96 GT Starting/Running issues

[Mike97gt]

"ITS FIXED" Update, I finished changing the plugs, and I found a stud that was grounded and pushed the black wire on to it... The car runs perfect now... I couldnt be happier right now, I got the car on a real good deal with this problem, and just expected it to have a blown head gasket or something....

Try and look for the wire I am talking about maybe it worked its way loose on your car also..

lucky bastard, some idiot sold it cheap because it needed plugs. I have wet dreams about finds like that. I got a turbo regal that way one for next to nothing, the woman owner was told by a trans shop that she needed a trans. All she needed was a TCC solinoid.

I always run into the smart guys that try to pawn a bad motor off as needing a tune up. I even told one guy before I came out that I am a ford master tech so he is not going to snake a clunker by me. The ******* still had me waste my time.

 

[reevesracing]

If you are smelling fuel that obvious at startup, you may want to check/replace your ECT sensor that is on the front of the intake manifold opposite the thermostat. It is one of the main inputs used to control startup fuel strategies.

Isn't the ECT the one that sends the PCM the actual coolant temperature? If so, that is working properly because it was increasing when I was watching the car warm up on the monitoring software.

 

[LaserRed01GT]

Isn't the ECT the one that sends the PCM the actual coolant temperature? If so, that is working properly because it was increasing when I was watching the car warm up on the monitoring software.

Yes, the one on the intake manifold is the one the PCM uses. I still think your HO2S is not being properly activated upon key on.

Did you reset the PCM when you replaced the MAF sensor?

 

[reevesracing]

Yes. The battery had been dead for a few days (Problem #3), before I installed the MAF, and had to charge the battery up to get it started after I installed it.

 

[reevesracing]

Getting this car going soon has become a #1 priority today because on my way to get the O2 sensor, my '01 vic p71 suffered a catastrophic incident....

While midway up an overpass, the car suddenly dropped to low gear at 70 MPH under load for about 3 seconds and spun a bearing and seized up the motor.

At least I can salvage the heads (PI heads) and hopefully some other parts to install on the '96 at a later date....

 

[LaserRed01GT]

Yes. The battery had been dead for a few days (Problem #3), before I installed the MAF, and had to charge the battery up to get it started after I installed it.

Did you disconnect the negative terminal ever? The KAM (Keep Alive Memory) portion of the PCM requires very little power to keep the stored memory intact. There is a good chance the battery still had enough power to feed the KAM, but not enough to turn the starter or power the rest of the car.

That bites about your Crown Vic.

 

[reevesracing]

I didn't even think about that. I will disconnect it in the morning and let it sit for about an hour while I install the O2 sensor, clean out the vic, and mow the lawn.

And yes, it does suck because it was such a good dependable car. One of the codes had to do with losing signal to the solenoid on the transmission, which must have caused it to suddenly downshift. I can't believe that happened....

Anyway, I will post more information tomorrow, since now I have added incentive to get the Mustang going this weekend (Especially since the wife needs her car during the week as well).

 

[reevesracing]

Here is the print screen from ProScan during the monitoring:

http://www.reevesracing.com/myfiles/proscan.jpg

 

[Awoods226]

My 96 gt does the exact same thing about getting up to speed. I am also getting the same O2 sensor code as you. But I dont have cats, and
I have mil eliminators going to the rear 02 sensors. So I don't understand how I can be receiving a code from them.

 

[reevesracing]

My passenger side front O2 sensor was bad, and that eliminated the code being thrown.

As for the bogginess and the power drain, I am now on the fuel pump relay and fuel pump as being the issue. Still tracing back.

 

[LaserRed01GT]

Cool, one down one to go. Let us know what you find..

 

[98bluevert]

My 96 gt does the exact same thing about getting up to speed. I am also getting the same O2 sensor code as you. But I dont have cats, and
I have mil eliminators going to the rear 02 sensors. So I don't understand how I can be receiving a code from them.

don't mark my words as anything correct but don't the mil's just send back a converted code to the computer to say the cats are still there.

if the o2 sensor wasn't needed wouldn't companies just weld the hole shut and we would have different mil's that don't need to be connected to o2 sensors.

 

[Mike97gt]

don't mark my words as anything correct but don't the mil's just send back a converted code to the computer to say the cats are still there.

if the o2 sensor wasn't needed wouldn't companies just weld the hole shut and we would have different mil's that don't need to be connected to o2 sensors.

Why weld them shut, that is a lot of work for nothing, shuting them off in the tune or tricking the pcm with elims works just fine.

the rear 02 can come into play on air/fuel in some failue cases, like a EXTREME case where the short and long term fuel trims are maxing out and the front sensors are not switching, then the PCM will look at the rear 02's and see what they are reading to try and bring the fronts back to switching and the ratio back to stoch.. This is not something that is common so I would not worry about it.

