Need serious help

[JDwhite98gt]

well I'm posting this again because I cant figure this out. Bought a 98 gt about year and a half ago, had pi heads, cams,intake and it kept smashing sparkplugs and it would breakup at the top of the rev range. I had a full 03 motor sitting in my wrecked stang so I said F it and swapped it in. Ok, now whats confusing me is that the car still breaks up, feels almost like a missfire of complete loss in power. For example, if I stop a red light, take off, bang through first four gears feels very strong(except my clutch is on its way out so torque feels low), I stop accelerating and let fourth whine down from 4k rpms to 2.5k rpms(for example) and get back on the gas, the car will momentarily stop responding like the the throttle body is not opening or no fuel is being pumped in and then suddenly its as everything is fine. Now I have a fuel gauge tapped into my fuel rail and it reads about 28 psi at idle, full throttle is about 35 psi and when the issue happens the gauge still reads about thirty I think I'll have to take a trip and try to make it happen because it is intermitent. I have replace plugs, wires, fuel filter, cleaned maf, IAC, throttle body and plenum. I checked for spark out of the CP's they are still strong..somehow(they are old). So something is wrong with something that stayed on the car despite the motor swap all I can think of is a bad ground somewhere or maybe fuel pump but wouldnt the fuel pump make the pressure drop off at other times? Pressure stays steady so WTF? HELP PLEASE.

 

[glittle75]

i would say fuel system. start from the injectors and work your way back. maybe clogged injector(s), maybe bad injector wires that are shorting/grounding at high rpm's. then look at the lines all the way back, and then check or replace the fuel pump.

 

[JDwhite98gt]

how do I check to find a clogged injector? Is there a way to test the fuel pump? I know it doesnt whine really loud like my last car when I first turn on the ignition. I've been advised that since my cars fuel pressure doesnt drop at any rpm it's most likely not the pump.

 

[DropTopPony]

when you check the CP's is it at idle? Maybe they are breaking up at higher RPM's. A new set wouldn't hurt just to cross that off the list.

 

[JDwhite98gt]

Well honestly money is tight so if there are ways to really test the stuff before replacing that would be ideal. And yes I've only tested at idle, but if it was the COP's wouldn't the breakingup happen more often than every once in a while? And it doesnt happen when I'm on the throttle. Only happens when I stretch out the gear, let it coast (while in gear) and then go to get back on the gas.

 

[JDwhite98gt]

Anything else guys?

 

[glittle75]

coil packs aren't to expensive. 50 bucks each for stock replacements. do you have a friend with a mustang? see if they will let you swap coil packs and see if it still does it. its 4 small bolts and a couple plugs off the wiring harness. then you could eliminate that.

so far as your injectors, i would check for a leaking / clogged one. one way to check for a leaking inector is to take the injectors out of the ports in the intake, but keep them on the fuel rail, i.e. connected, but not in the engine. have someone turn the key to the 'on' position, but not crank it, so it primes the fuel system, and pressurizes it. look at the injectors and see if one is leaking, dripping, etc.

for clogged injectors, you can run some fuel injector cleaner through your engine..........

OR, and try this at yor own risk.........

take the injectors off just like before but crank the engine and look to see if all the injectors are spraying fuel evenly. if your going to do this you MUST REALIZE that your injectors are spraying atomized fuel, you cannot smoke or have ANY ignition source remotly around you. the stuff will go up. i would even reccomend you bring your kitchen fire extinguisher out and have it by you just in case.

 

[JDwhite98gt]

yea I have replaced almost every part on a mustang since owning one since I was 17 so I know they're easy. I should have an extra one laying around but then I have to swap it, take it out on the highway go balls out and waste gas lol but guess I have to do what I have to do. Maybe it is a leaky injector...because it happens when I let off the gas for a few seconds, let the revs drop and then step back on the gas... maybe its flooding a cylinder? The car feels like its choking more than missfiring i dunno it's so irritating it could be almost anything :BangHead:

 

[reivaxtorres]

that sounds like a problem i had with my car......basically when i was on the gas (either at full throttle or part throttle driving normal), once i got off the gas and went back on it, it would hessitate a bit, almost as if i hadnt done anything, then it would kick in strong. the momentary pause lasts maybe about a second or so. i had my car tuned, and i never had the issue again.

 

[AaRoN]

I'm assuming you're using the coilpacks from the 98 motor. Those were the culprit that was eating up your plugs. Change'em.

