CEL: Front and Rear Banks Rich

[ckinart]

Hi all,

My CEL has come on twice in the past week. Both times it has come on after the car has been running for only about 3 minutes and the outside temperature has been 35 to 40 degrees F. On both occasions, the light stayed on for only about 2 minutes and went off. I checked the codes the first time, and the only ones that came up were continuous codes 173 and 177 which indicate front and rear banks rich. Both O2 sensors are OEM and were replaced about 6 months ago.

I'm under the impression that the engine system is not supposed to evaluate emissions until the engine has reached operating temperature. In addition, I thought I read somewhere that the control system purposefully runs the engine rich until it reaches operating temperature. Is this correct? Clearly, having the CEL come on after only 3 minutes of running in cold weather is not long enough for the engine to reach operating temp. Is this an ECT problem?

Can anyone validate these statements? Any ideas what might be happening here? FWIW, the t-stat and ECT were both replaced last spring, top end 60K done this summer with new OEM plugs/wires, O2s, etc.

Any thoughts would be much appreciated!

<small>[ November 29, 2003, 10:45 AM: Message edited by: ckinart ]</small>

 

[ckinart]

Nobody has any input on this one, huh? I did a search before I originally posted and found numerous posts regarding the codes I have individually, but not both at the same time and specifically when the engine is still cold.

If anyone has any ideas or pointers, they'd be much appreciated!

 

[AutoSHO]

Check your fuel pressure. If you get both banks running rich chances are you have a problem with fuel pressure. Also, try cleaning your MAF sensor.

Whats your fuel mileage like?

 

[ckinart]

Chris,

I've recently cleaned my MAF sensor, but perhaps I could try that again. As for fuel pressure, I'm hoping that isn't the issue since I just replaced the fuel pump last spring. Would a failed fuel pressure regulator give me this problem? I'll look into checking the pressure ASAP. My fuel mileage is about 21 mpg with mixed city and highway driving (I think that's about average, right?).

Thanx for the pointer!

 

[Rockledge]

Can we assume you replaced the fuel filter recently, as well?

Check for vacuum and exhaust leaks, too.

 

[ckinart]

Rockledge:
Can we assume you replaced the fuel filter recently, as well?

Check for vacuum and exhaust leaks, too.

Yes, the fuel filter was replaced at the same time as the fuel pump (last spring). As for vacuum leaks, I would expect any leak sufficient to cause this problem would likely result in an erratic idle or other problems which I do not see. The car runs great. Not ruling it out though, I'll take a look. Also, no signs of an exhaust leak (sounds and runs great), but I'll take a look at that as well.

From my perspective (which isn't always that clear wink ), it seems that because the CEL is intermittent (doesn't come on every trip), it only comes on for two or three minutes and only when the car is cold, I'm thinking that this would be sensor related -- a more likely culprit for an intermittent problem.

<small>[ November 30, 2003, 05:27 PM: Message edited by: ckinart ]</small>

 

[rangerj]

ckinart,

Here's my 2/100ths of a Loonie worth! The codes 173 and 177 are consistant, that is the 172 indicates a lack of O-2 sensor switches (from rich to lean and back)in both the Running and Continuous Memory Modes, and the 177 indicates that the front side is always rich.

Logic would tell us that the relatively new O-2 sensors are giving us accurate information. So, the question becomes what is causing the rich condition when the engine is cold.

The vehicle has a throttle body and cold idle is controlled by the IAB. Is it clean and operating properly? Is it a little sluggish, maybe? Does the air cleaner need to be cleaned or replaced?

Are the injectors partially clogged and staying open, and spraying excess fuel into the cylinders? Add just a little extra fuel to an IAB that is set for a cold condition and the mixture could get rich enough, long enough, to trigger the codes.

FWIW, the O-2 sensors become active after about two minutes at RPM above idle.

So, If we believe the O-2 sensors, then you are infact running rich for a long enough time to trigger the codes. You could confirm this if the exaust is dark gray, or black, during the "rich" period. You could also have the exaust tested at your local Petro Canada, or Canadian Tyre facility (or a Husky station).

If the O-2 sensors are providing false information, then they are starting to fail. Since they are only six months old this is unlikely, possible, but unlikely.

Can the fuel pressure regulator fail on the HIGH side, that is provide a little too much pressure, or allow too much fuel to get through at a time when the system has restricted the air flow (cold)?

Lastly, is it an ignition problem? This would seem to be unlikely because the problem is only present for a short while when the engine is cold.

It would seem that there has to an air flow restriction somewhere, or an excess of fuel being introduced somehow! How is that for overstateing the obvious. Just some thoughts! rangerj

 

[Rockledge]

ckinart:
...As for vacuum leaks, I would expect any leak sufficient to cause this problem would likely result in an erratic idle or other problems which I do not see. The car runs great.

