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Vortec TBi problem, need help..

Emmettology 101

Emmettology 101

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A friend of mine has a 97 Tahoe with a Vortec 350... Not long ago someone replaced the intake gasket and it hasn't runned right since. From idle until right before aroudn half to 3/4 throttle, it runs fine. But after that it bogs down and has no power. When this happens the sucking noise from the air cleaner gets very loud. It blows no smoke when this happens so were thinking its not being overloaded with fuel.

I am wondering if it could possibly be a timing issue or a TPS.....

Anyone?
 
No codes? I'd almost think something got knocked loose or wasn't reconnected. That or a bad EGR maybe. And Vortec is CFI not TBI ;)
 
I am not sure, but I think it maybe throwing codes.. Told my friend to stop by auto zone to have them check the codes. Supposedly everything is connected.

See I though all Vortecs were CFI also... The 4.3's and newer 350's were with the Tpi style intake... But this one has a TB sitting up on top of the intake like a nromal TBI engine. Or is this still a CFI with just the TB controlling air?
 
CFI with TB controlling air flow. Even Diesels have throttle bodies. And no 96 to 99 350s were all CFI. (excluding Camaros, Corvettes, and Firebirds) Gen III and Gen IV motors are multi port. Namely the LS1, LT1, LQ4, LS6, blah blah blah :)

Auto Zone should be able to tell you exactly whats going on by reading the codes. Its not like OBD I where it comes back running rich, it will say, running rich cause of this O2 sensor.
 
So what year did they switch from the TBI style mounting to the actual TPI-like intake?

He should be getting the codes checked today...
 
I am going to take a wild guess and tell you to check the fuel pressure regulator to see if the vacume line is off it. I am not sure if yours is vaccum controlled but if it is. The symptoms you describe sound exactly like what happens to a FPR without vaccum line connected, or if it goes bad. FPRs use vaccum to sense when power is needed. Low vaccum like when you mash the throttle, cause them to increase fuel pressure giving more fuel for higher RPM performance. In normal driving high vaccum causes them to reduce pressure for better fuel economy.

Might also replace the fuel filter too.
 
Thunder said:
I am going to take a wild guess and tell you to check the fuel pressure regulator to see if the vacume line is off it. I am not sure if yours is vaccum controlled but if it is. The symptoms you describe sound exactly like what happens to a FPR without vaccum line connected, or if it goes bad. FPRs use vaccum to sense when power is needed. Low vaccum like when you mash the throttle, cause them to increase fuel pressure giving more fuel for higher RPM performance. In normal driving high vaccum causes them to reduce pressure for better fuel economy.

Might also replace the fuel filter too.
Click to expand...

That was something I told him to change also... Have an idea where-about the FPR is located on these things?
 
The FPR is usually located on the fuel rails. its a round can looking thing with a vaccum line going to it.
But if I rember right.
CFI has a big fuel meeter thing that the regulator is a part of. The fuel meeter is the thing that all the injector lines come out of. I know that if one of the lines gets put on the wrong injector it will cause driveability problems. The injector lines are numbered on the meeter as to what cylinder injector it goes to. you might want to check that also.
fuel pressure should be around 66 lbs key on engine off.
I admit i dont know a whole lot about CFI. maby someone else will post up and share their knowlage.:ears:
 
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The fuel pressure regulator on a vortec motor is under the plastic intake and it does not use any hoses that run to it instead it uses the vacuum in the intake to operate the regulator. I work on them all the time and if I had to guest they probaly got it out of time because you have to use a computer to get the timing set to within plus or minus 2 degrees. You can not use a timing light to set them because there are no timing marks on the timing cover and the one tab on the cover is to get it set on number one. Hope this helps out some.


bigred81
 
My friend called last night and said another friend of ours is coming over to look at it.... Not sure when.. But I'll let ya know what I find out.

We talked about timing, but if you need a GM comp to set it, we're sh!t out of luck. :D
 
I believe you can set initial timing same as a TBI motor and if its not right it will run like crap most likely. My TBI motor spit and sputter when the timing was off. So bad that it blew back through the TB and started a fire. He should really get the damn codes read. The first time you have it doen on an OBD II car you realize how freaking easy it is and how much simpler it makes your life. Hes doing it the hard way if this thing is throwing any codes or ever threw a code(the computer stores them even if they aren't happening at the moment).
 
Well I just heard from my friend. He changed the fuel filter this morning before school and it runs great now. :rotfl: DOH!

Thanks for all the help and suggestions!
 
always the simple ****. I would have replaced something like that and the EGR when I did the intake gasket, but thats me.
 
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