PLEASE HELP I HAVE A BIG PROBLEM....

It could be running really lean. See if it is poppin through the intake or the exhaust. If it's through the intake it's too lean.....if it's through the exhaust it's too rich. Either way it could be the O2 sensors. I had a lean condition (really bad one) poppin through the intake and it turned out to be a slice in the 2 inch long fuel line in the tank that goes from the pick up tube to the pump. It's weird I know...i still havent figured out how it happened.

O2's begin to be used when they themselves reach a certain temp (which with HEGOs takes less than two mins and can occur as quickly as 20 seconds). It doesnt matter what the coolant temp is.

Have you looked at your TPS signal when the car is acting up? I would.

Good luck.

Run a fuel pressure check then. See if it matches to the specs in ay ford manuel. I forgot the specs myself. Also check and see if it holds pressure when the ignition is off and on. Then work from there. If it dosen't check for leaks, a bad pressure regulator, so on and so forth.

mustangfan1990 said:

Well see when the 5.0s are cold the O2 do not affect anything until the motor hits a certain temp, but I unplugged the O2s and no difference

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mustangfan1990 said:

I didnt say the temp of the coolant. The O2s wont heat up it the motor doesnt. I have not checked the TPS while is doing this but I have adjusted it to read .99volts will that help?

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In your first quote, I took your bolded part to mean coolant temps. I guess not.

Regarding the second quote: The O2's have their own heater circuit (why I mentioned HEGO's, not EGO's). The HEGO's could care less how cold the motor is, and a motor making combustion will heat the exhaust no matter what. This helps the O2's to light off.


You would need to test the TPS when it acts up if there's an issue with debris affecting the wiper.

Good luck.

Hissin is one of the best here for these type of problems. Listen and he can most likely help you.

Backfiring out the intake is either a valve stuck open or a lean mixture or spark plug wire(s) connected to the wrong cylinder(s). Check compression on all cylinders and then look for vacuum hoses loose, cracked, or misconnected. Check the line for the vapor recirculation system – it is easy to knock loose and not see it when you connect the air pump plumbing. If the vacuum line for the EGR valve and the air pump are cross connected, some very strange things can happen. Check the mass air flow electrical connection and see that it is tight, the same goes for the fuel injection wiring harness connectors up on top of the manifold near the firewall.

Sticking valves: If a intake valve is bent, has a bad spring or is misadjusted, the engine will sometimes backfire through the intake. Use a vacuum gauge connected to any convenient spot on the intake manifold. Run the engine at 1000 RPM & look for 18-21 inches of vacuum with a steady needle. A problem intake valve will make the vacuum gauge needle sweep 5-10 inches.

Lean fuel mixture breaks out into several sub categories:
A.). Vacuum leaks
B.) Air entering the intake without passing through the MAF.
C.) Failure of the MAF, BAP/MAP (Baro or Manifold Air Pressure, same sensor, different name), ACT (air charge temp), or ECT (engine coolant temp). These should set a code in the computer.
D.) Leaking exhaust gases from EGR valve at WOT or EGR opening when it should not be open.
E.) Poor fuel delivery due to bad fuel pump, clogged filter or bad fuel pump wiring. Look for low pressure or fluctuating pressure. Standard injector pressure is 39 PSI at idle, with the vacuum line disconnected from the regulator and capped.
F.) Clogged fuel injectors.- see the cylinder balance test below
H.) Fuel injector wiring problems causing injector not to deliver rated flow.
I.) Computer problems: (computer problems are not common like sensor problems)
J.). ROM has bad data in fuel or timing table. This should also set a code in the computer.
K.) Failure of one or more of the computer's driver transistors for the fuel injectors. No code set on this one. Use a noid test light to test the injector wiring & injector drivers,
L.) MAF calibration off or mismatched to injectors.
M.) ACT or ECT bad. Sometimes the sensors will be off calibration, but not bad enough to set a code. If they falsely read too high a temp, the engine will back off fuel delivery.

Cylinder balance test:
Warm the car's engine up to normal operating temperature. Use a jumper wire or paper clip to put the computer into test mode. Start the engine and let it go through the normal diagnostic tests, then quickly press the throttle to the floor. The engine RPM should exceed 2500 RPM's for a brief second. The engine RPM's will increase to about 1450-1600 RPM and hold steady. The engine will shut off power to each injector, one at a time. When it has sequenced through all 8 injectors, it will flash 9 for everything OK, or the number of the failing cylinder such as 2 for cylinder #2. Quickly pressing the throttle again up to 2500 RPM’s will cause the test to re-run with smaller qualifying figures. Do it a third time, and if the same cylinder shows up, the cylinder is weak and isn’t putting out power like it should. See the Chilton’s Shop manual for the complete test procedure

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.

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.

Yup hissin is correct. The engine coolant temp DOES NOT matter when dealing with O2 operation. They have a dedicated 12V heating circuit and they must reach about 450 degrees before they start switching.

You could turn the key to the ON position for a couple minutes...and then start your stone cold engine (ECT temps) and the HEGO's would start switching almost immediately. FYI

Did you take out your distributor recently? This could also be caused by a distributor being off one tooth or an incorrectly timed car. Also check if the bolt came loose that is holding it still.

It could be that the dizzy is moving around while you accelerate causing timing to wander all over the place.

However i think thats unlikely b/c the car is starting up and idling fine. You would have a noticeably different idle if the timing was way off. Is your idle speed normal?