Hot and bothered

[SHO EET 1]

Within the past 12 months I have fixed the following: 60K, CPS, Water pump, TPS, CID, radiator, ECT, front/rear O2 sensors, Non-OEM plugs/wires (grrrr), and cleaned the IAB & EGR. I have checked the grounding on the DIS and added more heat sink compound.

When the car is cold it runs like a champ. After driving 30-40 minutes in town, the car heats up and starts bucking( like your pulling a heavy trailer). After the bucking starts the CEL comes on and throws a rear O2 sensor code (172). The idle gets rough and it actually seems to shift crappy. If I leave the car cool down it goes away.

Any ideas are appreciated as I can't seem to get to the bottom of this one. headbang

 

[shojuan]

For me the root of all this evil was a weak fuel pump which eventually became an almost dead fuel pump. On its last legs it was putting out like 24 psi after running it for a while.

 

[jelloslug]

I would check the rear O2 sensor. Even though you changed the rear O2 sensor already it is possable that it is bad. Check the wiring, and connectors also. A quick check would be to swap the front and rear sensors, if the trouble code changes to a front O2 sensor code, its the sensor.

 

[SHO EET 1]

If the fuel pump was going wouldn't it be very noticable at high speeds? If I drive over 65 mph the bucking seems to go away or I just don't notice it anymore.

 

[LaTechSHO]

when it does this bucking...does it do it at idle as well as higher rpm?... neutral?park?drive?all the time?

i'm assuming its an ATX since you said something about an EGR and you don't live in california as per your info....

I Believe the AXOD-E has a lockup torque converter(not sure) but if so you might have a lock-up solenoid acting up... have your DIS module tested..... it might be acting up..... your fuel pump could get getting hot as previously stated...

give us a little more info about when and how it happens...

Louis

 

[SHO EET 1]

I have a 1994 ATX. After getting the car to warm up it all starts after going WOT like passing another car. Then while driving at a constant speed it bucks. I doesn't seem to happen if I drive it like an old lady. It bucks the worst around 40-60 mph, higher or lower speeds seem to lessen the effect.

I do not seem to have a problem in park/neutral, only in drive. I will get a very rough idle after the bucking starts, the tach will start to bounce around a little and the car just feels like it is missing.

On my work this morning I noticed it had a slight hesitation/buck/surge and the car was not warmed up. It seems to be happening more frequently. I have been thinking DIS but could this also be a faulty injector? I am going to have the fuel pressure tested on Sat to try and narrow it down some more.

<small>[ June 25, 2003, 07:15 PM: Message edited by: SHO EET 1 ]</small>

 

[LaTechSHO]

Actually, someone may trump me on this, but my initial thoughts are transmission related. If your troubles occur while the transmission is engaged and not while in park/neutral it is either a symptom of the engine acting up under load or the transmission/torque converter having trouble. I know the later model taurus transmissions have lockup converters... if your transmission is quickly going back and forth from lockup to non-lockup it would do exactly as you are describing and is actually a common issue with many GM transmissions. You of course want to rule out anything that is cheap and easy to rule out before jumping into the transmission, but have you looked at the tranny fluid?... do you have a leak? ... With regard to the engine do a quick check on all of your vacuum lines. I'm sure someone else will chime in on this...

Louis

 

[rangerj]

SHO EET 1,

Here is another thought to consider. Since you are getting a code 172, O2 sensor Lean, the Throttle Position Sensor (TPS) could be causing the problem. It is the TPS signal that (in part) causes the computer to activate the fuel injectors.

If the throttle is being opened, that is allowing more air to enter the engine, and the signal is weak or poor, and the injectors are not being told to supply more fuel, you will get the conditions you describe.

There is a three wire connector at the TPS. Thr gray wire with the red stripe is the signal return wire (SIG RTN). the Gray wire with the white stripe is the TP signal wire(TP SIG), and the Brown wire with the white stripe is the voltage reference (VREF) wire.

After the key has been off for a minimum of 10 seconds disconnect the TPS connector. Probe between the VREF and SIG RTN at the TPS harness connector. You shopuld get between 4 and 6 volts. If not check the VREF circuitry and wiring.

Test 2. Reconnect the TPS harness connector and the backprobe the connector between the TP sig and the SIG RTN wires with the KOEO (Key On, Engine Off). Move the throttle from fully closed through Wide Open Throttle (WOT).

Do this slowly. You should get approximately 0 volts (about .3V) up to just under 5 volts (4.7) at WOT. If not, the TPS is faulty. Watch for any breaks in the voltage. This would indicate a "flat" spot in the TPS.

These test should be done with a DMM, that is a digital multi meter, and not an analog or swing type meter.

I have seen the conditions you describe several times, but the cause has rarely been the same thing. So, the suggestions given by the others are also good ones. Let us know what you finally find as the cause.
rangerj

 

[AutoSHO]

Your IAB might be bad.

EDIT: In RangerJ's post, he says the TPS should go down to .3v, thats incorrect. Fully closed you should see around .9, no more than .98v closed.

<small>[ June 25, 2003, 11:33 PM: Message edited by: AutoSHO ]</small>

 

[SHO EET 1]

Is there a chance a new TPS can be faulty? I will give that a test this Sat when I start tearing into it. After I cleaned the IAB, it seemed to be moving fine but you never know.

 

[rangerj]

SHO EET 1,

Yes there is a chance that a new TPS could be faulty. However the odds are greater that if there is a fault, and a new TPS is in place, that the fault would be a poor connection or problem in the circuit.

Just for the record the auxilliary manual to the Helm shop manual, wherein the test proceedures and the test perameters are found for testing sensors, the test perameters for the TPS is 0 (zero) to 5 (five) volts.

The practical voltage ranges given are "Approximately" .3V at closed throttle, to 4.5 V at WOT. The optimal suggested voltage at closed throttle is 0.6v, suggested in several publications that address fine tuning Ford EEC-IV equipted vehicles for performance.

The literature, including Helm, suggests a variation of 15% as being acceptable. So, I use the word "approximately" in giving the voltage perameters.

For optimum performance try for 0.6v at closed throttle. There is a little looseness in the screw holes in the TPS that allows for slight "adjustment", but keep in mind that the TPS is not "adjustable" per se.

Please let us know what you find. Your problem is common and the solution is never easy to find. rangerj