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car will rev past 4,000rpm but wont drive past 4,000 rpm

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Old 06-11-2014, 10:00 AM   #1
BaltRavens
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Default car will rev past 4,000rpm but wont drive past 4,000 rpm

What are some possible problem areas? Its a 94 GT 5spd. At wide open throttle once you hit 3,800-4,000rpms its like its hits the rev limiter almost. The exhaust pops and crackles like crazy it sounds horrible. However sitting in the driveway idling I can floor it and it will bang off the rev limiter no problem.
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Old 06-11-2014, 11:26 AM   #2
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check it for codes first. Then the basics next, when was the last tune up? Check the distributor shaft they eat them also the pick up in the distributor goes bad often in those cars. Fuel pressure check.
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Old 06-11-2014, 12:08 PM   #3
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No codes being given. I have taken the car to 3 different shops and no one can make heads or tails out of the problem. They all have agreed its something electrical? The last guy I took the car to wanted a hefty price tag to fix the car. Couple grand to start... not something I am willing to pay. He even put the car on a dyno but apparently it didn't give him heads or tails of what the problem is exactly.

Saturday I have another mechanic who is going to look at it. I am just trying to get some ideas before I take the car to him and we work on it. The car starts and runs fine. It idles fine. Its just gets ti 3800ish RPMs and goes into a fit under wide open throttle.
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Old 06-11-2014, 01:02 PM   #4
88 orangepeel notch
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Maybe do a sweep test on the TPS, looking for a dead spot near WOT.
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Old 06-11-2014, 01:58 PM   #5
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Under load (when driving) the car will use way more fuel, have a bigger spark, and have higher timing than when just sitting and reving.

Could be a Coil, bad wires or a combo of both.
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if you are getting 29mpg in your 5.0, you aren't driving it correctly
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Old 06-11-2014, 02:23 PM   #6
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Quote:
Originally Posted by Derf00 View Post
Under load (when driving) the car will use way more fuel, have a bigger spark, and have higher timing than when just sitting and reving.

Could be a Coil, bad wires or a combo of both.
This or something as simple as clogged fuel filter.
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Old 06-11-2014, 07:53 PM   #7
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check to see if spout connector fell out
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Old 06-18-2014, 08:53 AM   #8
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My buddy ran his car out of gas. He walked to the gas station, grabbed a gallon, and put it in the car. It would start and idle, but it would not drive or rev past a certain rpm. Long story short ...Running it out of gas caused the fuel pump to suck up junk from in the tank. He replaced the pump and filter, and all was good. Might be something you should look into.
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Old 06-18-2014, 08:38 PM   #9
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I'm having almost the same issues.. This is my story: Installed a 75mm TB, with my IAC and TPS now the cars bucking at around 2,100rpms under a load,and I can't accelerate passed that. Stalls a little while cold at the same rpms, and again around 4,000. I also replaced the TFI module with an accel tfi at the same time. I'm thinking either the TFI is bad or the TPS isn't setup right/is bad.

I also put in a new hypertech coil about 2 weeks ago.

I drove home from work pissed off and tired after dealing with adjusting the tps voltage to .98 with KOEO
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Old 06-22-2014, 01:05 PM   #10
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I changed fuel filter. The only code thrown is code for o2 sensor but I replaced them and it didn't change... not sure whats up with that? I had a local performance shop look it over for vacuum leaks and set timing which they did and no leaks and time was good.

The car has 1.72RR(overkill imo) with GT40P heads. I am thinking when the guy installed these parts(guy I bought car from) he didn't install the valve upgrade kit for the bigger rockers. I ordered the upgrade kit from latemodel last week it should be here tomorrow. We will see if that helps the car out any.

I am at a pretty big loss mentally with the car I can't figure it out. I have replaced alot of sensors. I have had it to 3 mechanics who wasn't sure. I also had it to a dyno shop. The dyno shop wanted $2,000 for starters to fix the car but wouldn't give me heads or tails of whats actually wrong with the car... dyno shop wanted to start with new fuel rails, intake manifold, heads, injectors. It was more than I am willing to spend right now.

But for everyday driving the car runs fine its just underload it not at 100% power and like I said it hits its rev RPM limit at 3800-4100ish RPMs... It does search for idle a bit not bad. When you rev it to say 3k RPM. It will take a few seconds to descend back to idle RPM. It will search for idle RPM for about 3-4 seconds surging from 950 to 1300rpm.
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Old 06-22-2014, 02:46 PM   #11
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I'd probably check over the distributor (as mentioned above a few times) and valve springs if you've ruled vacuum leaks and such.
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Old 06-22-2014, 05:18 PM   #12
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My money is on a failed tfi. If it has one? I didn't look to see what year your car was.
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Old 07-06-2014, 07:51 PM   #13
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I am saying it was a vacuum leak. I spent all weekend taking the engine completely apart. The lower intake someone didn't even bolt it on... I took the bolts out by hand! The lower gasket was barely even on the intake. All the intake gaskets were in pretty rough shape including the head gaskets. 1 of the head gaskets was leaking fluid into the pistons. I still have the car tore apart but hoping this was the issue. I am certain it is because it was in pretty rough shape. Whoever put the car together last was either very drunk or didn't know what he was doing.
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Old 07-07-2014, 09:55 AM   #14
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There you go, lol. You never know what kind of suprises you'll find in a used vehicle. Good for you for riping it down.

And stay away from dyno shop for repairs lol.
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Old 07-07-2014, 03:55 PM   #15
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Quote:
Originally Posted by 88 orangepeel notch View Post
There you go, lol. You never know what kind of suprises you'll find in a used vehicle. Good for you for riping it down.

And stay away from dyno shop for repairs lol.
I know doing it yourself is the best way to do it! So now I just need to get my ECM lined out for the E303 cam going into the car. Does anyone know of a thread or have a link to a place talking about converting a 1994 computer to a 1993?
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Old 07-07-2014, 04:35 PM   #16
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Doesn't the 302 use 1.6" rocker arms? 1.7 seems way too big

TFS-51400510 - 1.6 3/8" Stud Mount Rocker Arms

that's the part from the Trick Flow top end kit, and searching on Summit shows the same 1.6" rocker ratio, so if you're running 1.72", that could cause some issues with higher RPM's as well
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Old 07-07-2014, 06:26 PM   #17
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A lot of guys use 1.72 in mustangs and are not having any problems. I think mine was a vacuum leak in the intake. We shall see come saturday when I put it back together.
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Old 07-07-2014, 06:26 PM
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