355 - Fuel Injectors (5.2) | Page 3 | FerrariChat

355 Fuel Injectors (5.2)

Discussion in '348/355' started by Qavion, Apr 5, 2022.

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  1. taz355

    taz355 F1 Veteran
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    When mine was good for smog it was all ways below 1 just a fyi Ian
    Around .7 to .9 I think.
    I believe originally cali spec was below 3.5 but got tighter in about 2o14 maybe but not possitive because I imported the car back to Canada
     
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  2. Qavion

    Qavion F1 World Champ
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    As far as I can recall, during open loop, the MAF is used to measure airflow and the ECU map provides fuel injector opening times corresponding to that airflow. There may be other sensor inputs.
     
  3. Qavion

    Qavion F1 World Champ
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    Here's the formula again:

    [​IMG]
    T5 is fixed during open loop. T1 is based on rpms and airflow.
     
  4. INTMD8

    INTMD8 F1 Veteran
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    All vehicles I calibrate of the same era have no wide open throttle o2 correction (as they are in open loop) but do directly take mass airflow rate into wot fuel calculations.

    Also, injector duty cycle at WOT generally increases with rpm if still within an efficient range and wouldn't ever be running at max duty cycle on a stock vehicle. (though some have more overhead than others). Still, you would find IPW generally following the engines torque curve rather than just going static at WOT.

    While there is no WOT fuel adjustment via o2 feedback on an F355, being they have narrowband sensors, any other vehicle of the same era that I'm familiar with, directly correlates maf (mass airflow) with fuel delivery. So, generally if you made a change that increased airflow, it would be measured by the maf and the ecu would command an increase in fuel flow to match the increased airflow.

    ^ The above, along with manifold air pressure is necessary even in stock form as the induction from low speed to high speed would go from a pressure drop across the filters to higher than ambient pressure.
     
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  5. Qavion

    Qavion F1 World Champ
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    IWP?
     
  6. Qavion

    Qavion F1 World Champ
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    Some new spark plugs were tried (NGK PMR8A's because they were on the shelf in my tech's workshop) and the rough idle seemed to disappear. My old spark plugs are PMR7A's and are about 6 years/1,200kms old. However, I bought a set of PMR8B's, a few months ago because I thought they were suitable. Some old posts on this:

    https://www.ferrarichat.com/forum/posts/136554840/

    https://www.ferrarichat.com/forum/posts/139249631/

    https://www.ferrarichat.com/forum/posts/143975151/

    But then I looked on the Ricambi site and both the 2.7 and 5.2 are supposed to have the PMR7A's

    https://www.ricambiamerica.com/pmr7a-ngk-spark-plug.html

    @taz355 says:

    Note: Apparently the PMR8A's are basically the same as PMR8B's. The PMR7A's have a different temperature rating.
     
  7. Ricambi America

    Ricambi America F1 World Champ
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    1994/1995 = PMR8B
    1996- PMR7A
     
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  8. Qavion

    Qavion F1 World Champ
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    Thanks, Daniel. It's just that your webpage has both 1995 and 1996+ cars listed. Seems there is still a lot of confusion.
     
  9. 26street

    26street Formula Junior

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    What is the heat range on the plugs I can’t find the specs

    Is one (cooler) then the other or (hotter) and which is the ones you are using ????

    Ps once your car car is in close loop all fuel trims are based off of O2 (rich or lean) the MAF , MAP, ECT and all other inputs that are then calculated by the ECM to regulate the pulse width of the injectors and timing to try to keep the engine in legal limits of emissions and trying to get as much power it can — with a balance of air and fuel to the cat’s this is what makes them work too much of one or the other will damage them this is why a O2 (narrow band and wide band) will cycle above (up too 750mv) and below (down to 250mv) with the middle being (450mv Stoichiometry 14.7:1) some many’s times in a second (think not 100% sure but it’s like 1800) in open loop the fuel and timing map (not MAP sensor) is to bring the engine and cat’s up to temps so that they will start the catalyst reaction to reduce emissions and adjust engine output’s for close loop

    If you replace the plugs to have it run better maybe you should scope the secondary ignition if the tech knows what he is looking at he should be able to see if the cylinders are running lean/rich and in balance the fire line spark duration and etc is greatly effected by fuel air mixture and compression which will show up on a scope
     
  10. Qavion

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    I was using the PMR7A's for a while. I can't recall why I chose them.

    https://www.ngk.com/ngk-4259-pmr7a-laser-platinum-spark-plug

    Heat range "7" (from PMR7A)

    My tech tried a PMR8A. The higher the number, the colder it is.
     
  11. Qavion

    Qavion F1 World Champ
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    Not sure what you mean by "secondary ignition".

    Unfortunately, I won't know much more until after the Easter Holidays.
     
  12. 26street

    26street Formula Junior

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    Ok thanks
    heat range basically means the transfer of heat by how much porcelain is located in the body of the plug which sits in the cylinder

    Colder plugs have a higher chance of fouling do to not enough temp to clean deposits off the plug

    hotter plugs will retain too much heat which can not be dissipated through the body and cause Predictation

    There is a sweet spot that cars will run good at

    If you are have lean or rich problems in individual cylinders and the ecm is not able to control fueling and timing all you are doing is compensating a good spark capability to bad fuel management

    This why “reading the plugs or using a scope” is probably your next step

    Prolong running of a engine like this can damage the valves and pistons over time

    Matching a plugs heat range to a good running engine is so important once modifications are made
    A stock engine running good on pump gas (92 octane if using E85 might need to change the heat range of your plugs ) will work fine on manufactures recommended plugs


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  13. 26street

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    Secondary ignition it the spark that is produce by the coil that goes the the plugs primary ignition is the 12 v supplied by the battery


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  14. Qavion

    Qavion F1 World Champ
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    We normally use 98 octane here. Do you go up or down (with heat range) with higher octane?

