DBRjeep350TPI

I decided to check the voltage on my 5.7L TPI this weekend, cause i have been having some stalling problems and also some rich fuel smell. Anyways I plugged in the voltage tester and checked my constant voltage and it is right on at 4.64V steady. I checked the signal and at closed throttle it was right on at 0.54V. But at wide open throttle it peaks at 3.90V.... The voltage does climb steady from 0.54 to 3.90V when i open the throttle, does not jump around at all.
I just thought that the higher end of the voltage at WOT should be around 4.5V? Is it bad????

seawolf18

iTrader: (1)

wide open should be 4 plus volts.

DBRjeep350TPI

would you say it is a bad TPS or you think that there is adjustment to bring it up to 4.25-4.5V? I am going to try this weekend.

seawolf18

iTrader: (1)

.54 is where it should be with the throttle closed. I would make sure the throttle blades are opening all the way. You can take the sensor off the throttle body, and do a sweep with it still plugged in to see if it does over 4 volts at max.

DBRjeep350TPI

good call. i will take it off and do a full sweep and see what the min and max voltage is.
thanks

LB9GTA

iTrader: (1)

So can you take the TPS off and test it?

So does it have to have power running through it to test it?

ASE doc

I was going to say be careful sweeping the TPS off the car. They are fairly delicate. I always sweep test the TPS on the car. Be sure that the batt is fully charged. If you get a low reading using the pedal to open the throttle, try with your hand on the throttle linkage. If there is a difference, you may want to adjust(bend) your pedal arm to achieve full open throttle from the pedal. Reference voltage should be a solid 5v. The fact that you are only getting 4.64v is part of your low TPS voltage problem. Are you using a DVOM with 10 Megaohms input impedance? Lower input impedance will cause false low readings on EFI sensor circuits.

The TPS only moves as much as the throttle linkage moves it so proving that it can read higher in your hand doesn't really serve any purpose. If you can't achieve at least 4.2 volts on the signal circuit with the battery fully charged, you likely have a bad TPS. Depending on the year of the car, minimum TPS voltage may be as high as .96 volts(90-92). This would be a non adjustable TPS.

LB9GTA

iTrader: (1)

I tried testing it off the car.

I could get it to do a resistance test. It worked.

But because I didn't have 5volts of power to it, I couldn't get it to read volts.

I'll have to try it back on the car.

cha_chard

how did you test the voltage, i need to test my tps because i have a check engine light and has harsh hesitation i don't know how

ASE doc

First of all, what code(s) do you have? Need to read codes first. Then, to test TPS voltage, test between a known good ground and the blue signal wire of the TPS. You either need a back probe attachment or test jumpers to do the test. Also, verify 5 volts at the gray reference wire and a solid ground at the black wire. Avoid piercing the insulation and don't try to jam the voltmeter's test lead into the weatherpack connector as you will destroy the connector.

jack1012t

I am excavating this nearly 8 year old grave to check for some answers for my recent purchase, which has not run in at least 10 years!

Would a reading of 0.18 volts at closed throttle cause the car not to start?

So far, I have replaced the pump, sending unit, tank and filter, and as of now, I have 43 PSI at the fuel rail. I am going to check spark tomorrow with the tool to be sure, but the car has started on ether a few times, and immediately dies. That said, the fact that it starts indicates I do have spark.

Right now, my assumption is clogged injectors, since the flashing noid lite on all 8 cylinders indicates that the ECM is telling the injectors to squirt. Additionally, I pulled a plug, and it was not wet/did not smell of fuel.

However, I wanted to check and see if I also need a TPS. I may replace it anyway, considering the age.

Let me know your thoughts!

DBRjeep350TPI

If you don't have fuel on any plugs or smell fuel it is hard to believe you have that many plugged injectors.... not saying that you may have one or two plugged up. I would look at your fuel filter being clogged or restricted "but it would have to be reallllly plugged". Fuel pressure regulator on the rail is more of the corporate that would look at. unplug that vacuum line and see if it starts up...
0.18 volts on the TPS sensor I am guessing? is ok. Should be 0.0 closed throttle -4.5v @ wide open throttle ( you can dermal the holes out or file one hole out to make it slightly adjustable also....

