Replacing TPS Mustang EFI update

[Timmy390]

Long story sort, I have all of the symptoms of a failing TPS. Started as a small "blip" and now is starting to happen more and more. Idle randomly hangs at 1500 (sometimes higher) and will not reset unless you turn off the key, hesitation under very light throttle while cruising, CEL pops on when it hesitates with "lean" condition. Sometimes it seems under powered at WOT.

Anyone have a good step by step process for changing the TPS? Is the process year specific? I've got an odd combo. 97 Explorer T-body and 95 Mustang EFI. Same TPS was OEM on both.

Tim

 

[EPB72]

So a MAF system ..and can you get/see actual data on a scan tool? If yes on data you dhould have TPS data in Volts ,,,, .8v closed throttle - 4.8v at WOT .scan data refreash rate is slow on a range sweep so yu can easily miss a drop in signal and not see it,,, So a Lab scope ..graphing meter .or you multi meter would work with a MIN/MAX feature .....so either meter option back probe Signal wire and ground other lead .. KOEO and cycle throttle slowly lok for any drop outs ,, since your Not setting and tps codes usually pretty quick to set {prove that by disconnecting TPS connecter and rerun code read.. replacing is easy just make sure you get the contact flags on the correct side of each other ..voltages noted above after instal, Now the Lean code well fuel pressure ,, air intake/ vaccum leaks.. MAF are the hot wires clean, Dirty can set lean faults and drivability

 

[Timmy390]

Reading that SN95 is different than other mustang EFI......Yes I know it's different as in red headed step child but maybe TPS is also different? Setting the TPS voltage is needed for 86-93 5.0's but not 94-95. SN95 automatically zero out the TPS on startup.

Interesting.....From veryuseful.com
Two types of TPS are used on EEC-IV system. "Level C" type is adjustable and "Level D/RD" type is nonadjustable. Throttle positioning sensors without slotted mounting holes are not adjustable. If voltage reading on nonadjustable TPS is not .9-1.1 volts at idle, and greater than 4 volts at wide open throttle, replace throttle positioning sensor.

Also, there appears to be 2 sensors listed for the SN95. I got to run this down. Get the P/N off the OEM one.

Tim

 

[EPB72]

Reading that SN95 is different than other mustang EFI......Yes I know it's different as in red headed step child but maybe TPS is also different? Setting the TPS voltage is needed for 86-93 5.0's but not 94-95. SN95 automatically zero out the TPS on startup.

Interesting.....From veryuseful.com
Two types of TPS are used on EEC-IV system. "Level C" type is adjustable and "Level D/RD" type is nonadjustable. Throttle positioning sensors without slotted mounting holes are not adjustable. If voltage reading on nonadjustable TPS is not .9-1.1 volts at idle, and greater than 4 volts at wide open throttle, replace throttle positioning sensor. So is yours at closed throttle .9-1.1v and above 4v usually 4.5-4.7v is what seen .. range .3--4.8v above or below will set a circuit high or circuit low fault,,or range performance fault..check cold and different temps intermittants can be fun.. Note if voltage is slightly at closed throttle sometimes carbon built up at throttle plate can cause this,, none of this would necessarly set a lean fault though. Also, there appears to be 2 sensors listed for the SN95. I got to run this down. Get the P/N off the OEM one.

Tim

 

[Timmy390]

Got the P/N.... F4SF-98989-AA Seems it's been replaced with P/N F4SZ9B989AA

1997 Explorer 5.0 AWD 4.0 used the same. I run a 1997 Explorer full upper intake. It is a different part than the SN95 Stang as 1995 Mustang is not listed in the vehicle fitment however the 1996 mustang is. I provided Gary the info on what T-body I was running when he chipped my ECM. Not sure if he needed to do any programing because of this or not. If it truly automatically zero out the TPS on startup does voltage even matter? I mean as long as it's in a range right? The ECM compensates? IDK

I've not checked voltages yet. It runs great till it don't which is not to say it runs bad. Idle hangs 1 or of 15 times I drive it. Turn key off and back on, idles fine 850rpm. I've tried bumping the throttle when it hangs and it seem to increase the hung idle with each bump. The hesitation is generally less than a second then clears up. On occasion it does it twice in quick succession maybe 3 times (that's when I get the lean code which clears if I turn the key off).. Always when doing 40-45 in 4th or 5th gear on back roads. Just putting along.

