My 1989 mustang lx 5.0l started out of the blue surging while driving the Friday before last. I was on my way home and it just started bucking and surging.

In the last week I have:

-swapped maf sensor
-swapped ECT with a known good one
-bought new wires
-swapped distributor
-checked all plugs (which have 1500km on them)
-checked fuel pressure (42 with line off / 36-38 with line on)
-swapped coil and replaced coil plug that was falling apart
-changed positive battery cable with a new one
-new fuel filter
-new cai fender style
-tried driving with iac unplugged
-played with timing everywhere from 9-18 degrees
-put on fuel injector cleaner today

There is some more stuff but I can't think of it right now. Surges and has a lack of power anywhere below 2500rpm but not all the time, sometimes I can drive somewhere and it works fine and other times im not even a kilometer down the road and it does it. The motor was completely rebuilt 1500km ago and worked perfect til it started surging. I only use 91 octane fuel which is the highest we have around here. I'm running out of ideas quickly. I mean i'm getting to the point of switching to a carb setup and saying screw efi. So any help would be greatly appreciated.

my friend just mentioned the fuel pump relay could possibly be getting hot. any ideas?

 

Take the EGR sensor off the back of the EGR valve and shave 1mm off of the pintle with a bench grinder, reinstall it and take it for a spin. See what happens.

 

forgot to mention, egr is deleted.

 

have you checked tfi could be going bad

 

i swapped distributors with one in a car that ran perfect. I too assumed a possible tfi failure but the new distributor didn't change anything.