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  1. #1
    Join Date
    Oct 2009
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    New Haven, CT, USA
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    Default 8.1 - bunch of codes

    I’m working my way through a punch list of items while I break in these new engines. On my Stb engine, I noticed a low RPM (1,500 or so) surging of a few hundred RPM’s. If I throttled past that, it was fine and I cruised at 3,500 for a few short periods. When I tried to briefly push past 3,600 on the same engine, I could feel it being limited. I didn’t have a CEL/MIL on the gauge and didn’t really expect any codes but got 8 when I checked tonight:

    these are all code 81 - historical fault:

    - TAC error, no TAC reply
    - 5 volt reference fault
    - injector bank A voltage low
    - fuel pump circuit low
    - throttle actuator (TAC) fault
    - ECM calibration memory error
    - engine shutdown/emergency stop (assume this is what I felt at higher RPM’s.)

    Does this seem like maybe a bad battery? I’ve had these random voltage codes on cars before when the battery is marginal. I’m stumped why it didn’t trip the gauge light because I would have scanned right away.

    Any thoughts appreciated. Also, all of the pos/neg cables are new as part of the install so corrosion is def not an issue but I will start checking the cable ends. Finally, both engines start fine and my running voltage is ok at 13+. They do automatically bridge when starting so a bad battery could be masked by the good one.

    thanks
    Bob
    Last edited by bobct; 05-05-2021 at 09:17 PM.

  2. #2
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    Default Re: 8.1 - bunch of codes

    That is an ugly list....if you are sure the all of the *! codes are 'historic', I'd be inclined to delete them and start with a fresh baseline....i know there are a handful of 'historic' codes in my truck and every time I pull ALL CODES, it's scary because the screen is full....

    I would also check the fuel pressure on the trouble maker as I don't think the MEFI-4 ECU monitors the fuel pressure in the rail...I would also bring the scan tool and do a real time monitor (logging) run next time out...if tis within the ECU's control, the logging functions will give you the opportunity to find it...

  3. #3
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    Default Re: 8.1 - bunch of codes

    Quote Originally Posted by makomark View Post
    That is an ugly list....if you are sure the all of the *! codes are 'historic', I'd be inclined to delete them and start with a fresh baseline....i know there are a handful of 'historic' codes in my truck and every time I pull ALL CODES, it's scary because the screen is full....

    I would also check the fuel pressure on the trouble maker as I don't think the MEFI-4 ECU monitors the fuel pressure in the rail...I would also bring the scan tool and do a real time monitor (logging) run next time out...if tis within the ECU's control, the logging functions will give you the opportunity to find it...

    good idea, the weather isn’t great but going to try and make a run today. I’ll bring my fuel gauge and rule that in/out. I cleared all of the codes and going to take my time and check all wiring this morning. I’m hoping that I really have ONE problem which will clear up everything.

  4. #4
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    Default Re: 8.1 - bunch of codes

    I was thinking the first handful suggested a bad connection somewhere (but common across a few areas)....then things diverged.

    good luck...

  5. #5
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    Default Re: 8.1 - bunch of codes

    Ok, so I have a bit up an update on a few fronts:

    1) I reseated the ECU connections and disconnected the slave/master connector so I could keep any issues isolated. I load tested the battery (good) and double checked all of the ground connections, then cleared the codes. Went out for about a 90 minute run and had the Diacom plugged in the whole time. No codes appeared. Maybe these were stored from running it on the hard and the battery was low. I’m calling this issue good for now. This is where the plot thickens

    2) Mark, I took your suggestion and hooked up a fuel pressure tester for the entire ride. The Crusader spec I believe is 37-43 @ idle and 44-48 @ WOT. I had 37 at idle but only 39-40 at my highest RPM’s which were around 4,400 with a huge caveat:

    I’ve never had a scanner (Rinda Techmate Pro) connected while underway. I happened to glance at the engine RPM’s and noticed they were about 450 RPM’s higher compared to my tachs. (This is “engine speed”). I have been judging my speed, fuel burn (all much better than the 454’s) compared to my tach readings since the first run. These are the same tachs I had with the old engines as well. These 8.1’s are supposed to hit 5,000/5,200. If this is based upon engine speed and not what I’m seeing on the tachs then I’m not looking nearly as good as I thought numbers wise.

    Putting that aside for a minute, it did feel like the engine I tested today was either starving for fuel at my highest RPM’s and maybe the fuel pressure number bears that out. If you recall, Crusader calls for 1/2” fuel line. I have 1/2” coming OUT of my Racor to the engine but my original 3/8” from the tank to Racor. I can upgrade this section on both engines. My original theory was that the 8.1’s would need less fuel at WOT but the RPM’s are higher so maybe not the case.