 

[LaserRed01GT]

the rear 02 can come into play on air/fuel in some failue cases, like a EXTREME case where the short and long term fuel trims are maxing out and the front sensors are not switching, then the PCM will look at the rear 02's and see what they are reading to try and bring the fronts back to switching and the ratio back to stoch.. This is not something that is common so I would not worry about it.

That was only the case with the old 1994-1996 20 second steady state catalyst efficiency monitor. The 1996 and later PCM’s have absolutely no way of actually using input from the rear O2 sensors to control fuel trim. Before the older style steady state CEM would run, it first required the correct input from the ECT, TPS, IAT, OSS (VSS), CKP, and a sufficient amount of vehicle run time. Once this was all satisfied the older steady state CEM would briefly temporarily transfer CL fuel control from the front O2 sensors to the rear O2 sensors. This was done to force a change to the switching rate of the rear O2 sensors to see if the cats were still good. The newer FTP switch ratio and index ratio OBD-II PCM’s have no way of allowing the rear O2’s to manipulate fuel trims.

There are two kinds of ways the Ford OBD-II (EEC-V) monitors catalyst efficiency. The switch ratio and index ratio. The switch ratio was used on Ford cars with PCM model year hardware platforms used between 1996-2003. The index ratio was used on some 2001 and later cars.

Obviously the PCM monitors catalyst efficiency by calculating the amount of oxygen storage the cat is capable of. The CEM counts front and rear HO2S switches (cross counts) during part-throttle, CL fuel conditions after sufficient ECT and inferred catalyst temperature is reached. There are up to 9 different load cells or air mass regions that the front O2 sensor switch (cross) counts can be stored in and used to dynamically change the CL fuel trims. 3 cells/air mass regions are typically only used though under normal operation. The rear O2 sensor switch counts can only be stored and used in 1 cell for all air mass measurements or observed load. This eliminates the rear O2’s from being able to be used for any type of fuel trim control.

EDIT: You might also be thinking about a FTP functional test that is performed on the rear O2 sensors during normal vehicle operation. On our FTP type CEM systems, the rear O2 sensor peak and low voltages are continuously monitored. Voltages that exceed the dynamic low/high thresholds will tell the PCM there is functional sensor and everything continues as normal. If the voltages have not exceeded the thresholds after a long period of vehicle operation, the air/fuel ratio may be forced rich or lean by the PCM in an attempt to get the rear sensor to switch, but this forced change to the air/fuel ratio is pre-determined by an algorithm and at no time is the input from the rear 02 sensors used actually control CL fuel trims.

 

[Mike97gt]

That was only the case with the old 1994-1996 20 second steady state catalyst efficiency monitor. The 1996 and later PCM’s have absolutely no way of actually using input from the rear O2 sensors to control fuel trim. Before the older style steady state CEM would run, it first required the correct input from the ECT, TPS, IAT, OSS (VSS), CKP, and a sufficient amount of vehicle run time. Once this was all satisfied the older steady state CEM would briefly temporarily transfer CL fuel control from the front O2 sensors to the rear O2 sensors. This was done to force a change to the switching rate of the rear O2 sensors to see if the cats were still good. The newer FTP switch ratio and index ratio OBD-II PCM’s have no way of allowing the rear O2’s to manipulate fuel trims.

There are two kinds of ways the Ford OBD-II (EEC-V) monitors catalyst efficiency. The switch ratio and index ratio. The switch ratio was used on Ford cars with PCM model year hardware platforms used between 1996-2003. The index ratio was used on some 2001 and later cars.

Obviously the PCM monitors catalyst efficiency by calculating the amount of oxygen storage the cat is capable of. The CEM counts front and rear HO2S switches (cross counts) during part-throttle, CL fuel conditions after sufficient ECT and inferred catalyst temperature is reached. There are up to 9 different load cells or air mass regions that the front O2 sensor switch (cross) counts can be stored in and used to dynamically change the CL fuel trims. 3 cells/air mass regions are typically only used though under normal operation. The rear O2 sensor switch counts can only be stored and used in 1 cell for all air mass measurements or observed load. This eliminates the rear O2’s from being able to be used for any type of fuel trim control.

EDIT: You might also be thinking about a FTP functional test that is performed on the rear O2 sensors during normal vehicle operation. On our FTP type CEM systems, the rear O2 sensor peak and low voltages are continuously monitored. Voltages that exceed the dynamic low/high thresholds will tell the PCM there is functional sensor and everything continues as normal. If the voltages have not exceeded the thresholds after a long period of vehicle operation, the air/fuel ratio may be forced rich or lean by the PCM in an attempt to get the rear sensor to switch, but this forced change to the air/fuel ratio is pre-determined by an algorithm and at no time is the input from the rear 02 sensors used actually control CL fuel trims.

