Still cant get the car to run at part throttle

BigHairyMonkey · Mar 16, 2008

Ever since ive owned the car ive had a problem with driveability at less than 50% throttle. It happened when the car was cold at first and then when the 02's would come on it would get a lot better. Now it happens when the car is cold AND when warm. Basically what happens is the car will lose any kind of part throttle acceleration. I will go to shift and the car will buck between shifts or i will put my foot into it to accelerate and it will hesitate and the more and more throttle i feed it the harder it bogs down.. then sometimes it will even pop outa of the intake manifold (like its running really lean). The only way to get around that is either go 100% throttle (it clears up and takes off like a bat outa hell), or just get off the gas completely.. and after a couple of seconds it clears up enough to get back into it. What the hell is going on? I have replaced the 02 sensors, tps sensor, the act, ect, cleaned the maf, put in a new fuel filter & air filter. All sensors were replaced with their new ford original motorcraft components. The car runs strong as hell full throttle, always has, but i just cant get it to run good part throttle and it takes the fun outa driving the car. When i went and got it tuned @ gforce (timing and fuel pressure only), the car needed 50 psi of fuel pressure (vacuum off) to go 13.4:1 afr at full throttle. I always thought that was ridiculous as seeing normal cars of my caliber only need 38-42psi. I also bought a vacuum gauge and at 750-800 rpm the car pulls 17 in Hg. I dont know what a "normal" vacuum reading for a stock car is. Has anyone experienced anything like this? I HAVE to get this fixed because this is my daily and im tired of getting frustrated in traffic.

jrichker · Mar 16, 2008

Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

See http://www.troublecodes.net/Ford/

If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

For those who are intimidated by all the wires & connections, see http://www.actron.com/product_detail.php?pid=16153 for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see http://www.midwayautosupply.com/pc-7208-90-equus-digital-ford-code-reader-3145.aspx – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.

ShortThrow50 · Mar 16, 2008

need a lttle more info on your mods to determine what the cause could be. I see your dyno numbers to be a little high for a stock h/c/i. Are you running stock fuel pump?

enyawix · Mar 16, 2008

check for vacuum leaks first. spray wd40 around the engine if the sound changes in any area you have a vacuum leak in that area. also test the IAC. and check your fuel pressure. "38-42psi". Spark would not do this. This issue is in the fuel to air mix.

BigHairyMonkey · Mar 16, 2008

jrich the codes i got for key on car OFF were just code 67, and the all clear code. I tried to pull the codes with the engine on and all the car did was flash the cel "4" times and not do anything.

BigHairyMonkey · Mar 16, 2008

ShortThrow50 said:
need a lttle more info on your mods to determine what the cause could be. I see your dyno numbers to be a little high for a stock h/c/i. Are you running stock fuel pump?

the car has always been stronger than where it should be for its mods, so i dont know what to tell you. Only mods are

-MAC CAI
-BBK shorties
-BBK O/R H
-Pypes SS catback w/ 40 series flows welded in.
-SHO E-fan
-Pro-M 75mm Fan
-Kirban AFPR

-Stock E7 heads, pushrods, rockers, etc.
-Stock Cam
-Stock Upper/lower intake, stock tb, stock egr spacer.

To my knowledge the fuel pump is stock.

DrMaxit · Mar 16, 2008

find some one that'll rent/loan you one or go to a shop that has an intake smoker and find out if you have a vac leak, sure sounds like it to me.

==Chuck

mustangfan1990 · Mar 16, 2008

I know this sounds stupid but for the LONGEST TIME I use to have that problem. I had an optima battery so it never crossed my mind but one day the battery died so I took one out of another car and all my problems cleared up....just my case maybe dont know

DrMaxit · Mar 16, 2008

mustangfan1990 said:
I know this sounds stupid but for the LONGEST TIME I use to have that problem. I had an optima battery so it never crossed my mind but one day the battery died so I took one out of another car and all my problems cleared up....just my case maybe dont know

Ground problem maybe?

BigHairyMonkey · Mar 17, 2008

but see all the things that have been mentioned would also show their ugly head at WOT.. like if the fuel pump was bad, it would go lean under WOT, if the injectors were clogged, same thing, if the fuel filter was clogged, still the same, etc, etc.

This leads me to believe it is some kind of sensor problem/computer issue. As the car runs like silk for a minute or two sometimes and then i goes back to running like crap. For the most part it runs somewhere in between.

jrichker · Mar 17, 2008

Code 67 - clutch not depressed (5 speed) or car not in neutral or park (auto) or A/C in On position when codes where dumped. Possible neutral safety switch or wiring problem. This code may prevent you from running the Key On Engine On tests. You can generally ignore this code, since it has no effect on engine performance.

The computer wants to make sure the A/C is off due to the added load on the engine for the engine running tests. It also checks to see that the transmission is in Neutral and the clutch depressed (T5, T56, Tremec 3550 & TKO)). This prevents the car from being driven while the computer is in test mode. Key On Engine Running test mode takes the throttle control away from the driver for several tests. This could prove hazardous if the computer was jumpered into test mode and then driven.

