How much effect do O2 Sensors have on driveability?

[morebhp]

This is all very helpful.

Markus, I see also there is no BAP or MAP sensors on your list. If that wasn't just an oversight, you may consider those as well. AutoSHO says it made a big difference for his low end torque. --Can anyone concur with AutoSHO? Someone stated earlier in this thread that the BAP is only used during WOT. Can anyone varify that? If so, that seems to rule out the BAP for low-end power problems.

How about the MAP sensor? Anyone have any miracle stories after replacing that? (we are awash with sensors.... where's Mr. Spock when you need him...)

Markus, I hope the AIB does some good for you. Be sure to get the new model. According to shotimes.com: "the 1996 design part Prefix is F96x-xxxxxx-***"

 

[projectSHO89]

The MAP/BARO sensor is the same as the MAP/BAP.
There is only one sensor and it is only on the MTX.

You can unplug it for diagnostic purposes and run without it. You will get a CEL under this circumstance, but you can do this to see whether or the sensor's absence makes any difference.

Steve

 

[Markus]

shoinoff95:

Markus
- O2 sensors - Ford specifies two different sensors for the 95 ATX depending on vehicle calibration - this is why I stay away from Bosch - they provide just 1 sensor for both calibrations

Markus, I need to replace my front O2, and I was planning on just getting the Bosch, but I don't know now. How do you know what calibration that you need and which brand of O2 should you get? I have never heard of this before? shrug

I have a sticker on the door jamb of the rear left door. This is the calibration sticker. I had my local Ford dealer search for the correct sensor. The calibration sticker actually didn't help them. I had to remove a sensor to take to the dealer. I think there was "DY-nnn" (where nnn is a 3 digit number) engraved on it. The dealer used this info to order the correct sensor. I don't know what the difference between the two sensors is, and neither does my dealer. Hope this helps.

 

[Markus]

AutoSHO:
I have the sensors Autozone specified for the MTX in my car, made by Bosch, and I've gotten 34 MPG. 'nuff said.

But I think there is only one possible OEM sensor for MTX cars, and using a Bosch sensor instead of an OEM sensor is fine. You won't go wrong.

As I previously stated, there are two different sensors for my 95 ATX. Bosch specifies just one sensor as a replacement for BOTH OEM sensors. Given that I do not know how the two ATX sensors differ, choosing the correct OEM sensor makes more sense (to me, at least) than using the one-size-fits-all Bosch sensor. Given that I pay only trade prices for parts at my dealer, and that these are almost always less that non OEM parts, I see no reason to buy non OEM parts.

 

[92greensho]

To all. What do you mean by AIB??

Do you mean IAC (Idle Air Control valve)?

 

[SHOZ123]

FWIW OEM O2 sensors are made by NGK.

 

[AutoSHO]

morebhp:
This is all very helpful.

Markus, I see also there is no BAP or MAP sensors on your list. If that wasn't just an oversight, you may consider those as well. AutoSHO says it made a big difference for his low end torque. --Can anyone concur with AutoSHO? Someone stated earlier in this thread that the BAP is only used during WOT. Can anyone varify that? If so, that seems to rule out the BAP for low-end power problems.

How about the MAP sensor? Anyone have any miracle stories after replacing that? (we are awash with sensors.... where's Mr. Spock when you need him...)

Markus, I hope the AIB does some good for you. Be sure to get the new model. According to shotimes.com: "the 1996 design part Prefix is F96x-xxxxxx-***"

The BAP also made a difference in starting, so I am pretty sure its not only used at WOT.

 

[morebhp]

Right. Some call it IAB for "Idle air bypass". If I called it AIB I was being dyslexic.

