Need Some help

[Kidd7]

I have a 99 Ex with 4.0 SOHC ~ 130K; owned for about 2 years.
Things repaired: Tranny rebuilt about a year ago; crank sensor; spark plugs; wires; PCV; TPS; All 4 O2 sensors.
I had an intermittent stall that I traced to a bad O2 sensor Bank 2 sensor 1. It would fall out, flat line at 0V, and the fuel trim would go through the roof, rough idle and stalls at times.
I didn't like the way Bank 1 sensor 2 looked on my data log, so I replaced it. The new O2 looks the same, I'm wondering if there is something wrong with the cat? The link below is the graph of my new O2 sensor, any advice? Thanks.
https://drive.google.com/open?id=0B6e7fQMCMygPRmZmRGN3aGd4SVE

Also, this was a previous thread from the first set of issues:
http://www.explorerforum.com/forums/index.php?threads/99-v6-sohc-stall-on-left-turn.450999/

 

[J_C]

AFAIK, a bad O2 sensor (alone) would just cause it to run rich but not rough or stall, and set an OBDII code. Same for the cat. I'm wondering if you just have a vac leak somewhere.

 

[Kidd7]

Honestly I didn't think of a vac leak. It generally happens when accelerating. Does the tranny shift with vacuum?
What do you think of that O2 graph? the other side looks completely different, high / low back and forth like normal.

 

[96eb96]

The cat monitor looks at pre and post o2 sensors. It looks at the switch ratio. If pre is switching 20 times a second, post should switch(for example) at 2 times a second. There should be no "rich" exhaust after the cat. If they both follow each other(switch ratio close to 1 over a few cycles) the cat is deemed bad. A post 02 sensor moving around is a concern, but you would get a cat code if it was really bad.

Exhaust leaks could also throw off o2 readings.

 

[J_C]

Honestly I didn't think of a vac leak. It generally happens when accelerating. Does the tranny shift with vacuum?

Don't know but I did have a Buick Lesabre that was shifting all funky due to a loose vac line, though the 3800 engine was running reasonably well still. It was a great relief when I found that loose line !

 

[Kidd7]

Here is a shot of the rear O2 sensor on the opposite bank:

https://drive.google.com/open?id=0B6e7fQMCMygPdFVrc1REX0hKSHM

So are you stating that is concerning? It is flipping about 1/2 as much as the forward O2 sensor.

 

[96eb96]

Here is a shot of the rear O2 sensor on the opposite bank:

https://drive.google.com/open?id=0B6e7fQMCMygPdFVrc1REX0hKSHM

So are you stating that is concerning? It is flipping about 1/2 as much as the forward O2 sensor.

I wouldn't really worry about the post 02 without a code. It does look like a lot of activity though. If they follow each other closely the cat isn't working well, but the calibration(this can vary for example for a California vs 49 state car) is the final judge. There may be mode $06 tests to find out the switch ratio.

 

[96eb96]

When do you stall? On acceleration?

 

[UtahX]

Why the PCV? What was it doing to need replacing?

 

[Kidd7]

The stall is always on acceleration, usually mid acceleration. Meaning I'm being a little aggressive to get into traffic.
At first it seemed to be only on left turns, but I think that is just coincidence. I would say it stalls at a fast change of acceleration, but very intermittently and usually only when hot, like coming off of 20+ minutes on the highway over 70. Very rarely do I accel hard.

 

[96eb96]

Can your scanner read the BARO parameter? If so what is it, and your approx height above sea level. If you can't read BARO get Forscan.

Also., I need your LTFT and STFT @
idle
1500 RPM
2500 RPM

 

[Kidd7]

I have all my data in excel spreadsheets. I use torque on my phone to log and don't think BARO is in there. I'll try to compile that data today. Thanks.

 

[96eb96]

Download forscan. It is the best app for Ford. Free for PC. You can check lots of other things like ABS. I think the phone version is free if you want a single PID. Units of Baro should be in Hz.

 

[Kidd7]

96eb96, Here you go; I'm traveling so grabbed what I had on this PC to share, hope it makes sense.
What does BARO stand for? Elevation is ~325 ft.

https://drive.google.com/open?id=0B6e7fQMCMygPUXg4aldlS01xNUk

 

[96eb96]

Ok, someone likes Excel

BARO is real barometric pressure that varies with altitude. You should read about 158Hz give or take 4 or 5. It can also read in inHG. It is a parameter that gives me an idea of the health of your MAF sensor and exhaust flow. It is computed from a bunch of variables during different RPMs and Loads. A skewed baro could indicated a dirty or bad MAF sensor, or exhaust issue.

Ideally Total Trim should hover around ZERO, it does on mine after I fixed some small issues. STFTs are instantaneous corrections, while LTFT is learned over minutes or hours. To get real actual total fuel trim we sum those two values. Also, Max isn't the most helpful quantity, because the PCM runs tests that can force trims high and low (no so much at idle though). If the test was done while in park the last sentence may not apply. If done over 20 miles....then it may. Given what I see, this is my analysis:

As it stands now, your idle LTFT is getting into the danger zone, around 16-17. 20-25 could trigger a CEL with P0171/P0174 codes.
At 1500 RPM, the LTFT drops. This could indicate a vacuum leak. At idle, a vacuum leak is significant. At higher RPM, it becomes the proverbial fart in the wind, and the TRIMS don't really care about it.
At 2500 RPM, it rises again. This could be a MAF issue too. Positive fuel trim generally means adding fuel, so it could also be a weak fuel pump, or some temporary condition as discussed above.

P0171/P0174 codes generally come from either a MAF issue (because it affects both banks) or a vacuum leak, pr possibly fuel delivery.

So, the BARO would be helpful, but it wouldn't hurt to do a MAF cleaning procedure, and redo the tests. MAF could also be defective too, there are some other tests for that too.

A big symptom of a bad/dirty maf is stalling on hesitation.

 

[Kidd7]

I love Excel LOL, NO it's a necessary evil. Thanks for all the detail, some of which I knew. I had a failed MAF cause the lean codes on my cougar recently. The torque app only displays MAF in cfm, any ideas what my flow should be at those RPMs? I have cleaned the MAF, I'll clean again and look for vac leaks.

 

[96eb96]

No idea about CFM, but if you want to test a MAF with OBD-II you have to do a snap throttle test and observe the max voltage. There is a spec in volts for flow at idle, I would have to look it up. That is why the BARO is helpful.

 

[Kidd7]

Looks like I can get BARO. I've got to move the vehicles around in so I'll take her around the block and see what I can get. I did log yesterday and she bogged down once when I hit the gas. Looking at the data at that point in time when I hit the gas my timing went to -10 both banks fuel trim went to -20. So it seems at the point of failure the engine is leaning out. I'm going to check vac lines, look for manifold leaks & take some MAF voltages. Then report back.

 

[Kidd7]

BARO doesn't work.

 

[Kidd7]

It's Vacuum leak. I can hear it at the back of the engine when I open the throttle a real quick whistle. Can't pin point it. I smoked it and can't find a leak. What's the chances it's the intake gaskets? Alot of the vacuum lines are buried under that crazy intake.