    Now I'm with you. I thought you meant unburnt fuel igniting outside the combustion chamber. Like an afterburner.
     
  15. 26street

    26street Formula Junior

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    Higher the octane the slower the burn and more heat needed to start the ignition of the fuel —— too say the need of going up in heat range might not be needed but you can put more timing in to the car to start the power stroke aka Advance the timing with higher octane —— which will give you more power—-
    Ideally you want to burn all the fuel and air
    If the mixture stays on the rich side you will see most tuners will go up in heat range and play a lot with timing to get a full or close too full burn
    The O2 sensor (in close loop) is changing fuel and timing and does get to its limits too this is where tuners come in to play

    Tuning is an art in itself so if your engine is running good with what ever octane you choose (above 89) staying with manufacture specs should be fine in my opinion but if you want all you can get out of the car and want to run e85 or race fuel then changing the plugs will be needed and proper assessment how the engine reacts to the changes and alot more homework is need on your part and the tuner




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  16. taz355

    taz355 F1 Veteran
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    As stated above I believe they went to 7 plugs because the 8 is colder and as stated above foul more easily.
    I would think if you drive the car relatively hard 8 would be fine as well and I have used them before with no issues.
    Not your problem I don’t believe
     
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  17. Qavion

    Qavion F1 World Champ
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    Although a new set of PMR8A's seemed to improve my imbalance issue, my tech will be fitting the approved 7A's as he thinks one or more of the old spark 7A plugs was faulty.

    I don't know why the old ones have failed (other than lack of use). Visually they look fine.
     
  18. Zamboniman308

    Zamboniman308 Formula Junior

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    No science here but you read this a lot. A new plug fixes a gremlin that you've been chasing your tail on.. and the entire plug set was changed within the last couple thousand.

    Coincidence?? Poor quality control or prone to early mortality of the spec'd plug model??

    There are so many things that make my head spin with these quirky Italian beauty's... granted this is an extreme application.. but you don't hear of temperamental spark plugs, temperamental engine management systems that require cleaning or even swapping to gold connectors on any other platform of millions of automobiles.
     
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  19. Qavion

    Qavion F1 World Champ
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    You mean the "quirky Italian beauty with German engine management and Japanese spark plugs".... which is 24 years old (in my case) ;)
     
  20. Zamboniman308

    Zamboniman308 Formula Junior

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    Not exactly impressed with the bosch components of this vintage thats for absolute sure.
     
  21. INTMD8

    INTMD8 F1 Veteran
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    "Higher the octane the slower the burn"


    Often repeated but incorrect. Higher octane doesn't mean slower burning.

    It means more resistance to auto/abnormal ignition (or pre-ignition/detonation/combustion event initiated by heat rather than the ignition system, multiple flame fronts colliding).

    Most gasoline of any octane has comparably similar burn rate. If anything, many race fuels are tailored to a faster burn rate simply because it's necessary.

    You'll find burn rate more influenced by engine design than fuel used. As observed by different engines requiring vastly different ignition advance to achieve max power on the same fuel. (combustion chamber design/plug location/bore size/etc/etc)

    You aren't running high compression/high rpm (10,000,15,000+rpm) on a slow burning fuel.

    The myth is perpetuated by guys with a relative slug of an engine going from 87 swill to 116 race fuel and the car slows down.

    Determination is made that the car is slower because the fuel burns slower. -Or- they dumped more timing in it along with the fuel which is beyond ideal.

    Actual explanation is more complicated but generally it isn't that higher octane = slower burning but many times higher octane means lower energy density (btu/lb).

    And with that, not usually the same specific gravity/stoichiometric value as the pump fuel it's replacing. So jetting or efi calibration changes necessary to make an accurate back to back comparison at the same air/fuel ratio.

    As for plug heat range, generally I would be hesitant to move hotter than stock. Can make your own determination by chopping ignition at the end of a WOT pull and observing the color mark on the ground strap.

    -If it's a problem solved temporarily by changing plugs, not likely because you are chasing ideal heat range but the plugs are fouling for another reason regardless.

    You describe it as an intermittent problem. Can you post a video of it going from running well to not?
     
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  22. Qavion

    Qavion F1 World Champ
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    I'm try. Assuming it's not fixed by the time I next see it.

    This is the not running well (but I was primarily concerned about the rattle)...

     
  23. 26street

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    It was been around 35 years since studied thermal dynamics in college but a quick google search came up with ——- again this is for pump gas not race or Aviation fuels I don’t think any one here is going to the track or airport to fill up their tanks

    I m not here to argue facts and probably wrong about some or most things

    I’m here to try to help and with the question that is being ask I tried to give a answer I thought was right

    I regards to his problem at this time it’s my opinion that a oscilloscope be used to see the secondary ignition wave form this will give you a lot of insight too what is going on

    This type of diagnostics is a lost art and was a go to back on the day because it was the only way to really see how the engine is preforming

    with controllers doing fuel management there is still so old school thinking need here if you are replacing spark plugs and seeing the engine run better then it’s time to go the next step the ecm will only tell you so much and because it can make fuel and timing adjustments which can mask problems that makes it harder to find them

    by looking at spark firing line and etc with a oscilloscope you see what the cylinders are using and need from the ignition system there’s a lot of information using a scope if tech’s know what they are looking at

    This is just the way I would go it doesn’t cost much and not throwing parts and money at the unknown








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  24. INTMD8

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  25. 26street

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    Here is some old reference material I have about secondary spark firing

    I’m sure if you search the net there will be more Information with better explanations of what you are looking at but this should give you an idea what good and bad is if you do decide to use a Scope




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