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Old 05-21-2011, 04:30 PM
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TBI issues

About a month ago I took the TBI off my 4.3 V6 and decided to finish porting the upper section. I reinstalled the TBI and connected everything back up.
Needless to say, now it runs like crap. Fuel pressure up to par. All connections good. It`s got a massive vacuum leak somewhere. I`ve checked all the hoses and fittings all good. Vacuum gauge shows it`s pulling 12 inches of vacuum which is way to low. At idle I can disconnect the IAC valve and nothing happens which again means vacuum leak. Got out the carb cleaner, went high and low spraying, no change. Pulled TBI back off and inspected gasket. Looks fine and no signs of any visable leaks. The only thing left would be the intake gaskets. I pulled the EGR valve off and it has a light coat of oil on it as if oil was making it`s way from the lifter valley into it. There`s a lot of junk sitting on top of it and if I don`t have to change intake gaskets I won`t so I`m asking if anyone else has any clues to where the leak maybe I`d appreciate it. The truck doesn`t skip, valves are in adjustment, no changes to it other than finished porting the TBI. At idle I could rev it and it`ll pop back up out of the throttle body. Sometimes when first started the truck would puff oil smoke and I`m positive the valve guides and seals are good, they only have 25,000 miles on them. Any guesses anyone?

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Old 05-21-2011, 04:40 PM
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Yank the EGR valve off , look inside . Its probably stuck open with carbon.
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Old 05-21-2011, 11:04 PM
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I already removed the EGR valve as I wanted to check the passages. The EGR had a light coat of oil on it as if it`s a hint the intake gaskets are leaking. However, the EGR valve has not been in use since I did the rebuild. It was replaced with a new unit after the rebuild was complete and when in use the power of the engine would fall flat on it`s face. The cam I`m using has what is called "Built in EGR" so it was my guess I used the wrong sized restrictor in the EGR which was hampering the burn characteristics since it was over diluting it.
The intake gaskets are the likely suspects, since I couldn`t find any leaks on the top end so that`s going to lead me into a compression check on all cylinders plus run a fine tooth comb over the valve train. The leak has to be pretty severe considering it used to pull 18 inches of vacuum and now it`s lucky to pull 12. I don`t see how the intake gaskets just gave up as before I removed the TBI the truck ran great. Sometimes when I start it I do see it blow out a cloud of oil smoke, but not all the time and I know that`s another sign of leakng intake gaskets since I`m positive the valve guides and seals are in good shape. It`s not missing on any cylinders but the reason I`m doing a compression check is to be sure I don`t have a cylinder that`s running low compaired to the rest.
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Old 05-22-2011, 02:34 AM
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Well it sounds like you made your own diagnosis, the intake is leaking internally.
While I do still use carb clean to check for leaks, I have a better method. I use a stethoscope with the end of the hose open. You can pinpoint even the tiniest leak with it. But probably won't detect the internal leak.
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Old 05-22-2011, 06:05 AM
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If the intake is leaking, check it by plugging the air intake from the air cleaner and pull the PCV valve and insert a vacuum gauge into the pcv grommet in the valve cover. Be sure to plug the fresh air intake side on the other side, If it pulls a good vacuum then you have a leak.
Oil burning like you described is more likely worn valve guides seals but could be intake gasket given your issue.
I have a problem with a cam that say the EGR is built in. It just means the exhaust is probably closing late, wich could cause lower vacuum in the engine,
but check the intake first.If you have an internal leak it will build vacuum, if it is OK it will build slight pressure (from blow by)

Last edited by latech; 05-22-2011 at 06:20 AM.
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