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Thread: engine not idling correctly after tbi conversion

  1. #1
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    engine not idling correctly after tbi conversion

    Gentlemen,
    We finally got the ecm and TBI engine up and running. Again on a 94 stock 350 with automatic tran. for rock crawlwer apllication. The engine is running but we do not have the diagnostic port tied into the harness yet. It only seems to want to idle while the gas is held down a little bit to keep from dieing. And when it is running it, it seems to be slightly throttling back and forth like in some kind of loop.? Does any body have any ideas on this? After reading some of the posts, they say that the EGR valve could be sticky or also the I.A.C may need some type of calibration?
    Is this the right direction to start troubleshooting?
    Thanks for any info on this.
    -Tyree

  2. #2
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    EGR stuck open usually causes rough idle condition. I would lean more toward the idle needing to be adjusted. That said, without knowing what the computer is seeing or trying to do it's a crap shoot as to what the actual problem is. Might try placing a matchbook between the throttle screw and lever and see if that changes the idle.
    If it don't fit force it, if it don't force fit f&%@ it!

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    Yeah, this can be a number of things...on my conversion i had a vacuum leak, bad spray pattern on my injectors, and my distributor internals were rusted...After this it was purring nicely. You can easily test all of those, also make sure your timing is right at 0*, if you're using all stock parts you shouldn't need to adjust the idle position screw. Also here's a link to IAC cleaning - http://www.thirdgen.org/techboard/po...221-post6.html

  4. #4
    EFI GearHead ! EagleMark's Avatar
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    Quote Originally Posted by Tyree View Post
    Is this the right direction to start troubleshooting?
    -Tyree
    No! Right direction would be the ALDL port and checking error codes and getting a data log. If you don't do that first it's just a crap shoot in all directions.

    Basic maintence could be the issue. Maybe it was running that way before you got it? Distributors on these are OLD at this point even if they've had new cap and rotors, the other parts are way past service life as are all other parts. Engines could still be in a very good condition depending on miles and maintenance.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  5. #5
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    Gentlemen,I just wired up the diagnostic connector according to the schematic for the 1227747 and I am getting information off the A8 serial data connection pin on ecm(I checked it with my oscilloscope). But my obd reader will not acknowledge for whatever reason. Does anybody know about this.? Thanks for the continued help to everybody.

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    ok. so I jumped a and b together on the diagnostic connector and was trying to read the A5 pin which is also pin D on the diagnostic connector directly for SES codes and saw nothing.. I am lost on this. I also notices that when in the key is in the accessory position the IAC is vibrating a little bit.?

  7. #7
    EFI GearHead ! EagleMark's Avatar
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    When you jump the A and B it will flash the CEL. The check Engine Light coming out of ECM is ground and it needs to go to Key On Power.

    Without the jumper and the key turned on the CEL should come on, blink once and stay on till engine is started, then go off.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  8. #8
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    Thanks eagle mark, I will try that. I must have been interpreting the schematic incorrectly. I will connect the aldl pin D to ignition power and try again. thanks

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    eagle mark, tyree and i are doing the tbi swap.I was wondering the steps in wiring the aldl directly to the ecm and do you jumper A to B then turn on the key for the code reader to pick up the connection? also we got the motor running ok without the MAP sensor.When you hook up the MAP the motor wants to run like a vacuum leak. we triewd taking a test drive and felt like it was bogging down and running rich. Also the motor runs better with the EGR and tbi port for EGR plugged. Any idea why?

  10. #10
    EFI GearHead ! EagleMark's Avatar
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    Quote Originally Posted by tra1nwreckage View Post
    eagle mark, tyree and i are doing the tbi swap.I was wondering the steps in wiring the aldl directly to the ecm and do you jumper A to B then turn on the key for the code reader to pick up the connection?
    Sounds right? But I usually have an ALDL port...

    Quote Originally Posted by tra1nwreckage View Post
    also we got the motor running ok without the MAP sensor.When you hook up the MAP the motor wants to run like a vacuum leak. we triewd taking a test drive and felt like it was bogging down and running rich. Also the motor runs better with the EGR and tbi port for EGR plugged. Any idea why?
    There's something majorly wrong!

    Should be way rich without a MAP sensor as it's reading full throttle.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  11. #11
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    Okay so plugged the map back in. Got a little bulb to go between pin d and A5 on ecm to key switched 12v. Shows a code 12 which if everything is fine, but still runs like a vacuume leak........ its driving me crazy i sprayed carb cleaner around the motor and vacuume leaks. Did show a code 34 before plugging in the map but is gone now. Still boggs at open throttle, and the timing mark is straight up not on the indicater marks....... bad egr possibly? And had to delete the knock sensor because it kept my block huggers from bolting flush with the heads..... any help is help :)

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    Ment no vacuume leaks by the way oops

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    I also cant get any change in rpms by turning the dizzy it just kills the motor. Thanks all for input

  14. #14
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    Gentleman, We were finally able to get error codes from the service engine light bulb that we added to the harness. When connecting a 12 pin connector and attempting to get obd1 info, the obd1 reader will not communicate with the ecm. Does anybody know if there are any additional wires to hookup? we have been using the wiring diagrams from www.gearhead-efi.com/Fuel-Injection/showthread.php?304-1227747-ECM-Information-42 for this. We want to be using the aldl but cannot get communication and everything looks like is hooked up correctly and like I said, we can at least get error codes. Does it still have to be jumpered from A and B when using an obd1 code reader?

  15. #15
    EFI GearHead ! EagleMark's Avatar
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    Quote Originally Posted by tra1nwreckage View Post
    I also cant get any change in rpms by turning the dizzy it just kills the motor. Thanks all for input
    RIght, and you won't because the RPM is computor controlled, not mechanically controlled.

    Quote Originally Posted by Tyree View Post
    Gentleman, We were finally able to get error codes from the service engine light bulb that we added to the harness. When connecting a 12 pin connector and attempting to get obd1 info, the obd1 reader will not communicate with the ecm. Does anybody know if there are any additional wires to hookup? we have been using the wiring diagrams from www.gearhead-efi.com/Fuel-Injection/showthread.php?304-1227747-ECM-Information-42 for this. We want to be using the aldl but cannot get communication and everything looks like is hooked up correctly and like I said, we can at least get error codes. Does it still have to be jumpered from A and B when using an obd1 code reader?
    No jumpers for ALDL data or when hooked up to scanner.

    Getting flashing code 12 and nothing else is good! No codes. I've seen many scanners not show data when it comes to OBDI. All you need on ALDL port is A, B and E. Some old scanners need cig lighter power.

    Re-reading your thread it does seem like you have a bad EGR, block it off. Still need a chip with EGR turned off for fueling and spark to be correct. With no knock sensor your knock counts keep counting so knock retard is in full force. Still need a chip with knock removed for correct spark advance.

    What is fuel pressure?

    Have you set timing to 0 with bypass wire dis-connected? Then connect, clear codes and re=start.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

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