I never said CL fuel trims, I said it was certain fault situations where this can happen, if the PCM can no longer get the front 02s switching after the long and short term fuel trims are maxed out then the PCM will look to the rear 02's and try to use those readings to find stoch again...

This was covered in the first ford EEC classroom they showed us this on a 2002 crown vic, the pid data even looks funny when the PCM attempts to make up front 02 readings off of the rear 02's..

To be exact it's not the rear 02 reading it will use directly but rather a PCM generated front 02 readout that is determined by rear 02 readings and other factors.

Your right that the rear 02's can not directly control closed loop fuel trim and I did not say it did.... I think your misunderstanding what I am saying.. latter on today i will see if I still have my old book from ford EEC classes, or I bet i can find it online to show you what I mean.

 

[LaserRed01GT]

I never said CL fuel trims, I said it was certain fault situations where this can happen, if the PCM can no longer get the front 02s switching after the long and short term fuel trims are maxed out then the PCM will look to the rear 02's and try to use those readings to find stoch again...

This was covered in the first ford EEC classroom they showed us this on a 2002 crown vic, the pid data even looks funny when the PCM attempts to make up front 02 readings off of the rear 02's..

To be exact it's not the rear 02 reading it will use directly but rather a PCM generated front 02 readout that is determined by rear 02 readings and other factors.

Your right that the rear 02's can not directly control closed loop fuel trim and I did not say it did.... I think your misunderstanding what I am saying.. latter on today i will see if I still have my old book from ford EEC classes, or I bet i can find it online to show you what I mean.

No, I understand what you mean, and I also understand the OBD-II theories and algorithms. I just see a lot of posts where people think that the rear O2's can come into play for fuel control and they cannot.

Even when the LTFT's and STFT's go beyond the allowed threshold, the PCM doesn't look at the rear O2's to try and control stoich. It physically cannot due to the nature of the way the rear O2's are used by the software. I used to be a service writer/manger at a couple of Ford/Mazda/Mercury dealerships and I couldn't believe some of the BS that they tried to teach us. In order for the PCM to use the rear O2's in an attempt to set a desired stoich baseline, the rear 02 sensor data would have to be dynamically used in more than one air mass cell and it is not. It is hard limited to one specific air mass cell and that makes it physically impossible to use input from the rear 02's get a baseline stoich calculation. The rear O2's are simply monitored for peak and low thresholds. If the cats are funcitoning properly, the rear O2 voltage will stay low and they will switch VERY slowly.

The only time the PCM will alter switching to the fronts in attempt to satisfy the desired stoich is at closed throttle closed loop. The absolute only time that the PCM "gives up" the normal front O2 switching is when the PCM decides it wants to do a FTP functional test. This is usually about every 6 driving cycles.

Have they taught you guys exponentially weighted moving average (EWMA) theories yet? That gets really interesting.

 

[Awoods226]

So your saying a bad rear 02 sensor could still throw a code even though I have MIL's on it. Also I was wondering If buying a hand-held tuner (SctXcal2) and shutting of the rear o2's would prevent the code.

 

[LaserRed01GT]

So your saying a bad rear 02 sensor could still throw a code even though I have MIL's on it. Also I was wondering If buying a hand-held tuner (SctXcal2) and shutting of the rear o2's would prevent the code.

Sometimes codes are accurate, sometimes they are not. PCM's are just whacky like that. What is the exact code you are getting? And yes, if you program out the rear O2's you will not get any rear O2 sensor specific codes.

 

[Mike97gt]

No, I understand what you mean, and I also understand the OBD-II theories and algorithms. I just see a lot of posts where people think that the rear O2's can come into play for fuel control and they cannot.

Even when the LTFT's and STFT's go beyond the allowed threshold, the PCM doesn't look at the rear O2's to try and control stoich. It physically cannot due to the nature of the way the rear O2's are used by the software. I used to be a service writer/manger at a couple of Ford/Mazda/Mercury dealerships and I couldn't believe some of the BS that they tried to teach us. In order for the PCM to use the rear O2's in an attempt to set a desired stoich baseline, the rear 02 sensor data would have to be dynamically used in more than one air mass cell and it is not. It is hard limited to one specific air mass cell and that makes it physically impossible to use input from the rear 02's get a baseline stoich calculation. The rear O2's are simply monitored for peak and low thresholds. If the cats are funcitoning properly, the rear O2 voltage will stay low and they will switch VERY slowly.