The WOT power might be all in my head.

Clean the T-body......Good idea......

Tim

 

[EPB72]

Got the P/N.... F4SF-98989-AA Seems it's been replaced with P/N F4SZ9B989AA

1997 Explorer 5.0 AWD 4.0 used the same. I run a 1997 Explorer full upper intake. It is a different part than the SN95 Stang as 1995 Mustang is not listed in the vehicle fitment however the 1996 mustang is. I provided Gary the info on what T-body I was running when he chipped my ECM. Not sure if he needed to do any programing because of this or not. If it truly automatically zero out the TPS on startup does voltage even matter? I mean as long as it's in a range right? The ECM compensates? IDK Yeah,NO, the ECU is not changing the signal output of the TPS...what it might do is take a initial reading and use that as a learned value for closed throttle position for that drive cycle , I know if you full throttle it cycle the key on and crank it the ECU persives this as a clear flood mode and allows spark and cuts off injectors this great of ford when your doing a relative compression test with the Lab scope,, On a side note this is what the BARO/MAP does it takes a BARO reading prior to starting on a key cycle.

I've not checked voltages yet. It runs great till it don't which is not to say it runs bad. Idle hangs 1 or of 15 times I drive it. Turn key off and back on, idles fine 850rpm. I've tried bumping the throttle when it hangs and it seem to increase the hung idle with each bump. The hesitation is generally less than a second then clears up. On occasion it does it twice in quick succession maybe 3 times (that's when I get the lean code which clears if I turn the key off).. Always when doing 40-45 in 4th or 5th gear on back roads. Just putting along.

The WOT power might be all in my head.

Clean the T-body......Good idea.........as well as check cleaning MAF, any changes like this you should reset Keep alive memory,
Tim

 

[Timmy390]

Yes my understanding the TPS volts for idle are baselined as idle reference for that drive cycle meaning the ECM reads the volts i.e. position and calls that idle.

Taking the above off the Stng sites......

Tim

 

[Broncobowsher]

One of my tricks for a flaky sensor, unplug it and go without. There are other drivability issues with the ECM not seeing TPS, but it can read enough MAF to stay happy and drive decent. There will be some tip in issues. If it still has the issues with the TPS unhooked, and the added from the TPS being unhooked, it probably isn't the TPS.

Failed sensors are the best to deal with. Failing, or out of spec are a pain

I'm not convinced that your problem is TPS. Not saying it isn't, but not a sure it is either.

 

[Jdgephar]

Did you check for any codes from the ECM? What code was stored when the CEL light came on?

 

[Timmy390]

As luck would have it.....I had this issue on the 15th and I haven't checked codes yet. Been busy on the 69 Mach 1 third member and then yanked the intake to fix the china wall oil leak. Got it back together yesterday. Sniper is the next project.......

So checked for codes and I got some this time. The issue has been getting worse so maybe that's helped with the codes. In the past I've gotten a CEL and before turning off the engine I would read a lean code. It really acted up this time......twice in a 8 mile drive and once when sitting at a stop light......Same drive.

This time things are a bit different....
124 (M) TP voltage was higher than expected – Fuel control
173 (R,M) Oxygen sensor not switching – system is or was rich – Single, Right or Rear HO2S – Fuel control
177 (M) Oxygen sensor not switching – system was rich Left or Front HO2S – Fuel control

So it went rich this time......

Tim

 

[EFI Guy]

The PCM uses the lowest TPS voltage of the drive cycle as a baseline, all of it's commands are done relative to the baseline. So it doesn't matter if your closed voltage is .8 or .95 it will behave the same. There are a handful of tools out there that can read a data stream from a 94-95. They were all very expensive back in the day but dirt cheap now that they are almost obsolete. Worth looking into IMHO.

