm

when probing these wire you should use special needle peircing tools that make tiny holes in the insulation, be sure to coat that area with RTV sealent when done and apply liquid tape over that
use a seamless non insulated butt connector with quality sealing shrink tube to splice the wire when completed
sent a PM to you a number to call

[lpugh]

Red70, disconect both tps sensors, key on and compare voltage readings on both tps return wires from the PCM, maybe high voltage from PCM is causing tps failure when connected on that ckt

[Red70]

Here are readings from both TPI connectors disconnected. (A=GRD B=sensor return C=5 volt )

TPI 2
A-B 4.75v
A-C 4.98v
B-C 0 v

TPI 1
A-B 0 v
A-C 4.98v
B-C 4.73v

[EuropeanAM]

Nice speaking with you today. YOu need a replacement TPI (replacement is DOA).

[lpugh]

RED70 be positive the reference ground for that sensor is actually providing a ground and has continuity thru the connector to the pin on the sensor.
A loss ground will cause the signal to read reference voltage in any position.

[EuropeanAM]

If he puts the outer one in it's place (inner), it reads backwards (consistently) as would be expected. Given that this is repeatable, and the new one is output-dead repeatable, I'm inclined to believe more than one faulty sensor has been on the engine (even though new).

[lpugh]

If he puts the outer one in it's place (inner), it reads backwards (consistently) as would be expected. Given that this is repeatable, and the new one is output-dead repeatable, I'm inclined to believe more than one faulty sensor has been on the engine (even though new).

I do agree with you, but I have seen that ground circuit confuse more than one tech, in testing.