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Any help, 6.2l runs at idle all day but will not drive or reverse.

Chopchop82

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So my 86 3/4 ton suburban will idle all day but as soon as I start to drive it or reverse it, it has no power, I can push gas pedal all the way to the floor and engine stays just at idle and then stalls out. It will start back up over and over but won't drive. I've replaced the lift pump, the fuel filter (square one) , and installed a new electric fuel pump on the line before the LP. I've bleed the system to remove air and I've tried pressurizing the fuel tank. I have not found any leaks and I don't see air in the system so i don't understand why its doing this. Any help would be much appreciated! Thanks! I have read through a lot of posts and every time it leads me to think there's air in the system but with a clear tube on the IP I have no bubbles so I'm stumped.
 

Will L.

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Can you rev the engine up while in park?

Remove the airfilter and see if that makes any difference (not permanent, just for a Minute).

Any chance you can do a short YouTube video and post a link?

Operate the throttle by hand while parked and running incase the cable is bad.

Locked brakes, bad differential,trans, etc can hold it from moving, but it should still rev up to max in park/neutral. Then rev up in gear to around +-1400 rpm

I can imagine a bad torque converter creating havoc and stalling the engine, but the engine should still rev in park-

Hey trans experts- is there some way bad trans would limit rpm in park that I am forgetting?

An option NOT TO BE TAKEN LIGHTLY could be unbolting converter from flex plate, saftey wire tie back converter using 4 wires, 2 on each of the 2 converter holes you can get to, then start. But WAY CRITICAL—CONVERTER CAN NOT SLIP FOREWARD AND CONTACT FLEX PLATE!!! If it hits while engine is running it will destroy flex plate, converter both, and possibly more. The flex plate will go grenade. Not may, it will. Seen it. But that trans was race trans and it broke bellhousing and parts hit scatter shield. It also damaged starter.
This can be and is done safely, but be aware how bad it can get.
 

Chopchop82

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Yes it will rev up in park. I don't understand how it would not rev up in drive or reverse though, even if it is the torque converter. Wouldn't it still rev up regardless of if it actually moves anywhere? It really is weird. I'll make a video tomorrow when I get home from work and thanks for the help!
 

Will L.

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Please fill out your signature line with rig details. It makes this part SO MUCH easier. Only reason I assumed you have an auto trans is pic of suburban.

What modifications have you or previous owner done to it? Tc lock up mod? Reprogram? Trans controller? Any and all mods please, even if you dont think it could be related. I have seen some wacky stuff like flashing led tailights because of aftermarket alternator causing cruise to fail and abs to go crazy causing surging on the freeway- so all mods.

Pull tc cover and inspect it’s mounting, color, and flexplate condition.

4wd? Shift transfer case in neutral, put trans in gear and try it.
2wd? Block the front wheels REALLY WELL. Jack up rear of rig, and try it. See if wheels spin and allow rev up.

If not: get a drain pan under tail stock, remove drive shaft and try it.

Have you checked trans fluid? Level and condition...
 
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