There aren't a lot of things that will cause a rich condition. Assuming ECT and IAT are reading properly, your looking at a bad pressure regulator, restriction on the return side, etc...
I have never seen a MAF fail and cause a rich condition but it's not out of the realm of possibility. I have seen o2's do it, but it's rare and you have both banks showing rich. It may be worth checking to make sure SIG RTN is ok at the o2 plugs.

 

[Timmy390]

I'm guessing TwEECer RT would be your go to?

Pretty sure its not the ecm as you gave it a good lookover I've cleaned the mas. At present I have no way of knowing if the ETC and IAT are within spec. Not throwing codes and are newish meaning new when I did the efi conversion. I'll check ths O2 wiring. I haven't been under the rig in a while.

It acts up randomly. The idle issue (where it hangs at like 1500 or sometimes higher) is separate from the hesitation best I can tell. Always acts up when driving easy. Never when I'm driving with spirit.

Did some research on the TPS. Lots of eBay and Amazon listings with the old part number. I call fakes as the Ford dealer has a new part number for the part and the old part number hasn't been used in years.

Tim

 

[Timmy390]

Well I guess I really am That Guy........I threw a TPS sensor at the problem. Yes yes I know but I had my reasons. It was the original TPS from 1997 and was pulled from a junk yard from an explorer with no hood......Justification RIGHT?

SO, new Motorcraft part from a Ford dealer. Not one of those $30 fakes off Amazon and Ebay that have no part number stamped on the top.

Had the Bronco out for 2 drives......First one was fine....Second one....I came to a stop and idle was 1400 and would not drop no matter what I did. CEL not on. Turned key off, and restarted. Idle was fine...850 Still no CEL. Was dine all the way home and idle was perfect at all stops.

Pulled codes....111 10 452 Vehicle Speed Sensor (VSS) code, specifically indicating a problem with the VSS or its circuit

Would the VSS cause this? Can I just unplug the VSS and see if the issue goes away or will it throw other codes? I know some don't run VSS

1995 Mustang didn't have a speedo cable so I'm running a 1993 Mustang VSS if that matters.....

Tim

 

[DirtDonk]

A missing or malfunctioning VSS can definitely cause a stall when coming to a stop. However, I don’t think I’ve ever heard of them causing a high idle.
Certainly not an expert, but that’s what I remember.

 

[tasker]

Tim, have you cleaned the IAC valve? those used to stick and would do just what you are describing...

 

[Timmy390]

Tim, have you cleaned the IAC valve? those used to stick and would do just what you are describing...

Not yet.....It's a couple years old.....came from the local parts store so quality is suspect. I'll give it a spray down.

Tim

 

[Timmy390]

It's fricken HOT out. Even hotter sitting in the Bronco in direct sun. Did a KOEO test again and got same 452 KOER has no codes. Nothing in memory.

Tim

 

[Timmy390]

Tim, have you cleaned the IAC valve? those used to stick and would do just what you are describing...

Before I clean it, I need to order the broken connector I found. The clip that holds the connector on the IAC is broken. I guess it got brittle and snapped. The connector was not fully on. Not saying that's the issue BUT needs addressing before going further.

Tim

 

[Timmy390]

So.....replaced the broken connector a couple weeks back. It acted up once with a bobble when driving but has been fine till today.

Stopped at a light and the engine just shut off. It restarted fine. Engine temp just over 180. Was only 5 miles from home.

Drove 1.5 blocks to another light. While sitting there the idle suddenly went from 850 to 1800. Light turned green and I pulled into a gas station. Turned the rig off and restarted Engine. Idle back at 850. No CEL.

Went home checked for codes in memory....it was clean. Ran koeo test. It passed. Ran koer test...it passed.

Went for another drive this afternoon. Pulled up to a light sat there waiting and idle went to 1800 again. Pulled into Lowes and idle was 850. Popped the hood and while messing with the IAC, idle went back up. I unplugged the IAC and idle went back down. Did this several time with same result. No CEL no codes stored.

Came out of lowes and rig Ran great. 12 mile run....fine. mowed a yard and came home...Ran fine.

Ideas? Suggestions?

Tim

 

[Speedrdr]

It’s possessed, maybe? Have you offended someone from Haiti?? lol