I ended up pulling the rail and putting a pan under it and just wrapping some "zip-tie" around the heads of the injectors to the rail and pressurize the rail and see first if it holds pressure. 2nd no bleed off "drip" bad injector. 3rd crank and see if all of them squirt with a pan underneath them and pull the ignition fuse.

If it all checks out put some Vaseline on the O-rings and put back in the manifold... Check for fouled plugs, return and incoming fuel lines are not restricted (I like 3/8" on both).
hope this helped somewhat.

jack1012t

Thank you for the reply. Fuel filter is brand new, so I doubt it is that. I unplugged the vacuum on the fuel pressure regulator, but no start still. I thought TPS was supposed to read at 0.54 volts and 4.5 at WOT.

I tested all of the injectors, they read 14.5-14.8 ohms, so all in range. Agreed, it would be kinda strange for all 8 to be clogged, but the gas in the car was super old, so just a thought.

You also mention pulling the fuel rail. Is there a way to do that without removing the upper plenum and the runners?

Thanks again for the info!

bad03chief

Hi there, I have a 92 Z28 with a 5.7. My car runs ok but the idle will change when I turn the car off and on. I too have an odd reading at the TPS. My reading at idle is .15 volts, not .54 volts. I need to open the throttle like half way to achieve .54 volts. It's a new TPS. I'm kind of baffled.

Rick

Tuned Performance

iTrader: (92)

What is the voltage on the grey wire with the tps unplugged koeo ?

bad03chief

I'll check. What should it be? 12V?

Tuned Performance

iTrader: (92)

5v ref

bad03chief

I got 5V on the money

bad03chief

The one thing my car is doing is not maintaining a stable idle speed. The car does not stumble, or perform poorly, it's just when i turn off the car the idle speed will change. The idle sometimes goes so low it will want to die. I will adjust the idle screw just to prevent the car from dying. Then when I turn the car off, and start it again a little later the car will be idling at like 1500 rpm. It doesn't seem like the ECM is effectively controlling the idle speed. I purchased a new TPS and put it on. I tried to set the voltage to the .54v at idle but the reading i got was .15v? My TPS is not adjustable, so I open the throttle to like half way in order to reach .54v readout.

I saw the below in another thread and I am wondering if this IAC is the problem?

IAC and TPS Adjustment

Idle Air Control

Tools needed:

1. Torx bit # T-20
2. Paper Clip
3. Small Punch

Take the paper clip and open it up and form it into a big "U" shape. Insert the clip ends into the ALDL in the ‘A’ and ‘B’ pins.

Turn on the ignition, but don’t start the engine. Wait 30 seconds. Now, go remove the connector from the IAC.

Start engine. You are now going to adjust "minimum air". There is a Torx screw on the side of the throttle body. This is what needs to be turned to adjust minimum air, or more commonly known as "idle speed". It comes from the factory with a protective metal cap over it. If the cap is still there, use a small punch to knock it out. Set the idle speed to 450 rpm, rotating the Torx screw clockwise to raise rpm, and counter-clockwise to lower rpm. Once the idle rpm is set, turn off the engine.

Re-connect the connector onto the IAC. Start engine. Idle speed is now once again governed by the ECM, but your idle should be smooth and steady, approximately 600 rpm in Drive (for unmodified cars).

bad03chief

"Take the paper clip and open it up and form it into a big "U" shape. Insert the clip ends into the ALDL in the ‘A’ and ‘B’ pins." Does anyone have a picture of which are the A and B pins?

Tuned Performance

iTrader: (92)

Are getting a code 22 ?
the aldl is under the dashboard knee level right side of the steering wheel.

bad03chief

Funny thing, no codes.

Tuned Performance

iTrader: (92)

The tps seems low, when you tested the 5v ref did you use the tps ground black wire ?
speed density looks at initial apart up tps position and calls that zero %. What’s voltage at wide open throttle on the blue wire key on engine off holding the throttle open by hand.