Fried ECU? Please help
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Senior User
Joined: May 2008
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I started trying to check the tps voltage and I am not sure which wire is what. The Haynes manual says I have a "signal return", "TP signal", and "VREF". Then in the instructions is says to back probe the ground wire and signal wire. Well which one is the ground wire and which signal are they talking about? Also, they show the connector so you have a reference point as to which wire is which comparted to the notch on the connector, but which direction am I supposed to look at it and is it the tps connector or the harness connector?
By the way, the only voltage I have been able to get is 5.03 volts between the black and orange wires (on the new tps connector). I have not found any other voltage on any other combinations of wires
Thanks for feedback.
By the way, the only voltage I have been able to get is 5.03 volts between the black and orange wires (on the new tps connector). I have not found any other voltage on any other combinations of wires
Thanks for feedback.
Lead Driver
Joined: Nov 2002
Posts: 9,555
Likes: 40
From: Concord, NC
The signal return wire is the computer ground circuit (or 0V if you prefer to think of it that way), the TP signal is the output from the sensor, and the VREF is a reference voltage signal of 5V. The idle voltage signal should be just less than 1V when measuring between TP signal (green wire maybe) and signal return (black wire). You can also check resistance between those two wires with everything turned off, and it should sweep from high resistance to low resistance, and opposite if you measure between VREF and TP signal, as you sweep the throttle from closed to open.
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From the best I can tell, between TP SIG and SIG RTN I do not have any voltage. I am supposed to have .5 to 1.0 volt. When I go WOT I still have no voltage. I do have 5 volts between SIG RTN and VREF.
When I check resistance with the connector disconnected, I receive .9K ohms when I should have 3 to 4K. And at WOT it goes to about 3.5K when it should go to 350 ohms.
Now that shows a screwed up TPS, but this one is brand new. Plus my old one was just replaced about six months ago. I find it hard to believe that the problem is the TPS.
After putting the new computer in and still not running right, that is when I got the 122 tps code. So I replaced it and nothing has changed.
What gives?
When I check resistance with the connector disconnected, I receive .9K ohms when I should have 3 to 4K. And at WOT it goes to about 3.5K when it should go to 350 ohms.
Now that shows a screwed up TPS, but this one is brand new. Plus my old one was just replaced about six months ago. I find it hard to believe that the problem is the TPS.
After putting the new computer in and still not running right, that is when I got the 122 tps code. So I replaced it and nothing has changed.
What gives?
Fleet Owner
Joined: Aug 2005
Posts: 23,666
Likes: 301
From: Easton,Ks
For the TPS you might want to look at this URL:
Ford Fuel Injection Throttle Position Sensor (TPS)
Ford Fuel Injection Throttle Position Sensor (TPS)
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No, 215K ohms. I have not got any voltage from the signal wire at all. I am getting the 5 volts on the reference though. Also, when I checked the resistance, it was backwards. Closed throttle was low then went high at WOT.
I just took it back to NAPA for an exchange. They offer an OE tps, but it will be saturday before I get it. He does not think it is the problem but with not getting a signal voltage out of it, what do you do?
I just took it back to NAPA for an exchange. They offer an OE tps, but it will be saturday before I get it. He does not think it is the problem but with not getting a signal voltage out of it, what do you do?
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Thread Starter
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Senior User
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With battery and tps disconnected I get about 550 ohms between signal return and voltage reference. When I disconnect the computer connector, that reading goes to about 2.1k ohms.
The other readings are above 200K ohms.
The guy at NAPA told me that if the flash was not done exact on the computer, it will give problems.
The other readings are above 200K ohms.
The guy at NAPA told me that if the flash was not done exact on the computer, it will give problems.
Lead Driver
Joined: Aug 2006
Posts: 5,670
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From: Sand Lake, MI
The EPC solenoid is part of the solenoid pack and is replaceable as a unit with the pan removed.