    My biggest concern right now, is the engine speed THE source of truth or do I have a tach issue x2? (and props that are nowhere near correct)? The delta is at lower RPM’s as well:

    tach 2,600 = 3,150 scanner
    tach 3,000 = 3,440 scanner
    tach 3,400 = 3,850 scanner


    thanks
    Bob





    Last edited by bobct; 05-08-2021 at 05:53 PM.

  6. #6
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    Default Re: 8.1 - bunch of codes

    I will have to ponder the tach offset...looks like the value on the scanner is 'off' at 2600
    RPM compared to the other values...

    On the fuel pressure, there is the key on engine off test point...the pressure should have came up with the throttle open enough at 4400 RPM...so I'd say check the inlet side of the pump to see if there is too much restriction (the installation manual has a discussion there)... that will tell you if there is a restriction...and I also think they discuss the anti-syphon valve, too.

    the rinda should have given you the fuel consumption values, too...

    as far as truth, I'd be inclined to go with the rinda but both tachs being off a fixed amount is rather unique...again, I'll ponder that one some more..

  7. #7
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    Default Re: 8.1 - bunch of codes

    Mark, they’re analog tachs so it’s likely that 2,600 reading was actually 2,700 which would make the pattern match. Yes, the Rinda does show fuel consumption which was really close to my analog flo-scan gauge. I didn’t check that at my highest RPM’s though.

    The scary part is I only stumbled across this because I wanted to check fuel pressure real time. I guess if I only had digital tachs on my Garmin, I would be working off the higher numbers. I can’t imagine how the Scanner output could be off? I’ll give Rinda a call tomorrow just on the off chance they tell me something different.

  8. #8
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    Default Re: 8.1 - bunch of codes

    Bob:

    I doubt the digital reading has much error...the only way I can see two tachs with a fixed bias was if they were calibrated with it...and being it is likely they are same brand from same batch, it is plausible...

    On the fuel pressure, with the vacuum referenced regulator, the change in pressure should vary with the change in vacuum with the engine running...so I would have expected a bigger swing...the KOEO test should give the max reading...

  9. #9
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    Default Re: 8.1 - bunch of codes

    Yes, I was probably reading between the lines on the tach which I believe is increments of 200 or 250. So, I think I’m consistently 450 RPM’s higher at least in the range where I care. The idle isn’t 450 RPM’s too low so the issue starts over 2k if I had to guess. Ugh, I never expected this as an issue.

    I’ll continue troubleshooting the fuel pressure in the meantime. Faria is located in CT so I could potentially drive up there with both tachs and have them checked.

    thanks
    Bob

  10. #10
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    Default Re: 8.1 - bunch of codes


  11. #11
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    Default Re: 8.1 - bunch of codes

    if you were closer, I could let you use my 'stroboscope'....a piece of reflective tape on the balancer and you get the non-contact reading....it also has a rubber nose for making a contact measurement...but i've never been brave enough to use it on anything above idle....

  12. #12
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    Default Re: 8.1 - bunch of codes

    Mark,

    I appreciate that offer. I do own an IR tach and actually had the foresight to apply the tape when I had the engines in the garage. I didn't really think I would need it though. I called Faria and they said the scanner RPM's are "the" source so adjust the tach to those numbers and call it a day. The guy I spoke with wasn't surprised that both were off the same amount. Thinking back, I'm pretty sure I was coming up short on the old engines but didn't press it because of their age.

    This is a bummer for sure but there's nothing I can do but correct the difference. I'll be cruising in the 21k range which I was never able to do with the 454's but a 24k cruise is off the table. I believe my RPM's at that speed are really around 4,100 vs the 3,600 I'm seeing now. Scary to think that I literally tripped over this issue. If I get to 5,000, which now I think I came close to unknowingly, 75% of that number puts me at 3,750 RPMs.

    Time to adjust the tachs and hopefully my punch list will start trending down

  13. #13
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    Default Re: 8.1 - bunch of codes

    that's scary...that they are that 'loose' with their products (calibration-wise)....

    agreed, its time to go fishing down here...

  14. #14
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    Default Re: 8.1 - bunch of codes

    I agree, not loving Faria right now. I adjusted both tachs in the slip last night and took it for a run. While underway, I connected the scanner to each engine and double checked underway. At cruise, I'm 100% positive that I'm seeing the correct RPMS. Now my idle is reading high but I'll deal with that later or just live with it.

    With all that, it looks like I'll be cruising around 21k at around 3,500/3,600 burning 30 GPH. I only have a couple of hours of break in left, then oil change and I'll see if my WOT is 5,000. With the tach issue, I think I came close already but not by design. I'm 90% the props are in the ballpark.

    Yes, I'll let you know if I wind up down that way....which I might for work.

  15. #15
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    Default Re: 8.1 - bunch of codes

    At least you are making progress....

    if the boat doesn't load the engines too bad, you could consider a custom tune...there may be a little more left. I haven't tried an 8.1 w/ the MEFI-4 so can't say from any experience....

    We are still on tele-work, no traveling (except by exception), at work...

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