1995 F150 Help - Can not fix!

I have a 1995 F150 4X4 with a 5.0 Automatic. It runs fine sometimes but then it will bog under part throttle, pop back and run crappy until wide open throttle then it takes off and runs great. Always runs great at wide open throttle. Occasionally it will stumble at an idle but most of the time it idles perfect. It gives a lean code but as it is obd 1(stupid as I call it) no data stream. Here is what I have done so far. A lot of this is as it is my sons first truck and I just want it all ready as soon as he gets his license in the next month.

New plugs, wires, cap, rotor & distributor Changed computer - same exact symptoms as the original one Fuel pressure test while driving on two tanks all is fine New mass air New fuel filter New throttle position sensor Cat is punched out O2 sensor was replaced before I got it Cleaned all grounds

It doesn't skip or run bad on any cylinder but just like something is not telling the injectors to open all of the way until you hit wide open throttle then it goes great. It is worse up a hill but will do it on the flat also. The check engine light will cycle on and off but only shows the lean bank 1 code. I am hoping the different computer may come up with a new code.

Thanks in advance for all of your suggestions!

Reply to
LOOK2X
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Sounds like the timing is way off. Spdloader

Reply to
Spdloader

The timing has been set at 10 BTDC when the new distributor was installed.

Reply to
LOOK2X

Lean is lean. I'd be careful if it is truly having trouble with a cylinder as you could fry an exhaust valve or a piston if the cylinder isn't getting enough fuel.

Have you got a code scanner? Have you run the cylinder balance test to check for a weak cylinder?

Beyond that, understand that at WOT, the engine computer goes into open loop mode where it basically ignores the oxygen sensor input and just uses some tables it stores and just pushes fuel out the injectors like crazy. Try wot in a building and you'll smell the unburned fuel.

So if this is at part throttle, it would lead me to think perhaps an issue related to computer control. I would recommend making sure that the cooling system is functioning properly and that the sensors that check coolant temperature are working. This is an input to the computer.

I'd try running with the MAF sensor disconnected to see how it does and if the behavior changes any. Without the maf sensor you'll get a check engine code but the computer will use defaults and should run o.k.

After that you have to consider a possible issue like a bad distributor or worn distributor allowing too much movement.

Reply to
Mike H

Even so, the new distributor may not be working properly. Also, was the timing set with the pigtail to the distributor unplugged? Then, plugged back in?

Spdloader

Reply to
Spdloader

Yes the pitail was removed and reinstalled after timing.

Reply to
LOOK2X

tp

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Reply to
Steve Barker

I have already replaced the tps and no change.

Reply to
LOOK2X

"LOOK2X" wrote: 1995 F150 4X4 5.0 Automatic.

Runs fine then will bog under part throttle, pop back and run crappy, always runs great with WOT. Occasional stumble at an idle but most of the time idles perfect.

Gives a lean code (OBD-I). Here is what I have done:

New plugs, wires, cap, rotor & distributor Changed computer - same exact symptoms as the original one Fuel pressure test while driving on two tanks all is fine New mass air New fuel filter New throttle position sensor Cat is punched out O2 sensor was replaced before I got it Cleaned all grounds _______________________________________________

Possibly loose bolts holding throttle body, or sticking IAC.

Good luck.

Rodan.

Reply to
Rodan

Punched out cat can affect exhaust temp, which is what an O2 sensor measures. Its nothing more than thermocouple like on a hot water heater. If the exhaust is to cool its voltage out put will be low which tells the ecm its running rich, so the ecm leans out the fuel mix, which raises combustion temps which can cause back fires. WOT, the O2 is ignored. How many O2's on this model?

Whitelightning

Reply to
Whitelightning

On Sun, 22 Oct 2006 02:08:36 +0000, Whitelightning rearranged some electrons to form:

That is not correct. The O2 sensor measures the presense of oxygen via an electrochemical reaction on a ceramic element. It is not a thermocouple.

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Reply to
David M

How do you bench test a O2 sensor?

Whitelightning

Reply to
Whitelightning

On Sun, 22 Oct 2006 03:13:13 +0000, Whitelightning rearranged some electrons to form:

I haven't tried this, but the theory says that since the chemical reaction doesn't occur unless it's hot, you would have to heat it with a propane torch, or something like that. When it was in the flame, it should indicate rich, or centered (since the propane was consuming the oxygen) and out of the flame, it should indicate lean (lower voltage) until it cools off, then it would read nothing.

YMMV

Reply to
David M

PS, you left out your statement from earlier:

On Sun, 22 Oct 2006 02:08:36 +0000, Whitelightning rearranged some electrons to form: Punched out cat can affect exhaust temp, which is what an O2 sensor measures. Its nothing more than thermocouple like on a hot water heater.

Reply to
David M

You can do the same thing with an electric heat gun, such as a paint stripper, which has no flame.

Whitelightning

Reply to
Whitelightning

On Mon, 23 Oct 2006 02:50:40 +0000, Whitelightning rearranged some electrons to form:

Perhaps, but you're original statement is still wrong.

An O2 sensor is

*not* a temperature sensor. It measures the partial pressure of oxygen. It requires heat for the chemical reaction to occur between the oxygen and the ceramic element. At a given temperature, it will output a different voltage based on the oxygen content of the gas around it. If you heated it with a heat gun, the voltage will drop as the sensor cools off, as the chemical reaction stops... thus the reason that most O2 sensors have a built-in heater so they will come up to temperature quickly.

Don't believe me? Read it yourself:

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A thermocouple is a junction of dissimlar metals, which generates a very small voltage (millivolts) based on temperature based on the Seebeck effect. The presence or absence of oxygen has no effect on a thermocouple.

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There are many more references out there, if you'll take the time to search.

Reply to
David M

On Mon, 23 Oct 2006 09:23:42 +0000, David M rearranged some electrons to form:

Here's some more:

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(select oxygen sensors)

Reply to
David M

I concede the point that they are 'different" devices. I can learn and admit when I am wrong. However, if the temperature isn't correct it is going to read wrong. What is hard to understand here is the bank one lean error code. If there is only one O2 sensor, how can the system determine a lean bank?

Whitelightning

Reply to
Whitelightning

Some of those trucks had two O2 sensors, one in each downpipe, (one from each bank(head)) just before they entered the converter. Maybe that's how.

Spdloader

Reply to
Spdloader

On Tue, 24 Oct 2006 01:02:10 +0000, Whitelightning rearranged some electrons to form:

Correct, that's why they have a built-in heater to get them up to temperature quickly. Older ones didn't have the heater and thus ran open-loop until the engine warmed up, spewing a lot of unburned fuel. I can't remember the exact number, but a model from this decade (2000's) has something like 100 times cleaner emissions than something from 20 years ago.

It probably has more than one sensor. My OBD-II '98 has four. I haven't had to change them (yet) after 123k on the clock. I've replaced the one on the wife's '94 Jeep twice in the past 12 years, though. Go figure.

Reply to
David M

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