How much effect do O2 Sensors have on driveability?

[morebhp]

I just replace my stock MAF with an certified rebuilt replacement and I still have a power loss between 2500 and 4000 rpm. --Especially in 3rd gear. Still feels like a mixture problem. Acts like it cant make up its mind to go until the runners open.

Oddly, it seems to run better with air temps around 75 degrees. Now, with it in the 40s... the problem is back.

The ACT sensor wouldn't do this would it? Perhaps the BAP? I've had both of these off and felt no change. I don't know what else to try.

Freaking thing is driving me nuts. headbang

So far I've replaced:
CID
MAF
Plugs
Wires
TPS

Thanks for any suggestions...

 

[Bizzy]

The first thing to do would be to check your codes and then run the KOEO & KOER tests . I never noticed any difference in runability (is that a word?) when my O2 sensors needed to be replaced, though your circumstances could be entirely different. O2 sensors will affect your gas mileage though as they tell the car's computer if you're rich or lean and the computer then will make adjustments according to what they "see". Keep in mind that if you are running rich it can cause premature failure of the catalytic converters.

A good article to read is here if you haven't already read it.

<small>[ October 30, 2003, 08:50 AM: Message edited by: Bizzy ]</small>

 

[morebhp]

Okay, I will try the KOEO & KEOR tests again. It showed nothing askew when I ran them about a year ago chasing the same ghost.

What about coil packs? When they act up, what happens? Does the car stop running? Does it just reduce performace partially?

My car feels fine at WOT. Its only the "pre-runner" stage that seems to be afflicted.

I've meticulously maintained this car and tried just about everthing in an effort to find the cause but the solution continues to alude me.

 

[sdpatt]

You mention a power loss, but is it due to a misfire? Do you feel any engine vibration or rough running during these power deficits or is it more of a fuel starvation type of loss? Gotta run those codes.

 

[morebhp]

Well, it feels like a fuel issue. I did have a bad plug wire a few years ago. I know what that feels like. It's there all day every day, in all weather conditions.

This one is more intermittent. It's worse in colder weather. It can be stopped by clearing the EEC memory but then gradually returns over the period of a few weeks. --It's this fact that tells me its a fuel/mixture issue. Otherwise there's no way this would happen. It would do it all the time.

So, to answer your question... I don't feel an engine "vibration" but it does seem to sputter, not audibly but you can feel it just kinda wimp out. And when 4K RPMs hit, the power really comes on strong. The transition is very abrupt. I wish I knew what exactly happened in the EEC system at this point. I know the butterflys open but there must be something else that changes in the air metering that brings this effect. At WOT there's not problem so I know I'm getting fuel. Its just at low RPM under load that it is hesitant.

On bad days it will sometimes bog when I start out. I was sure it was the MAF but switching between the new on and the old one bares no improvment.

Grr! I'm so tired of this problem I could scream.

 

[Kurt]

I have the same type of problem with my '95 MTX but I have not run the codes yet. I was told that if you have ever had the engine steam cleaned, this may have affected the electrical system. Can't tell you where to start but I have done plugs & wires already but it hasn't helped.

 

[rangerj]

morebhp,

You started your thread asking about O2 sensors affect on performance. Why? Do you have reason to suspect the O2 sensors?

In answer to your question, yes the O2 sensors can indirectly affect performance. The computer will go into what I call the "limp in mode" if it does not receive the expected signals from the O2 sensors.

The computer enrichens the mixture, because a lean mixture can burn valves and/or burn holes in the top of pistons.

The computer also goes into a very conservative advance curve. The idea is for the car to be drivable, but just well enough to be able to "limp in" to the dealership.

This is also true for most, if not all, sensor failures that will trigger the Check Engine light.

So, check your codes. O2 sensors do not usually fail all at once. They usually deteriorate gradually, and work intermittantly before they quit working altogether.

I recommend changing the O-2 sensors at 50K to 75K max. rangerj

 

[morebhp]

[You started your thread asking about O2 sensors affect on performance. Why? Do you have reason to suspect the O2 sensors?] ?

Well, I'm only considering them because they are one of the few items that I haven't replaced that has an effect on air/fuel mixture.

I have been told that there won't necessarily be any codes if the O2 sensors haven't degraded to a severe level. So, I'm thinking perhaps they are partially malfunctioning causing just enough misinformation for the EEC to screw up the mixture. Perhaps someone has had these symptoms, replaced the sensors, and solved the probelm. Just fishing for clues here.

I've been chasing this problem for quite some time. I've tried over and over but I've never found a code in memory that would indicate the cause.

So this leaves me two choices: Ask you guys for suggestions, or take it to a mechanic and pay him to tinker with it for months and still never solve the problem.

Any help is appreciated.

Thanks.

 

[rangerj]

morebhp,

If I remember right there is an FAQ at SHO Times on how to test the O2 sensors by heating them with propane, and measuring either the current flow or resistance (?).

The other way to test them is to use a scanner that can watch them switch (from rich to lean and back) in real time. The sensors "switch" continuosly when they are working properly.

The "tell tale" sign of a failing sensor is one that stops switching periodically or one that switches slower than expected.

If the O2 sensors are at least 50k old I would change them as a maintanence item. rangerj

 

[morebhp]

Thanks RangerJ,

I think they will be my next thing to eliminate from the pool of possible culprits. I only have 43K miles but that's close enough. They are still nearly 9 years old. Any brand recommendations? Bosch? Denso?