Thinking about it, I tend to agree with you. The "leak" would probably have to be before the MAF (like the airbox, for example) for it to cause a rich condition.

Also, along the lines of your sensor-related hypothesis, I would think that the IAT would be one of the sensors that might contribute to a rich condition if faulty? shrug

<small>[ November 30, 2003, 08:51 PM: Message edited by: Rockledge ]</small>

 

[ckinart]

rangerj,

Thanx very much for all of your thoughts! Everything you've mentioned is what I've been trying to go over to figure out what the problem may be. I've been thinking about the fuel pressure regulator, and from what I can tell, the regulator would either have to jam closed (doubtful) allowing little or no fuel to return to the tank and overpressure the injectors (giving a rich condition) or insufficient vacuum could keep the regulator from opening up enough. I just inspected the vacuum line to the regulator tonite, and it looks just fine. It was dark at the time, so I didn't pull it off to ensure there were no restrictions, but I'll verify tomorrow.

Having said all of that, both of the above scenarios also would be unlikely to cause only a momentary and intermittent condition as I'm experiencing.

My IAB is an OEM replacement from last year, but it's possible that it has gotten gummed up. I'll look into that as well. If it's performance were marginal, would the IAB have any effect on the A/F ratio above idle? Both times I've seen the CEL I was above idle (i.e. driving, not idling).

As for the airflow restriction, it has been some time since I've replaced my air filter, so perhaps it's time I take a good look at that. I've been planning on putting a panel K&N filter in at some point, so maybe I'll do that in the very near future and see if that helps things...

EDIT:

rangerj
You could also have the exaust tested at your local Petro Canada, or Canadian Tyre facility (or a Husky station).

It's funny that you mentioned Canadian Tire. I just took my car to them today to switch out my summer to winter tires on my slicers (I haven't gotten around to getting a second set of rims). I told them that the rims are directional and have to go on the correct side. When I went to pick the car up, the rights were on the left, and the lefts were on the right. I politely asked them to switch them, which they did. Then, while taking my car out of the shop and parking it out front for me, the gentlemen who switched the wheels out let my car roll into the back of an ******. He claimed that he was "looking for the handbrake" while the car rolled forward on a slight slope (I don't know why his foot was not on the brake at the time). No damage, but not a good show for my local Canadian Tire store...

Anyway, thanx again for your input!

<small>[ November 30, 2003, 09:21 PM: Message edited by: ckinart ]</small>

 

[ckinart]

Rockledge
I would think that the IAT would be one of the sensors that might contribute to a rich condition if faulty? shrug

That's a possibility. Since I replaced that ECT last spring, I'd like to think that it is still operating correctly. Perhaps the IAT is overdue for replacement. Do you know if it's possible to test this part? Any idea what one is worth?

 

[Rockledge]

Well, once again I must reconsider what I have been thinking. According to my Ford Manual:

"Ambient temperature should be above 10°C (50°F) to receive acceptable input from the Intake Air Temperature (IAT) sensor."

So I'm not sure how the IAT could be causing your problem, based on the ambient temperatures you describe, unless the computer is reading information from it that it shouldn't be (or when it shouldn't be).

In any case, I sent you an email with information from the manual on what the IAT voltage and resistence readings should be at various temperatures, with a nice little pinout diagram. The good thing about it is the IAT and ECT are the same type of sensor and work on the same principles so you can use the info to test the ECT if you want to.

<small>[ November 30, 2003, 10:26 PM: Message edited by: Rockledge ]</small>

 

[SHODWN]

Change the thermostat.. If its old and stuck OPEN the car will never get to operating temp, and continue to throw to much fuel at it..

This has been happening for years guys and one of the most commonly overlooked things. Also its cheap and VERY easy to change.

 

[ckinart]

Rockledge,

Thanx very much for the diagnostic info! I don't know if we'll see any ambient temperatures above 10 C any time soon, but I'll take a look anyway.

SHODWN:
Change the thermostat.. If its old and stuck OPEN the car will never get to operating temp, and continue to throw to much fuel at it..

This has been happening for years guys and one of the most commonly overlooked things. Also its cheap and VERY easy to change.

I replaced both the thermostat and ECT sensor last spring, so I'm hoping that the t-stat hasn't failed already. The car seems to warm up within a reasonable amount of time and, according to the "dummy gauge" seems to run within the expected range. The upper rad hose gets hot to the touch (as would be expected) but I haven't had it tested via infrared or anything. Not ruling it out, but I think the t-stat situation is okay. Thanx for the tip!