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Author Topic: remanufactured tbi problem  (Read 4815 times)

Offline GMCTed

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remanufactured tbi problem
« on: November 23, 2007, 06:51:37 pm »
the tbi on my 87 suburban was sticking badly due to the throttle shaft wearing so i bought a remanufactured tbi unit on ebay.

i put the new tbi on the truck today and it started right up but soon after the engine would almost stall, then rev up to about 1,000 rpm repeatedly and eventually die. when i would try to rev the engine up i had to really work the throttle to get it to rev up.  when i got it to rev up i`d try to maintain a steady rpm but it wouldn`t  and it would bog down and stall. it was running extremely rich the whole time too.

i put the old tbi back on and it ran fine.

i have very little knowledge of tbi`s so i don`t know what the problem could be. any help will be greatly appreciated.

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Offline VileZambonie

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Re: remanufactured tbi problem
« Reply #1 on: November 23, 2007, 07:12:49 pm »
Is the TPS voltage set to .55v with the throttle closed? Do you have the correct Base gasket installed? Back probe the TPS sensor with your meter at cavity B the dark blue wire. Put your other meter lead to ground. Key on engine off adjust the TPS to read .55v with the throttle closed. Once you do this disconnect the negative battery cab;e for 30 seconds. REconnect, cycle the key on then attempt to restart it.
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Offline Captkaos

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Re: remanufactured tbi problem
« Reply #2 on: November 28, 2007, 09:14:40 am »
Is the replacement the exact same unit or is it a Holley Unit?
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Offline GMCTed

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Re: remanufactured tbi problem
« Reply #3 on: November 28, 2007, 08:04:22 pm »
it`s a stock rebuilt unit. the only difference is that the new one has only three vacuum ports on the front of it and the old one had four.   i just disconnected the vacuum line that went to the top of the emissions tubes on the passenger side. i took the belt off long ago so i don`t think thats the problem.

the strange thing is that after i put the old one back on it idles very high and when it`s cold the engine will stumble and die, but start right up again.  i checked for vacuum leaks and didn`t find any. and the really strange thing is that when i put the truck in gear (TH400) the engine will rev up to like 1400 rpm ??? if i put it in neutral it goes back down to around 900 rpm, even i i move the gear selector a fraction of an inch the idle goes up. very strange! 

when i put the new one on and it was running poorly i swapped the new TPS with the old one to see if that was the problem but when i unbolted the old one i could swear that the little tab was on the wrong side of the spring rendering it useless but i`m not 100% sure.  the truck ran great before all of this, is it possible that it could run great without a TPS? and now that it`s on correctly it`s screwing it up?
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