ELM320 OBDII does not show HO2S

Not familiar with that particular scanner, but all "low budget" scanners do the same thing on all '96 - '97 Explorers. This is due to the information is not available through Generic OBD-II mode which is all that most "low budget" OBD-II scanners do. You'll need to monitor the O2 sensors in the Ford Enhanced OBD-II mode to see the results if it is available for your scanner. If not, then you'll need a different scanner. The information is available, you just have to have the right equipment. My AutoXray Pro-Pak would only let me see the information after I updated it to Ford Enhanced OBD-II mode which also let me see about three times the number of parameters than before. The vehicle speed will read 0 MPH regardless of what you do though. The only time I've seen a speed from my VSS was in the data capture after a fault code was detected. Then it will report the speed that the vehicle was driving at when the fault code was set. This only applies to '96 - '98 Explorers. It seems that Ford got it fixed with the '99 since I have talked to someone with the same scanner as I have but with a '99 Explorer and his showed the O2 sensors without the Ford Enhanced OBD-II upgrade. I've tried several different scanners and software versions on my '97 as well as a '96 and '98 and they all behaved the same. I tried my scanner on my Mother's '96 T-Bird and it showed the O2 sensor readings without the Enhanced Upgrade as well. I was working with the manufacturer of my scanner since they are located a couple of miles from where I used to work, they were even using my Explorer as their test vehicle. They eventually came to the conclusion that Ford didn't follow standard OBD-II protocol on the '96-'98 Explorers since all of the lower priced scanners that they had performed the same. They let me borrow their master scanner to troubleshoot with at the time but I can't remember the manufacturer. They did say the scanner cost a couple thousand $ though so warned me to be careful and make sure I returned it. It enabled me to read my O2 sensors and my fuel trims to troubleshoot my leaking lower intake manifold o-rings. A few months later they released their Ford Enhanced OBD-II upgrade and installed it on my scanner at no charge for the use of my Explorer.

Thank you Alpine for your comprehensive explanation. BTW, I dont expect much, just for curiosity, dont you know, is a computer firmware upgradeable? Or, is it possible to change entire computer from 98 to 99?

So, in my case I have to go to shop. :(

BTW, if somebody can narrow the possible problem by my description of symptoms? When weather is cold, i.e. -10C(14F) or lower, when I start, the engine works 1-2 second on 2000-2500 rpm, then it drops to 100-500, and idleing

2-5 sec very roughly, with misfiers and shaking the car. Then again, it zooms to 2000rpm for 1-3 sec, then drops to 100-500rmp. Such oscillations continue with waning of amplitude gradually. Finally when car got warmed, engine ideling on ~500 rpm, but sligtly(very slightly) rough. It happens on ideling or on slow motion, when I can not accelerate enough to compensate this effect. When I go on a road with normal speed, this effect disappears. No errors in OBD, no Check Engine light appears. It can give "Multiple misfire" sometime when ideling was too rough and engine shut down.

I checked Coolant Temperature Sensor, and MAF sensor, they look OK. I wanted to monitor oxigen sensors. But.. :(

Thanks

Alp> Not familiar with that particular scanner, but all "low budget" scanners do

The engine problem you described below could not be related to the oxygen sensors since at start up the computer does not use the oxygen sensor signals for engine operation. For your engine, about 20 to 30 seconds are required before the computer can enter "closed-loop fuel control". Then, the computer will start using the oxygen sensors to control the fuel system around stoichiometry. Additionally, at the temps you mentioned (i.e., -10C), the engine may require up to 60 seconds to enter closed-loop fuel control. At start-up, the engine is operating in "open-loop fuel control", i.e., no need for oxygen sensor.

If you still need to look at oxygen sensor signals and your scan tool will not pick them up, use a DVM on the signal going to the computer (ECM). This method is referred to as back-probing.

However, to fix your problem, it sounds like the idle air control valve is sticking.

Hope this helps,

Tom

I think it would probably be cheaper to buy a scanner with the capabilities rather than try and make a PCM from a '99 work in a '98. There probably wasn't that much different, but any minor change in electronics somewhere could cause a major incompatibility.

