Fuel trim help

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  • mrgerrard
    Junior Member
    • Sep 2013
    • 4

    Fuel trim help

    Hey guys.

    I hope this is the right place to post rhis. Im just getting back into diagnostics so please bear with me im a bit rusty.
    Im doing some work on a car i have recently brought. These are its details
    1997 Toyota Caldina GTT
    2.0ltr turbo 3SGTE engine (generation 4engine)
    3" exhaust
    295000kms
    New airfilter
    Have new plugs and fuel filter to be put in

    everything else stock relating to my query

    So it has a backfire at times whilst driving and a cough at idle.
    On my solus ultra i noticed a few things at IDLE
    1.LT fuel trim constant -20% -trying to remove fuel(rich)
    2.ST fuel trim -9% - -14% -teying to remove fuel(rich)
    3.TPS 13% fully closed and max 80% fully opened(engine off during test)
    4.O2 switching ok .1-.8v
    5. From memory the inj pulse was around 1.5 at idle

    Ok so its obvios its running rich and my backfire is unburnt fuel reigniting. This is what im trying to sort but am not sure where to go from here.
    i know its either too much fuel or not enough air.
    i was wondering if my TPS might be confusing the ECU, i would of thought that ot should be reading 0% at closed and 100% at WOT? If someone has info on these engine they could email me for testing it that would be good.
    Also i wondered if this larger exhaust is playing some part aswell?

    Finally a general question how does if at all turbo boost pressure effect fuel trim. Eg going from a vacuume to a pressure?

    i would love your thoughts. Thanks heaps

    Mat.
  • greasybob
    Senior Member
    • May 2008
    • 1590

    #2
    Is there any MAF or MAP/Boost data that you could post. How are the fuel trims when driving ?

    Comment

    • Witsend
      Banned
      • Nov 2012
      • 2942

      #3
      Maybe the Fuel Regulator leaking gas into vacuum line attached to it? Fuel pressure could be too high, crankcase dilution from past flooding and excess fuel in crankcase. KOEO throttle position on scanner opening the throttle body plate by hand to WOT should be at or close to 100% I would think that would eliminate stretched cable or floor mats keeping it from getting to WOT position.
      Also if you put a bigger cam , exhaust pipes and turbo , and other non stock aftermarket **** on it,and a big sub in da trunk, good luck with that one, lol

      Comment

      • mrgerrard
        Junior Member
        • Sep 2013
        • 4

        #4
        Originally posted by greasybob
        Is there any MAF or MAP/Boost data that you could post. How are the fuel trims when driving ?
        Yup there should be. Ill take a look later today and let you know. I do notice the odd hesitation/flat spot around 3000rpm. Ill try record my readings when it occurs.

        Originally posted by Witsend
        Maybe the Fuel Regulator leaking gas into vacuum line attached to it? Fuel pressure could be too high, crankcase dilution from past flooding and excess fuel in crankcase. KOEO throttle position on scanner opening the throttle body plate by hand to WOT should be at or close to 100% I would think that would eliminate stretched cable or floor mats keeping it from getting to WOT position.
        Also if you put a bigger cam , exhaust pipes and turbo , and other non stock aftermarket **** on it,and a big sub in da trunk, good luck with that one, lol

        Well with regards to the fuel in crankcase oil looks good, clean and fells and smells like oil.
        being an older car the fuel pressure reg. Crossed my mind too. So ill take a look.
        KOEO and manually operating throttle plate made no change. This also crossed my mind.
        Lastly i take it you not a performance car man lol. I brought the car like this. Only aftermarket item on it is exhaust but i cant see it causing the issue.

        Thanks for your thoughts guys we are thinking along the same lines which is good.

