[osmax12]

I am new to write here, but I,ve been in the background reading for some monthe now. I recentley bouht a 98 mustang GT and have been trying to get it to run right. It feels like it's not gettin' the fuel at anything over about 4500rpm. The power comes in and out like somebody playin' wit the light switch or something! I've changed 1 fuel injector, replaced the all plastic intake manifold, changed spark plugs, fuel filter, added a 75mm throttlebody w/ plenum. We've got a mustang guy down here in Louisana (custom shop), who says it might be the fuel pump. Is this true? I'm lookin' for Casper to answer, or anybody for that matter to give me a clue on this problem-Thanks!

[96Snaker]

Yes, it could be a fuel pump problem, however if that were the case you'd notice a significant power loss throughout the powerband, not solely above 4500 rpms. Might try cleaning out your IAC valve, and replace your fuel filter, as those are good starting points. If you bought it used and have no idea about its history, possibly someone tried tuning it and screwed up the timing. Who knows. Good luck, and welcome to MM btw.

[Casper98GT]

Well you started in the right areas and have replaced almost everything possible. Next thing i would do it put a fuel gauge on it and drive it. Check to see where youre loosing power and if youre fuel pressure drops off. You could have something in more than just one of youre injectors and like you said a possible fuel pump. I had one that i would go fine in the cold and once it warmed up i was limited to 2500rpms. Then it finally just wouldnt start.

Just a question....how did it run before you started modding it ?

Are the plugs the right ones? I wouldnt EVER use Bosch by the way, i dont know what you use. But just letting you know. I would have guessed fuel filter from youre first few lines, but i know you already replaced it. So next step would be make sure you have fuel when its occuring.

[osmax12]

I did use the Bosch plat +4 plugs, and so far it's running better than when I got it.....I've been through 3 sets of plugs! It came with motorcraft plugs so thats what I put back in it at 54 gap and it ran horrible- but they told me to set the gap at .054 so thats what I did. The plugs came at like .41 gap=was I suppose to leave them at that setting? Anyways I went to Autolites, then these Boschs because you can't set them. (nothin' to mess up!) IT can't be nothin' else but the fuel pump...I guess.

[Casper98GT]

yeah motorcraft plugs you dont regap, they come pregapped. Sticker under hood with engine info will tell you the gap setting.

[osmax12]

how hard is it to get that fuel pump outta there?

[96Snaker]

I haven't yet needed to take my fuel pump out from the stang, however I did in my Probe's and it took a couple of days for I didn't realize how hard the job is to do from lying on the ground (ie, no car lift). It sounds pretty simple, run your gas until near empty, deplete the fuel pressure (not hard at all), then unhook your fuel lines, drop the tank and poof there's your fuel pump. I would recommend you get the car on a lift for I almost killed myself when the tank fell on me as I had no assistant handy to help lower the thing. Re-installing a new pump was just reversing the steps.

Now I'm sure this probably isn't of much help, sorry bout that, but it was my experience that this job was of no fun to do and next time, if there is a next time, I'm taking it to a shop for sure. lol

[Casper98GT]

You dont need a lift or a shop. You can do it on the ground. Mustangs are pretty simple. Few hours on the ground. Just put a jack under it. remove the strap bolts, one on each side, remove the filler neck ( make sure you get a filler neck gasket, they always leak ) then drop it lower, disc onnected all evap lines and fuel lines. Then drop it all the way out, get a new metal snap ring too and pump gasket. then get a screwdriver and tap the ring out counterclock wise, yank the pump/sender out and swap...reverse install