92 Mustang Lx 5.0 not running right please help - Forums at Modded Mustangs
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post #1 of 23 Old March 1st, 2013, 12:37 PM Thread Starter
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92 Mustang Lx 5.0 not running right please help

I need some help, my 92 mustang Lx 5.0 convertable is not running good. It seems like a miss but every time it has a miss the fuel pressure drops as well. I have replaced the fuel pump, filter. Checked the relay, throttle senser destributer and coil and the timing is right new spark plugs and fairly new wires. Has anyone had this problem before problem before and can help me solve it before my head explodes? Has this happened to anyone and if so what is the fix? If you need more info ask and i will try to provide it.

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post #2 of 23 Old March 1st, 2013, 05:25 PM
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Post the video here


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post #3 of 23 Old March 1st, 2013, 06:29 PM
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wow, so many variables. Is the fuel pump losing power when the fuel pressure drops?

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post #4 of 23 Old March 1st, 2013, 07:32 PM Thread Starter
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It is a new fuel pump but can't hear anything different. When i turn the key it sounds fine.

---------- Post added at 07:32 PM ---------- Previous post was at 07:30 PM ----------

I will post a video tomorrow afternoon.
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post #5 of 23 Old March 2nd, 2013, 11:48 AM Thread Starter
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post #6 of 23 Old March 5th, 2013, 10:11 AM Thread Starter
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Has anyone heard of this?
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post #7 of 23 Old March 5th, 2013, 01:49 PM
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Were you pushing on the gas to get it to 2000 rpms or did it do it on its own.

Ive never seen that, sorry i cant help


DART 331ci stroker, AFR 185 heads,
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post #8 of 23 Old March 5th, 2013, 02:22 PM
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92 Mustang Lx 5.0 not running right please help

He has to be stepping on the gas when I climbs to 2 no? Have you tried adjusting the idle with the throttle body? Have you looked to see if the. TB needs to be cleaned?


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post #9 of 23 Old March 7th, 2013, 02:15 PM Thread Starter
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TB is clean, and when at idle it is smooth only for a few min then it starts. When i step on the gas it gets real bad and that is when fuel pressure gage start to drop when the tac drops. It has a new fuel pump in it and it did not help any.

---------- Post added at 02:14 PM ---------- Previous post was at 02:13 PM ----------

The fuel pressure gage will go from 35 psi to 30-25 psi everytime it has a miss of some sort.

---------- Post added at 02:15 PM ---------- Previous post was at 02:14 PM ----------

Could there be air getting in the gas line somewhere causing this to happen?
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post #10 of 23 Old March 7th, 2013, 02:22 PM
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Codes?

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post #11 of 23 Old March 7th, 2013, 02:24 PM
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I bet money it's a lean spot, not a miss. Go floor it. If it pops through the intake it will give you a good idea. Diaphram in the fuel pressure regulator probably went bad.

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post #12 of 23 Old March 7th, 2013, 09:38 PM
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92 Mustang Lx 5.0 not running right please help

Quote:
Originally Posted by Graves5.0 View Post
TB is clean, and when at idle it is smooth only for a few min then it starts. When i step on the gas it gets real bad and that is when fuel pressure gage start to drop when the tac drops. It has a new fuel pump in it and it did not help any.

---------- Post added at 02:14 PM ---------- Previous post was at 02:13 PM ----------

The fuel pressure gage will go from 35 psi to 30-25 psi everytime it has a miss of some sort.

---------- Post added at 02:15 PM ---------- Previous post was at 02:14 PM ----------

Could there be air getting in the gas line somewhere causing this to happen?
I know it's a repeated question but did you try to adjust the TB screw?


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post #13 of 23 Old March 8th, 2013, 03:39 PM Thread Starter
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Not throwing any codes and yes on the screw.

---------- Post added at 03:39 PM ---------- Previous post was at 03:38 PM ----------

Is there away to test the fuel pressure regulator?
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post #14 of 23 Old March 8th, 2013, 04:23 PM
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Re: 92 Mustang Lx 5.0 not running right please help

That video was kinda rough with the door chime going on, but from what I could tell it was wanting to skip around 2k, which makes me think TPS. If you gradually increase rpm and it gas a bad spot then its probably TPS.

But with you mentioning your fuel pressure maybe its your regulator. Is your pressure going down when on the gas? Or is it staying down constantly when you are rough running? What pressure regulator are you running? I THINK you check regulator by having a pressure gauge hooked up and with the vacuum hose disconnected and plugged you see what you are reading. Normal is about 38lb. If I remember correct.

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post #15 of 23 Old March 8th, 2013, 05:17 PM
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Originally Posted by Graves5.0 View Post
Not throwing any codes and yes on the screw.

---------- Post added at 03:39 PM ---------- Previous post was at 03:38 PM ----------

Is there away to test the fuel pressure regulator?
Just cause the light isn't on doesn't mean it's not storing codes.
Pull the vacuum hose off the fpr and give it a sniff, raw fuel smell is bad.
Function is checked by hooking up the pressure gauge to the Schrader valve on the return line, vacuum off. Make sure you cap the line so you don't have a leak.

Have you done the base idle reset?

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post #16 of 23 Old March 8th, 2013, 09:24 PM
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92 Mustang Lx 5.0 not running right please help

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Originally Posted by narleycarley View Post
That video was kinda rough with the door chime going on, but from what I could tell it was wanting to skip around 2k, which makes me think TPS. If you gradually increase rpm and it gas a bad spot then its probably TPS.

But with you mentioning your fuel pressure maybe its your regulator. Is your pressure going down when on the gas? Or is it staying down constantly when you are rough running? What pressure regulator are you running? I THINK you check regulator by having a pressure gauge hooked up and with the vacuum hose disconnected and plugged you see what you are reading. Normal is about 38lb. If I remember correct.

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Yeah it's almost like the tps is being taken off the way it shoots up like that I'm thinking tps too


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---------- Post added at 09:24 PM ---------- Previous post was at 09:21 PM ----------

Graves if it turns out to be the tps let me know I have a extra one you can have for the cost of shipping.


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post #17 of 23 Old March 9th, 2013, 08:30 AM
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Quote:
Originally Posted by flattusmaximus78 View Post
I bet money it's a lean spot, not a miss. Go floor it. If it pops through the intake it will give you a good idea. Diaphram in the fuel pressure regulator probably went bad.
Mine does this right now when I floor it. Havn't had much time to get it figured out yet. Car runs rough.

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post #18 of 23 Old March 9th, 2013, 09:47 AM
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Mine does this right now when I floor it. Havn't had much time to get it figured out yet. Car runs rough.
Now, I may be way wrong here, but if the fpr crapped out it would RAISE your fuel pressure causing an extremely rich condition. I just went thru this (sorta) on my build.

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post #19 of 23 Old March 9th, 2013, 11:50 AM
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Now, I may be way wrong here, but if the fpr crapped out it would RAISE your fuel pressure causing an extremely rich condition. I just went thru this (sorta) on my build.
No idea. And maybe that's what's wrong with mine is it's running rich like I have it set to high. I dunno, the car sits alot now, I needs to get to the old girl!



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post #20 of 23 Old March 9th, 2013, 12:00 PM
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Quote:
Originally Posted by dbshea View Post
Now, I may be way wrong here, but if the fpr crapped out it would RAISE your fuel pressure causing an extremely rich condition. I just went thru this (sorta) on my build.
Not if its leaking. It will lower pressure as it leaks.

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