        Comment

        • greasybob
          Senior Member
          • May 2008
          • 1590

          #5
          Not familiar with this vehicle but I wouldn't rule out an ignition problem causing the back fire or "flat spot". Weak coil or out of time.. Also if it has adjustable valve lash, tight lifters will cause a rich condition

          Comment

          • Witsend
            Banned
            • Nov 2012
            • 2942

            #6
            IMHO anything with a K&N airfilter or something similar with one of those cold air intakes the MAF hot wire gonna get contaminated a lot quicker especially if the car has been lowered and the intake is vacuuming up standing water off the pavement.Drastically Lowered suspensions , cold air intakes ,large non stock wing on back, and large mettallic flake paint-jobs to me is worse than having a Salvage title .LOL

            Comment

            • monzanick
              Member
              • Dec 2011
              • 38

              #7
              running rich?

              I would monitor your post cat o2 readings. If it is always rich(600mv+) I would trust the rich codes. Verify the cold air intake isn't corrupting fuel trims by putting stock stuff back on. If ya can't, get tubing cross section measurement from stock. Verify MAF is installed the correctly.

              If all else looks o/k, start looking @ valve timing.

              Comment

              • JamesO
                Junior Member
                • Dec 2014
                • 23

                #8
                Any vehicle that is running Fuel Trims in the high negative (-) values is usually not really running rich. Most modern vehicles it is almost impossible for them to run rich with the exception of a very few circumstances.

                I would be looking closely for a questionable/counterfeit Asian MAF, if the engine has multiple pre-Cat O2 sensors to make sure the O2 sensor wiring is not crossed up an look closely at the pre-Cat O2 sensor behavior.

                Sorry to say this but you cannot make a judgment on the O2 sensor health by looking at the O2 sensor Voltage swings. The only way to determine good O2 sensor health is to have a cold start fingerprint. I never see anything other than O2 sensor heater failure codes, but I can always flag a lazy O2 sensor by watching the cold start finger print.

                You also have to be very careful about thinking you can relay on the post-Cat O2 sensor Voltage. When the catalytic converters are storing Oxygen, the post-Cat sensor Voltage will be high.

                Attached is a before and after narrow band O2 sensor cold start finger print.

                BTW, the O2 sensor graphing is done with a $5 OBDII smart phone App and a $15 interface.
                Attached Files

                Comment

                • mrgerrard
                  Junior Member
                  • Sep 2013
                  • 4

                  #9
                  Originally posted by JamesO
                  Any vehicle that is running Fuel Trims in the high negative (-) values is usually not really running rich. Most modern vehicles it is almost impossible for them to run rich with the exception of a very few circumstances.

                  I would be looking closely for a questionable/counterfeit Asian MAF, if the engine has multiple pre-Cat O2 sensors to make sure the O2 sensor wiring is not crossed up an look closely at the pre-Cat O2 sensor behavior.

                  Sorry to say this but you cannot make a judgment on the O2 sensor health by looking at the O2 sensor Voltage swings. The only way to determine good O2 sensor health is to have a cold start fingerprint. I never see anything other than O2 sensor heater failure codes, but I can always flag a lazy O2 sensor by watching the cold start finger print.

                  You also have to be very careful about thinking you can relay on the post-Cat O2 sensor Voltage. When the catalytic converters are storing Oxygen, the post-Cat sensor Voltage will be high.

                  Attached is a before and after narrow band O2 sensor cold start finger print.

                  BTW, the O2 sensor graphing is done with a $5 OBDII smart phone App and a $15 interface.
                  Interesting. So a good o2 sensor should drop down to very low volts before operating. Can you shed some light on why it does this?


                  On another note i found something plain as day. The vacuum hose to the fuel pressure reg had split right where the regulator vacuum pipe stops. It was by chance i found it. Fixed that and things seem a lot better now.

                  Comment

                  • JamesO
                    Junior Member
                    • Dec 2014
                    • 23

                    #10
                    Each car and technology is slightly different, but as you work on different cars you will soon get a good idea of how the O2 sensors behave on cold start up.

