*** Restricting New Posts to SD Premium Members ONLY *** (09 May 2025)

Just made a new account? Can't post? Click above.

Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!

Re:Diverging fuel trims, help me understand

  • Speedwagon
  • Speedwagon's Avatar Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
4 years 6 months ago - 4 years 6 months ago #47941 by Speedwagon
Diverging fuel trims, help me understand was created by Speedwagon
2002 Ford Explorer 4.0. Idles ok, but throws misifire codes on bank 2 when under load, and doesn't want to climb anything somewhat steep faster than about 45mph.

I was looking at several data points, and noticed the fuel trims diverge from each other when the vehicle is climbing.

The other odd thing I'm seeing, is the fuel trims and O2 sensors flatline when the cruise control is set

Is this telling me the O2 sensors are going bad? They appear to be original to the vehicle (connector colors match the vehicle connector colors), and it has 200k miles.


.
Last edit: 4 years 6 months ago by Speedwagon.

Please Log in or Create an account to join the conversation.

More
4 years 6 months ago #47946 by Matt T
Replied by Matt T on topic Diverging fuel trims, help me understand
Looks like a bank to bank breathing problem. Bank 1 getting too much air and Bank 2 not enough. Maybe a plugged Bank 2 cat or a cam timing problem.

The flatlining with cruise set it might be going into open loop for some reason??? Try monitoring loop status PID to see if it goes open when you set the cruise. Pretty sure it's just a symptom caused by the breathing problem but I'm just wondering why the PCM is doing it......

Please Log in or Create an account to join the conversation.

  • VegasJAK
  • VegasJAK's Avatar
  • Offline
  • Platinum Member
  • Platinum Member
  • Silencing the Parts Cannon
More
4 years 6 months ago #47950 by VegasJAK
Replied by VegasJAK on topic Diverging fuel trims, help me understand
Does B1S1 peg lean and B2S1 peg rich at 2500 rpm while not on cruise?

Not while driving, check the 02's from idle then increase to 2500. What the readings?
"an open mind let's knowledge flow in and wisdom flow out for a man who has neither never listens to those who have both".
Being wrong doesn't bother me, it's being right and not understanding why that does

Please Log in or Create an account to join the conversation.

  • Speedwagon
  • Speedwagon's Avatar Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
4 years 6 months ago #47951 by Speedwagon
Replied by Speedwagon on topic Diverging fuel trims, help me understand
Turns out, I have an 'error' for bank 2 fuel loop. Before is idle, and 2500 rpm in neutral

Please Log in or Create an account to join the conversation.

  • Noah
  • Noah's Avatar
  • Offline
  • Moderator
  • Moderator
  • Give code definitions with numbers!
More
4 years 6 months ago #47961 by Noah
Replied by Noah on topic Diverging fuel trims, help me understand
Error is likey a default message for a missing pid.
I've never worked on anything that actually used that fuel system 2.
The FuelSys pid is the only one you want to use.
"Ground cannot be checked with a 10mm socket"
The following user(s) said Thank You: Speedwagon

Please Log in or Create an account to join the conversation.

  • Speedwagon
  • Speedwagon's Avatar Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
4 years 6 months ago - 4 years 6 months ago #47975 by Speedwagon
Replied by Speedwagon on topic Diverging fuel trims, help me understand
Appreciate that info.

Trying to eliminate things, just did a compression test. 145-152 on all cylinders (warmed up for a few minutes, but not at operating temp, and at 5000ft Denver)

Resistant check all injectors, 15.5-15.8 warm (cold, they all measured around 14.5 if I recall correctly)

edit to add: Injector pressure drop test, starting at 59 psi on each, I got 30, 31, 30, 32, 32, 30

These are the plugs. 1 in bottom left. Doesn't look like 3 is firing correctly.
Last edit: 4 years 6 months ago by Speedwagon.
The following user(s) said Thank You: Noah

Please Log in or Create an account to join the conversation.

  • Tyler
  • Tyler's Avatar
  • Offline
  • Moderator
  • Moderator
  • Full time HACK since 2012
More
4 years 6 months ago #47981 by Tyler
Replied by Tyler on topic Diverging fuel trims, help me understand
I agree with Matt T, this screams VE problem. Restricted cat on bank two.

With FORScan, capture at least one wide open throttle run from a stop through first gear and into second. Watch engine speed, MAF, BARO, IAT, both upstream O2's and throttle position.

The OBD PIDS in FORScan are a little goofy. :silly: It's cool that they're provided, but they don't always work perfectly. Like the Loop Status. The OEM PID designations can be confusing, but I think you'll have better results that way.

Please Log in or Create an account to join the conversation.

More
4 years 6 months ago #47982 by Matt T
Replied by Matt T on topic Diverging fuel trims, help me understand

Speedwagon wrote: These are the plugs. 1 in bottom left. Doesn't look like 3 is firing correctly.


#3 looks a lot newer than the other plugs. Maybe it ain't been in there long enough to get dirty? Do you know the history on this vehicle?

Please Log in or Create an account to join the conversation.

  • Speedwagon
  • Speedwagon's Avatar Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
4 years 6 months ago - 4 years 6 months ago #47983 by Speedwagon
Replied by Speedwagon on topic Diverging fuel trims, help me understand
Somewhat. I went through it after purchasing it for my mother, and found #3 had some random plug in it. So I replaced that one with what should be in there. Several of the plugs weren't in tight when purchased, either.

If memory serves, bank 2 is where I found 2 loose spark plugs. 4 and 6, with 6 being buggered threads that I had to reverse chase.
Last edit: 4 years 6 months ago by Speedwagon.

Please Log in or Create an account to join the conversation.