Here's another thing. Today its 72 here in Michigan. My car is running very well. Back last week when it was cold it was really acting up. Stumbling when I started off in 1st gear and then giving me the weezing/sputtering thing as I wound through 2K-4K rpm in 2nd and 3rd. It does it even when its warmed up. Even 30 minutes after starting. Today its pulling strong and even. Almost no "retartation".

I swear this problem is temperature related. That sort of rules out the 02 sensors.

I've considered replacing the ACT sensor and/or the BAP sensor but I'm just not convinced they could cause this much trouble.

Comments?

Thanks again.

<small>[ October 31, 2003, 12:50 PM: Message edited by: morebhp ]</small>

 

[rangerj]

morebhp,

Here are a couple of thoughts. Keep in mind that I am just thinking out loud and make no claims that the following will solve your problem!

Colder air is more dense, and warmer air is less dense, and usually more moist. Next thought, what is affected by the density of the air? Mass Air Flow, Manifold Absolute Pressure/Barometric Pressure, Idle Speed Control/By Pass Air?

What is affected by the air temperature and/or ambient temperature? ACT (air charge temperature sensor)?

Does any of this mean anything? It may help to make sure that connections are clean and making good contact.

Another thought. The colder temperatures will cause hoses, like vacuum hoses, to contract and open up very small cracks.

Does your "snorkle tube" from the air box to the throttle body have any cracks in it?

As I said, just some thoughts. Please keep us informed. As the dude said in Dirty Harry, "I gots to know". rangerj

 

[morebhp]

Thanks again RangerJ, I will check as much of that stuff as I can this weekend and report back. I've looked in the past for hose cracks but that's one of those needle-in-a-hay-stack jobs. I'll look again.

I'll also double check all my connectors and make sure there's not a bunch of oxidation built up.

Good stuff.

 

[SHOZ123]

You can test the IAT with an ohm meter. The BARO sensor is only used at WOT.

50F, 3.51V, 58.75 Kohms
68F, 3.07V, 37.30 Kohms
86F, 2.60V, 24.27 Kohms

<small>[ November 01, 2003, 10:00 AM: Message edited by: SHOZ123 ]</small>

 

[Markus]

morebhp:
It can be stopped by clearing the EEC memory but then gradually returns over the period of a few weeks.

I experience the same thing but over a period of 6-8 weeks. Low end power will gradually drop and resetting the EEC restores the power. My car is completely stock and in the last 6 months I have replaced (all new OEM parts unless otherwise specified):

- MAF
- 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
- timing belt
- radiator (Modine)
- water pump
- spark plugs & wires
- coil pack
- EGR valve
- DPFE sensor
- crank sensor
- cam sensor
- knock sensor
- TPS
- IAT sensor
- both coolant temp sensors
- oil pressure sensor
- air filter
- EGR controller
- EGR sample tube
- fuel pressure regulator
- fuel pressure dampener
- fuel filter
- fuel pump
- valve cover gaskets and plug well seals (Felpro, not OEM)
- injectors and their o-rings

Other service in last six months
-complete tear down, clean, rebuild intake manifold with all new gaskets
- thorough cleaning of throttle body
- valve shim service
- complete fuel line flush when replacing other fuel system components
- complete brake fluid flush
- complete PS fluid flush

All of this makes me wonder if there is a bug or other flaw in the EEC software. I have even swapped EECs with a friend with the same car and still experience the power drop. My friend experiences it too.

 

[morebhp]

Well Markus, I think you have described my situation exactly. I haven't replaced nearly as many things as you but no matter what I try... the problem persists. It's completely illusive. One day it does it.. and you think you fixed it. And the next its back with a vengeance and you cuss and move on to the next idea. The only thing that has a noticeable effect is to clear the EEC memory.. as you said.

I'm about out of ideas, and after reading your account, it appears to me that I might as well give up now. If you still have it after all that... then I see no point in repeating it on my car.

Thanks for the info... even though its discouraging.

 

[morebhp]

Markus,

I do have one question. Did you ever replace the AIB? I've been told by many that sometime in 1993 or 1994 Ford went to a "cheaper" design. Later they realized it wasn't working properly so in 1996 they redesigned it.. or went back to the old design from the gen 1 cars. Supposedly this thing is supposed to solve stumbling problems in lower RPMs.

I have replaced my AIB but back when I did, I was not aware of this TSB. Of course the "professor" at the parts dept. didn't alert me of it either. So I bot the same inferior part. That was about 4 years ago and Ive never since gone back and asked for the replacement design. I guess I'm too pessimistic that it will help.

As this problem has become a sort of "mission" for me, I have decided to "experiment" with my old AIB valve that came off when I had to replace it for stalling the engine. This weekend I opened up the old one and took it completely apart. I pryed off the end cap and unscrewed the plastic piece inside that holds the spring which provides the tension on the valve stem.

I replaced the spring with a softer one and installed the modified valve on the engine. At first it ran like crap. It was really weak in the low-end but after about 5 minutes it seemed to adapt. I should have reset the EEC memory but I had to go out immediately to pick up our order of Chinese food. I'm going to reset it tonight and see how it goes tomorrow.

The only reason I'm focusing on the AIB is because that is one thing I KNOW they changed on the later models. My '90 and my dad's '91 never had this problem. Ever. So its something they did after '91 or '92. But what.....

 

[Markus]

Damn, I knew I forgot to replace something. I'm going to order an AIB tomorrow. I've never had an idle problem (except when the O2 sensors went bad) but it's worth a try. I'll let you know how I fare on Wednesday or Thursday.

 

[AutoSHO]

My car's BAP made a big difference when I changed it. Much more low end power and easier starting.

 

[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

 

[AutoSHO]

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