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Thread: Lean surge 7.4L with TBI

  1. #31
    Fuel Injected!
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    Quote Originally Posted by PlayingWithTBI View Post
    I honestly don't remember any small ground wires going to the back of the engine, only the ground strap that goes from the head to the fire wall. As @Dieselsj said I found both the black/white and tan wires double crimped to the eye on the T-Stat housing. Maybe GM changed its location later on?
    It is possible. I'm used to seeing a dedicated ground. Perhaps GM initially tied it in with the other grounds, then later switched to giving it it's own grounding point. Any difference of potential or noise here would reek havoc on the O2 signal. Eventually GM, and everyone else, switched to 4 wire O2 sensors to ensure a good sensor reference.

  2. #32
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    Quote Originally Posted by CottonPicker View Post
    O2. Use a air powered Die Grinder with a wire brush. Remove the O2. Run the wire brush over the Ex manifold until it shines bare metal. Wire brush off the O2 threads. Anti-seize the O2 threads. screw it in a few times and recoat. Tighten.
    Measure the O2 Ground at the ECM Pin Back probe. DVOM Ground needs to be connected to Battery Negative post. Start/Run engine hot. Measure O2 Grd. Running and hit the throttle to see max volts. More than 0.1/0.2 is a poor ground. (Measuring with DVOM on OHMs Scale is Deceiving. Had some measure 0.1 ohm this way. DVOM Voltage measured 0.4 volts on O2 Ground when throttle hit. Car ran just as a plugged Cat converter. Dealer spent $4,500 in parts for poor ground at head.)
    Thanks. That will be part of my testing this evening.

    BBC. China MAP Replace with Delco/GM. in BBC and others under load, Fuel will WICK up the Vac tube. Contaminate the sub-strait of the strain gauge. This shifts the MAP output voltage and the engine runs very lean/LEAN mixture. (No Codes set either back in those days) So lean the EGTs will be over 1600 Deg. Ex Valve grow longer or tulip, then engine destruction. Remove MAP. Place white cloth/Kleenex on palm, Tap vac inlet of MAP. Any liquid of any kind is shifted lean.)

    Insure MAP is manifold Vac. NO LOW POINTS IN MAP LINE. Install MAP at the top of the firewall run vac line, no sags, to Manifold vac.
    That would certainly explain the high EGT and glowing exhaust manifolds. It has gotten so hot that wire loom has deformed. New Delco MAP has been ordered.

    BBC If you live in the frozen tundra keep the thermac active in temps starting at 48 deg F and lower Esp on humid days. Stops TB Icing. If not in cold, run the thermac Vac line plugged so thermac is INOP 100% & remove hot sir tube. In MI I never had any iced TB with any carb/TBI BBC. Run air cleaner housing intake tube to Rad support as Suburbans. Helps when under hood temps are Very hot during loads. Use Small Block Large Truck air cleaner TOP. Use Large A/C Filter. (#753? vs #248) Double air flow. BBC needs cold air. In some cases VE may need to be touched up. (Injector pulse width at low %. With higher fuel pressure it is difficult for the Injector to overcome the pres and begins to be unstable. Physics)
    While most of the year here in AZ we are warm, we do get a few weeks/month where we are in the 20's overnight and 50's during the day. I'm not ready to remove the coolant flow through the intake just yet. I do have the factory cold air tube in place which is routed to the radiator support. I've been looking at a dual snorkel setup from RamAirBox, but that is a project for later.

    In some yrs Idle BLM was meant to be at 140. Anticipates Full Carbon Canister. No sag with Canister purge at 100%.

    Back to the Farm.
    Interesting. Good to know.

  3. #33
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    Update -
    Unwrapped loom and checked all wiring. Traced all grounds and cleaned/replaced. Verified all ohm at 0 between ECU connector and negative battery terminal. Verified all pins in connector at ECU 0-ohm out to each sensor connector. Installed new O2 sensor and MAP sensor. Reset all TBI settings - idle set for IAC to be approx 20 steps, TPS is currently at 0.53v. Fuel pressure set at 12psi. EGR is gone and a block-off plate installed. AIR also gone and manifolds plugged.

