Ford Mustang Forum banner

surging and bucking

2K views 4 replies 4 participants last post by  my89foxbody 
#1 ·
I did the search, so decided to ask the question. My 93 Cobra, Mods are KB2.1 Flowzilla, MSD distributer and Coil, everything else is stock, well cam from a 89 5.0, but everything else stock Cobra. I have bucking and jerking at slow speeds with light throttle. More noticeably around 1500 RPMs. Good acceleration, but once it reaches speed and cruising, I can feel/hear a skip here and there, but worst at low speeds. One more thing it does, while normal accelerations, once it reaches speed, it seems like everything stops as if I remove my foot off the gas, very noticeable, like it is hitting a limit or something. In third gear it is the worst, I go through the gears, hit third, once it reaches a point where the acceleration should stop due to throttle position, it seems like it just hit a headwind, like instantly. I don't know what is causing this. I have new plugs, wires, IAC, and TPS. Reset idle, TPS at .96. Also cleaned the MAF with MAF cleaner and cleaned the throttle body thoroughly. VAC holds steady at 17-18. I tried looking for vac leaks, none to be found (used the propane and carb cleaner methods) It idles kind of roughly, it will skip here and there, but sometimes it will stumble so bad, it will almost die, then rebounds. sometimes I start it and it will die instantly. If you experienced this, chim in and let me know what you done to fix it. My next step is to pull the dizzy from my other cobra and see if the MSD distributer or coil is giving me the issues. After that, maybe putting in my 60lb injectors and remove the 24s. Any help is appreciated.
 
See less See more
#3 ·
Ive definitely heard of alot of guys having issues because of their MSD components.I would definitely swap distributers since you've got another one close by or you can test the TFI module & pip sensor first before swapping.The link shown below will help.
Have you tested the TPS through its whole range of motion?? The TPS is bad about developing dead spots.Turn the key on,connect the multimeter leads to the same TPS wires you used before,slowly open the throttle from the closed to wot position while watching the meter.Voltage should increase smoothly.Do the same test,but this time,lightly tap on the TPS with a screwdriver handle & look for any voltage spikes or dead spots.If any are noticed during either test,the sensor is bad.
I would also test the egr valve to make sure its not opening when its not supposed to.When the valve is open,the ecm leans the fuel mixture & advances timing.Those are two things you don't need at idle or when accelerating.If you remove the vacuum hose from the egr valve & plug it,the ecm will delete its function in the logic & the ecm will set the fuel mixture & timing back to normal values.So just remove its vacuum hose & plug it then test drive the car to see if the symptoms disappear or continue.If they disappear,that means the egr valve is sticking open or the evr solenoid is defective.The evr solenoid supplies vacuum to the egr valve.
It might also be a good idea to run koeo & koer tests to see if any sensors are triggering codes.You can use a jumper wire & the check engine light to run these tests.You don't need a scanner.Just insert one end of the jumper wire into the STI terminal & the other end into the signal return terminal on the VIP connecter, turn the key on and start counting the flashes on the check engine light then write them down.Post any codes you get on here.
***Make sure you connect the jumper wire to the GREY STI terminal,not the BLACK underhood light terminal.If you use the underhood light terminal,youll burn the signal return trace on the ecm,as soon as you turn the key on to trigger the koeo test***
The connection diagram shown below will help.
SBFTech.com TFI Module/Hall Sensor Testing Procedure
 

Attachments

#4 ·
I have a diagnostic test set for my car. I ran codes and none registered. I have replaced the TPS and tested the entire sweep, don't seem to be any issues there. EGR valve is inoperable. I have it connected to keep check engine light off, but no vaccum is attached. I switched out the MSD dizzy with an OEM one, idle is much much better. I will use it for the next few days to see if it is better or the same while driving it. It's been burning more fuel lately.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top