Please help troubleshoot: one bank rich, one bank lean

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snoutmeat
Posts: 4
Joined: Sun May 26, 2019 7:14 am
Vehicle: 1996 Ford Windstar 3.8

Please help troubleshoot: one bank rich, one bank lean

Post by snoutmeat » Tue May 28, 2019 6:07 am

Greetings! I'm trying to help my father repair his pristine, 2-owner (my grandfather, and now my father) 1996 Ford Windstar with 80K miles. It has the 3800 V6 engine. His Check Engine Light came on, and we pulled the DTCs with a cheap scan tool I own. They were:

P0172 -- System too RICH bank 1
P0174 -- System too LEAN bank 2
There was also a misfire on one of the cylinders. The car has 80k miles and was still on its original spark plugs, so we figured we might as well change the plugs. This made no difference.

Then my dad discovered FORScan and installed on his Android phone. We drove around with FORScan running and enjoyed watching the realtime data on the engine...but we don't have enough experience to know what all the data mean. We did notice that all 3 cylinders in bank 1 were misfiring (and none of the 3 in Bank 2).

My dad mentioned that the Windows version has even more information, so I installed on my laptop -- this is a tremendous, fantastic app, but I'm still new to it (I own no Fords or Mazdas myself).

The app confirms that that the fuel trim on 1 is high, the fuel trim on 2 is low, that the 3 spark plugs in bank 1 are misfiring. When I blip the throttle or increase the rpms, the fuel trim lines are mirror images of each other -- as one bank gets richer, the other gets leaner, and vice versa. Is this normal, or is this helpful information?

Here is my thought process:
--if one bank is too rich and the other bank is too lean, then the problem is some component that has separate systems for each bank. For example, the fuel pump and fuel filter should affect both banks equally (because one component serves both banks). I think this narrows it down to:

--vacuum leak
--slipped cam timing
--oxygen sensors
--partially clogged catalytic converter


(are there other possibilities?)

--to test for vacuum leak, we used a propane wand and moved it all around the engine compartment, especially around the intake manifold. We saw no difference. We also tried spraying a mist of water. We did not detect any change in the engine for either of these tests (though it is hard to get around to the back side of bank 1 with the spray bottle). I think it's not a leaking intake manifold.

--I don't think the cam timing has slipped. It's a well maintained engine with 80k. It runs quietly (no rattles). It's my understanding that an engine with enough slop in the timing chain to slip a tooth would be a very noisy, rattly engine.

--If an oxygen sensor goes bad, shouldn't it generate a "bad oxygen sensor" DTC? Or can an oxygen sensor fail in such a way that it won't generate an o2 sensor DTC?

--I have read on other forums (particularly a couple of Ford posts) that a disintegrating catalytic converter can cause these symptoms -- a restriction in flow in one bank can lead to the "one bank rich, one bank lean" symptoms. The car has two cats -- one for each bank -- and then the exhaust pipes come together after the catalytic converters.

My plan of attack now is to order an 02 sensor or two and try installing to see if it makes a difference. While the sensor is out, I plan to try inserting my inspection camera into the hole to see if I can see any problem with the catalytic converters.

My questions:
1) does this diagnosis seem accurate?
2) is there a way to use FORScan to further narrow down the probable problem? When I run FORScan, I'm capturing the values for all 4 oxygen sensors and all 4 fuel trims, plus misfires on each cylinder. Not sure what the 02 readings are supposed to look like, though, so not sure how to tell if they are working properly or not.
3) Is there a way to assess catalytic converter health, exhaust obstruction, and cam timing with tools -- a vacuum gauge, an infrared non-contact thermometer, a compression tester, or ???
4) can an 02 sensor go bad without generating an 02 sensor DTC?
5) Is it normal, when I step on the gas, to see one bank's trim to go rich while the other goes lean, and vice versa?
6) I read in the rules that you're not supposed to randomly upload FORScan logs...is it ok to put up a screen shot? How can I make it easier for you to help me diagnose this problem?

Thank you in advance for your comments and suggestions. This problem came up just before his license plate tabs expired, and he can't get them renewed while the CEL is on, so the car sits in the driveway waiting for me to fix it.