    Fired it up and let it warm and it idles great. Come off idle and it goes lean again (O2 voltage dropping to <0.01v and error flag for lean condition is triggered, and INT in the 160s) right at 1600rpm up through 2000rpm at which point everything seems to come back and I see O2 voltages cycling as they should and no surging. Holding the RPM anywhere over 2100 RPM and there is no surging, O2 voltages are cycling as expected, and BLMs are in the 140 range (expected based on opened up exhaust and aftermarket intake).

    Something I noticed is that as I bring it up off idle, I don't see an increase in fuel flow from the injectors up through where it goes lean and starts to surge. If I snap the throttle and get past 2100 I really see the injector output jump and if I steadily increase from 2100 on I can see more fuel flowing. If I steadily decrease from 2100 then I see a significant drop in output from the injectors and it goes back into the lean surge again.

    If this was a carburetor, I'd say that it isn't transitioning off of the idle circuit quickly enough.

    I played with fuel pressure some and I got BLMs at the higher RPMs down to 126-128 (INT at 128-130) by bumping fuel pressure up to about 20psi. That made it rich at idle, but not unbearable. That had little or no effect on the lean surge at 1600. I currently have the fuel pressure set at 15 which seems to give a nice idle without stinking up the garage.

    What parameters effect that off-idle transition? I see the closed-loop flag get set very quickly after I start increasing RPM (around 1000rpm or so).

    I have tried 2 different ECUs. But I used the same chip in both. Is is possible that something happened and data on the chip got corrupted or ?? Currently has an AZFT in it. It had an ACLX when I bought it - the AZFT was in the glove box and I installed it because it was a later code. When I get back out there this evening I'm going to dig ou tthe ACLX and give it a try.

  4. #34
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    I quickly scanned this thread so I might have missed it. You have the EGR blocked off, is the EGR turned off in the chip? When the ecu thinks egr is active it WILL remove fuel based on EGR fuel settings in the calibration and therefore the learning process will attempt to fix the NOW lean condition due to the EGR not being functional.
    -Carl

  5. #35
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    Quote Originally Posted by In-Tech View Post
    I quickly scanned this thread so I might have missed it. You have the EGR blocked off, is the EGR turned off in the chip? When the ecu thinks egr is active it WILL remove fuel based on EGR fuel settings in the calibration and therefore the learning process will attempt to fix the NOW lean condition due to the EGR not being functional.
    EGR is not turned off in the chip. It was having this issue with the EGR installed and removed it to eliminate the possibility of it leaking. Also, the conditions in which I'm having the issue aren't any times that the EGR would be commanded. And it is going extremely lean...significantly more lean than a non-functional EGR would cause.

  6. #36
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    Can you post the stock bin file? I will modify it for no EGR. I assume you can program the chip? I could be wrong but it sounds like an area where the EGR would be active, I'll know better after looking at the file you are using. Thanks
    -Carl

  7. #37
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    Quote Originally Posted by In-Tech View Post
    Can you post the stock bin file? I will modify it for no EGR. I assume you can program the chip? I could be wrong but it sounds like an area where the EGR would be active, I'll know better after looking at the file you are using. Thanks
    I am currently not set up to program. It is running a stock AZFT now. Since I have converted from the TH400 to a NV4500, if I make any changes I think I'd start with a AZFU or ATPZ as those are manual bins. Those bins are posted over in the 7747 thread. Thanks for the offer. I can send you a stock chip to burn if that works. I have the ACLX prom sitting on a shelf.
    Last edited by Dieselsj; 11-04-2020 at 08:51 AM.

  8. #38
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    Put in the ACLX (known good - was in the truck when I bought it) and same issue.

