tps ground problem

[richrd]

My 94 has more drivability issues than I can count. but right now I'm looking at the tps.

when I check the supply voltage at wot I get 5.1 volts when I ground to the block or battery, but only 3.8 with the ground wire in the plug.

what controls this and can I just tap in a ground jumper to the plug?

Thanks
Rich

 

[MrShorty]

There are three leads on the TPS. As noted, the supply voltage should be about 5 V relative to ground. Which of the other two leads are you calling "ground?" They both go back to the computer, one lead represents the opposite side of the resistor, and the other lead is the "moving" lead that represents the variable resistance of the potentiometer.

Do you have a voltage drop across the PCM's grounds?

 

[richrd]

As per the manual, the middle terminal of the plug is the ground.

 

[btexpress]

Why the focus on TPS? Codes? Maybe if you share the symptoms some of us can be of more help.

 

[MrShorty]

As per the manual, the middle terminal of the plug is the ground.

INteresting that they would call that ground, I doubt that I would.

A typical potentiometer consists of a fixed resistor with a "slider" that moves along the resistor. The two outside leads measure the ends of the fixed resistor, and the middle lead is the "slider". The voltage drop across the outside leads should be approximately the 5 V. The voltage drop across one of the fixed leads and the slider should vary smoothly from ~1 V to ~4V (the voltage drop across the slider and the other fixed lead will be 5 V minus the other reading).

What state was the throttle when you read 3.8? Closed? WOT? If that's a closed throttle reading, that seems a little off, but not horribly so. Most people here believe that 0.96 V (or 4.04 V, depends on which fixed lead your referencing to, and I can never remember which one is which) is the "ideal" value for the TPS reading. You can do a search for this, as it has been discussed in detail elsewhere. That appears to me to be a normal (maybe slightly off of optimum) reading for the TPS, as long as the voltage drop across the resistor changes smoothly throughout the range of motion.

 

[richrd]

I'm not measuring at the tps. I am measuring at the plug. not connected. Checking what the feed is to the tps, but not thru the tps. The Book says 5 to 5.1 volts. It says the middle wire is ground. I do not have 5.1

If I do not have a ground, then how can I check voltage at the terminal.

If I have a problem before the sensor, then it does not matter what the sensor does. Are it is, is a glorified reostat.

 

[MrShorty]

If I may ask, what manual are you using? I don't recall seeing a test like that for the TPS. I've seen several steps that call for checking the voltage between Vref and TPS Sig return, but none that call for checking the voltage between VREF and TPS signal wires like that.

As you say, the TPs is a glorified rheostat. For that matter, the PCM is a glorified voltmeter. As I understand, the PCM is monitoring the voltage drop between TPS signal (pin47 according to a '95 wiring diagram) and TPs sig return (pin 46), based on the 5V reference signal that the PCM generates. At this point, I don't see the logic in measuring the voltage between Vref and the TPs signal wire with the TPs disconnected.

The manuals I have suggest measuring continuity between the TPS connector and the PCM 60 pin connector with them both disconnected for checking the wiring between the TPS and the PCM.

However, to answer your initial question:

can I just tap in a ground jumper to the plug?

No, I seriously doubt it.

 

[richrd]

Ok, let's start over. I need to check the TPS.

I want 5 volts at wide open throttle.

I back probe the signal wire and the middle wire which is ground.

If there is no ground, the multimeter will not read.

Any weak spot, either within the sensor or wire connections will cause a voltage drop. That also aplies to the ground side.

I have 3.8 volts coming out at wot. But if I ground the probe to the block it's 5.1.

So even if I repace the tps, I still won't have more voltage than what the circuit is flowing.

 

[gsmaclean]

So just what is your TPS reporting?

Sorry, someone had to say it.

 

[MrShorty]

Sometimes a practical is what's needed. I went out last night and ran some similar tests on my '92. Here's what I got.

With the TPS unplugged, so I'm measuring what's coming from the PCM:

Outside leads: 5.0 V
supply to middle lead: 4.8 V
middle lead to other outside lead: 0.0 V

So there's a discrepancy between what I get between supply and the middle lead and what you get between supply and middle lead.

There are basically three components between the TPS connector and ground: The wires between the connector and the PCM, the PCM itself, and the wires that connect the PCM to ground.

You said in your initial post that you are having many driveability problems. Some times, multiple problems/multiple codes can be traced to a bad ground between the PCM and the battery post. It's not unheard of for corrosion to build up in the negative battery cable to the point that the pigtail that goes to the PCM ground doesn't make a good connection. I mentioned it in my initial response, have you had a chance to verify the PCM grounds?

Have you checked the resistance of the middle wire between the TPS connector and the PCM's 60 pin connector? Should be next to 0.

 

[richrd]

"I mentioned it in my initial response, have you had a chance to verify the PCM grounds?

Have you checked the resistance of the middle wire between the TPS connector and the PCM's 60 pin connector? Should be next to 0."""
-----------

That is what I intend to do. I have checked ground from battery to engine block, but I have never (yet) even seen a naked PCM.

