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TPS voltage problems

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  #1  
Old 06-04-2012, 04:03 PM
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TPS voltage problems

Recently when I was coming home from a trip I went to pass a guy and no power and truck went into limp mode. Soon it died and would not restart unless gas pedal was floored. Towed it home and checked codes. "TPS inconsistent with mass air flow meter". Replaced TPS same problem. Checked voltage at TPS it has 5 volts at the harness unhooked. As soon as I hook up to the harness it shows 4 volts with koeo at where idle should be and lower as the throttle plate opens. Completly opposite of what the repair manual says. Weird thing is truck is hard to start but will start and run with the maf unplugged. Thinking its a PCM or wiring issue but I am at a loss. I also replced the fuel filter and cleaned the IAC. Tried the old TPS sensor same result. If its in the TPS sesnor wiring why would it run with the maf unhooked. Please help!!! Truck is a 2000 ford f150 with the 5.4 it has a procharger and a SCT tuner program on it.
 
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  #2  
Old 06-04-2012, 08:52 PM
glc
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You sure it's not a bad MAF?
 
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  #3  
Old 06-04-2012, 09:53 PM
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no im not sure, will a bad MAF cause a faulty TPS voltage? I have a extra MAF but its possible that one could be bad it was the original one that came with the truck. I was thinking of cutting the wires from the TPS sensor to the PCM and replacing them with new ones thinking they may have rubbed through. I appreciate the input
 
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  #4  
Old 06-04-2012, 11:41 PM
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try cleaning the original maf and swap it in. use maf cleaner.. the stock one rarely fails..
 
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  #5  
Old 06-05-2012, 12:37 PM
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Please do not begin cutting wires before you prove the need.
What are the codes stored in computer memory as the first step?
There may be a harness issue, but prove it first.
In testing the TPS, the voltage is measured from the 2 leads to the common side 'return' and NOT to ground.
One lead is the supply voltage from the PCM internal supply.
One is the varying signal back to the PCM to tell what the position is.
One is the 'return' back to the PCM internal supply. This is why measument to chassis ground is not correct.
If you measue to chassis ground, it wil be inaccurae and false.
.
At rest, you should see about 1 volt +/- a tenth and should increase with throttle application. Too high or to low by some larger amount is out of limits.
.
Do not worry about the 'exact' value at rest because the system self zeros (floating zero) it 'as it's own reference point' each time you start the motor.

Also it does not do any good to ask why the air meter does anythng before proving the fault as the fault may be some other area.

I'm not trying to be smart with you but to get you to look at things within a logical order and not begin hacking and wondering, as a way to fix anything.
If you were to do this, it results in more confusion and more self inflicted issues.
Good luck.
 

Last edited by Bluegrass; 06-05-2012 at 12:40 PM.
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  #6  
Old 06-05-2012, 12:51 PM
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The exact code was:P1121 - Throttle Position Sensor Inconsistent with Mass Air Flow Sensor. I replaced the TPS first thinking this was my problem. With the key on engine off using a voltmeter and the harness unhooked I am reading 5 volts, this is with the red probe in the top wire and the black probe in the second wire. I know one is the power wire and one is the signal wire. and the third bottom wire is the ground. If i hook the harness up to the TPS sensor with the key on engine off I get 4 volts at where idle should be and .32 at wide open throttle. this is the same with the old sesnor and also is the same with the sensor removed and moving the inside of the sensor by hand(part that the throttle plate would move) im really lost considering towing to dealer but trying to save money please any help would be appreciated im desperate truck has been broke down for a week now.
 
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  #7  
Old 06-05-2012, 01:21 PM
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New results you were so right bluegrass. Put negative probe of volt meter to grey and red wire on bottom and positive lead to grey and white wire results were perfect .96 volts at idle 4 volts at full throttle. Could a bad MAF cause the trouble code I listed?
 
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  #8  
Old 06-05-2012, 03:09 PM
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Problem solved!!!! It was not electrical or sensor related at all. It is a pro charged truck running an inter-cooler. One of the big rubber hoses going out of the inter-cooler had slipped off. Apparently when I went to pass and the truck downshifted the torque form the motor was just enough at that time to pull the hose off causing the mass air flow meter to get bad readings. It was a tight fit anyways but had an extra hose and fixed it for good. Makes me mad if I would have thought about that it would have been fixed on the road in 5 minutes. Thanks everyone for there replies makes me proud to be a member of this site
 
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  #9  
Old 06-05-2012, 04:24 PM
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Shame on you, you never said anything about being 'blown'.
The blower pressure will do things like that if the clamps are not checked and tightened often enough.
The code does implicate an air leak in the intake tract as a possible cause.
Remeber the discription does say the airflow through the meter does not track with the Throttle position.
Think it's a good reason why?
Good luck.
 

Last edited by Bluegrass; 06-05-2012 at 04:29 PM.
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  #10  
Old 06-05-2012, 06:27 PM
glc
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Originally Posted by Bluegrass View Post
Shame on you, you never said anything about being 'blown'.
Yeah he did -

Originally Posted by tat00844 View Post
Truck is a 2000 ford f150 with the 5.4 it has a procharger and a SCT tuner program on it.
 
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