TPS issues

[Elutheros]

I've got a 5.0 with GT40P heads, Explorer intake, EFI obviously, A9L ECU from a 1989 Mustang. It has always thrown a TPS code (23) no matter which TPS I use and I've tried several including Explorer, a new mustang TPS, and some old ones I had laying around.

I've never been able to get the base voltage close and consistently get .2 volts with the throttle closed. Voltage from the ECU is never more than 4.5 volts. WOT is .95 max. I cleaned all the grounding points for the ECU and got no change. (I've always used a digital VM to check it and I have 3 different meters--all give the same readings)

It starts and drives well, but I think it is running pretty rich. One of the Explorer TPSs kept giving a CEL when the throttle position was changed, so I swapped that out and now no CEL. MPG is pretty consistently 14 which I think could be better if I got this fixed. It idles at 750-850.

I'm beginning to think it is an ECU issue. BTW, ACT and Coolant Temp sensor are new)

Anyone see something I'm missing? Something else I should try?

 

[prymetime1]

Hey bud, I'm no pro on tracing these kind of issues down but as a fox mustang owner, I've had to research alot of ish. There is a ton of material on tps issues over on stangnet.com. being it's running rich, have u checked 02 sensors? Those can cause tricky problems that get over looked if they not throwing codes.

 

[kimcrwbr1]

Have you replaced the PCV valve lately? Disconnect the battery for 1/2 an hour after replacing or cleaning a senser?

 

[RonD]

TPS should get 5volts from the computer, ECT sensor(not sender) shares this voltage as well so check that 1 of its wires has 5volts.
Top wire on TPS should be the 5v wire

Center wire is the voltage the computer uses to ID throttle position
When throttle is closed center wire should show .69 to .99volts.
Wide open above 4.5v

 

[Elutheros]

@RonD thanks--I didn't think of checking voltage to other sensors. Been working on this on and off for 10 months, so I've done plenty of research on other forums, etc. and have all the numbers memorized by now.

 

[RonD]

The return wire(center) is the only "independent" wire on the TPS, the 5v and Ground are both daisy chained/spliced to other sensors.

You could check that wire between TPS and computer
Also if you have a OHM meter put it on a TPS, top and center wire connections
OHMS should be high with "throttle" closed, then gradually go down as "throttle" is opened until OHMS are almost or at 0 at WOT.

If it does this then that TPS is good issue is in wiring