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Discussion Starter #1
1998 mustang gt...125k....h-pipe....flowmasters....cold air.....shorty shifter....pretty basic.

so as before i have this random misfire and she is still coming back.

I've done it all plugs,wires,egr,iac,vac lines,maf clean,fuel filter,fuel additives, clean air filter, vac solonoid, leak checked intake with carb cleaner.

1. what fuel pressure should i see at the rail?(im trying to catch it when it acts up)

2. how to test injectors...both injectors them selves and plugs to make sure there getting a good signal.(im trying to catch it when it acting up)

3. could a bad fuel pump that acts up randomly cause this? Even if it shows good pressure( it would be a long shot to catch it when its running like crap)

READ BELOW

When she acts up she only likes to idle at 500-700rpm and there is a EXTREMELY loud knock in the engine, you can hear the valves or something clear as day 10ft away....when she runs fine there is no noise and no problems what so ever, full power and torque when running fine.

I'm going to change plugs and wires again to make sure i didn't get a bad batch.

The fact that it goes away when your 95% throttle in any gear and you can literally be at 90% for minutes and minutes and the second you push a little more its like it wakes back up.

What all kicks in 100% when you floor it? EX: max fuel pressure and full juice through plugs and wires...

Also if you live near the little rock air force base area, i'd be glad to come show you what it does in person with a test drive.

Any help is welcome.....guess's welcome to as long as they don't cost me
$$$ :bigthumbsup


-Kubic

p.s. I have full use of any and all tools, lifts, jacks, and whatever autozone has to rent tester wise(fuel pressure, compression ect)
 

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1) Fuel pressure should be right near 40 psi, +/- a few, at idle and under load. And shouldn't fluctuate by more than a few lbs when transitioning between idle/rev/load conditions.

2) Not sure.

3) Anything's possible, but I tend to believe that if a fuel pump is weak or acting up that it would be fairly consistant and not random.

Do you have a check engine light on? Checked the code(s)? If so post them. Does it flash semi-rapidly during the occurrence of the misfire?

I don't wish for you to jump to conclusions and go spend money based on a hunch, but at this point I wouldn't rule out the possibility of one or both coil packs being bad. Intermittent misfires, like most other misfires, tend to be ignition component related at least 90% of the time. The fact that yours is intermittent/random makes me think that it is non-mechanically related (fuel pump, vac leak, etc.) as something mechanical would be more likely to do it all the time regardless of load/idle etc. The problem is that without a dtc to pinpoint what cylinders or side of the engine the misfire is occurring at, it's kind of a guess as to which coil pack possibly needs replaced. I went through this same issue myself a few months ago; random misfire, no dtc, tried all the same sh!t you did. I was able to diagnose it finally as bad coils, but how I did it was I swapped coils with another Mustang. His car ran like crap with my coils and mine ran like a raped ape with his. If not for being able to borrow coils from another car though, I would have just been buying replacements as a last resort guess.
 

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Discussion Starter #3
Sorry forgot to mention both coil packs are brand spanking new not even 500 miles on them..

Cam sensor the same way.


Im going to replace wires and plug again just to.be sure...but like i said almost the entire ignition system is new.

Code wise it throws o2 down stream due to h-pipe and before these id have a lean on bank 2 code come up when hard hard on the gas.

Il get it run again today and post them

Thanks for the socalv2 will post back tonight
 

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Discussion Starter #4
codes are as follows.

p1152
p1151
p1443
p0420
p0430
p0171
p0174
p1150

was told to go get a diagnostics done by ford to see if they can pin-point what exactly it is...but $116 is steep....especially if it throws codes regardless because of h-pipe


could me not having down stream o2 sensors be causing this? o2 mil deletes im guessing is a good place to start.

also i ran through all the vac lines...not one leak or break and it has very good suction coming from hoses.
 

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Discussion Starter #5
Ok just ran pressure test on fuel.

30 key on

32 when reving pretty hard.

When vac line on regulator pulled 40.


Im not fuel expect so please chim in.
 

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1997 mustang gt with same prob

hey my wife has been talking to you about my mustang haveing the same problem for the past month or two i have the 97 gt and i have put the o2 mil eliminators on back then front but no change i have replaced the pressure reg maf an basically the same stuff as you i am stumped the codes that pop up for me from auto zone is o2 sensor because i have no cats bad maf fpr and dirty injectors cleaned the injectors not through a mechanic though and replaced the others plus more like you the iac vac lines ect but still in the same boat it seams that it has eased up a little bit lately but when it acts up it seems to last longer and when shes idleing during that time i have the knock as well i dont know honestly im getting to my point with it i honestly am i really hope we can figure this out because im running out of time money and patience and if you want you can email me directly "the husband" at [email protected]
 

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hey my wife has been talking to you about my mustang haveing the same problem for the past month or two i have the 97 gt and i have put the o2 mil eliminators on back then front but no change i have replaced the pressure reg maf an basically the same stuff as you i am stumped the codes that pop up for me from auto zone is o2 sensor because i have no cats bad maf fpr and dirty injectors cleaned the injectors not through a mechanic though and replaced the others plus more like you the iac vac lines ect but still in the same boat it seams that it has eased up a little bit lately but when it acts up it seems to last longer and when shes idleing during that time i have the knock as well i dont know honestly im getting to my point with it i honestly am i really hope we can figure this out because im running out of time money and patience and if you want you can email me directly "the husband" at [email protected]
Hmmm, I'm just such a sucker for a good threadjacking.

First things first, keep the MIL eliminators on the rear sensors. The front sensors are crucial to engine management, whereas the rears simply measure catalyst efficiency; meaning that if a dtc related to the rear sensors is triggered there will be no driveability issues.

But let's get to the real stuff. What code(s) are you getting? If the code is for the rear sensors, then that's not your problem. Post back with the code.

Next, to what lengths have you gone toward solving the issue? Have you already ruled out the simple stuff like spark plugs and whatever?

I advise that you start your own thread for this, as your question will get more attention that way instead of being buried in someone else's thread and also so that this guy's thread stays on topic relative to his issues. In said thread, try to answer the questions I gave and also any details you can give might be helpful. See you on the other side.
 
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