I just installed an RPM Extender in my 94 GT that was designed for a fox. Is it normal for the car to run rough at first? The car starts and drives but it is running rough. I figured this is just normal after unhooking the computer. I had my a/f ratio at 12.5 then upped it to 13 but no change. I have only driven the car a few miles so far.
Installed RPM Extender, questions????
- Thread starter cmozez
- Start date
ProCharge94
20+ Year Stangneter 
Your ECU needing time to adjust should not make your car run that rough. You may want to make sure you didn't accidentally unplug some vacuum lines or leave something still disconnected.
HoofnIt
Founding Member
It is my understanding that an extender made for a FOX will NOT work on our cars. The computers are different. I think this is your problem.
dstanggt50
Founding Member
HoofnIt said:
When I bought my extender I think they asked what year, maybe the fact that it was for a fox that you are having problems?? When I connected my extender, my car might have acted funny for about 10 min, but it corrected its idle. The instructions also say that the extender doesn't operate until full throttle, or over 4000 or so rpms, ( don't remember exactly). Also, don't know if this is true for the fox extender, but the one for the 94-95 adds 4 degrees initial timing, I had some issues, backed the timing down, runs a lot better. Also, I think they even want you to run an aftermarket ignition w/it as well.
94CobraPace
Founding Member
The fox extender is different than the 94\95's & would probly make the car run bad. Did you unhook the battery when you installed it? Should have. The fox extenders take over at 4k, the 94\95 extender takes over @ 2500 rpms, I can feel mine swith when not driving hard\fast, just going over 2500 rpms & cruising.
OrangeMustangGt
Founding Member
Its a black box that plugs inbetween the ECU and main harness. It gives more aggressive fuel and timing curves, gets rid of the annoying timing retard inbetween shift, and allows you to set the a/f ratio and rev limiter. It was made by SVO back in the day (date on mine was from 95 
), but theyre not made anymore. Best bet is Ebay and classifieds. I got mine for $250 2 months ago from the Corral classifieds. A couple weeks ago though someone posted that they were selling theirs for $100.
), but theyre not made anymore. Best bet is Ebay and classifieds. I got mine for $250 2 months ago from the Corral classifieds. A couple weeks ago though someone posted that they were selling theirs for $100.Damn fellas, that was almost five months ago that I posted this question, I guess better late than never! Heres the skinny.... I took the extender for the fox body out and sold it and got one 94-95 specific and all was good. I am very satisfied with it.I got $280 for the fox extender on ebay and bought an sn-95 extender for $190 on ebay, I thought it would be the other way around but not so. I have a PPI ignition package on with the extender, it has really woke my car up. Highly recommended.
dstanggt50
Founding Member
fastf50rd said:
When I first started looking up info on it, the test car I read about was a 95 cobra w/a vortech. It had a boost ret. and turned timing down. I had timing set to around 14-16 s/spout out, and backed it down to about 8-10, so w/the extra timing (4 initial) from the extender, should be around my 12-14. I think though most would recommend a different type of piggyback w/more features. (maybe pms or tweecer, ect..)
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