TechLuke84
Posts: 31
Joined: Sat Feb 04, 2017 11:19 am
Vehicle: Ford Fiesta Focus Mondeo Kuga

Re: Please help troubleshoot: one bank rich, one bank lean

Post by TechLuke84 » Wed May 29, 2019 3:18 pm

Is the misfire constant?

denbo
Posts: 563
Joined: Mon Feb 06, 2017 3:00 pm
Vehicle: ford focus 16 zetec

Re: Please help troubleshoot: one bank rich, one bank lean

Post by denbo » Wed May 29, 2019 5:44 pm

What side does the vac pipe to the brake booster go?

snoutmeat
Posts: 4
Joined: Sun May 26, 2019 7:14 am
Vehicle: 1996 Ford Windstar 3.8

Re: Please help troubleshoot: one bank rich, one bank lean

Post by snoutmeat » Thu May 30, 2019 5:29 pm

TechLuke84 wrote:
Wed May 29, 2019 3:18 pm
Is the misfire constant?
Depending what you mean by "constant", yes. :) While the car is running, with FORScan running, the misfire count keeps going up, and at a roughly constant rate. Are you asking if the misfire comes and goes, or if it misfires more or less under certain conditions? It seems to misfire at about the same rate regardless of throttle position (though this was all tested while the car was sitting motionless).

snoutmeat
Posts: 4
Joined: Sun May 26, 2019 7:14 am
Vehicle: 1996 Ford Windstar 3.8

Re: Please help troubleshoot: one bank rich, one bank lean

Post by snoutmeat » Thu May 30, 2019 5:30 pm

denbo wrote:
Wed May 29, 2019 5:44 pm
What side does the vac pipe to the brake booster go?
Interesting thought. You're suspecting that there could be a vacuum leak associated with the brake booster? I'll investigate that today. Thanks!

TechLuke84
Posts: 31
Joined: Sat Feb 04, 2017 11:19 am
Vehicle: Ford Fiesta Focus Mondeo Kuga

Re: Please help troubleshoot: one bank rich, one bank lean

Post by TechLuke84 » Thu May 30, 2019 8:12 pm

I think you should start with the basics first, spark! You need to check if there is a spark on the cylinder with a misfire. I’m guessing you have a coil pack and HT leads, a spark tester would be ideal but if not there are other ways. Check YouTube. Misfire caused by vacuum leak usual goes as the engine rpm increases, this is due to less vacuum at higher revs.

snoutmeat
Posts: 4
Joined: Sun May 26, 2019 7:14 am
Vehicle: 1996 Ford Windstar 3.8

Re: Please help troubleshoot: one bank rich, one bank lean

Post by snoutmeat » Fri May 31, 2019 7:45 pm

TechLuke84 wrote:
Thu May 30, 2019 8:12 pm
I think you should start with the basics first, spark! You need to check if there is a spark on the cylinder with a misfire. I’m guessing you have a coil pack and HT leads, a spark tester would be ideal but if not there are other ways. Check YouTube. Misfire caused by vacuum leak usual goes as the engine rpm increases, this is due to less vacuum at higher revs.
Thank you for taking the time to reply! Three cylinders are showing misfires, all in bank 1. When the check engine light came on, the computer was showing a misfire in one cylinder, so we replaced all of the plugs with Ford's recommended replacement. It does have a coil pack, but doesn't a coil pack typically share a coil between 2 cylinders in opposing banks? In other words, I don't see how a bad coil would lead to misfires in all 3 cylinders in one bank.

I get what you are saying about misfires versus engine RPM. I did not really investigate that, so I will go back with forscan and see if my misfires are the same whether it is running at idle or at a higher RPM. Also, I think vacuum leaks due to a leaking intake manifold usually get less extreme as the engine warms up and pieces expand. so I will go back with the tools and assess my misfire count at idle, at higher revs, when it's cold, and when it's hot. Thanks!

TechLuke84
Posts: 31
Joined: Sat Feb 04, 2017 11:19 am
Vehicle: Ford Fiesta Focus Mondeo Kuga

Re: Please help troubleshoot: one bank rich, one bank lean

Post by TechLuke84 » Sat Jun 01, 2019 7:29 am

Your in danger of over complicating the issue!
Misfires are caused by one of three things though there are exceptions to a degree. No spark, No fuel or No compression. Concentrate on the cylinder/cylinders with the misfire counters, it’s not uncommon for a misfire on one cylinder to set codes for other cylinders, but the counter will isolate this. Checking spark is the easiest first option, then compression and finally fuel, I may take a different approach sometimes depending on what I see in front of me but I’m not standing in front of the vehicle! This is good professional advice....

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