                    Although the "bad" O2 sensors in this graph may have eventually warmed up and functioned reasonably well, in this case and this car, the cold start O2 sensor behavior will impact the Emission Readiness Monitor and also possibly cause Secondary Air System errors.

                    What everyone needs to remember is almost all of the Emission Readiness Monitors require the O2 sensors to be in good operational shape.

                    In this attached graph, this car has a Secondary Air System and Variable Valve Timing. What I call as the "Deep V" at cold start is caused by the SAS pumping additional air into the exhaust and causing the O2 sensor Voltage to go very Lean. Then once the SAS pump shut off, in this case at the 60 second mark, the O2 sensor Voltage swings high, then starts toggling as it should. So between the changes in Ingnition timing, Valve timing and the SAS running, you basically have almost an afterburner effect in the exhaust stream to warm up the O2 sensors (along with the electrical heaters) and the catalytic converters.

                    Note that this car pretty much is going into Closed loop fuel feedback in the first minute of cold start. Closed loop is really no longer a function of engine temperature.

                    As for finding the split Fuel Pressure Regulator hose on the car you are working on, this may have been one reason the Fuel Trims were so negative, however, not all cars actually have vacuum controlled FPR, some may have hoses attached to the FPR, but they often just lead to filtered air inside the air filter box, the FPR holds a static fuel pressure and the injector pulse width is varied during accelerating for enrichment purposes.

                    Attached are graphs that show how the post-Cat sensors. Note that the high post-Cat sensor Voltage is normal while the converters are charging or storing Oxygen. Note you can see that the Bank #2 catalytic converter is not storing Oxygen like the bank #1 converter, it is likely contaminated with carbon, oil or may just be bad. Sometimes contaminated converters can be recovered, sometimes they have to be replaced.

                    You also know about the P0420/P0430 codes and catalytic converter inefficiency. On this car with a questionable performing converter, it did not trigger a P0430 code.

                    I had an argument with a CA SMOG tech that was stating this car had good catalytic converters but it failed CA SMOG testing for other reasons. I put my $20 tool up against is 6 figure 4 gas exhaust gas analyzer and was able to pinpoint that there was at least one catalytic converter that was not functioning properly and this was the problem with the car!
                    Attached Files

                    Comment

                    • scottmechanics
                      Member
                      • Jun 2013
                      • 42

                      #11
                      Rich readings

                      Hello after reading your problem I would suggest
                      You look at 02 sensors on idle and at 3000 rpm in garage engine warm
                      When you get results go from there looking at scan data you must reduce pids
                      To a min 3 or 4 at most ,when reading 02 sensor on the signal wire a scope is needed

                      Comment

                      • mrgerrard
                        Junior Member
                        • Sep 2013
                        • 4

                        #12
                        Originally posted by scottmechanics
                        Hello after reading your problem I would suggest
                        You look at 02 sensors on idle and at 3000 rpm in garage engine warm
                        When you get results go from there looking at scan data you must reduce pids
                        To a min 3 or 4 at most ,when reading 02 sensor on the signal wire a scope is needed
                        Hey appreciate your feedback. My o2 sensor was switching correctly as it should. However because of my split fuel pressure regulator vacuume hose my regulator was supplying to much fuel to the fuel rail causing a rich condition even tho my o2 sensor was switching correctly my fuel trim readings were telling me the ecu had to trim the fuel by - 20% to allow for correct o2 sensor readings. Once the air leak was fixed my long term fuel trim now reads around -6% to +4% which is perfectly acceptable. This fix had also remedied the backfire issue due to less unburned fuel entering the exhaust.
                        Also another unknown issues that has been fixed is the turbo boost pressure had dropped and no longer spikes.

                        As a tech I have always followed what the o2 sensor tells me as gospel. Yes it is an important reading to follow but my first port of call is now LT fuel trim and ST fuel trim then onto o2 sensors.

                        Now onto repairing the brakes on this damn car hahaha.

                        Comment

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