    Interesting thing - as I tip in the throttle, I don't see an increase in fuel flow until I really snap the throttle and get it up to about 2500 rpm then the flow really increases. As I let the revs come back down it goes into the area where it surges..but it does not surge on the way down...until I get under about 1900rpm then I can see the fuel flow suddenly decrease and the surge starts.

    When I installed the external regulator I accidentally put 60+ psi into the injectors. Could I have damaged the injectors in some way?

  9. #39
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    PM sent
    -Carl

  10. #40
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    Quote Originally Posted by Dieselsj View Post
    Put in the ACLX (known good - was in the truck when I bought it) and same issue.

    Interesting thing - as I tip in the throttle, I don't see an increase in fuel flow until I really snap the throttle and get it up to about 2500 rpm then the flow really increases. As I let the revs come back down it goes into the area where it surges..but it does not surge on the way down...until I get under about 1900rpm then I can see the fuel flow suddenly decrease and the surge starts.

    When I installed the external regulator I accidentally put 60+ psi into the injectors. Could I have damaged the injectors in some way?
    What are you using to scan with? Can you graph the TPS and look for dips or stalls in the voltage during a sweep?
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  11. #41
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    Quote Originally Posted by brian617 View Post
    What are you using to scan with? Can you graph the TPS and look for dips or stalls in the voltage during a sweep?
    Using WinALDL. I'll log it and see. From what I'm seeing in the real time feed the TPS is increasing as expected as I tip in the throttle.

  12. #42
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    Well, I gave in and went to Moates and ordered all the stuff. I read through the Tunerpro tutorial and opened some of the bins in the 7747 thread and checked them out.

    I managed to find a AZFW prom, which looks to be the last 7.4/Manual/4.10 version that was released. I will add that to the 7747 thread as soon as everything arrives and I can read it.

    I'm going to play with it tonight and see if I can get TunerPro to work with my existing ALDL cable and try to do some initial logging with hopefully way better resolution that I can get with Winaldl.

    Thank you to everyone who has helped out. Other than some funky issue with the injectors, I'm thinking that the VE tables are just so far off with my mods that it just can't compensate. The issue is right at peak torque.

  13. #43
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    Finally got time to work with the Moates stuff.

    Removed old pins from ECU and soldered in new socket. Put in factory chip and fired it up to make sure the socket connections were good. Burned a chip based on the existing chip and put new chip in to test that and all was good. Burned the new AZFW tune and put that in as a test. AZFW is the first manual based bin that I have tried and first thing I have noticed is that it has a much slower return to idle when you release the throttle compared to the automatic trans bins that I had been using.

    Now that I know it all works, it is time to try to tune out that lean spot. I have a log file so I know which cells need to be tweaked as a start.

    Cover me...I'm going in...

  14. #44
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    I've burned a few new tunes and have gone about 60% higher than the factory VE values in the affected cells (and blended the surrounding cells) and still have the exact same issue. RPM going up...all looking good from a tuning standpoint...as soon as I hit that RPM the 02 output drops to <0.1v and it goes into the lean surge.

    I haven't tried any live tuning yet and that is my next step. I would have expected some change with pushing my VEs that far over the factory values. I'll try pushing the VEs ridiculously high and see what happens.

    I must say that I'm leaning towards a hardware problem. Thinking an injector issue. Like something is keeping the injector from cycling properly.

    More later...

  15. #45
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    Tried some live tuning tonight. I was able to make changes to the idle so I know my changes were pushing to the emulator. I increased the cells in the main fuel table in increments of 10 and went all the way to 100 with zero change to the way it was running. It would do the same thing where I would hit a certain RPM and the O2 sensor voltage would drop and BLM/INT would max out and it would go into a lean surge. I went the other way with the VE values in the active cells and the engine died.

    I am not happy with my truck right now.

    Everyone says these injectors don't go bad, or when they go bad they just leak. At this point I'm not sure where to go with it.

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