 

[92greensho]

The IAC only has one purpose. It meters the correct amount of air needed to maintain the idle RPM (700-800). It is simply a valve that allows a variable amount of air to bypass the throttle body. A bad IAC will have one of 3 symptoms.
1- Rolling Idle. If the IAC valve is sticky the PCM will command the valve to adjust idle, but the valve will be unable to respond smoothly. This will cause the PCM to open and close the valve sporadically in an attempt to maintain the correct idle RPM.
2-Check engine light. If there is an electrical problem internal to the IAC, or in the IAC wiring it will set a code
3- Stall/ No-Start. The throttle body is normally closed, and if the IAC is stuck closed, there is no way for air to reach the intake manifold. If this is the case the car would stay running/start running as soon as you stepped on the throttle.

Bottom line, an IAC will only affect idle (closed throttle) situations. Any loss of power will not be caused by an IAC. (unless for some reason the IAC is shorting out the reference voltage circuit, witch is VERY HIGHLY unlikely).

 

[morebhp]

What you say up there is all true. I would ad that the IAB can cause surging at steady throttle if it is sticking. That's not an uncommon problem. But right, it won't cause the mixture to be compromized because it's all "metered" air.

 

[SHOZ123]

<strong>

The BAP also made a difference in starting, so I am pretty sure its not only used at WOT.

Seems you are correct.

• <font size="2" face="Verdana, Helvetica, sans-serif">The Manifold Absolute Pressure (MAP) sensor operates as a piezoelectric (pressure-sensing) disc. However, rather than generating a voltage, its output is a frequency change. The sensor changes frequency relative to intake manifold vacuum. The sensor frequency increases as vacuum increases. The MAP sensor allows the PCM to determine what the engine load is. Its signal affects air/fuel ratio, ignition timing, EGR flow and altitude compensation.
  
  The BARO sensor is used to sense the changes in barometric pressure, allowing the PCM to sense the altitude at which the vehicle is operating. Its signal affects air/fuel ratio, spark and EGR for altitude compensation.

<font size="2" face="Verdana, Helvetica, sans-serif">

 

[92greensho]

The IAC will NOT create a surge at cruise. The amount of air that the IAC is capable of
flowing at 100% open insignificant compared to a partially open TB. Besides during
cruise, the IAC is commanded wide open regardless of RPM. The reason for this is so
that when you take your foot off the throttle and close the butterfly you don’t get a
“almost stall” concern.

Also, and correct me if I’m wrong, but I don’t believe the SHO’s have a MAP sensor.
Engine load is calculated by MAF voltage and TPS.

 

[morebhp]

Quote: The IAC will NOT create a surge at cruise.

I'm not going to argue this point. I will only submit this section from Shotimes.com.

My SHO surges at steady throttle... why?

I can also site many letters from Doug Lewis and Vito from the <U>SHO Registry</U> Magazine.

All I will say is: if I were having surging problems, I certainly wouldn't rule out the IAB/IAC valve without checking it out.

 

[AutoSHO]

92greensho:
The IAC will NOT create a surge at cruise. The amount of air that the IAC is capable of
flowing at 100% open insignificant compared to a partially open TB. Besides during
cruise, the IAC is commanded wide open regardless of RPM. The reason for this is so
that when you take your foot off the throttle and close the butterfly you don’t get a
“almost stall” concern.

Also, and correct me if I’m wrong, but I don’t believe the SHO’s have a MAP sensor.
Engine load is calculated by MAF voltage and TPS.

Okay, you're wrong. They use the MAP sensor as a baromatric pressure sensor, MTX only. And you'd be surprised how much air the IAB can flow... When I had an improperly installed LPM, the IAB and timing systems together could make my car surge to 3,000 rpms, with a closed throttle.

 

[AutoSHO]

SHOZ123:
<strong>

The BAP also made a difference in starting, so I am pretty sure its not only used at WOT.

Seems you are correct.

• <font size="2" face="Verdana, Helvetica, sans-serif">The Manifold Absolute Pressure (MAP) sensor operates as a piezoelectric (pressure-sensing) disc. However, rather than generating a voltage, its output is a frequency change. The sensor changes frequency relative to intake manifold vacuum. The sensor frequency increases as vacuum increases. The MAP sensor allows the PCM to determine what the engine load is. Its signal affects air/fuel ratio, ignition timing, EGR flow and altitude compensation.
  