I would like to add it sounds like the EPC is doing exactly as designed to, I think you need to find out why it has the need to do so.
If the computer doesn't know how much gas you're giving it at any given point it could hold a shift to long then slam the next gear when it suddenly figures it out.
Find out what the problem is with the TPS.
I would like to add it sounds like the EPC is doing exactly as designed to, I think you need to find out why it has the need to do so.
If the computer doesn't know how much gas you're giving it at any given point it could hold a shift to long then slam the next gear when it suddenly figures it out.
Find out what the problem is with the TPS.
From what you said TPS is failing the KOEO test, its not going to work when driving it if it can not or does not pass that test before leaving the driveway.
Don't be quick to find fault with the tranny, I really doubt it has a problem. The problem is the information it receives from the computer. The computer is not getting all the information it needs to control the tranny as it should.
I was doing to many things at one time earlier and my post suffered some because of it, sorry about that.
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I really do appreciate all the help. I am going to try to get the tps problem fixed and go from there. I don't know if the computer could have damaged the tps or not, so I am a little reluctant to put another new one in there. If this one goes bad, I believe I am going to send the computer back. I have not took loose the wiring harness that is under the upper intake, but there are no signs of anything wrong. I really doubt, if I have a wiring problem, that it would be inside of a harness that is perfectly intact. I think it would have to be at a rub point or very near heat.
Anyway, I get the new tps on Saturday so I will report back then. Thanks.
Anyway, I get the new tps on Saturday so I will report back then. Thanks.
Lead Driver
Joined: Nov 2002
Posts: 9,555
Likes: 40
From: Concord, NC
You can do the continuity check on the wiring that I mentioned earlier without having to pull the harness out from under the intake manifold. It might be worth checking in case there is a problem that might be screwing up the TPS. On a junkyard harness I got for my truck, I found a few burned wires where the harness passed over (or under) the EGR tube on the passenger side, so that could be a possible problem spot that wouldn't be easy to see from above.
New User
Joined: Aug 2008
Posts: 7
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From: Yorktown, Va
I am new to this forum and would like to say great job fellas with the advice.
I would second the continuity check over a visual inspection u R looking for a direct short across coductors or to ground or both. With all connectors disconected check both ends of each harness. for any resistance especialy low.
I have a 91 w I6 having similar problems and just today would not fire and heard what sounded like a bad short under dash around radio then it went away and truck fired up and ran rough but ran.
I would second the continuity check over a visual inspection u R looking for a direct short across coductors or to ground or both. With all connectors disconected check both ends of each harness. for any resistance especialy low.
I have a 91 w I6 having similar problems and just today would not fire and heard what sounded like a bad short under dash around radio then it went away and truck fired up and ran rough but ran.
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Okay, I have my new tps but I have been doing some checks before I install it. Pin #6 is VSS(-) with .2 ohms. When I unplug it from the rear end it does not change at all. I have shook the wires around all the way under the truck and it does not change at all. The 1992 wiring diagram just shows two wires going the the VSS. But the 1991 diagram shows the pin #6 going to ground.
I also checked pin #8 (FPM) with 2.5 ohms. When I trip the fuel inertia switch the meter shows open. When I switch the tank selector to rear tank it goes from 2.5 ohms to 59.8 ohms. I have suspected a weak fuel pump for some time now but I don't know if this may be a problem or not.
I have been trying to disconnect the connectors that I have showed some resistance on at the computer's connector.
You can look at one of my earlier posts to see all the resistance values I received from before.
Thanks for all the help.
I also checked pin #8 (FPM) with 2.5 ohms. When I trip the fuel inertia switch the meter shows open. When I switch the tank selector to rear tank it goes from 2.5 ohms to 59.8 ohms. I have suspected a weak fuel pump for some time now but I don't know if this may be a problem or not.
I have been trying to disconnect the connectors that I have showed some resistance on at the computer's connector.
You can look at one of my earlier posts to see all the resistance values I received from before.
Thanks for all the help.