Truthfully, I hate working on anything with 4 or more wheels.

Sitting at red lights today, my wandering (overly simplistic) mind got to figuring on this. there is a box (PCM) that sends 5 volts down a wire to a resistor / reostat (tps) That knocks the voltage down at anything less than wide open throttle then sends that amount of voltage back to say "the pedal is pushed down x amount so we need to send out x amount of gas molacules."

There is no need for a ground wire at the sensor and the engineers only put it there so had something to probe.

That about cover it?

 

[btexpress]

Ford does not call this circuit a ground. Three wire sensors (Like a potentiometer) have a signal circuit, a signal return circuit, and reference voltage. Signal return is common to all the sensors, and some may call it the ground side but it goes directly to the pcm. Reference voltage is output by the pcm and is 5v, signal circuit is the output of the sensor.

Like others who have responded I am still wondering what you are looking for, has a code pointed at the TPS or is there some curiosity involved?

IF there is a problem in your signal return circuit, affecting the TPS, the problem would be in the TPS or wiring, if the problem was in the PCM or a ground connection it would most likely affect more sensors.

 

[cjones101812]

richrd,
run this test (link below) and if it fails check the gound wires for the computer. at the ECM connector, connector disconnected. check grounds Key in RUN, Pin16 O/R, Pin20 BK/LG, Pin40 BK/W, Pin60 BK/W.

http://www.explorerforum.com/forums/attachment.php?attachmentid=44036&d=1197189819 with TPS connector disconnected.

 

[richrd]

Ok, here's the story. '94 explorer 4.0 160,000 miles. bought four years ago with bad tranny. Had rebuild put in by reputable shop. Always seemed low on power. Check engine light on from the beginning when warm. EGR code. Mechanic said to bring it in someday. someday never came.

never was happy in overdrive. ran better and better mpg in drive below 65.

started running worse and I parked it. Now I need it. No power, codes for egr voltage, dplf, stumbles, backfires.

change fuel filter and check fuel pressure at running speed. ok.
Had same problem with my car. Asked advice on forum and heard everything from blown up motor to wrong air in tires. One guy kept trying to say something about injectors and another guy kept calling him stupid and trying to pick fights. Others said injecters were a major job on this car and not worth it. I found two bad injecters. entire job took one hour with pepsi break. So much for online diagnoses.

Back to Ford. I posted a ? about this vehical last summer. Everyone said it was the egr. Sorry, I don't believe the egr could make it this bad.

Ohmed out the coil pack and compared to a new coil. Ohms good. replaced coil and now runs 75% better. Yesterday am started running even better.

Still stumbles on long hills. Feels like it's in too high of a gear. has new plug wires. maybe bad coil caused plugs to foul. Guess I'll have to look.

I'm looking at the tps because of the way the engine responds to pedal imput.

Feels like it's being stranggled. Makes me suspect catalyic converter.

Now you know the rest of the story.

 

[btexpress]

Based on what you just revealed about the engine seeming strangled, I suggest you disconnect the MAF sensor and drive it, see if that makes a difference. If it is a MAF issue, it should run with power, it may not seem like normal, but that is because when you disconnect the sensor you put the PCM into limp mode, which fixes the timing and other factors.

If the symptoms you describe are not noticeable with this sensor disconnected, there is a good chance the MAF is bad, also the MAF connectors on these 90s Explorers also created similar problems.

 

[btexpress]

The most frustrating part for me, and maybe others, is understanding why you were focusing on the TPS ground. Either the sensor works or it doesn't, and a high percentage of the time the TPS will set a code if it has a problem.

 

[MrShorty]

Everyone said it was the egr. Sorry, I don't believe the egr could make it this bad.

FWIW, I believe a fault in the EGR system could explain your symptoms. In any case, I wouldn't advocate simply ignoring trouble codes like that.

It almost seems like I heard of someone in the last couple of weeks who thought he had a problem with his TPS and ended up tracking it down to a shorted out DPFE sensor that was throwing off the Vref circuit (which feeds both TPS and DPFE).

If you want to ignore the EGr codes, I can't force you to handle them. At this point, though, my advice would be to deal with the trouble codes you are getting before chasing down something else.

 

[richrd]

Yes, now I will go to the egr codes. But the problem I was chasing then was the coil pack. Now that is fixed and 80% of the problems.

As for the tps. It felt like a problem in the fuel system. Check sensors, can't hurt, takes only minutes. Spec says 5 volts out at wfo. can't get 5 out if only putting 3.8 in. Makes sense to me but I'm only a motorcycle mech.

LOOK OUT MAF, HERE I COME

 

[cjones101812]

since you have an EGR codes start there. what code # is it??

 

[richrd]

Yes, now I will go to the egr codes. But the problem I was chasing then was the coil pack. Now that is fixed and 80% of the problems.

As for the tps. It felt like a problem in the fuel system. Check sensors, can't hurt, takes only minutes. Spec says 5 volts out at wfo. can't get 5 out if only putting 3.8 in. Makes sense to me but I'm only a motorcycle mech.

LOOK OUT MAF, HERE I COME