Sputtering Below 2k Rpm

Discussion in 'SN95 4.6L Mustang Tech' started by gotchopsticks, Jul 9, 2014.

  1. Hello all, been a few years since I've posted here, but I'm running into some problems with my car. 2002 GT, 5 speed, 102k miles. I noticed a few thousand miles ago that I was having some trouble accelerating below 2000 rpm. It seems as if I'm flooding the car if I give too much throttle, but if I try to make it sputter/bog down above 2k rpm, it accelerates no problem to 6k. It does seem to have a little more difficulty getting to red-line than before, but that can be expected after 100k miles. My first thought was rotten spark plugs, but they were changed around 55k and looked fine when I changed them. I have a clean K&N and already tried cleaning the MAF. I have tried removing the Predator tune with no effect. Ford is telling me it's the fuel pump, but I wanted to get a second (or more) opinion on the matter. I changed the fuel filter at 85k with OEM filter.

    Bottom line: if I ease into the throttle <2k it is fine, but if I'm at, say, 1600 rpm and give it too much throttle it acts like it wants to die and bogs down. Above 2k rpm however, it runs like a dream, but with a weird power band that surges multiple times. Clean air filter, clean MAF, tune & no tune (tried both), and tried different grades of fuel. Thoughts? Thanks in advance!
  2. Pull codes please and report your findings
  3. madspeed, no codes. I ran the car with the live feed on, fuel rail pressure was 42-45, timing went from +40 to +15 or so depending on the RPM, but no codes. No misfire, no pre-detonation, nothing. Could it be my TPS? The car miscalculating the proper air/fuel mixture for how open the throttle is? Also, not sure if this is related or not, but on a cold start it take much longer to start than it did 20k miles ago. I'll crank it for like 5 seconds or more before it actually fires and starts, even after priming the pump/rails several times.
  4. How old are your spark plugs?
  5. madspeed, my plugs have around 50k on them. I checked and cleaned the connection between the coils and plugs, and the signal wiers for both the COPs and fuel injectors. I usually run Lucas fuel injector cleaner every 10k or so on a full tank of gas. Advice from the dealer (without diagnosis) is that the fuel pump is failing. My first thought was plugs because I know it runs a little rich due to 2 cats being cut out, and the original owner didn't have them at time of sale, and the Pred tune which turned off the rear bank O2 sensors...but it passes smog. Could running slightly rich cause my plugs to fail this soon? Not sure if it's related, but I average 27 mpg on the hwy with 87 octane at 75mph....
  6. 50,000 is more than I'd ever go on a set of plugs. Plugs are cheap
  7. Sounds nothing like a failing fuel pump to me
  8. Sounds nothing like a failing fuel pump to me.

    50,000 is more than I'd ever go on a set of plugs. Get some fresh plugs in there
  9. Agreed. I have a 2002 GT. Same story, plugs is what it needs. Motor craft will do just fine but go with Bosch 4 if you want the better spark.
  10. Ok, that was my initial thought. Thanks guys, I'll report back if the problem continues. Any thoughts on if the plugs could also be causing the starting issue? The fact that on a cold start it takes 5 seconds or more of cranking, but on a warm start it fires up normally.
  11. Spark plug change fixed the problem. She runs like a dream again. I did not know that I needed to change the plugs so often, and the service advisor at the dealer said they should be good for 100k and I was wasting my money having them changed (I have a helicoil in 2 plugs and didn't want to take the change of accidentally pulling them out). It was a good choice taking the word of the members here, thanks again all!