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Thread: Help with '99 L31 ECM Tune

  1. #21
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    Quote Originally Posted by CJstein View Post
    I'll fire it up this afternoon. I'm assuming there are channels for reading the individual injectors?
    He's asking for the injector part # so the injector data in the tune can be verified.

  2. #22
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    Quote Originally Posted by SiriusC1024 View Post
    Looks like it's calling for a lot of fuel. Has anything been done to the engine or is it stock? Read the numbers on the physical injectors and write them here. Need to verify injector data.
    The part number for the Injectors is FJ504 and the link to them is https://www.summitracing.com/parts/smp-fj504
    Ireplaced everything but the crank, cam, pistons, and rods, with OEM replacements, except for the rocker arms. I replaced those with Comp Cams 1417-16s here https://www.summitracing.com/parts/CCA-1417-16. The crank, cam, pistons, and rods were inspected at a machine shop and didn't need replacing.

  3. #23
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    Engine>Fuel>General>Injector Control

    Put 19.1 lb/h for Flow Rate.

    Post another log and updated tune with injector rate.

  4. #24
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    Quote Originally Posted by SiriusC1024 View Post
    Engine>Fuel>General>Injector Control

    Put 19.1 lb/h for Flow Rate.

    Post another log and updated tune with injector rate.
    Took me minute, due to some VIN issues, but I was able to write the flow rate change. Here's another log after the changeFirst run after changing Fuel Flow to 19.1 lb per hr.hpl. It ran pretty rough and still had the misfire.

  5. #25
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    Much better fuel trims. See how it's still calling for extra fuel at idle? That looks like a vacuum leak. Log shows DTC P0452. Try capping off the manifold-side vacuum port to the evap solenoid and see if the idle improves.

  6. #26
    Tuning Addict blindsquirrel's Avatar
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    A vacuum leak? On an L31 intake?? Unpossible.

  7. #27
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    Quote Originally Posted by blindsquirrel View Post
    A vacuum leak? On an L31 intake?? Unpossible.
    Solenoid valve is stuck open, thus behaving like a vacuum leak. My guess.

    Or you were joking idk. Hard to read tone on text. That upper plenum gasket design does look suspect. Should be ok since OP would've been in there to change injectors. I don't see why a new gasket set wouldn't have gone in.
    Last edited by SiriusC1024; 05-25-2023 at 08:38 PM.

  8. #28
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    Quote Originally Posted by SiriusC1024 View Post
    Solenoid valve is stuck open, thus behaving like a vacuum leak. My guess.

    Or you were joking idk. Hard to read tone on text. That upper plenum gasket design does look suspect. Should be ok since OP would've been in there to change injectors. I don't see why a new gasket set wouldn't have gone in.
    I did go in and replace the injector assembly, but re-installed the same gasket, because it was brand new and I didn't see the need to replace it again. I'll run it again and cover each vacuum port one at a time, to see which one is giving the rought idle. One question I do have now though, because the engine went into my CJ7, I didn't put everything back on. It doesn't have the EGR, or most of the EVAP system. I have the Purge Solenoid, the MAP sensor, and the breather hose that goes from the valve cover to the intake. The purge solenoid is capped, but I noticed one of the ears where it mounts to the plenum is broken, so that might be where the vacuum leak is. I'll order a new one and see if that helps. The rest are connected like they should be.

  9. #29
    Senior Tuner TheMechanic's Avatar
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    I have changed hundreds of spiders on these. Before you spend a ton of $$ on anything do a simple fuel pressure drop on it. Can be performed with a fuel pressure gauge and a scan tool. Go to function test and you can activate individual cylinders. KOEO. Each will drop a specific pressure as it is activated for 1 second. They will all be within a pound or so.

  10. #30
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    One other thing I forgot to mention. When I ran it, using the repository tune, and before adjusting the fuel pressure to 19.1, the ECM wouldn't let the engine rev up past 1500 ish RPMs. It did the same thing, when I first tried using it, back when it had the stock tune from a Chevy Express 5.7l. Since then, I've read and written to it quite a few times. Is it possible the data on the memory chip got jumbled through all the reading and writing, and the rev limit is now stuck on the repository tune as well, or is there a setting in the tune that keeps the engine from revving too high? Maybe to avoid damage being done to the engine.

