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I don’t know Indy, it’s a speed density car, so there’s a good chance it hasn’t been modified at all.
No need to play with the throttle stop if nobody modified it. Not that you can really modify anything on SD to begin with, 🤷🏻‍♂️

I still say there’s a vacuum leak.
I do agree, there is an air leak,

but people seem to always play with that stop, cant help themselves
 
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Ok so it may have been touched over 21 years ago by a previous owner. What can I do about it if it's not properly adjusted?

Why code 98 (most likely due to 63) after installing a new TPS? If ECM sees the same voltage as the new TPS, how can the signal be too low? What else can I troubleshoot? I operated the throttle while key on and the new TPS voltage did change all the way to WOT (read ~4.79v).

Like I said in a previous post, I'm a fish out of water here when it comes to this situation so more details you can provide, the better.

erase the kam

put a few drive cycles on it, then re check for codes

you may have done something when the power was on.
 

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Discussion Starter · #43 ·
Ok sounds good. I’ll get that leak check done also.
 

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Discussion Starter · #44 ·
Update: Had the -ve battery cable off overnight to erase any codes. Car started up great and idled ~700rpm once warm. About 20 miles into my test drive, felt the car bucking a little. Stopped at a light and my idle was back up to 900rpm. Pulled codes and 63/98 are back again. Probed the green and black wires at the new TPS and read 0.749 (Key on). With black lead at battery -ve, read 0.801V. Pulled the -ve battery again to erase codes and I'm going to swap the TPS back to the old one that I modified (I'll set voltage ~0.97V). I'll go for a drive and see if the codes come back again. The issue I had with the car stalling at warm start-up is gone.
 

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use the new TPS

its not the tps, its the wiring most likely

perform voltage drop on the black wire at the TPS, and the sig rtn at the ecm
 

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Discussion Starter · #46 ·
Agree on the new TPS. Just tried what I said with the old TPS and the car bucked like an enraged bull! (had -ve cable removed for 45 min before trying). Undriveable.

perform voltage drop on the black wire at the TPS, and the sig rtn at the ecm

You mean probe black wire on TPS with PIN 47 on ECM, key on? Similar to what I did before but instead of battery -ve, go from TPS ground (black). Sorry for all the questions just want to be sure I understand.
 

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Discussion Starter · #48 ·
Look at your codes
The 98 code is "Hard Fault is present - FMEM mode. That 63 code makes the ECM think the sensor is dead and goes into "Failure Mode".

Interesting that the Hayne's manual indicates "don't attempt to replace the TP sensor. Specialized calibration equipment is necessary to adjust the switch once it's installed, making adjustment beyond the scope of the home mechanic".
 

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Discussion Starter · #49 ·
use the new TPS

its not the tps, its the wiring most likely

perform voltage drop on the black wire at the TPS, and the sig rtn at the ecm
Ok so I installed the new TPS back on, and did the following checks:

Battery -ve to Green TPS wire - 0.806V
Green TPS wire to Black TPS wire - 0.750V
Black TPS wire to PIN 47 on ECM - 0.750V

When I came back from my drive and had the codes, Green -Black on the TPS were reading 0.749V which I assume ECM was seeing the same thing. Could it be that ~0.750V is the threshold? Still doesn't explain how the old sensor putting out 0.671V had a code 23 and now that I have a little more voltage, I'm in failure mode after a short drive.
 

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Discussion Starter · #50 · (Edited)
use the new TPS

its not the tps, its the wiring most likely

perform voltage drop on the black wire at the TPS, and the sig rtn at the ecm
Sorry Indy I just read your recommendation again. Signal return at ECM is PIN 46 (black wire). I probed PIN 46 and black wire at TPS and did a quick resistance check to make sure nothing was open (read 0.04 ohms). When I checked voltage on black TPS and PIN 46, I get 0 volts (key on). Quickly looked at what a voltage drop test is and I'm definitely doing something wrong!
 

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0 volt drop along a conductor is exactly what you want to see

resistance tests are useless, so leave that feature alone

were you able to cycle the throttle through it range while looking at voltage drop?

if it remains at 0volts, take the lead from sig rtn at place at ecm ground on driver fender apron next to the washer bottle, and remeasure
 
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Discussion Starter · #52 ·
0 volt drop along a conductor is exactly what you want to see

resistance tests are useless, so leave that feature alone

were you able to cycle the throttle through it range while looking at voltage drop?

if it remains at 0volts, take the lead from sig rtn at place at ecm ground on driver fender apron next to the washer bottle, and remeasure
Ok here's what I got:

Key On - Pin 46 to TPS black 0.00V (also cycled throttle with no change in voltage)

Key ON - Pin 46 to ECM ground near washer bottle (attached pic below to confirm ground location) - 0.039 V

Key ON - ECM ground to TPS black (0.037V)

IMG_2759.JPG
 

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key on

backprobe orange wire and black wire at TPS connector

what is voltage?
 

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Discussion Starter · #54 ·

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the only part of circuit left is from the ecm pin to processor

if you were able to see real time processed data, like quaterhorse or tweecer we could confirm this

can you borrow one, from a friend?

otherwise the problem is in the eec........without the data, cannot be 100%
 

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Discussion Starter · #56 ·
Oh man unfortunately I don't know anyone personally that has a fox body or the tools you mentioned. Sounds like these are tuning software that you would have on a laptop? How do you connect it to the ECM? I might be forced to find a garage that has experience with fox bodies. I know of a place that might be able to help but they're 30 miles away. I appreciate your help Indy very much. Very strange that this problem popped up when I installed the old sensor that I modified. Hopefully I didn't damage the ECM.
 

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Sometimes they just get damaged with age.
Like failing capacitors and such. It happens.

so anyway, how about that smoke test?
 

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Oh man unfortunately I don't know anyone personally that has a fox body or the tools you mentioned. Sounds like these are tuning software that you would have on a laptop? How do you connect it to the ECM? I might be forced to find a garage that has experience with fox bodies. I know of a place that might be able to help but they're 30 miles away. I appreciate your help Indy very much. Very strange that this problem popped up when I installed the old sensor that I modified. Hopefully I didn't damage the ECM.

you had a code 23 in your first post, this issue is NOT new, it just turned into a hard fault causing limp mode

changing TPS didn't do it

a shop with an old snap on scan or with a eecIV adapter should be able to verify

the ecm is the only thing left to diagnose.
 

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Discussion Starter · #59 ·
Sometimes they just get damaged with age.
Like failing capacitors and such. It happens.

so anyway, how about that smoke test?
Just started her up to drive her on ramps so I can change the oil/filter (last oil change to confirm no more coolant in oil, just replaced lower intake gaskets). She fired up and idled nicely. Even though I didn't drive it, KOEO - Code 11, KOER - Code 21 (she not at temp so expected this one). I have a smoke test scheduled with a shop down the road for Friday (no time to build my own). I'll bring it just to rule any air leaks out.
 

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Discussion Starter · #60 ·
you had a code 23 in your first post, this issue is NOT new, it just turned into a hard fault causing limp mode

changing TPS didn't do it

a shop with an old snap on scan or with a eecIV adapter should be able to verify

the ecm is the only thing left to diagnose.
The shop that is doing the smoke test for me on Friday might be able to help. I'll give them a call and see if they can handle it. I'll put together a nice write up for them on what was performed. Might go a long way to help them out. Thanks again Indy and also Hybred for your assistance. Learned a lot and would not have gotten this far without you.
 
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