The NSS code 67 can be bypassed for testing. You will need to temporarily ground computer pin 30 to the chassis.

Computer pin 30 uses a Lt blue/yellow wire. Remove the passenger side kick panel and then remove the plastic cover from the computer wiring connector. Use a safety pin to probe the connector from the rear. Jumper the safety pin to the ground near the computer.
Be sure to remove the jumper BEFORE attempting to drive the car!!!

The T5 neutral safety switch has nothing to do with starting the car. The clutch safety switch controls whether or not the starter cranks the engine.

Snake1 · Mar 17, 2008

Try this for vacuum gauge settings might be of use to you.
http://www.therangerstation.com/Magazine/Summer2003/VacuumLeaks.htm

Black1987Stang · Mar 17, 2008

I know what you mean, mine does the EXACT same thing. Well, it used to. I called it vtec cuz it would be slow then once it hits that WOT it takes off like crazy. Sounds crazy but try disconnecting your 02 sensors (has to be both of them) mine doesn't do it anymore. I will warn you tho if you just unplug them and drive it like that it might ruin the sensor since the heater isn't on (someone correct me if I'm wrong please), unless you just tempparily disconnect cut the signal return wires which is pins 29 and 43 at the computer. It should be alright to just try for a quick drive though. Also a 18mm drain plug works as a nice 02 sensor plug. I also have the tps disconnected and it actually runs alot better, idles smoother and all.

enyawix · Mar 17, 2008

DrMaxit said:
find some one that'll rent/loan you one or go to a shop that has an intake smoker and find out if you have a vac leak, sure sounds like it to me.

==Chuck

+ 1

sounds like it to me also

DrMaxit · Mar 17, 2008

BigHairyMonkey said:
but see all the things that have been mentioned would also show their ugly head at WOT.. like if the fuel pump was bad, it would go lean under WOT, if the injectors were clogged, same thing, if the fuel filter was clogged, still the same, etc, etc.

This leads me to believe it is some kind of sensor problem/computer issue. As the car runs like silk for a minute or two sometimes and then i goes back to running like crap. For the most part it runs somewhere in between.

A Vacuum leak wont show up at WOT for the most part. There should be little to no vacuum at WOT if your components are matched up. At least rule this one out, then we can venture deeper. You can check via vacuum gauge as listed earlier or my favorite the intake smoker. Start with the basics, and vacuum leaks can be a BIG PITA to find, the wd40/carb spray trick doesn't always find little ones, or several little ones you might have (hairline crack, slight leak in the intake gasket ect.) Also small cracks in hoses and lines can be sporadic, and can go away as the engine gets warm (seals/swells the hose). As the condition of the hose/gasket whatever it may be worsens, it could start acting bad even when warm, such as you have mentioned. Like I said, at least rule it out. Let us know what you find.

--Chuck

BigHairyMonkey · Mar 17, 2008

Black1987Stang said:
I know what you mean, mine does the EXACT same thing. Well, it used to. I called it vtec cuz it would be slow then once it hits that WOT it takes off like crazy. Sounds crazy but try disconnecting your 02 sensors (has to be both of them) mine doesn't do it anymore. I will warn you tho if you just unplug them and drive it like that it might ruin the sensor since the heater isn't on (someone correct me if I'm wrong please), unless you just tempparily disconnect cut the signal return wires which is pins 29 and 43 at the computer. It should be alright to just try for a quick drive though. Also a 18mm drain plug works as a nice 02 sensor plug. I also have the tps disconnected and it actually runs alot better, idles smoother and all.

i dont wanna disconnect the 02's as its a bandaid at best (even if it works), and my gas mileage cant get any worse than it already is @ 3.50 a gallon.

BigHairyMonkey · Mar 17, 2008

DrMaxit said:
A Vacuum leak wont show up at WOT for the most part. There should be little to no vacuum at WOT if your components are matched up. At least rule this one out, then we can venture deeper. You can check via vacuum gauge as listed earlier or my favorite the intake smoker. Start with the basics, and vacuum leaks can be a BIG PITA to find, the wd40/carb spray trick doesn't always find little ones, or several little ones you might have (hairline crack, slight leak in the intake gasket ect.) Also small cracks in hoses and lines can be sporadic, and can go away as the engine gets warm (seals/swells the hose). As the condition of the hose/gasket whatever it may be worsens, it could start acting bad even when warm, such as you have mentioned. Like I said, at least rule it out. Let us know what you find.

--Chuck

ill start calling around for the intake smoker, god i hate dealing with auto mechanics places, i know this will be an expensive 'smoke job' lol.

Ddaniels750 · Apr 11, 2008

This is my 5th 5.0 and I have never had this problem...until now. I also am leaning towards a vacuum leak as I have tried everything else that you have mentioned besides removing the O2 sensors. I agree that is a temporary fix if it works at all. Keep us updated

Ddaniels750 · Apr 13, 2008

Well I finally got mine figured out. It turned out to be the HEGO ground. I pulled the upper manifold last night and noticed that the wire had broken. I extended it and grounded it against the back of the block and that took care of it.

Still cant get the car to run at part throttle

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