Goes up to 25 mph, no faster


TWH

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I have an 89 Ranger, 2wd, auto, A4LD. Been sitting idle for several years and I just can't seem to make it stay running. I got a reader and it coded out with a code 53 "throttle positioning sensor above max voltage," and a code 89 "AXOD Lock-Up Solenoid (LUS) circuit failure or Clutch Converter Override (CCO) failure." I noticed that the front bumper was bent, so I made sure the fuel cutoff (kill switch) was reset. I can get it up to 14 mph, runs great, shifts into 2nd and starts to surge. Keeps on surging till I let off the gas just a little bit and then runs great up to 25 mph. Starts to surge again and then won't go over 25 mph. On 2 separate test drives the surging just went away for no apparent reason, ran great. Stopped, started, took off fast, took off slow. It did great, but as soon as I put it back in park and drove it the next time the surging started all over again. It idles fine, BTW.

Partial list of new parts: Fuel pump, alternator, fuel filter, tank has been flushed out, ignition switch, steering column switch (slider), throttle positioning sensor, but it has not been set by a computer.

Before I was given the vehicle, it sat on the tarmac at the airport with a blown tranny for about 2 years. Transmission has been replaced by another mechanic. Numerous mechanics could never get vehicle to stay running. They all worked out on the tarmac on the vehicle over a period of 3 years on and off, with no special tools that I could tell. They all threw in many parts (i.e. rebuilt computer, mass airflow, sensor, throttle position sensor, one coil pack, maybe more?) just trying to get it to run.

HELP!! What should I try next?:dunno:
 


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RobbieD

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Sounds like a real frustrating head-scratcher you've got there. Given the weirdness of the problem, the truck's history and all of hands that have been on it without resolution, have you checked all of the wiring harness grounds? The 1989 EVTM (wiring manual)would show all of them, but basically you're looking for loose or disconnected wires with ring terminals (usually, not always, black colored wires), which are screwed to body or chassis metal with a bolt. Check along the inner fender wells, in the kick panels (especially passenger side), the firewall and the radiator support. Also make sure that the battery has ground cables from its negative post to the engine, and body and/or frame. If for anything else, at the least this would get an ungrounded electrical system ruled out as the cause. Good luck with it, and welcome to TRS.
 

MAKG

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That TPS fault indicates the TPS, at least, is not grounded. Grab a voltmeter and a circuit diagram and see where ground got lost. There will be a voltage drop there -- with no ground, all three TPS leads will be at 5V.

That may not be all of the grounding problems, but it MAY lead you to something important. So, I'd trace that down first, fix it, and then reevaluate.
 

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if the TPS sensor was bad, wouldnt it have smiler symptoms in park (once the throttle reaches a certain spot, hesitation, stalling, what-have-you)?

i have to wonder if the tranny is the root of the problems.
 

MAKG

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I don't see any indication here of a bad TPS. I do see indication that the TPS is not properly grounded, perhaps intermittently.
 

TWH

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I have been driving the truck around alot, it has messed up a few times. It seems the more I drive it, the better it shifts, so far anyway. Still have a ck engine light and the idle is not all that steady. When I am test driving and come to a stop and it is still in drive, it will run for a few min, then black smoke comes out the tail pipe and it dies. The TPS is new, and has not been set by a shop's computer. I have heard that it must be set that way. Is this true? I did a voltage test on the TPS; first wire on the left is 4.49, next is 4.99, last one is .032. THX for all your help!
 
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TWH

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Do you have any idea where I could find this ground?
 

MAKG

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IF you had your "common" connected to anything not on the TPS (engine block ground, negative battery terminal, whatever), then that TPS is ungrounded internally. I don't care if it's new; those are not correct readings. Especially if the throttle is closed.

Though to be honest, I'm really scratching my head as to how the signal can be higher than power.
 

RobbieD

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TWH- first of all, is there a thick cable between your battery (-) post and the engine?
 

Ranger5.0

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Higher then normal TPs voltage is caused by 1) a disconected sensor 2) An "open" in the suply wire, as in the 5V suply wire is damaged and 3) An open ground. Think of it thisway, your ECM is full of voltmeters, each meter is watching the suply voltage, and then the signal voltage, it then compares the two and makes a decision. If there is no path for the 5v referince signal to take,there will be no voltage drop, which then flags a active falt code. So, bottom line, new TPS or not, the tps and the tps circuit is where your looking. Disconect the tps, conect your Volt meter to the suply wire and the volt meter ground to the battery negative termanal. Get a buddy to mess around with the harness and watch the meter, if nothing happens, then conect the negative lead of the meter to the TPS ground wire, mess with the harness again and watch what happens. IF nothing happens with the meters ground lead is conected to the battery but the Voltage changes when its conected to the TPS ground, then thats a sign of a poor tps ground. If the voltage changes when the meters ground wire is attached then its a sign of the tps 5v suply wire is the suspect. This this, then report your finding. Also note that a "scan tool" doesnt help ya out most of the time. The DMM is your best friend when tracking electrical problems.
 

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An open in the supply wire will give a grounded (too low) signal, not too high.

There is no way to make the signal wire read higher than supply in a resistive circuit, so something is wacky. Given that the signal is almost exactly 5V, I suspect the voltmeter just didn't make good contact when measuring the supply wire (and it's really 5V as well).

But I think the ground side is open. Probably within the TPS itself, or the connector (depending on how the test was done).

A simple ohmmeter will confirm. What's the resistance between the two outer pins, on the TPS with the connector removed? If it's open, you need a TPS. This is not a common wear failure. This is a defect in manufacturing or breakage during shipping or somesuch.
 
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Ranger5.0

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lol, so your telling me everything i learned in electronic engine managment is wrong? The 5v referince signal is being monitored by the ecm as IT LEAVES the ecm and heads to the tps. IF THAT VOLTAGE does not make it to ground through the tps, it finds its way to ground internaly, through the ecm, which then flags a tps high code. if it it wasnt a missprint in a manual, and it REALY IS higher then suply, then somthing in the ecm is fucked, and its time for a replacment Fred...... Fuckin ridiculous electronic device. I duno what some of you do for a living, but i diagnose this stuff at work, and learn about it at school.
 

MAKG

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Not everything, but you're going to have to explain how the computer monitors the 5v reference signal as it leaves the ecm and heads to the tps. There is nothing between there except for the supply wire itself. The computer has no way to know if it "got there" or not. There are precious few redundant systems in an automobile. Running a whole bunch of wires to monitor one might be called for in the Space Shuttle (where that wire failing might kill someone) but it just isn't in a light truck.

If it didn't "make it there," the signal wire is grounded. A resistor with no current is the same as a wire. That's Ohm's Law.

Ungrounded circuits can sometimes behave the way you describe (not one so simple as this one, though). But not unpowered circuits.
 

Ranger5.0

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lol, the signal wire is OPEN if it didnt make it to the tps, its grounded if it contacts a ground wire, or a grounded component of the truck. I can drag this out and explain how the ecm is monitoring the reference voltage and the signal voltage if you like?
 

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The reference voltage doesn't change with an open. It would with a short to ground, but then you'll just burn out the VREF circuit and fry the computer.

You're confusing the signal wire with the supply wire. An open signal is floating and will read according to PCM internals. An open supply grounds the signal. It's not floating. Similarly, an open ground sets the signal to reference.

This is a very basic voltage divider circuit, which I'm sure you learned about in school. It's not at all a complex circuit. It's just a potentiometer with a 5V reference.
 
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