Rich and lean? (Ford)

[ExDelayed]

`96 Ford with a 2L. Somehow I am getting both codes. The lean code always comes first, with the rich code either second or pending. For the life of me I cannot figure out where it is coming from.

The car has 131K. The last oil sample showed no bad signs of fuel in oil, sill was below Blackstone's recommendation actually. Anyway, fuel filter is new (yearly maintence), the upstream O2 was sluggish so it was replaced (both old and new showed ~.38v at idle. The exhaust system is stock, with the exception of a aftermarket muffler (though I dont see how that could cause any problems). Both the exhaust manifold to head and manifold to cat gaskets have been replaced (cracked manifold), so I know I am not getting air in there. Intake system is stock, and sealed up like it should be (again going off of the oil sample reading on silicon and my triple check). I know no air is sneaking in after the MAF.

As far as driveability goes, the car seems like it always has. If the rich and lean codes are pulled, the car still drives fine for about a day then the light comes back. If the computer is reset by means of disconnecting power to the ECM, the car is downright dangerous. Throttle response sucks. If you are stopped and go to WOT, pedestrians could beat it across the intersection. Part throttle is pretty much the same. You have to barely touch the throttle, until about 3K rpms and then you can get on it more. If you go past about 75% throttle, it falls on its face again. It will slowly get better as the car learns, but by the time it is almost back to normal, the light is back on.

With the light on, power seems normal. There is an off-idle stumble, the idle can fluctuate sometimes as much as 200 rpms in gear, sometimes its perfect. Rarely idles below 500 rpms (which seems low for a 4 cyl, at least to me), occasionally it will be stable at 400. There is also a flat spot in the powerband between ~5K and ~6K rpms.

I honestly cant remember how the car drives with the light off, but I am creeping up on emmissions quickly, and need to get it taken care of. I had thought it was due to the sluggish 02 and was waiting for funds to replace it. Now I have them, and its in, I need it off.

I am thinking (hoping?) that whatever is causing the CEL, will also cure the flat spot and the off-idle stumble. It would seem like it would if I am lean at one end of the powerband and rich at the other.

I have yet to pull vacuum readings, but have the ability if so requested.

Suggestions?

 

[ExDelayed]

Oh ya, forgot to add. Plugs are fine and gapped correctly. They have the normal Chevron fuel discoloration but other then that, perfect for 10K. The wires fall well below Ford's recommendation of 6000 ohms/foot discard rating. I havent tested the coil.

 

[JTK]

Could be a dirty or faulty MAF sensor. It's quick & easy to check atleast!
G/luck
Joel

 

[ExDelayed]

Its been awhile since I have cleaned it, so I will grab some cleaner tomorrow on my way to work.

 

[DavoNF]

If you are getting both, it would seem to point to faulty O2 sensors.

You could also check the ECT (coolant sensor). A lean condition can also be caused by exhaust manifold leaks.

Dave

[ April 29, 2004, 05:09 AM: Message edited by: DavoNF ]

 

[T-Keith]

The O2 should occilate at idle, but stay steady at WOT. A monitering software would do wonders in helping diagnose this.

I'd check what others have mentioned, MAF and fuel pressure.

What your saying makes sense. Obviously some sensor is throwing your fuel curve out of whack. This explains the poor running when the computer has been reset. When the computer realizes the problem, it puts the car into a "safe mode" where the fuel curve is preset, restoring driveability, but it's still far from opitmal.

How is WOT when the light is on?

-T

 

[jsharp]

The earlier Fords run open loop at WOT. Are the OBD-II cars that way also?

 

[ExDelayed]

quote:

---

Originally posted by DavoNF:
If you are getting both, it would seem to point to faulty O2 sensors.

You could also check the ECT (coolant sensor). A lean condition can also be caused by exhaust manifold leaks.

---

O2s are good, the ECT has been checked, and the exhaust manifold leaks havent existed for almost a month. The light wont stay off.

 

[The_Jeff]

I wonder how your fuel pressure is. Do you have vacuum going to the regulator at the fuel rail? Seems like you've got something off spec that the 'puter is madly compensating for, and almost succeeding.

If your long-term fuel trim is heavily richened, for example, because your pressure is low due to a faulty pressure regulator, the occasional moment where things work properly results in too much fuel and your "rich" code.

 

[friendly_jacek]

quote:

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Originally posted by ExDelayed:
the upstream O2 was sluggish so it was replaced (both old and new showed ~.38v at idle.

---

Are you sure?
Isn't front O2 supposed to oscilate between reach and lean? If you get a flat line with warm sensor, it is dead.

 

[ExDelayed]

I was under the impression that all the EEC V Fords (96+) run rich at WOT to keep the cats cool. I have also heard that ignoring the O2s can begin as early as 70% throttle, which could explain that flat spot that I was mentioning if it was ignoring the O2s and my fuel curve wasnt correct.

