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MoM Fanatic
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Discussion Starter #1
I havent really been on much lately but i thought id ask for some help.
When you first start the car it runs perfectly fine. After its warmed up a bit the car will climb to 5000 rpm just fine and then it sounds like the timing will degrade. By the time it hits 5500 rpms the car will not climb any rmps and sounds like its on the rev limiter but the timing is retarded or something, also if you go to mash it around a corner and the car jerks it will shut off and not run for a few seconds. Well yesterday i was driving and i drove about an hour. Well there was a murdered out charger next to me and we stopped at the traffic light and he was reving at me and i never reved back but when i took off i was playing and mashed it. My car hit 3500rpms and it shut off and dropped maybe 1000 rpms before the motor refired(standard) after it refired i was like wtf so i brought it up to 3500 again and it lost power to the point where it would fall 250rpms(to 3250) then it would accelerate to 3500 and repeat and run like it was struggling. At idle the car was perfectly fine. Free revving it would rev up but the higher you rev the worse it missed.
So i went ahead and went to dinner came out, car was still warm so i tried it again. When i pulled out Went right to 6000 rpm no problem. I drove to a friends house 15 minutes away and no problem. I dropped it down in the highway to check it again. Wouldnt go over 5000 rpm. When i pulled onto his street i opened it up and it wouldnt go over 4500 rpm and it was bucking like i described earlyer.
Just keeps acting like that, i changed the fuel filter 3 months ago. There are no codes and the motor isnt in reduced power mode. I dont think its a clogged cat because it bucks. Clogged cats act like what it does at 5500 rpm when it sounds like the timing is retarded.
Also does it with traction control on or off.
Any ideas would be appriciated i have alot of spare parts to swap around.

Also dad gave me this off the built 4.6 motor since were running the boss now

so ill put the long tubes, the cai, im gonna order a bama tuner and a ford racing high rise intake manifold in the next couple weeks. Im excited but id like to know the problem before i jump into this
 

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I would try doing some data logging while this is going on. And I am assuming that you looked over all of the other obvious mechanical stuff like intake tubing and vacuum hoses and what not. And I don't see any mods listed but could be spark blowout too but probably not. Have you pulled the plugs to check them out and see what they look like? Just taking stabs at it, you need to data log.
 

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I guess the fuel pump could be crapping out on you. It's hard to say without experiencing it in person. I know the pcm monitors the fuel system to some extent, but a cavitating fuel pump might not be picked up. Be careful turning up the R's in case it is fuel related.
 

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Insomniac
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Hmmm quite the oddity youre having. Could be a number of issues, if it were fuel related id think it would throw a lean code and youd be having detonation. If it were vct related I, almost sure it throw a code. Im gonna lean towards the tps or throttle body itself
 

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I just wonder if a momentary lean condition due to a pump problem would possibly not throw a code. I wouldn't doubt a TPS problem either. The one TPS I had go bad threw a code.
 

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Resident Headbanger
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2,410 Posts
Any ideas would be appriciated i have alot of spare parts to swap around.
Sticking charge motion control valves?
You could do a CMCV delete on the stock manifold but if you're planning on getting the FRPP manifold, the CMCVs will be deleted anyway.
 

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MoM Fanatic
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Discussion Starter #7
Well there was no engine light or anything but i ran my code reader on it to do live diagnostics and when i plugged it in p0191 came up.
Fuel rail pressure sensor/range and it wasnt even pending
I figured the light would come on for any code showingnup but i guess not. Im gonna try replacing the fuel filter again since i just did it a few months ago

What i find weird is its not throwing a lean code when it was obviously rjnning lean at 3000 rpms enough to effect the performance, i know ive starved the pump a few times on the track from all the cornering gs so i hope its not the pump... Ill keep it updated. I cant wait to slap those parts on my car
 

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It sounds like the FRPS malfunctioning and not seeing fuel pressure. Thus making the car bog, and not put enough fuel in it for the mixture.
 

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MoM Fanatic
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Discussion Starter #12
Cleared codes swapped sensor and no cure(actually this Driving it to work tommoro to change the fuel filter and go from there. Any more suggestions
 

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MoM Fanatic
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Discussion Starter #13
changed the fuel filter, that sensor wasnt the problem either so im assuming fuel pump.... dad believes so also. i have a fitting in the fuel hose running into the rail so when it starts acting up again i will get pressure readings but i noticed if i shut it off and turn it back on it runs fine again then degrades the more i run it.
also i have video. it wouldnt climb over 4000 in any gear
free revving to the floor nothing over 4500 and it would bounce back and forth.

videos are uploading on youtube

---------- Post added at 08:55 PM ---------- Previous post was at 08:48 PM ----------

flooring it in 1st
984 - YouTube
driving down the road in 3rd
http://youtu.be/eiYJgl2vp-c
free revving
http://youtu.be/eiYJgl2vp-c
 

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Try to find a good used pump from someone on the forums. I know I had one, but gave it to my son in law for his build. You could get a used one for a song and lots of guys have removed stock pumps. It could also be the fuel lines in the tank. I've heard of a split line causing cavitation due to pulling fuel and then air through the split line.
 

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I have a stock fuel pump sitting in my garage it you are interested in it. Have you data logged yet? And why not? You could eliminate quite a lot of this guess work as opposed to just chasing it with parts.
 

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^ That's sound advice. One thing I never do is try parts unless I have parts to rob off of something else or parts laying around. You can make a cheap fix very expensive without proper diagnostics. I know there are situations where you have to try parts, but be smart about it. At least pull the pump and inspect the hoses, but on the other hand if you can score a cheap used pump and that's not the problem you could always sell a used pump yourself.
 

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MoM Fanatic
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Discussion Starter #17
Ill score a cheap pump and im waiting on my sct to come in and im gonna datalog on it. Boss i may send you a pm here in a bit if the local dealer doesnt still has his out of his american iron car laying around
 

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MoM Fanatic
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Discussion Starter #20
The owner of the dealership gave me a whole fuel tank with pump and sensor included. I replaced it and its just fine now, thanks for everybodys assistance!! In the next few weeks im gonma tackle the headers!
 
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