No Computer Codes

[Aaron]

For a while now, I've had that "oh so common" intermittant idle surge problem where after the car warms up, occasionally the idle will sit at 1500-1800 RPM's until I turn the car off and restart it again.
Well my plan was to follow the "surging idle checklist", but I can't get past dumping any computer codes.
I bought an Actron scanner http://www.actron.com/product_detail.php?pid=16153 to make code reading easy. However it's not doing anything. I know the thing has power - you can put a piece of metal between connectors as a test and it beeps. When I plug the scanner into the test ports, the light turns red, until I turn the key on (key on - engine off test). Then the light turns off - and does nothing - no light codes or beep codes.
Here's my question....The former owner of my car installed a Hypertech chip and I'm wondering if the chip installed will disable code generation in the computer. I guess if it's overriding pre-programmed tables, one could assume it WOULD NOT generate any codes, but I figured I'd ask before yanking it out. I'm sure it's not doing much anyways on my un-modified car, but I just never got around to taking it out.
Comments?

 

[jrichker]

The only way you will ever know is to remove it.

An idle that goes high & stays high until you turn the engine off & restart it is a sign of a defective TPS sensor.

 

[HISSIN50]

A chip will often toss a ROM error but codes should still be dumpable.

Here's some info about no code situations.

Good luck.

 

[Aaron]

The only way you will ever know is to remove it.

An idle that goes high & stays high until you turn the engine off & restart it is a sign of a defective TPS sensor.

That's what I was thinking too, but it's intermittant - shouldn't it ALWAYS be a problem if it's defective?

 

[jrichker]

That's what I was thinking too, but it's intermittant - shouldn't it ALWAYS be a problem if it's defective?

The problem is in part due to the carbon that the TPS is made of. It is nothing more than a volume control from a radio fancied up and made to fit. The carbon resistor element will wear and small flakes of carbon will collect around the slider arm. That changes the resistance and the voltage sent back to the computer. Cut the engine off & floor the throttle several times and all the loose carbon flakes get pushed off the end of the element and pile up. Sooner or later they will migrate back on to the resistor element's surface and cause problems again.

 

[Aaron]

A chip will often toss a ROM error but codes should still be dumpable.

Here's some info about no code situations.

Good luck.

Thanks for the info - I hope I don't have some of those problems - that will really suck.
I wonder if the scanner is bad? I didn't hear any relays switch on/off - NOTHING happened.

 

[Aaron]

The problem is in part due to the carbon that the TPS is made of. It is nothing more than a volume control from a radio fancied up and made to fit. The carbon resistor element will wear and small flakes of carbon will collect around the slider arm. That changes the resistance and the voltage sent back to the computer. Cut the engine off & floor the throttle several times and all the loose carbon flakes get pushed off the end of the element and pile up. Sooner or later they will migrate back on to the resistor element's surface and cause problems again.

Well - you're the man when it comes to diagnosing our cars - I'll check out the TPS first. Thanks!

 

[HISSIN50]

The problem is in part due to the carbon that the TPS is made of. It is nothing more than a volume control from a radio fancied up and made to fit. The carbon resistor element will wear and small flakes of carbon will collect around the slider arm. That changes the resistance and the voltage sent back to the computer. Cut the engine off & floor the throttle several times and all the loose carbon flakes get pushed off the end of the element and pile up. Sooner or later they will migrate back on to the resistor element's surface and cause problems again.

Joe, growing up, my Dad had an old transistor radio where the volume rheostat would allow crackly noise or even mute the speaker if you moved the knob a little. He'd spin the knob up and down a few times to clear it out. This sounds very similar.

 

[Aaron]

jrichker - one more question -

If I do have a faulty TPS, could that cause an intermittant hesitation problem while cruising @ 55-60 mph in 5th gear? That is another problem the car has at times. If I put it into 4th gear to get the RPM's up, it goes away.

 

[Aaron]

2nd question - should I spend $50 on a genuine Ford TPS, or is the $30 Autozone variety ok? I have an Autozone 5 minutes away, but some Autozone parts are a failure waiting to happen.

 

[jrichker]

jrichker - one more question -

If I do have a faulty TPS, could that cause an intermittant hesitation problem while cruising @ 55-60 mph in 5th gear? That is another problem the car has at times. If I put it into 4th gear to get the RPM's up, it goes away.

The TPS problems seem to manifest themselves more when you change speeds. Or maybe its just that you don't notice them until you change speeds and it doesn't happen like you would expect it to.

 

[afast93stang]

I had a similar problem with the Actron Scanner, I couldnt pull codes so I tried the wire method as described on this page http://www.troublecodes.net/Ford/ (look at the top left diagram)

What the problem was is that the scanner wasnt grounded enough to pull codes but I had to ground the jumper wire to the body so it would work. Doing this enabled me to work through and clear all my codes.

Just a thought...

 

[Aaron]

2nd question - should I spend $50 on a genuine Ford TPS, or is the $30 Autozone variety ok? I have an Autozone 5 minutes away, but some Autozone parts are a failure waiting to happen.

Bump

 

[ALMOST STOCK]

Here's my question....The former owner of my car installed a Hypertech chip and I'm wondering if the chip installed will disable code generation in the computer. I guess if it's overriding pre-programmed tables, one could assume it WOULD NOT generate any codes, but I figured I'd ask before yanking it out. I'm sure it's not doing much anyways on my un-modified car, but I just never got around to taking it out.
Comments?

I've have the Hypertech Chip in my car for over 6 yrs and the Actron ScanTool CP9110 for more than 5 yrs, and I've never had a problem getting codes or retrieving test codes after the test.
My best guess would be that I’ve scanned for codes 5 or 6 times and I’ve never had a problem.

 

[jrichker]

With the power off, measure the resistance between the computer
test ground (black/white wire) on the self test connector and battery
ground. You should see less than 1.5 ohms.

If that checks good, remove the passenger side kick panel and
disconnect the computer connector. There is a 10 MM bolt that holds
it in place. Measure the resistance between the STI computer self
test connector (red/white wire) and pin 48 on the computer main
connector.

Diagram courtesy of Tmoss & Stang&2birds

See the following website for some help from Tmoss
(diagram designer) & Stang&2Birds (website host) for help
on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine

The following is a view from the computer side of the computer connector.

 

[Aaron]

Well I replaced the TPS and I think I have a new car now!
I can feather the gas pedal very slowly and all hesitation and bucking is gone. The car idled at 800 RPM every time I stopped, and I think my RPMs are dropping quicker between shifts.
THANK YOU JRICHKER and HISSIN50 for all of your advice. You guys are awesome!
I'm going to work on my code dump problem next, but all driveability problems are now gone and that's a major relief!