Close



Results 1 to 8 of 8
  1. #1

    Default 86GT running lean- codes 41 and 91

    Greetings, everyone:

    Went over the 86GT today as it was nice out. Ran and drove great. Smooth and lots of power. Pulled codes. KOEO-11
    KOER- 41 and 91. Did the cylinder balance test- all good code 90. No other codes. Checked fuel pressure with KOEO, solid 39 lbs. KOER fuel pressure is about 32 to 34 lbs. Should be a little higher, no? Turned the engine off and checked residual pressure. Pressure slowly rose from 34 lbs to 38 lbs over two minutes. No smell of fuel. Checked secondary air system. Switches to downstream when given throttle. I'll check for vacuum leaks tomorrow.
    Last March the entire fuel system except the fuel pump was replaced. New regulator, fuel injectors, fuel lines, and filter. All correct parts. Many vacuum lines are new as is the PCV valve. Here is one repair that shouldn't be related but is.
    The fog lights stopped working last summer and I tracked down the culprit to a fusible link that also protects the O2 sensors. Thought that might be the explanation as the lean codes showed up last summer about the same time. Found a correct Ford fusible link and connected it as best I could. Fog lights work great but still running lean. I'll check that repair tomorrow also.
    O2 sensors are four years old with less than 40,000 miles on them. Might they really be bad? Shop manual at this point says to check their electrical circuits and grounds.
    I suppose a leak in the exhaust system could also cause a lean problem. Will check tomorrow. Any ideas?
    Thanks much.

  2. #2
    FEP Super Member erratic50's Avatar
    Join Date
    Dec 2016
    Location
    Nebraska
    Posts
    4,575

    Default

    If the exhaust is leaking before the O2's that's a good guess.

    O2 sensors usually last a LONG time. I only replace mine when the code scanner says they are bad, but then I replace both of them.

    Isolate your fog lamps on another fuseable link and make sure your connections are solid. Also check your chassis to battery ground to be certain.

    Too much base timing advance can cause a lean condition. Also, when's the last time you changed the fuel filter? Pickup sock intact? Full or empty tank? Does your pressure stay where it should with fuel demand or drop rapidly?

    A lot of times when you clean fuel systems it breaks crud loose - that can clog injectors. Pull the rains and injectors and inspect them.

    one thought - head to the nearest you pull-it style place and pulling a set from something compatible 19lb/hr.... Bench firing them before you install them to make sure they are good. Otherwise pick up new ones and test those before putting them in.

    A noid light set from harbor freight would be a good investment too. Then you can confirm its not injector wiring related.

  3. #3

    Default

    I reviewed the repairs from last March. I keep returning to the fuel pressure regulator. The new one is a little shorter than the original that came off the car. I'll post some pix on this reply to show what I mean. Even though part numbers are correct, the parts are different and perhaps that is why things are lean. I'll still check for vacuum leaks and the exhaust pipes but the different regulators bothers me. Both Ford units. I could put the old one back on and check pressure I suppose.Name:  Fuel Pressure 079.jpg
Views: 41
Size:  103.2 KB Here's the new one on the car. Part number F4CE-9C968-AA.
    Name:  Fuel Pressure 082.jpg
Views: 41
Size:  98.7 KB Here's a comparison with the old. Part number E#EE-9C968-AA.

  4. #4

    Default

    That's E3EE-9C968-AA.

  5. #5
    FEP Super Member erratic50's Avatar
    Join Date
    Dec 2016
    Location
    Nebraska
    Posts
    4,575

    Default

    Get an adjustable with gauge or put the old one back on. They last just about forever - mine was an original when I removed it with a ton of miles on it and it still worked perfectly.

    bear in mind that if you mess with pressure too much you will see hard starting.

    for example - I increased my fuel pressure to remedy a lean condition at WOT and high RPM and it runs a little fat now everywhere else. I have the quarterhorse board and have done a MAF conversion but I'm being lazy - I know it needs to be tuned.

  6. #6

    Default

    I just went through my parts stash and I actually do have a new correct regulator. Looks like the old one plus has the correct part number. Shop manual says to test them by applying 20 lbs of vacuum to the return port on the regulator and measuring the drop. Both pass but the old one didn't hold vacuum as well. I checked all the vacuum lines and exhaust and everything looks connected and secure. Since my car is factory, I'll probably put the new one on soon. But as I've had fuel pump trouble many times, I may replace the pump and the filter at the same time. Nice all day job but worth it.

  7. #7
    FEP Super Member erratic50's Avatar
    Join Date
    Dec 2016
    Location
    Nebraska
    Posts
    4,575

    Default

    Yep - those in tank pumps do go bad. Biggest lessons for me were

    - change the fuel filter annually if you drive it often
    - never run lower than 1/4 tank when above 80 degrees outside
    - alway run premium fuel because it's more sense and heats up slower
    - alway replace the sock with the pump
    - insulate the fuel lines (especially by the RR exhaust tailpipe)

    Lessons learned the hard way. I cooked my share of pumps before I wised up. My current pump is a lifetime autozone 155 and has about 175K hard miles on it. So far so good - still works great.

  8. #8
    FEP Senior Member
    Join Date
    May 2016
    Location
    Lake City Pa 16423
    Posts
    510

    Default

    Fuel pressures sound fine. Vacuum pulls pressure down when running. A small vacuum leak will cause a lean code, exhaust leaks before the O2 sensors and even lazy O2's. As O2's get old, they slow down on switching from rich to lean. Yes they will still work all the way up to 100k miles, but will not switch fast enough, or may not reach full lean or full rich limits. 40k isn't a lot, but I would tap into the wires for them and check the switching speeds with a good meter that can record min max.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •