|
|
1997 Ford Explorer OBD2 and fuel control system
|
|
|
| |
|
|
petpeswick
New User
Jan 16, 2014, 5:09 PM
Post #1 of 8
(2371 views)
|
|
1997 Ford Explorer OBD2 and fuel control system
|
Sign In
|
|
I have a 1997 Ford Explorer and recently had the check engine light on (4l V6). The light was for P0171 and P0174 (lean bank 1 and 2). I had lost my old code reader (that is another story), so I bought a Bluetooth OBD widget and cleared the fault with the Torque app. P0171 and P0174 have not reoccurred, however, using the torque app, I have discovered that in Mode1, the short and long term fuel trim (both sides) are -100 (rich) and not varying. Also the 4 O2 sensor voltages are 0v and not varying. The fuel control mode achieves "closed loop" and there are no OBD faults detected by the system. What could be happening here? Appreciate any insight...
Tim
|
|
| |
|
|
Discretesignals
Ultimate Carjunky
/ Moderator
Jan 16, 2014, 6:06 PM
Post #2 of 8
(2353 views)
|
|
Re: 1997 Ford Explorer OBD2 and fuel control system
|
Sign In
|
|
Could be your blue tooth widget has some sort of software problem. You should try a different scan tool and see if it reads the same. I highly doubt all four O2s would be registering zero volts with a fuel trim reading of -100%.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jan 16, 2014, 6:07 PM)
|
|
| |
|
|
petpeswick
New User
Jan 16, 2014, 6:22 PM
Post #3 of 8
(2347 views)
|
|
Re: 1997 Ford Explorer OBD2 and fuel control system
|
Sign In
|
|
I was suspecting that it might be a computer measurement issue, but all other available PIDs read correctly. I have 160,000kms and have owned it since 120,000 kms so it is likely that the 02 sensors have never been changed. Is it possible that if the heaters work and if all 02s read the same (0v), that an error wouldn't be triggered? If the 02 sensors had 0v, wouldn't that cause the fuel trim to go rich? From that perspective the readings make sense, but like you say, having them degrade together seems unlikely.
|
|
| |
|
|
Discretesignals
Ultimate Carjunky
/ Moderator
Jan 16, 2014, 6:41 PM
Post #4 of 8
(2345 views)
|
|
Re: 1997 Ford Explorer OBD2 and fuel control system
|
Sign In
|
|
Are you getting these zero readings at idle and while cruising? Is the engine fully warmed up? If you nail it while driving, what does the O2 sensor voltages do?
Have you tested the O2 sensor heater circuits? If you connect a volt meter to one of the front O2 sensor signal circuits, is the voltage the same as what is stated on your scan tool?
Have you tried injecting propane into the intake to see if you can get the O2s to swing to the rich state (above 450mV)
If a front O2 is hanging at 0 volts, the PCM is going to add fuel which will make your fuel trims go positive. If it can't make a correction, the PCM will disable O2 feedback, go into open loop, and trigger trouble codes.
It could be you have a really lean condition causing the O2s to stay low, but you need to prove that is the case by doing an O2 function check.
I really don't understand how it can be in closed loop with zero volts on all sensors and have -100% fuel trims.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
|
|
| |
|
|
Hammer Time
Ultimate Carjunky
/ Moderator
Jan 16, 2014, 6:42 PM
Post #5 of 8
(2344 views)
|
|
Re: 1997 Ford Explorer OBD2 and fuel control system
|
Sign In
|
|
I too doubt the scan tool data but based on the codes alone I would bet you are looking at a bad vacuum leak. I see these codes very often on Fords and it's almost always a vacuum leak. They have a lot of problem with the rubber connectors at the manifold and the PCV hose. Listen for a hissing noise at idle and try to follow it to it's source.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
|
|
| |
|
|
petpeswick
New User
Jan 16, 2014, 7:20 PM
Post #6 of 8
(2341 views)
|
|
Re: 1997 Ford Explorer OBD2 and fuel control system
|
Sign In
|
|
Thanks Discretesignals and Hammertime,
I've been worried about a possible vacuum leak since the P0171 & P0174 errors, but I didn't think that these might be related to the 0v on the O2. It stalled when I was driving through a snow drift and when I restarted it the MEL came on. I also get a bad low idle on startup occasionally. I will get under the hood on the weekend and look into your suggestions. Will repost with findings.
Thanks,
|
|
| |
|
|
nickwarner
Veteran
/ Moderator
Jan 17, 2014, 8:49 AM
Post #8 of 8
(2323 views)
|
|
Re: 1997 Ford Explorer OBD2 and fuel control system
|
Sign In
|
|
That doesn't make any sense though. The thing with fuel trim numbers is that the ECM has a set amount of fuel that it thinks it should need based on temp, load and a host of other variables. However it uses the O2 readings and such to alter that to make the engine run correctly and stay within emissions guidelines. When you see a negative number, that is a percentage of what it thinks you should need being taken away. If it needs more fuel than calculated, it goes positive and adds fuel. The O2 works on a 0-1v scale, with .1v being lean and .9 being rich. .45v is stoichometric, a 14.7:1 ratio of air to fuel which is considered premium operation and efficiency. So if the ECM was seeing .1v, it would think you were running very lean (which coincides with the P0171 and P0174 codes) and the fuel trims would read positive to compensate. I doubt you are getting the correct data from your widget, and it could be very likely that the other man you are quoting on that other forum is using a cheap scanner or phone app as well. To get the right software, scan tool manufacturers pay dearly to the OEM for licensing. Thats one reason why tech-level scanners cost many thousands of dollars but can do so much.
These are known for vacuum leaks and also air leaks between the engine and the MAF along the ducting. Sometimes you really have to flex it at each rib to see it, but every leak is unmetered air getting in. MAF systems are very touchy about that and will act up.
Personally, I think I would have to see that datastream on a Snap-On scanner or an IDS to believe it was right. It just contradicts itself entirely. If the engine was already lean and the fuel trims were getting pegged down negative, the engine wouldn't have enough fuel to even run.
Watch this vid and you'll get a better understanding about this. The man making these vids does a great job and has many other vids that you may find helpful to you in understanding how your ECM is working to keep your car running right. http://www.youtube.com/watch?v=oRX2V6_a3dc
|
|
| |
|
| | |
|
Auto Repair Home
SEARCH
WHO'S 
LOG 
2006 Toyoto Camry XLE Driver Side Electric Window Trouble
Tierod end change caused some kind of leak
Grounding Cable, 2017 Jeep Renegade Trailhawk
equipment
Howdy