The only time the PCM will alter switching to the fronts in attempt to satisfy the desired stoich is at closed throttle closed loop. The absolute only time that the PCM "gives up" the normal front O2 switching is when the PCM decides it wants to do a FTP functional test. This is usually about every 6 driving cycles.

Have they taught you guys exponentially weighted moving average (EWMA) theories yet? That gets really interesting.

Yeah I know about EWMA... that is used to filter out data that is excessivly variable, that is used to prevent "false" check engine lights. without EWMA these tests would be useless. Did you think you were talking over my head

I was talking about how the PCM handles some fault modes.. They teach us what to look out for that can cause a misdiag, such as on 2005 or newer fords the pcm can shut down up to two injectors to prevent cat converter damage.. this can lead to a misdiag of a bad injector.

back to what I was talking about, how the PCM has the ability to try and jumpstart front 02 switching when it looses the ability to do so with long and short term fuel trims. we were shown this at the training center, he told us that rear 02's were used as one of the inputs and he showed us how the pcm can draw up it's own front 02 readings based off of the rear 02 inputs.. When this was shown to us you can watch the PID graph readout for the front 02 sensors and you will see a jagged pattern instead of the normal 02 sensor waveform..

They showed us this because this has sometimes lead to misdiags

You are only looking at how the PCM handles it's OBD-2 monitoring, when your talking about air mass cells you are talking about the parameters that the PCM looks for to run a OBD-2 test such as catalyst efficency.. Plus the rear 02 readings are used as one of the parameters for type a misfire detection, it's also used by the pcm as a input for inferred catalyst temp

What i am saying is the PCM can and HAS been designed in some ford models to be able to look at the rear 02 sensor reading for more than the catalyst efficency monitor. These open loop failure modes are not covered in a lot of OBD-2 descriptions and differ from car to car and year to year. a lot of how this stuff works is considered trade secrets and is not shared with the general public or with techs like me.

Look at how different a 2004 model year ford handles a type a misfire than a 2005 in a 2005 injectors may shut off where that was not in the program of a 2004.

Well anyways we should get back on topic..

 

[LaserRed01GT]

EWMA is used for far more than just monitoring catalyst efficiency or any monitoring for fast/slow constant filters for that matter. It is used in conjunction with the MAF and IAT to accurately estimate air mass and air density for load and fueling spark calculations. Another example of EWMA implementation, the engine is monitored for excessive torque generation at idle. If excessive torque is being produced at idle, the injectors can be turned off in order to reduce torque. If the frequency of injector cut-off is higher than the EWMA threshold, a P2279 code will be set and the adaptive fuel strategy (AFS) table can also be altered.

The rear O2 sensors are controlled with a MUCH slower switching amplitude and don’t have their output voltages used by the PCM software in a dynamic fashion like the front O2 sensors are. There is no way for the PCM to use the rear O2 sensor data to somehow try to “draw up” a front O2 sensor pattern to be used in case of a failure or hard fault. When you saw the abnormal readings on the scope during your training session, that had nothing to do with the PCM trying to look at the rear O2 sensors to try and re-establish a “normal” front O2 sensor pattern, it was simply the botched multiplexed signal that was returned to the PCM. When you have a total failure of one or both front O2 sensors or a loss of STFT/LTFT control, the PCM will simply resort back to its stored and learned front O2 data within the KAM. When O2 sensor input is perceived to be out-of-limits by the PCM, the memorized data from the KAM will be instantly be initiated. The PCM constantly checks the sensors against records of normal readings during normal operating conditions similar to its current state, specifically during specific speed-load points. Information gathered at different speed-load points are stored in fuel trim cells in the fuel trim tables, which can be used in the actual final fuel calculation. The PCM looks at the previously stored front O2 data to see if the engine is operating within normal “historical” conditions and if it is, the PCM replaces the sensor reading with a “educated guess” from the KAM. Mike I think you are a good and knowledgeable tech, but just keep up with your studies and you will learn more about the PCM as your experience grows, and you understand more about how the PCM works. The PCM operation and theory used to be an industry secret, but it hasn’t been for some time. When I was going through my L1 cert, a few NATEF instructors on the advisory committee recommended a series of books to me that opened the door to PCMs for me. They are even endorsed by NATEF. The author of the books is named Barry Hollembeak. He covers just about everything including even some of the extrapolated algorithms. Some of his books are actually used in classroom instruction. I'd highly recommend them to anyone wanting to get a more in depth understanding of OBD/PCM fundamentals.

Additionally the air mass cells are used for much more than just monitoring or diagnostic tests. Depending on RPM, load, min-bed cat temp, and number of front crosscounts, the PCM makes the determination which air mass cell to use. Depending on which air mass cell the PCM is currently operating in will dictate which algorithms the PCM will use to calculate the fueling/spark strategies.