Tbi nightmare

Discussion in 'TBI & EFI Conversions' started by Spoonbill45, Aug 12, 2017 at 2:31 AM.

  1. Spoonbill45

    Spoonbill45 Junior Member

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    Dustin
    Truck Year:
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    Truck Model:
    C10 Silverado
    Engine Size:
    304
    Hey guys, I am brand new to this site and I am just looking so I needed to post so here it. I have an 87 c10 305 tbi with a 700r4. It is almost all original. Until last November it was original right down to tires and sparkpligs so I to get those, anyway, when I press the pedal it loads up just like a carb will do when it isn't tuned correctly. I am really stumped about this because fi isn't supposed to do the bad stylike carbs do. I have done everything I can think of and nothing. This a rare truck. First year with efi in trucks and the last year of production for this design. Please any one just let me what to cause I am lost. Thanks
     
  2. 1987 GMC Jimmy

    1987 GMC Jimmy Full Access Member

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    Truck Model:
    V1500 Jimmy
    Engine Size:
    350
    Okay, this sounds like a very low mileage truck that hasn't been driven much over the years. It also sounds like you've changed the plugs, which is a start. I'd do the basics first. You've already started an ignition tuneup with the plugs. Now, go ahead and inspect the plug wire contacts for corrosion or anything that isn't a fairly shiny contact. Also, check them very carefully for rat chewing. If the insulation and everything inside the boots looks good, they can stay. Next, check the distributor cap and rotor. What you'll be looking for here is corrosion on the inside of the cap. If you see any, replace it. I wouldn't think you'd see any excessive wear, but go ahead and get a new one if you don't feel right about it. Same with the rotor. If it looks corroded or worn, get a new one. I'd normally say replace the stuff without thinking, but if the miles are that super low, it would be a waste of money unless things degraded from sitting. Finally, make sure to use AC Delco ignition parts should you replace anything. I would also suggest getting a timing light if you don't have one and checking the base timing. I can tell you from experience that a nasty winter can retard your timing several degrees, and that'll make it act like a dog. On the TBI, you have to disconnect the EST bypass connector (a single wire weatherpack style connector on the driver's side of the firewall), and it's ready to check. Since it's a 305, I'd suggest a 5* BTDC setting. I used to suggest in the 8-12* range for any SBC/BBC, but I found from daily driving a 305 myself, they are not as flexible with the a higher initial setting as a 350 would be due to a higher compression ratio.

    Next, do a fuel tuneup. All you really need to do for now is borrow a fuel pressure tester from Autozone, and buy a new fuel filter. Remove the old filter from its location along the frame rail and tee in the pressure tester. You need to see about 13 pounds of pressure. If you see less than 11, I'd replace the whole fuel pump/sender assembly. If it looks good, just replace the filter and call it good there.

    Check for vacuum leaks. You can do a visual inspection for broken lines or disconnected boots, but I'd invest in a vacuum gauge that can tell you where you are rather than guessing. A good idle vacuum is about 18-21 inches. I'd get to repairing vacuum stuff if it's 17 or lower. Cracked lines are not good, either, and should be replaced. Another thing you can do is spray starter fluid around the base of the TBI to see if the idle changes. If it does, the gasket is bad. I'd shake the PCV valve and see if it rattles, too. A final thing on vacuum and emissions is the EGR valve. I'd just remove it, clean the carbon off the pintle, and make sure it moves freely. I'd replace it later if you find your vacuum reading still isn't where it should be.

    Last thing to look for is the SES light coming on when you have issues. If it is, that's a good thing because it can help expedite diagnosing this issue. If not, I'd proceed with the small maintenance things that I've mentioned above. If the light has come on for any reason, you can pull the codes and see what caused it to come on. What you do is get a paperclip, insert it on the two top right pins on the ALDL connector, turn the key to on but don't start the truck, and the orange light will start flashing various sequences at you. The codes are double digit numerals that will be represented by how the flashes are grouped. For example, the code flashing sequence will begin and end with three Code 12s. It'll flash once, pause, and flash two more times. That will happen thrice with slightly longer pauses in between, and it'll move on to show you more codes if it has any. They all flash in groups of three. Is it running rich by chance? If so, I'd replace the Coolant Temperature Sensor for starters but wait on replacing the other sensors as the ECM determines necessary.

    Sorry if you've done any of this already; I thought it made sense to go through everything.
     
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  3. Cuba

    Cuba Full Access Member

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    The only thing I'd add on the fuel tuneup is changing the fuel pressure regulator in the TBI... it's only a rubber diaphragm and this controls the fuel pressure after the fuel pump.

    I'd actually do this prior to the fuel pressure check because if the regulator is failing, this will give false pressure readings from the pump's output.
     
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  4. 1987 GMC Jimmy

    1987 GMC Jimmy Full Access Member

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    Good idea. I might go a step further and just buy the whole rebuild kit. Those o-rings and stuff may have suffered from sitting.
     
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  5. Cuba

    Cuba Full Access Member

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    The whole rebuild kit is better and comes out to be the same cost as just the pressure regulator itself... & doesn't come with the needed gaskets, like the TBI to Intake. The rebuild kit does.
     
  6. 4WDKC

    4WDKC Full Access Member

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