Ford Mustang Forums banner

21 - 40 of 60 Posts

·
Registered
Joined
·
1,939 Posts
A vacuum leak can be more than vacuum hoses. Like mentioned, a smoke test doesn't lie. I found a lower intake leak using a smoke machine. A visual look would have never found that.

Sent from my Moto E (4) Plus using Tapatalk
 

·
Registered
Joined
·
25,013 Posts
NO, you dont do resistance checks

you do, voltage drop, energized circuit
 

·
Registered
Joined
·
1,124 Posts
Discussion Starter · #23 ·
A vacuum leak can be more than vacuum hoses. Like mentioned, a smoke test doesn't lie. I found a lower intake leak using a smoke machine. A visual look would have never found that.

Sent from my Moto E (4) Plus using Tapatalk
I just finished installing new steel core lower intake gaskets a week ago due to finding coolant in the oil and oil leak in the back. Highly doubt I have a leak in the lower. It's acting up exactly the same as before I did the gaskets. I'll most likely call some local mechanics and inquire about getting a vacuum check done. I don't have a bad idle for long. After the car is warm and I stop, when I start, it hunts down low and sometimes stalls. Once I get the car moving and I stop down the road, it idles smoothly at ~750 - 800 rpm. It's just on that initial startup when at operating temp.
 

·
Registered
Joined
·
1,124 Posts
Discussion Starter · #24 ·
NO, you dont do resistance checks

you do, voltage drop, energized circuit
Just came back from a 50 mile trip and tested again key on:

TPS (idle) - 0.671V
Pin 47 - 0.054V. This time I had the black lead at the battery -ve and used some 14 gauge copper jacketed wire in pin 47 to my red lead. As you can see from my measurement, did not work. It's almost 40C here with the humidex so I'm done farting around with this POS.
 

·
Registered
Joined
·
25,013 Posts
not sure what you did there, farting around sounds appropriate

but its nothing i suggested

do you know what a voltage drop test is?

what does the heat have anything to do with it, suck it up buttacup!
 

·
Registered
Joined
·
1,124 Posts
Discussion Starter · #26 ·
Here's a pic of probing pin 47 and touching chassis ground. This gave me my best reading of 0.22V.

IMG_2745.JPG
 

·
Registered
Joined
·
25,013 Posts
. I don't have a bad idle for long. After the car is warm and I stop, when I start, it hunts down low and sometimes stalls. Once I get the car moving and I stop down the road, it idles smoothly at ~750 - 800 rpm. It's just on that initial startup when at operating temp.
why ask for help, if it dont bother you?

there is obviously a problem, if you want a quick easy fix, take it to a shop and pay for the repair
 

·
Registered
Joined
·
1,124 Posts
Discussion Starter · #29 ·
Ok now we're getting somewhere! Like when I tested the TPS, I was under the impression that by probing PIN 47, I should be seeing more or less the same voltage I did at the TPS. What exactly did I do wrong?

If this idle issue didn't bother me, I wouldn't be asking. Yes you're correct I could simply go to a shop, tell them I have a code 23 and fork out $$$ to have it repaired. I'm not like that and enjoy figuring things out and having the satisfaction of solving the issue myself. I'm just looking for a systematic approach on how to tackle this issue. Now that you saw my pic and obviously I pooched the test, what is it that you recommend?
 

·
Registered
Joined
·
491 Posts
Indy wants you to perform that test with the ecm connected and back probe or use a pick or sewing pin to pierce the wire of pin 41. key on engine off. Compare voltage to your previous test of the TPS directly.
 

·
Registered
Joined
·
25,013 Posts
everything connected

key in run

backprobe the signal at the ecm, the other lead at neg battery post

what is the voltage?
 

·
Registered
Joined
·
4,079 Posts
Systematic approach
  • probe TPS voltage properly
  • perform voltage drop test properly on positive & negative sides of the circuit
  • perform your own smoke test


Once I get the car moving and I stop down the road, it idles smoothly at ~750 - 800 rpm.
idle RPM is 675
Idle is not adjustable.
Your idle is High. Vacuum leak or someone has turned the throttle stop.
 

·
Registered
Joined
·
1,124 Posts
Discussion Starter · #33 ·
everything connected

key in run

backprobe the signal at the ecm, the other lead at neg battery post

what is the voltage?
Ok now I get it. I put a safety pin in pin 47 connector while EEC connector installed. Got long piece of 14 gauge copper from my negative battery terminal to inside the car. With key on, red probe on safety pin and black on copper, I now read 0.681V which is very close to the voltage I read at the TPS earlier on (0.671V). Looks like EEC is seeing exactly what the TPS is reporting which is a good thing!

IMG_2747.JPG
IMG_2748.JPG
 

·
Registered
Joined
·
1,124 Posts
Discussion Starter · #34 ·
Update: After confirming that the EEC was seeing the same voltage as the TPS, since I had code 23, I thought maybe the 0.671V out of the TPS at idle was too low so I purchased a new Motorcraft TPS. I put it in today and checked the voltage (key on) and read 0.822V. For fun, decided to oblong the holes on the old sensor and see what kind of voltage I could get and I set it at 0.966V. Went for a drive to get the car up to temp and I also stopped a couple of times to shut off the motor and start it up. My stalling issue has gone! I did notice my idle to sit around 900 RPM (up from the 750/800 I had before, did not touch the idle screw). I ran the KOEO test and my code 23 was gone but now I have a 63 O, C. When I ran the KOER I got 98 (operating in failure mode) and 63. I removed the modified sensor and installed the new one, used my code reader to wipe out the continuous memory and drove it again. Idle still sits at 900 RPM and same codes appeared after running KOEO and KOER. Maybe it's something to do when I disconnected the EEC with Key on (incorrectly performed voltage check)? I had the negative cable off before reconnecting the EEC and was off for a few days.

Thinking of retracing my steps and probing PIN 47 again to make sure it sees the 0.822V. If it does, not sure what else to do. Expecting to have no codes, I was then going to perform a vacuum leak check (saw some good home made smoke testers I'm going to make). Thanks guys for your patience.
 

·
Registered
Joined
·
25,013 Posts
are you the original owner, and can confirm the stop has never been touched since it came off the assembly line?

and with regards to where you see it idle

if you cannot see what the ecm is commanding for idle speed

you will NEVER know if it is correct or not

so ignore any temptation to say if idle is correct or Not

its NOT a carb, you CANNOT adjust it with a screwdriver
 

·
Registered
Joined
·
1,124 Posts
Discussion Starter · #36 ·
Thanks Indy for the reply. Just checked PIN 47 and it sees the same voltage as the new TPS. I've had the car for 21 years (3rd owner) so I cannot vouch that the stop was never touched since new (I have never touched it). I know the previous owner so I can try asking him (he's a mechanic).
 

·
Registered
Joined
·
25,013 Posts
I can guarantee its been jacked with
 

·
Registered
Joined
·
4,079 Posts
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.
 

·
Registered
Joined
·
1,124 Posts
Discussion Starter · #39 ·
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.
 

·
Registered
Joined
·
1,124 Posts
Discussion Starter · #40 ·
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.
Could very well have a leak and that is something else I was going to check until I ran into code 63 and 98 after installing a new TPS. This engine is bone stock except for EL headers (yes still SD).
 
21 - 40 of 60 Posts
Top