Dodge Truck Stalling At Idle

09 Dodge Ram with 5.9 engine had been sitting unused for awhile so the owner had to jumpstart the battery. He then had to keep one foot on the accelerator giving just a slight throttle or the engine would die. 

If you've been following my posts you know that when you lose battery power you lose adaptive memory. Lose adaptive memory and some things won't work properly until the adaptives are relearned. We'll be looking closely at idle control adaptives on this one but only after making sure we have a good battery. 

The truck idled with no stalling when I drove it into the shop. This means the computer had probably relearned idle on the way here. I wanted to save the adaptive memory but I needed to test the battery. A memory saver will keep the computer powered while you disconnect the battery and you won't lose adaptives. 

The old battery was bad, so out with the old and in with the new.

Once the replacement battery was installed I removed the memory saver. Since the idle adaptives were relearned and since I saved learned idle I could look at idle air control counts for a problem. There are some things you can only see with a scan tool. IAC counts are one of those things. The ideal range here is 10-24. If you see higher numbers the computer is having to command more idle air to maintain idle speed. Usually there is a buildup of carbon on the throttle causing this. 107 here meant the throttle plate might be dirty. 

After cleaning the throttle I checked the counts again. 

They were much better but still higher than our target range. I knew the throttle was clean. There is a minimum air adjustment that can be checked. Very easy to check when your scan tool will command it. Minimum air takes the idle control motor out of the picture. Only the air allowed past the throttle is maintaining idle speed. Just enough rpm to not stall when placed in gear is my rule of thumb. The minimum air was fine. Using the scan tool I did a minimum throttle relearn twice. I've ran into that before on Dodges, sometimes more than one relearn. But it worked.

Thanks for reading!

Kenneth Hayes

G&G Auto Repair

Another Ford Lean Code

This Mustang w/4.0 engine was setting a lean code for bank 2. 

At idle and low rpm both O2 sensors were switching normally so I ruled out a vacuum leak being present. A fuel delivery problem would most likely affect both banks and I only had a code set for bank 2. I took a look at the freeze frame for the lean code. Freeze frame is a sort of snapshot of sensor data during the event that set the code. 

Short fuel trim for bank 2 shows a LOT of fuel being added. It isn't likely I had a fuel delivery problem because bank1 looks to be in fine shape. I could also see this event was on a warm engine at highway speeds. I set up to monitor both O2 and went for a test drive. When I went from a steady cruise to a hard acceleration the bank 2 sensor went to full lean but bank 1 showed the increased fuel. 

It was at this point I felt I was dealing with a bad sensor, bad wiring, or bad ecm. Easiest test from here would be replace the sensor and re-test. I did a wiring harness wiggle test while monitoring the signal and found nothing. Replacing the sensor and recording again under hard accel I could see I found the fix. 

Not bad!

Thanks for reading.

Kenneth Hayes

G&G Auto Repair

Lean On Me, Or Not

I had this '97 Ford F150 in the shop with a P0174 code stored. The customer had the problem "diagnosed" by one of the parts stores as a bad pcv valve and hose. I imagine that was an employee armed with a code reader pulling a lean code and printing a list of suggested possible causes. A pcv vacuum hose leaking is a very common problem on a Ford but just a wild guess at this point in time as to the cause of the P0174. There is a lot of difference between diagnosing a problem and guessing what it might be..... but I digress. This engine has a fuel monitor O2 sensor on each engine bank. Passenger side is bank 1 (with cylinder 1,2,3,4) and driver side is bank 2 (cyls 5,6,7,8). P0174 means the trucks computer has determined bank 2 to be running a lean fuel mixture. Too much air or too little fuel, in other words. If I had a lean code for both banks, P0171 and P0174 then I might be thinking vacuum leak too. A pcv hose pulling extra air will usually put both banks lean at idle and it will be stored in freeze frame as a problem at idle or low rpm. I decided to not immediately look at freeze frame but to first look at the live data from both upstream O2 sensors. Now, most of the time a lean, or even a rich fuel condition code sets because the oxygen sensor is working fine. I mean the job of the sensor is to report the amount of oxygen in the fuel mixture. Don't kill the messenger, right? I even saw more than one tech site that said a lean fuel code won't be a bad sensor. Well..... never say never.

I captured the data from both upstream sensors. On the top half of the first picture is the sensor that did not set a lean code. The lower half of the pic is the O2 that did set a lean code. This is a live datastream with engine running at about 2000 rpm. An oxygen sensor range is from 1 volt to 0 volt. 1000mv to 0mv. Anything below 500mv is lean, anything above is rich. A good O2 sensor with a good fuel control should switch well between the two conditions. Now since I didn't find an obvious problem with the truck, such as a bad pcv hose and since I see no particular problem with the way it is running or with anything that would affect only bank 2 I think it would be worth replacing the bank 2 sensor and running another data capture. 

After replacing the bank 2 sensor the next capture looks like this:

Notice how the sweeps are in a much wider range now even on the "good" bank 1 sensor. The bank 2 difference is very substantial. I haven't done anything to change fuel mixture other than replacing the bank 2 sensor. Now we have full fuel control and fixed a lean code without finding a lean condition. 

Hope the pics are viewable. 

Thanks for reading,

Kenneth Hayes

G&G Auto Repair

Jeep Liberty stalls at idle.

This Jeep would not stay running if you released the accelerator and tried to let it idle on its own. Just a slight throttle opening and it would idle at normal speed. So, the idle rpms were too slow. I'm going to make this one quick and simple, because it turned out that way. I like to pull up iac counts and engine rpms for a quick way to see if the throttle plate may need cleaning. Ideally the counts should be between 10 and 24. Higher and it probably needs a throttle cleaning.

This one does need cleaning.

After cleaning you can see the counts have dropped dramatically.

I said 10-24 is ideal. A idle relearn and all is good. 

No stalling. Good numbers.

Thanks for viewing!

Kenneth Hayes

G&G Auto Repair