98 Mustang Gt Engine Hesitation Problem Can't Figure It Out

Tgriff27

New Member
Nov 24, 2014
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I have a 98 mustang gt, when warm or driving after about 30 min it will start like bogging down. Won't rev over3000-4000 rpms, I'll shut the engine off while rolling down the road and restart and it'll run fine for about 10 min then start doing it again. I just rebuilt the engine, also did it before that. So I changed fuel pump to Walbro 255, new fuel filter, fuel pressure regulator. And it's still doing it, I'm about to change injectors to 24lb. I have no idea what it is and everyone I talk to have no idea. I've read other posts on here that have the same problem but no one posted there results in the end.. It's been a year or more just want it fixed! Then it'll berunning perfect.
 
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Yea there's quite a few codes. O2 sensors of course, running longtube headers straight to 40s. But those shouldn't make it run this bad. If I'm right think DPFE sensor code, evap purge valve, been a few weeks since I've last checked but I think that's what they were called.
 
Plugs were replaced when the engine was rebuilt bout 10,000 miles ago. Wires were on it before I bought the car so not for sure, but they're aftermarket and look pretty good. What about that cam position sensor?
 
If there are "quit a few" codes, it seems silly to try to trouble shoot this without knowing WHICH DTC codes are being thrown. There are 1000's and they each have a story to tell.

A DPFE/EGR related code could cause the symptom you are reporting from excessive EGR flow.

A bad alternator diode (excessive AC ripple) could also cause the symptom. A bad alternator will CAUSE cam related DTC issues. It's short sighted to not test the alternator as almost any auto parts store will test it on the car for free.

With knowing what's really going on, changing to larger fuel injectors could actually make this problem worse.

Consider that the 98 MY Mustang uses a two speed fuel pump. Do you have any idea which speed the fuel pump is in when this problem occurs? What if the fuel pump is stuck in low speed? If true couldn't this explain why the motor won't rev above a certain point? It would be helpful to know the fuel pressure when the problem occurs.
 
My 98 GT was doing about the same thing. It would warm up to operating temp and start skipping and bogging. I changed out the plug wires and the issue went away. They must have had a small crack in them that would open up and misfire once they got heated up. Also, the vacuum hose behind the throttle body coming loose or having cracks caused mine to act very strange.
 
I also have a 98 stang with same issue. So far cleaned maf sensor, throttle body cleaned, new plugs wires and coils. Fuel pressure only coming in at 28 at idle and 38 with vacuum line off. Bought new fuel pump and filter. Looking to change that very soon, and may check alternator next. Will post results if fixed.