Help! Surge on Cruise Control Only??

[87hd]

Hi All,
I have a 93 GT 5-Speed, I bought this car yesterday, so I don't know a lot about it. I know it has Ford Performance Shortie Headers, UnderDrive Pulleys (unknown brand), Tri-Ax Short Throw shifter, Moroso Cold-Air intake into the fender well, MSD cap/rotor, Screamin Demon Coil Pack, Dynamod ignition module, BBK 65mm Throttlebody and EGR Spacer. I have no check engine light and it starts, runs and idles great. I have no surging except with the cruise on. It only goes up and down maybe three miles an hour but it does it rapidly, aggressively and over and over until I shut off the cruise control. I have adjusted the cable at the throttle body end to remove any slack, no affect. I have not inspected the check valve or looked inside the fender at the vacuum connections yet. Any divine insight?

 

[gt90stang]

Don't know in your case. I added SC and built motor and my 90GT cruise still works great without surging.

I had an 82 Suburban 6.2L diesel and added a Turbo and it surged while on cruise control, so I had to remove a small restrictor plug that was in the vacuum port on the cruise module. It was a plug with a small hole that was pressed into the vacuum port. Removing this plug stopped the surging because it increased the speed of the cruise controls compensation.

I've never torn apart the CC in my GT so don't know if this is applicable.

Good Luck, Don

 

[jrichker]

Dump the codes, look for codes 27, or 29 which are VSS sensor problems. Don't replace the sensor unless you get the codes. Throwing parts at a problem just makes you poorer and aggravated.

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

See http://www.troublecodes.net/Ford/
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

IF your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

For those who are intimidated by all the wires & connections, see http://www.actron.com/product_detail.php?pid=16153 for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Walmart.

Or for a nicer scanner see http://www.midwayautosupply.com/detailedproductdescription.asp?3829 – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $35.

 

[87hd]

Thanks, I'm gettin' there!

I used your jumper wire technique, worked great once I found the right wires. Apparently a previous owner liked to modify wiring harnesses. I had a code 26 and a code 27. I checked the vacuum line going from S/C to the fenderwell and the check valve. I have a friend at a local Ford garage who is going to look inside the fender today. Hopefully he will find something.

 

[87hd]

Oh, well...

It looks like it's the servo. Unfortunately ford no longer sells it and no one makes an aftermarket one. I found a used one, I hope it doesn't leak too.