  11. #31
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    Quote Originally Posted by TheMechanic View Post
    I have changed hundreds of spiders on these. Before you spend a ton of $$ on anything do a simple fuel pressure drop on it. Can be performed with a fuel pressure gauge and a scan tool. Go to function test and you can activate individual cylinders. KOEO. Each will drop a specific pressure as it is activated for 1 second. They will all be within a pound or so.
    I know I should probably know what this means, but what is KOEO and when you say pressure drop, you mean hook up my fuel pressure gauge to the rail, activate each injector one by one, using the special functions in VCM Scanner, and see if the gauge drops to show whether it's spraying or not?

  12. #32
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    Quote Originally Posted by TheMechanic View Post
    I have changed hundreds of spiders on these. Before you spend a ton of $$ on anything do a simple fuel pressure drop on it. Can be performed with a fuel pressure gauge and a scan tool. Go to function test and you can activate individual cylinders. KOEO. Each will drop a specific pressure as it is activated for 1 second. They will all be within a pound or so.
    Key On Engine Off. Never mind

  13. #33
    Tuning Addict blindsquirrel's Avatar
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    You pulse one injector, record the amount of fuel pressure drop, then re-cycle the key to reset fuel pressure to the same start point, and do the next injector. Comparing the amount each one drops tells you how well they are balanced. An injector that drops more pressure than the others is flowing more, drops less it's flowing less...

  14. #34
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    Quote Originally Posted by TheMechanic View Post
    I have changed hundreds of spiders on these. Before you spend a ton of $$ on anything do a simple fuel pressure drop on it. Can be performed with a fuel pressure gauge and a scan tool. Go to function test and you can activate individual cylinders. KOEO. Each will drop a specific pressure as it is activated for 1 second. They will all be within a pound or so.
    Quote Originally Posted by SiriusC1024 View Post
    Much better fuel trims. See how it's still calling for extra fuel at idle? That looks like a vacuum leak. Log shows DTC P0452. Try capping off the manifold-side vacuum port to the evap solenoid and see if the idle improves.
    So I connected the fuel pressure gauge and it showed a steady 52psi while it was running. Before starting it, I tried finding the option to activate each injector individually, but I could only find an option to disable each one and that didn't do anything. While it was running, I checked the vacuum lines and noticed the PCV vacuum port on the plenum has 2 ports, instead of 1. I had the second port capped off so I pulled it off and it stopped misfiring, but the whistling noise it made was distinct. I've attached the log I made while I made these changes. I tried attaching a picture of the vacuum port, but I'm unable to attach any pictures. 4476 ECM after adding INJ Duty % and pulling cap off PCV intake vacuum port.hpl

  15. #35
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    In your looking for leaks, have you blocked off the hose to the brake booster yet? Most people miss that, the booster can rupture inside and create a massive vacuum leak you won't find by soraying down the external things.

  16. #36
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    Quote Originally Posted by blindsquirrel View Post
    In your looking for leaks, have you blocked off the hose to the brake booster yet? Most people miss that, the booster can rupture inside and create a massive vacuum leak you won't find by soraying down the external things.
    I didn't block it off. I just installed it a few weeks ago so I didn't even think about it. I'll do it later today and post results. I'm also going to try running the cann ecm with the vacuum port uncapped to see if it gets rid of the misfire.

  17. #37
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    How about the lower intake gaskets?

  18. #38
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    Quote Originally Posted by SiriusC1024 View Post
    How about the lower intake gaskets?
    I didn't need to remove it so they're still in from when I installed it. I switched over to the cann ECM and left the vacuum port uncapped. Here's the log Cann tune after uncapping PCV vacuum port on intake.hpl. I'm not sure how much I can trust it though. It doesn't show any misfires, but I still hear the puff of air from the exhaust, like before. The short term fuel tables stay at 50% and the long term stay at 0. I wish there was a way to unlock the cann tune so I can see the tune file.

  19. #39
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    Creating a vacuum leak that solves/improves a misfire isn't a diagnostic test I've ever heard of and don't think will tell you anything useful, and I've been doing this for a whole bunch of years. How do you use that info to solve your problem?

    The plastic-framed lower intake gaskets on these engines have always been a problem even when brand new.

  20. #40
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    Quote Originally Posted by blindsquirrel View Post
    Creating a vacuum leak that solves/improves a misfire isn't a diagnostic test I've ever heard of and don't think will tell you anything useful, and I've been doing this for a whole bunch of years. How do you use that info to solve your problem?

    The plastic-framed lower intake gaskets on these engines have always been a problem even when brand new.
    This is only my second engine build and my first EFI build, so I'm still learning everything about it. Other than looking for a vacuum leak in the intake, is there anything you can recommend? I'll check the lower intake gasket later to make sure it's sealed.