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  1. #1

    Default TBI Part throttle Chugging/power loss

    I got my van out on the road yesterday after double checking the timing (which i thought to be causing this problem), and the problem still occurs. Only happens under load.

    At idle to 1/4 throttle, the engine runs smooth. When i reach 1/4 to about 1/2, 3/4 throttle it chugs bad, acts like it's missing/got no power. I can muscle it through if i give it closer to full throttle, and it'll come out of it and runs pretty well.

    Under no load, it runs smoothly.

    The suggestions that have been given to me already are disconnect the EGR, that it might be hanging open or dumping too much; or that it could be a problem with the map sensor.

    I probably won't have time or good weather to work on it until this weekend, so wanted to see what other suggestions were there before I got into it. I will be double checking all of my vacuum lines as well, and am going to try and datalog/pull codes if i can get WinALDL configured properly.
    1986 Chevy G20 Tow Rig - 5.7 TBI conversion
    1978 Mustang II King Cobra Road Racer - Holley 650, MSD 6AL, 5 speed, 10 point Roll Cage, 9" posi, fuel cell, custom interior.

  2. #2


    This is how my Suburban was acting when the transmission was giving out. The torque converter is putting a huge load on the engine until the engine got above an RPM range and then I guess could overpower the converter.

    1991 Chevy Suburban 1/2 ton 2WD w/ chevy SBC 350-3/4 ton drivetrain upgrade w/4.10 gears 200K miles
    2005 Saturn ION-2 Stock 265K miles
    1982 Bronco, 1993 Bronco (sold), 1971 M35A2 Deuce and a Half

    There are 10 kinds of people, those who understand binary, and those who dont...

    Remember kids, the only difference between screwing around and science is writing it down- Adam Savage

  3. #3


    sadly that's also a possibility. I didn't rebuild the trans when i put the new engine in, and it's going to need it in the next year or 2, but I was hoping I could get by until then. The trans is still behaving the same as it did with the old engine, so I *think* it's something related to the conversion to TBI and new engine, but not positive at this point.

    Another note is the trans I'm using is not the one that the ECU had attached originally (from the donor), it's the one from the 86 van, just a 3 speed auto (think turbo 350) with no computer control and no lockup torque converter.

    I got TunerPro RT downloaded and setup, which looks to be much better for logging than WinALDL, so going to try and get some logs soon and see how things are looking. blizzard incoming tonight though, bah.
    Last edited by dualdj1; 02-24-2011 at 03:50 PM.

  4. #4


    i was able to get a log in last night before the snow. From the best I can tell, most sensors (map, tps, etc) are reading properly. I think I may have a prob with the O2 sensor though, I'm getting readings between .400v and .450v, and that's it. it hangs pretty much around .442. I know I had it miswired in the change from 1 to 4 wire, so I may have fried it.

    At any rate, the logging software I have keeps telling me that ECU is saying that it's lean, and that it's not going into closed loop at all. I did not have time to check for vacuum leaks, etc.

  5. #5


    another possible corollary, is that i no longer have a speed sensor going into the computer, but I have not yet disabled it with tuning/chip/etc. I was told this probably wouldn't cause a problem, but could that be the issue at hand?

  6. #6


    Update: I fixed the O2 sensor wiring. When converting to a 4 wire sensor, you cannot just connect the ground from the sensor to the ECU O2 sensor low feed. Both wires have to be grounded. I'll try and make a write up about it, including pin numbers and wire colors. In short purple O2 wire from ECU goes to the sensor output +, sensor output - and ECU Brown O2 wire both get grounded, preferable at the same point near the ECU for accurate readings.

    After fixing the O2 sensor most of the hesitation is gone. There is still a bit but I think the plugs are slightly fouled at this point, and the fuel trims are still adjusting.

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