Rough idle, running rich, & black smoke

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Oleblue92

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Hello all, let me give you a rundown of the situation. I have recently had my mechanic to swap a motor from a 93 silverado into mine, as mine had a hole in the piston, floated valves, and blown head gasket. Anyways, ever since i got the engine back from him it has been running rough at idle. Cruising it seems to do fine. Well, really anything above 1500 rpm. When i go to crank it it cranks just fine but hesitates sometime and when it runs at first it is in 100-700 rpm range and wants do die. Once it finally catches itself itll have a pretty good lope to it like its got a cam. The motor i have in it is supposed to have a "RV" cam and it has an edelbrock torker II intake on it. It will idle like that until it goes into reverse or drive. When i shift it into either of those gears it will once again try to die and stay real low in rpms. It will have a lope to it (not all the time) on anything under 1500 rpms. But it does just fine at cruising. Once i let off the accelerator even if not to stop it will go real low in the rpm 2-500 and stay there until i either get back on the accelerator or it downshifts. Once i stop it will once again get real low in rpms and many times die. It has set up for quite a while before getting this other engine in it, which is supposed to have around 40-50k miles. Now another issue is today i saw soot, and small amounts of black smoke coming out at idle and maybe 5 mph but nothing beyond that. It had either water mixed with soot coming out hitting the ground or small amounts of oil coming out of the exhaust. Pretty sure it was water and soot but you could clearly see the small spots on the ground where the exhaust was spitting them out. I know before today i had a busted o2 sensor and i replaced it today and i think maybe i didnt tighten it enough but i plugged it in and went for a drive and it was the same. I know there was more than likely a bit of trash in the tank and i tried burning all of the old fuel. The fuel filter needs a change i know, im getting to that tomorrow. Its definitely running rich i can smell it, I have heard of the CTS causing these problems so i may change it but i dont have a clue where it is. Im not the most mechanic savy person but im trying to learn. I was thinking a ground could be loose or not on at all somewhere but thats why i am here to hopefully get some answers or suggestions on this problem. I have videos of it running i can post or you could see them on the GMT400 group on facebook. Please help, its much appreciated, Thank you!
 

someotherguy

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CTS is a very likely suspect, if we were talking about a bone stock engine. You can go ahead and try replacing it if you like; it's the 2 pin sensor on the intake right next to the thermostat housing - if they placed it in the same spot on that Torker intake.

The bigger, much bigger problem you have is the engine is not stock, sounds like it's not anywhere close to it. Once you do anything that deviates much from stock on a TBI, the computer can't deal with it and you dive head first into custom tuning, and it takes someone GOOD at it, along with lots of datalogging and work, to make it run right. And depending on the parts chosen, it still may be an uphill battle.

Sorry to break it to you like that but many have found themselves in this hole by going crazy modding a TBI engine and not being prepared to tune it.

Richard
 

Oleblue92

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Well played around with vaccum lines today, two of which on the front of the throttle body were switched backwards. Also replaced the CTS But i can't tell if it helped at all. After switching lines around enough i got it straightened out.but to the vacuum line diagram i seen for these trucks its no where near correct. But it seems to be working for now.
 

someotherguy

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Well if this helps, here's the basic vacuum layout for most TBI small blocks.

Front of TBI -
Large port in the middle is obviously the PCV valve
Small port towards passenger side goes to front of EGR solenoid
Small port towards driver side goes to charcoal cannister purge line (or purge solenoid 94-95)

Rear of TBI -
Only port back there goes to the MAP sensor

Also do note on the EGR solenoid (for negative backpressure valves, typical on 350 TBI half ton) - you'll notice the rear of the solenoid has what appears to be 2 ports. It's not. The one with the barbs on it is the port that connects to the EGR valve. The other one is smooth and should be left open; that's the vent for the solenoid. From the factory it sometimes has a small foam filter on it.

Richard
 

Oleblue92

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Thank you for the reply! I have seemed to gotten things figured out slightly. But i do have another question, The back of the TBI unit there is the vacuum that goes to the map sensor. Well I didnt install this intake or cant seem to remember from my other engine for that matter, But there is a threaded plug with a vacuum line on it right between that vaccum line and the EGR. Have no idea what it goes to. Could use some help as ive seen many pictures where a plug is in the same position. Should i remove and add a plug and if not what is this for? Thanks!
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