 

[JDwhite98gt]

that sounds like a problem i had with my car......basically when i was on the gas (either at full throttle or part throttle driving normal), once i got off the gas and went back on it, it would hessitate a bit, almost as if i hadnt done anything, then it would kick in strong. the momentary pause lasts maybe about a second or so. i had my car tuned, and i never had the issue again.

THAT IS EXACTLY WHAT IS HAPPENING!! It's just weird that I didnt have this problem when this same exact motor and mods were on my 96.

I'm assuming you're using the coilpacks from the 98 motor. Those were the culprit that was eating up your plugs. Change'em.

Why are 98 coilpacks a problem because of age? My coil packs from 96 lasted strong untill I wrecked the car I assume they are still good.

 

[AaRoN]

that sounds like a problem i had with my car......basically when i was on the gas (either at full throttle or part throttle driving normal), once i got off the gas and went back on it, it would hessitate a bit, almost as if i hadnt done anything, then it would kick in strong. the momentary pause lasts maybe about a second or so. i had my car tuned, and i never had the issue again.

THAT IS EXACTLY WHAT IS HAPPENING!! It's just weird that I didnt have this problem when this same exact motor and mods were on my 96.

I'm assuming you're using the coilpacks from the 98 motor. Those were the culprit that was eating up your plugs. Change'em.

Why are 98 coilpacks a problem because of age? My coil packs from 96 lasted strong untill I wrecked the car I assume they are still good.

No,no. I was just assuming you weren't using the C.O.P.s. How do your plugs look?

 

[JDwhite98gt]

yea I didnt do a C.O.P conversion I never knew that was an issue. Plugs look fine last time I checked them. I opened up the gap slightly but none looked as if I was running lean or rich and I just sanded the tips of the electrodes. I'm just confused because this setup ran awesome in my 96. Ran a 12.9 @ 104 with the same exact mods and the sucker was strong. I swapped EVERYTHING from that car to this one except the fuel tank and pump which i should of at least kept. The plug eating issue was from the engine that was originally in the car modded by the previous owner. I took that engine out and junked it except for the heads and intake which I have packed away.

 

[Willis_98GT]

looks to be a tuning issue

 

[98mstanggt]

that sounds like a problem i had with my car......basically when i was on the gas (either at full throttle or part throttle driving normal), once i got off the gas and went back on it, it would hessitate a bit, almost as if i hadnt done anything, then it would kick in strong. the momentary pause lasts maybe about a second or so. i had my car tuned, and i never had the issue again.

Im having the same problem with my car right now only it does it sometimes and its like it wanna cut off at idle :dontknow: I think its my spark plugs

 

[JDwhite98gt]

yea mine is only sometimes. Dont know why anyone would think spark plugs...I mean to each its own maybe your problem is a little different but I've worked as a mechanic been around cars for a long time and this is not a plug issue. Possibly its coil packs but usually if there is a spark problem its under load. I can only recreate this problem by going balls out(and car is running strong) then let the car coast or rev down while in gear then get back on the gas either gently or hard. It hesitates, a totally different feeling then a missfire. I'm going to check for a leaky injector tomorow i think it might be that. Aaron if you have any more info about the COPs fill me in please.

 

[AaRoN]

yea mine is only sometimes. Dont know why anyone would think spark plugs...I mean to each its own maybe your problem is a little different but I've worked as a mechanic been around cars for a long time and this is not a plug issue. Possibly its coil packs but usually if there is a spark problem its under load. I can only recreate this problem by going balls out(and car is running strong) then let the car coast or rev down while in gear then get back on the gas either gently or hard. It hesitates, a totally different feeling then a missfire. I'm going to check for a leaky injector tomorow i think it might be that. Aaron if you have any more info about the COPs fill me in please.

PM sent. Those won't help any, unless it is in fact your coil packs that are bad.

 

[JDwhite98gt]

oh ok AARON you just threw me off before by saying that the coilpacks were the culprit. :dontknow: Anyways, thanks guys. I'll still check for a leaky injector but its never that easy for me...meaning I dont think I'll be able to figure out this problem without taking it to a dyno and seeing where and how I'm loosing power.

 

[98mstanggt]

The reason i think its my spark plugs cause i didnt start having this problem till after i pressure washed my engine then a couple days or so after that i was traveling and it start getting this problem and i assumed i got water in my plugs but if you find out what the problem is make sure you let me know

 

[AaRoN]

I just meant that your coil packs are the problem. Meaning, they're bad.