  The BARO sensor is used to sense the changes in barometric pressure, allowing the PCM to sense the altitude at which the vehicle is operating. Its signal affects air/fuel ratio, spark and EGR for altitude compensation.

<font size="2" face="Verdana, Helvetica, sans-serif">

I did read a little more about it and it is used at heavier throttle application to update the fuel trim for all operating conditions. The TSB I was reading also stated that it can have an effect on idle quality because it could cause the fuel trim to be rich at idle and lean at WOT if the MAF or the Map(baro) was malfunctioning.

Edit: morebhp, I propose this: Take your car to a dyno. Get it dynoed (with Air/Fuel analyzation) while this low-end power loss is a problem. Then, reset the PCM, and dyno it again. I'd be willing to bet that your A/F ratio is getting leaned out over time (and that will be shown on the dyno).

<small>[ November 05, 2003, 02:15 PM: Message edited by: AutoSHO ]</small>

 

[92greensho]

"Okay, you're wrong. They use the MAP sensor as a baromatric pressure sensor, MTX only. And you'd be surprised how much air the IAB can flow... When I had an improperly installed LPM, the IAB and timing systems together could make my car surge to 3,000 rpms, with a closed throttle.

--------------------
Chris"


Chris, first of all a MAP sensor and a BARO sensor are different only in application. They both work the same way, but a BARO senses barometric pressure and a MAP sensor senses intake manifold vacuum (which is also pressure, only its less than 14.7psi or atmospheric pressure). A 5speed SHO has a BARO which senses pressure outside of the manifold unlike a MAP.

So its like I said before SHO’s do not have MAP sensors. They don’t need them. MAF and TP are a much more accurate way of measuring engine load.

Also about the IAC flow. An IAC is capable of flowing enough air to rev the engine to 3 probably 4k RPM with no load. But if your IAC was stuck wide open, and you put your SHO in gear it would barely move faster than a normally idling SHO. Its simple physics. Take your IAC off, and look inside at the plunger and seat. Then look at the size of the throttle body opening, and compare. Measure and calculate the openings if you want to. In the end you will find out that the IAC opening is insignificant when compared to the TB.

You can continue to argue with me if you want to, but just to let you know I am about 8 months away from receiving my Senior Master Technician certification from Ford, with a specialty in drive-ability.

-Travis

 

[morebhp]

Okay Travis, it sounds like you are a good person to ask this then.

What would you suggest I investigate if I am experiencing an approx 10% loss in power from 3K-4K RPM. Usually it includes a mild surging or stumbling, as if there were air pockets in the fuel line. (just to illustrate the sensation)

First let me varify a few things:

1. My plugs and wires are relatively new (10K miles). All OEM.
2. New TPS.
3. New MAF
4. Intake and runners are clean. (I looked)
5. CID is new.
6. Cannot find any vacuum leak.
7. Fuel mileage seems good.
8. Starts fine.
9. Disconnecting BAP renders no change.
10. Disconnecting ACT renders no change.
11. Stumbling gets worse over time. (2-4 weeks)
12. Can be greatly reduced by clearing EEC memory
13. Car has done it since it was a year old.
14. Never found a code to indicate a problem.
15. Power at WOT seems fine.
16. Problem seems worse when outdoor temp is real hot or cold. Runs better at 75 degress. (?)
17. All other maintenance has been done religiously.

Why the stumbling? What would you check first? I'll accept any guesses.

Thanks.

 

[92greensho]

Well, let me start with a couple of questions.