Anyway, picked up some cleaner today on my way to work, cleaned the big glob (big conisdering the size of the filaments in the MAF) off of the MAF springs. Reset the code, forgot to connect the MAF back up to the wiring harness and had it remind me on the way home.

Reset it again with the code reader tonight. From what the handheld was saying, the car is still in open loop and needs to get some more readings on the O2s before they go back online. I am expecing that on my way to work tomorrow.

I will pull fuel pressure on sat if my pressure/vacuum guage goes high enough. The previous and the new O2 do occiliate, the old one just did it very, very slowly. The ~.38v comment was meant to be roughly .38v. It does change. I rule out the O2s anyway, because the chance of having a sluggish one, and then buying a new one and having it be bad is very slim.

The only other three things I could see playing with my air fuel ratio, besides fuel pressure, are the emmissions equipment. The DPFE sensor(Differential Pressure Feeback for Egr) gives me good readings, which only leaves the EGR valve itself and the EVR (dont remember what that stands for but it controls the EGR valve). Those are simple tests. The Idle Air Control sensor could also be freaking out, but I would only expect that to give me a problem at idle. Either way, I need to disconnect the IAC to test the EGR valve.

WOT with the light on is acceptable. Like I said, I dont have much to compare it to because I cant remember how the car drove with the light off. It will still get up to speed acceptably, considering that its just a 2L with 125hp feeding into an automatic.

I did have someone recommend to check the compression pressures. He is saying that it sounds like a head gasket problem. He thinks that its bleeding off into my coolant system. Blackstone says that there is no coolant in my oil, and with a sealed coolant system, I would think I would be blowing hoses like crazy.

Thanks for the input so far.

 

[TheLoneRanger]

ExDelayed, hopefully it'll be fixed when you drive it again, after the MAF cleaning. If not, try doing a voltage check on the TPS. Basically you're looking for a smooth (1v-4v?) transition on the signal wire when the throttle is advanced. TPS's tend to wear out in the lower throttle area where most movement occurs, and this will give all sorts of drivability problems.

 

[jsharp]

quote:

---

Originally posted by T-Keith:

quote:

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Originally posted by jsharp:
The earlier Fords run open loop at WOT. Are the OBD-II cars that way also?

---

Technically they are in open loop. On most if not all MAF cars, O2s are ignored when the throttle is opened more than ~75%. Techically they run based off of MAF input. However they adjust fueling based on a previous adjustment number. This adjustment number is based on O2 input. So even though O2 readings are ignored during WOT, they can still affect it.

-T

---

Ok, sounds like you're talking about initial fuel map + trim numbers being used as a baseline for WOT operation.

To the OP. I didn't mean to highjack the thread. It just brought up some questions I've had for a while...

 

[T-Keith]

quote:

---

Originally posted by jsharp:
The earlier Fords run open loop at WOT. Are the OBD-II cars that way also?

---

Technically they are in open loop. On most if not all MAF cars, O2s are ignored when the throttle is opened more than ~75%. Techically they run based off of MAF input. However they adjust fueling based on a previous adjustment number. This adjustment number is based on O2 input. So even though O2 readings are ignored during WOT, they can still affect it.

-T

 

[ExDelayed]

Been a few days. If the light was going to come on it would have been back on by now. Throttle response is greatly improved, the car is quicker then pedestrians now too! Im so happy.

I guess I got ahead of myself and tried to overdiagnose the problem.

Thanks for your input everyone!

 

[DavoNF]

What was the problem then, dirty MAF?


Dave

 

[ExDelayed]

quote:

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Originally posted by DavoNF:
What was the problem then, dirty MAF?

---

Yes.

 

[DavoNF]

Thanks. Better give mine a clean soon.

The MAF must accumulate this gunge slowly, so the performance gradually decreases, but it is not noticed until it is really bad. Should be a regular maintence item IMHO.

Dave

 

[T-Keith]

quote:

---

Originally posted by jsharp:

quote:

---

Originally posted by T-Keith:

quote:

---

Originally posted by jsharp:
The earlier Fords run open loop at WOT. Are the OBD-II cars that way also?

---

Technically they are in open loop. On most if not all MAF cars, O2s are ignored when the throttle is opened more than ~75%. Techically they run based off of MAF input. However they adjust fueling based on a previous adjustment number. This adjustment number is based on O2 input. So even though O2 readings are ignored during WOT, they can still affect it.

-T

---

Ok, sounds like you're talking about initial fuel map + trim numbers being used as a baseline for WOT operation.

To the OP. I didn't mean to highjack the thread. It just brought up some questions I've had for a while...

---

You go it.

ExDelayed, glad it's running better.

-T