  • Speedwagon
  • Speedwagon's Avatar Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
4 years 6 months ago - 4 years 6 months ago #47985 by Speedwagon
Replied by Speedwagon on topic Diverging fuel trims, help me understand
I had to let off the throttle for it to shift info second.


I just figured out I can rig my compression tester hose to my vacuum/carb fuel pressure tester, and make it an exhaust back pressure gauge. So once it cools off a bit, I'm going to try that out.
Last edit: 4 years 6 months ago by Speedwagon.

Please Log in or Create an account to join the conversation.

  • Tyler
  • Tyler's Avatar
  • Offline
  • Moderator
  • Moderator
  • Full time HACK since 2012
More
4 years 6 months ago #47986 by Tyler
Replied by Tyler on topic Diverging fuel trims, help me understand
Thanks for that capture! Confirmed terrible VE:



Note that I added the actual BARO reading for Denver, which is currently 30ish inHg according to Google. But that's not what the scan data said. ;) The scan data says the local BARO is 72.something kPa, which is closer to 9000 feet. That's because the BARO is calculated by the PCM based on MAF readings. Because the engine isn't breathing correctly, the BARO calculation is impacted. With the skewed BARO reading, the VE numbers look like this:



That's closer to what they SHOULD be. But the first calculation tells the real story. I still maintain you're looking at a plugged cat on bank two. A timing problem is possible, but you'd think it'd show in the static compression readings.
The following user(s) said Thank You: Noah, Wightscope, Speedwagon

Please Log in or Create an account to join the conversation.

  • Speedwagon
  • Speedwagon's Avatar Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
4 years 6 months ago - 4 years 6 months ago #47987 by Speedwagon
Replied by Speedwagon on topic Diverging fuel trims, help me understand
Just did the back pressure test on bank 2. I got 3psi (fluctuating) at idle, and up to 6-8 revving it up a bit.

Bank 1 was 1 psi, with almost no increase with throttle.

I'm fairly certain this is solved now.
Last edit: 4 years 6 months ago by Speedwagon.

Please Log in or Create an account to join the conversation.

More
4 years 6 months ago - 4 years 6 months ago #48004 by Wightscope
Replied by Wightscope on topic Diverging fuel trims, help me understand
Thanks @tyler, went off to investigate that diagnostic method and learned a whole lot more at atgtraining.com/atg-volumetric-efficiency-calculator/
Last edit: 4 years 6 months ago by Wightscope.

Please Log in or Create an account to join the conversation.

More
4 years 6 months ago #48012 by Matt T
Replied by Matt T on topic Diverging fuel trims, help me understand

Speedwagon wrote: I'm fairly certain this is solved now.


Just bear in mind that cat might've been killed by misfires. So check for those after the cat has been dealt with.
The following user(s) said Thank You: Speedwagon

Please Log in or Create an account to join the conversation.

More
4 years 6 months ago #48013 by Matt T
Replied by Matt T on topic Diverging fuel trims, help me understand

Wightscope wrote: Thanks @tyler, went off to investigate that diagnostic method and learned a whole lot more at atgtraining.com/atg-volumetric-efficiency-calculator/


This is a good article on VE testing boosted engines.

www.vehicleservicepros.com/service-repai...d-engines?page=0%2C2
The following user(s) said Thank You: Wightscope

Please Log in or Create an account to join the conversation.

More
4 years 6 months ago #48018 by Wightscope
Replied by Wightscope on topic Diverging fuel trims, help me understand
Thanks that was really interesting. Seem to be getting a lot of good stuff from VSP site recently

Please Log in or Create an account to join the conversation.

More
4 years 6 months ago #48027 by Tutti57
Replied by Tutti57 on topic Re:Diverging fuel trims, help me understand
Here is another good article on VE and fuel trims being opposite bank to bank.

www.google.com/url?sa=t&source=web&rct=j...V45cCGn44omBMFb3D8Ic

Sent from my moto g fast using Tapatalk
The following user(s) said Thank You: Wightscope

Please Log in or Create an account to join the conversation.

  • Speedwagon
  • Speedwagon's Avatar Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
4 years 6 months ago - 4 years 6 months ago #48030 by Speedwagon
Replied by Speedwagon on topic Diverging fuel trims, help me understand

Matt T wrote:

Speedwagon wrote: I'm fairly certain this is solved now.


Just bear in mind that cat might've been killed by misfires. So check for those after the cat has been dealt with.


Yes, it probably was. But before I got the vehicle. 2 loose plugs, one of them being not threaded in correctly on that bank, and the electrode was horribly undergapped.

I did the right thing though, and just drilled a couple holes in the cat to test.
It's working much better now. Ordering a new cat to put in there.
Last edit: 4 years 6 months ago by Speedwagon.

Please Log in or Create an account to join the conversation.

More
4 years 6 months ago #48043 by Tutti57
Replied by Tutti57 on topic Re:Diverging fuel trims, help me understand
And if there isn't a core on the new cat, you can scrap that old one for some $$. Not sure if they'll care about the holes drilled in it or not. I just got $250 for three last week.

To test next time, and if possible, you can disconnect the exhaust before the cats and see if it gets better, and it's also possible for it to be clogged farther back than the cats. Just a heads up, since that would suck if a muffler or something was clogged and then you need cats too.

I remember seeing an SMA video where Eric got burned replacing a cat and it was farther back.

Sent from my moto g fast using Tapatalk

Please Log in or Create an account to join the conversation.

  • Speedwagon
  • Speedwagon's Avatar Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
4 years 6 months ago #48185 by Speedwagon
Replied by Speedwagon on topic Re:Diverging fuel trims, help me understand
Given that the bank 1 cat joins the pipe just behind the bank 2 cat, it seemed highly unlikely, in this case, it could be anything other than the bank 2 cat itself.

Please Log in or Create an account to join the conversation.

Time to create page: 0.391 seconds