Engine No voltage to TPS

[Mustang5L5]

With the ECU plugged in and key on, it's getting 12V and ground. An internal voltage regulator knocks down the 12V to 5V and outputs that on pin 26. backprobe the connector from pin 26 to either 47 or even pin 60 and you hopefully will see 5V.

If you do, it's a wiring issue. That's when you can uplug the ECU and start testing for continituty to see if the wire from pin 26 connects all the way to the 10-pin connectors and to the 60-pin.

TBH i would roll the dice, disassemble the 10-pins and clean then very well and then test for 5V (key on, ECU in) at the TPS sensor. You might get lucky because the 10-pins are a known connection issue.

 

[3054tony]

With the ECU plugged in and key on, it's getting 12V and ground. An internal voltage regulator knocks down the 12V to 5V and outputs that on pin 26. backprobe the connector from pin 26 to either 47 or even pin 60 and you hopefully will see 5V.

If you do, it's a wiring issue. That's when you can uplug the ECU and start testing for continituty to see if the wire from pin 26 connects all the way to the 10-pin connectors and to the 60-pin.

TBH i would roll the dice, disassemble the 10-pins and clean then very well and then test for 5V (key on, ECU in) at the TPS sensor. You might get lucky because the 10-pins are a known connection issue.

Making progress. Would you happen to know what pin in the 10 pin connects to the 26?

 

[Mustang5L5]

White connector. Pin 1 = 46 and pin 2 = 26. You can test for 5V here with the ecu connected as well.

 

[3054tony]

White connector. Pin 1 = 46 and pin 2 = 26. You can test for 5V here with the ecu connected as well.

ECU connected with KOEO I get 5 volts to the #2 pin
Battery and ECU disconnected, Continuity from pin #1 to 46 good
Continuity from pin #2 to 26 good

 

[Mustang5L5]

Clean the connections well and reconnect the 10 pins. Test for 5V at the TPS sensor connection. Orange to black.

 

[3054tony]

Clean the connections well and reconnect the 10 pins. Test for 5V at the TPS sensor connection. Orange to black.

Thank you for all the help. I now have 5 volts to the TPS orange wire and set the green to .99-1.00 volt. Cant get it lower unless I drill out the hole a little.

Runs absolutely horrible though, idle surges and if I unplug the IAC it instantly dies

 

[Mustang5L5]

Throttle stop screw is set too low then. With the IAC unplugged, you should be able to maintain a low idle. The IAC is just adding a little on top to keep it smooth, but the throttle blade needs to be opened enough to “help”

TPS can be set anywhere from 0.5 to 1.25 v. The 0.99 volts thing is a myth.

You’ll want to reset the ECU by unplugging battery for 15-30 mins after making these adjustment.

 

[AeroCoupe]

Base idle reset is in Post #2 here:

Help me create the "Surging Idle Checklist"

Updated 05 July 2022 to add rough idle when cold and smooth idle when up to normal operating temperature. See the EGR tech information, section #15 for more help. Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank...

stangnet.com

 

[3054tony]

Throttle stop screw is set too low then. With the IAC unplugged, you should be able to maintain a low idle. The IAC is just adding a little on top to keep it smooth, but the throttle blade needs to be opened enough to “help”

TPS can be set anywhere from 0.5 to 1.25 v. The 0.99 volts thing is a myth.

You’ll want to reset the ECU by unplugging battery for 15-30 mins after making these adjustment.

Seems like no matter how much I turn the idle up it won't stay running with the IAC unplugged. It will jump from 600 to 1500 for a few seconds then back down for and continue to do that for 15 minutes but as soon as I unplug the IAC it dies. I also took the throttle body off and cleaned it up but no change.

 

[3054tony]

Base idle reset is in Post #2 here:

Help me create the "Surging Idle Checklist"

Updated 05 July 2022 to add rough idle when cold and smooth idle when up to normal operating temperature. See the EGR tech information, section #15 for more help. Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank...

stangnet.com

Unfortunately I can't get it to run enough to do a base idle reset. No matter how high I set the idle screw it surges bad and will die the second I remove the IAC

 

[Mustang5L5]

Turn it waaaay in. Get it idling at 2000 rpm, and then back the screw out slowly. How low can you get it?

 

[3054tony]

Turn it waaaay in. Get it idling at 2000 rpm, and then back the screw out slowly. How low can you get it?

I wish I was able to upload a video to show you how it sounds. It will not stay at a constant rpm. If it drops too low like its going to die then jump back up to 1000+ and pop through the intake a few times. I have the timing set at 10 degrees but wondering if i should bump that up too

 

[General karthief]

Classic symptom of a pretty fair vacuum leak.

 

[3054tony]

Classic symptom of a pretty fair vacuum leak.

Had this one under the intake and got it fixed before this whole tps situation. Wouldn't surprise me if there was another but didn't find any with smoke

 

[AeroCoupe]

Have you checked the ECU for codes? Even if the CEL is not coming on there can be codes as the CEL only comes on in regards to emission codes.

Electrical - How To Pull Codes From EEC-IV In 86- 95 5.0 Mustangs

@Noobz347 - The code dump procedure isn't in the sticky - you may want to add it... Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on. Dumping the computer diagnostic codes on 86-95 Mustangs Revised 26-July-2011. Added need to make sure the clutch is...

stangnet.com

 

[3054tony]

Have you checked the ECU for codes? Even if the CEL is not coming on there can be codes as the CEL only comes on in regards to emission codes.

Electrical - How To Pull Codes From EEC-IV In 86- 95 5.0 Mustangs

@Noobz347 - The code dump procedure isn't in the sticky - you may want to add it... Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on. Dumping the computer diagnostic codes on 86-95 Mustangs Revised 26-July-2011. Added need to make sure the clutch is...

stangnet.com

I tried pulling codes when I was first trying to get it started and they were coolant temp was low, fuel pump circuit fault (replaced fuel pump) and a keep memory alive code. Haven't tried it since getting the computer back but can for sure try again

 

[Mustang5L5]

Try it again. Something major is amiss. Either a large vac leak, or a major sensor is not reading correctly.

Dump codes again and run the cylinder balance test at the end of the code dump process

 

[Mcmahst]

Sounds like a bad vacuum leak. I did the smoke test but it didn’t find my canister vacuum valve and EGR valve leaks. What vacuum reading are you getting while you try and get it to idle?

 

[3054tony]

Try it again. Something major is amiss. Either a large vac leak, or a major sensor is not reading correctly.

Dump codes again and run the cylinder balance test at the end of the code dump process

I'll pull them in the morning when i get some light and try to get a balance test but not sure if it will be able to. If I press the gas pedal down too fast it will die.

 

[3054tony]

Sounds like a bad vacuum leak. I did the smoke test but it didn’t find my canister vacuum valve and EGR valve leaks. What vacuum reading are you getting while you try and get it to idle?

I do not have a way to read vacuum. I was just pumping it in with a cheap smoke machine. I will check the egr and canister as well.