1) What do you mean clearing the EEC memory. Clearing DTC’s (diagnostic trouble codes) or clearing the KAM (keep alive memory)?
2) You said that it seems ambient temperature related. Do changes in engine temp show any differences?
3) Have you hooked up a fuel gauge and watched the reading wile you made a run in witch your power loss symptom was present? If so what were they?
4) How did you check for vacuum leaks?
5) You said the you never found a code to indicate a problem. What codes have you found?


Let me know on the above questions, an in the meantime try a couple of things.

1- unplug your IAT (intake air tem sensor) then reset the KAM. See if your problem returns.
2- Then do the same thing with the BARO sensor.

 

[morebhp]

1) What do you mean clearing the EEC memory. Clearing DTC’s (diagnostic trouble codes) or clearing the KAM (keep alive memory)

--> The KAM. Naturally it effects the engine's behavior.
------------------------------------------------

2) You said that it seems ambient temperature related. Do changes in engine temp show any differences?

---> No, it does this just after starting... or after running for 30 minutes.
------------------------------------------------

3) Have you hooked up a fuel gauge and watched the reading wile you made a run in witch your power loss symptom was present? If so what were they?

---> No, I've never suspected fuel starvation because WOT is strong. Where would I get one of these and how is it used?
------------------------------------------------

4) How did you check for vacuum leaks?

---> Well, I used a colored oil-like substance I found at an auto parts store desiged just for that. Its supposed to get sucked into any leaks. ---See, the reason I don't think its a vacuum leak is because this car has done this since nearly new. Its so unlikely I developed a leak after 9 months and 5K miles on a new car. The intake has never been removed.
------------------------------------------------

5) You said the you never found a code to indicate a problem. What codes have you found?

---> Well, I had a CID failure once. Fixed it. I've run the KOEO and KOER tests many times looking for clues but nothing ever appears. Neither CE faults or non CE faults.
------------------------------------------------


Let me know on the above questions, an in the meantime try a couple of things.

1- unplug your IAT (intake air tem sensor) then reset the KAM. See if your problem returns.
2- Then do the same thing with the BARO sensor.

---> Actually I just tried that this week. I'd tried it before and it made no difference. Same result this time. --Nothing seems to matter. I can even disconnect my MAF and still feel it.
------------------------------------------------

<small>[ November 07, 2003, 11:37 AM: Message edited by: morebhp ]</small>

 

[92greensho]

ATX or MTX? you talk about the BARO, so I assume the later.
Year?
Miles?

Do you think you are loosing a cylinder or two, or does it seem to smooth of a power loss for that? I ask because when you pull the MAF connector the PCM automatically pulls fuel calculations off a stored chart. Basically it makes a guess as to how much fuel it needs for a given TP position. And it fails on the rich side.

You also said that this problem happens at WOT? around 2-4k RPM? When the PCM reads WOT, it also ignores the learned fuel trim tables. It makes a transition from closed loop(reading O2 sensors) to open loop (ignoring O2, and using plenty of fuel to create maximum HP). Open loop injector pulse width duration (the amount of fuel needed) is pulled off of a table that is set in stone. It would not be affected by clearing KAM. So we can almost rule out electronic fuel delivery.

So what we are looking at is probably ignition or Base engine.

Firs ignition - Plugs and wires are new. Assuming that they are ok, what we have left is coil pack, ICM, CKP, PCM, and wiring harness.

-PCM is highly unlikely.
-wiring harness? Unlikely with no codes.
-CKP will almost always throw a circuit malfunction code. Or make your tach bounce.
-Coil pack and ICM on EEC IV systems will sometimes throw a code, but these are the two I would go after -first. Without a SBDS (Service Bay Diagnostic System scan tool) It is pretty much replace and check. Just to warn you an ICM is $300+ new, I would check a bone yard. The SHO’s also share the ICM with a T-Bird SC if that helps.

Second is base engine – This is unlikely as the problem seems to be related to KAM and because it’s a SHO, and they have almost no history of base engine failure. But I would still want to check compression anyway.

Try this for now, and let me know what you come up with.

Good Luck. Travis