My car is not very Nice

[snwbordr02]

Loss of power: Progressively worse when in higher gears. Occurring around 2000 rpm most often (since more noticeable in higher gears and under load). Feels similar to when the traction control cuts engine, but it is repetitive. Happens almost always when at half throttle or more, but not explicity; It has happened when hardly giving it gas at all. It will accelerate for about 300 rpm, then cut out and hesitate, then accelerate and so on all the way to redline. It happens most often on the freeway.

Sometimes it’s fine. It seems as though if I drive my car "nicely" gradually stepping on the gas it will drive fine. Alternatively if I don't drive smooth it happens. Especially if I’m irritated and drive it hard.

I changed fuel filter. Nothing. Ran fuel system cleaner through 2 tanks. Cleaned Throttle body and PCV. I've taken it to AutoZone to check any codes for misfires etc: Nothing. Reset computer, drove hard taken back to AutoZone, no codes. Taken to mechanic, no codes. They checked fuel pressure: fine, 37 psi at idle. They replaced MAF: drove great for 3 days, now its back. Probably was never fixed, I just drove it nice. $400 bucks down the drain.

I've searched threads about MAF, Fuel Pumps, Filters, Throttle position sensors, Traction control, hesitation, Misfiring. I feel like it has to be some sensor going bad maybe Throttle position or air temp. Maybe it’s the entire computer. Who knows hopefully someone on here?

01' GT 5 speed. Engine is stock. 67,000 miles.
Help

 

[snwbordr02]

I checked my Throttle Position Sensor with a voltometer between SIG and GND. The key was turned to the ON position with car not running. The results were 4.01 volts when TB is closed (idle), and 0.43 volts at WOT. Between SIG and REF readout was 5.01V.

My Haynes manual says that when the TB is closed (idle), readout should be between 0.5 and 1.0 volts. And between 4.0 and 5.0 volts at WOT.

So... conclusion on the surface is that the TPS is not working properly. What makes me curious is that the volt values are almost identical to what they should be BUT at opposite positions. Any comments to this or should I just replace the TPS.

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Update: I was drunk, had it on the wrong wires. TPS sensor is fine. .92V at idle and 4.56V at WOT

 

[03ghoststang]

you are going to have to drive it and do a live datalog on it to see what the MAF, TPS, FPR, and all those things are doing under load

 

[imblown-ru]

does it only happen when its below a 1/4 tank or all the time?

 

[hotmustang331]

Does your car have a seperate intake temperature sensor? It may be going bad, and that can cause the car to pull alot of timing.

 

[btolenti]

I think you are measuring TPS voltage wrong. I would think if you measured from REF to GND, you should get 5 volts all the time. Measuring from SIG to GND should read around .5V at idle and near 5V at full throttle...


Maybe your fuel pump is starting to die???

 

[snwbordr02]

It happens all of the time, when the fuel tank is full or nearly empty.

The mechanic did a fuel pressure test when trying to diagnose a problem. He said it's fine at 37 psi at idle.

I did measure the TPS voltage wrong the first time. I re-checked and got .92V at idle and 4.56V at WOT so its fine.

Today i'm going to check my Intake air temperature (IAT) sensor and Idle air control (IAC) sensor. I'll let you know the results.

 

[01Steeda]

I dont know if it applies, but our work vans were doing the same thing and it turned out to be the fuel pumps. they tested fine also, but once replace it went away.

 

[snwbordr02]

Interesting. I didn't replace my fuel filter until this started happening (67,000 mi) so naturally thats the first thing i replaced. I could not even blow through that thing and then finally rust and other crap fell out. Because of this i thought that excess stress had been put on the pump for all this time and so when i took it into the shop i told them i think my fuel pump is going out. I've already posted what my fuel pressure test was. Anyways, i'm still going to take it back to them tomorrow and tell them its not fixed.

 

[Shiroelex]

I'll bet you it's a COP. Your car is exactly like mine, and I had to replace two of them. Same symptoms as you are describing, too. Mine was worst in 5th gear on the expressway, whenever I would give it some gas. Work your way around all of the COPs, by disconnecting them, and seeing if it makes much of a difference. I happened to be lucky, with 1 and 5 being the first two I tested, being the bad ones. I threw in a set of new plugs afterwards, for good measure. Good luck!