If you have the SOHC, then there are two possibilities. One was mentioned below, the idle air control valve (IAC). When the IAC gets gummed up to the point that it is sticking, it won't throw any OBD codes unless it idles rough enough to cause a mis-fire. The second possibility is leaking lower intake manifold o-rings. When they start to leak, your engine runs very rough when the outside air temperature is below 50F or so. Once the engine warms up, the o-rings swell closing the leak and the idle problem goes away (until the next cold start). It is a very common problem on the SOHC, such that Ford extended the warranty on the o-rings to 6 years, 72K miles (whichever comes first). They lumped it in with noisy camshaft tensioners on the same owner notification program (ONP 00M12). When the problem first came to light several years ago, the troubleshooting routine called for spraying propane around the lower intake manifold while monitoring the short term fuel trims with a cold engine. Sudden changes in fuel trim while the propane was sprayed indicated a leak. The propane gets sucked into the cylinder through the leak which then burns off and consumes the extra oxygen. This will change your short term fuel trim by 10%-20% instantly. This was the very reason I needed to borrow the professional scanner from AutoXray since at the time my scanner wouldn't measure fuel trims on my Explorer. It was only after the Ford enhanced upgrade came out was my scanner able to read them. If it is leaking o-rings, eventually a code will be set. It will likely be either a P0171 or P0174 or both. If that is the problem and you have less than 72K miles, Ford will fix it for free. If you can get access to a scanner that is capable of reading the necessary parameters, you can at least narrow it down. If there is any chance you live in the Phoenix, AZ area let me know and I would be happy to read your codes for nothing.

Thanks again. Very comprehensive! Yes, I had P0171 and P0174, but they were happened in fast motion, usually on a highway. Looks like it is O-ring problem. Thank you for offer, I m in Canada. Ford mileage is about 175K. So I'll go to ford's shop and pay for repair.

The idea about the firmware upgrade is because I m a computer programmer, I used to fix computer problems by upgrades and patches. I see that in auto-world this approach is not very popular. :)

Thanks MM

Alp> I think it would probably be cheaper to buy a scanner with the capabilities

Actually, Mark, the factory quite often "fixes" problems with computer reflashes. While most of these deal with recurring, false codes, there have been those that solve drivability problems. There are programmable modules available for many applications... sort of like a superchip on steroids. I have yet to try any though customers are split on them..... many like them, others introduce running problems through their use. Ford is adamant that we remove any aftermarket chips before we even attempt to diagnose any running problems under warranty.

The PCM itself can allow for mechanical problems to a point. In the case of your apparently leaking intake manifold seals, the vacuum leak has gotten to the point where the PCM can no longer effectively modify the fuel curve.... it is outside the operating parmaeters programmed into the PCM. This is the adaptive strategy that you have probably heard about.... bringing us to another point. Having your car repaired at the dealer, you would expect that the tech would reset the KAM (Keep Alive Memory). If the tech forgets... (hey, some of us are old enough to do that), the vehicle will adapt to the new conditions in a couple or three days.

While you might be able to cobble something together to change the PCM programming, you must realize that you are dealing with many interactions..... fuel, timing and EGR curves, how many times and how long the PCM needs to see a problem before setting the MIL, when to revert to open loop operation (happens more than one might think).... the rest of it is totally beyond me.... I just fix 'em and try to pick up any balls the engineers may have dropped.

Now with Controller Area Networks on many new models, we are seeing data transfer rates that we have never seen or even dreamed about. , this old dog just keeps learning all the new tricks...

Incidentally, if you ever get the chance, check out the PID (Parameter Indication Data) data monitors available with the dedicated Ford scan tools like WDS and NGS. There are times when the data available is almost overwhelming. Used properly, these tools can go a long way to helping us provide a quick diagnosis for most problems...... of course, being a computer guy, you alrady know all about the dreaded "intermitent"...

Jim Warman snipped-for-privacy@telusplanet.net

Thank you Tom. Problem is narrowing with your and Alpine's help. IAC or O-rings vacuum leak. I'll try to check/clean IAC first.

Thanks, MM

Tom wrote: