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Old 07-11-2010, 06:50 PM
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TBI swap runs rough when put in to gear.

I have put a 1990 Chevy 5.7 TBI out of a pickup into an offroad vehicle. I used a painless TBI Harness and since getting it running it runs fine just sitting at idle, and revs up great. It is mated to a turbo 400 trans. When I put it in gear it runs a little rough, and when given throttle it stumbles and backfires. I seems like a really out of tuned carb. Ive gone through everything I can think of. Fuel system is good including pressure. timing is good, Plugs ,wires all good. checked all vacuum lines, all good. Oh and no codes from the computer. Any Ideas.

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Old 07-11-2010, 07:04 PM
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check your timing, there's no carb on a tbi. tbi= throttle body injection
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Old 07-11-2010, 07:36 PM
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Timing is good. Ididnt mean that I thought it was a badly tuned carb. I just used that as an example of what it seemed like. I know what TBI Means. Thanks for the help.
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Old 07-12-2010, 09:18 AM
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my firebird also felt like it was running ruff when in gear but it was just that it had a tight torque converter and the idle was a little slow, so it was struggling against the extra resistance. Try adjusting the idle a little faster and see if that's the problem. The turbo 400 is a bigger resistance on the engine than, say, a turbo 350 or 700r4 would be.
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Old 07-12-2010, 12:42 PM
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Thanks. that is one thing I have not considered. Ill give that a shot.
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Old 07-12-2010, 04:55 PM
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what is the fuel pressure?
whats the timing set to?
was anything done to the engine before it was swapped?
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Old 07-12-2010, 09:39 PM
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Fuel pressure is steady at about 13 psi, The timing is set to 0, and nothing was done to the engine before the swap. it was out of a truck that ive had for a while and it ran great.
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Old 07-13-2010, 05:59 AM
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new cap and rotor?
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Old 07-13-2010, 09:17 AM
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Timing set to 0? You need to advance your timing. Try about 12* initial.

Last edited by bigdog7373; 07-13-2010 at 10:57 AM.
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Old 07-13-2010, 01:31 PM
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Ya the cap and rotor are new.

The timing is suppose to be 0 with the plug disconnected.

This is really driving me nuts. Ive swapped everything in the ignition accept for the distributor. Mabey thats next.
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Old 07-13-2010, 02:18 PM
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try advancing it and see what happens.
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Old 07-13-2010, 05:08 PM
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i have a 90'k1500 with the tbi 350 of couse, now i dont know what you mean when you say set the timinig with it "unpluged", iv never unpluged anything on mine or know what that is, iv got mine set at 10 and it pings very little on 87 octane.....
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Old 07-13-2010, 05:24 PM
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there is a 1 wire connector that has to be unplugged when setting timing on a tbi engine. that disables the electronic spark control so the initial timing could be set. if you don't unplug it, the computer will try to compensate and you won't be able to properly set it. not sure about fullsized trucks, but on S10s the plug is under the dash on the passenger side right close to the computer
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Old 07-13-2010, 05:42 PM
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if anybody could tell me more and where i could find this on my fullsize truck,i will reset my timing withit "unpluged"....thanx..Tim
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Old 07-13-2010, 05:44 PM
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i found this by doing a quick google search
The base timing must be set to 0 degrees with the timing connector conduit disconnected to bypass automatic timing. With timing set to 0 degrees, reconnect the conduit and the computer controles the timing. This conduit is located on the wiring harness on the right side of the firewall, under a Y shaped plastic cover. It is a one wire connection that protrudes from the wiring harness. It is a tan/black stripe wire.
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