Howdy!
This is a TBI related question, I know it's in a truck, so please don't slap me, but you guys are in the know and I have to tap the source...

1989 Chevy 1/2 ton with 305 TBI replaced with new 305 Vortec. 200000 miles on truck, 1000 miles on engine. Using the GMPP 4bbl Vortec intake with Holley adapter plate. Custom chip from Fastchip. New wires, cap, rotor, #3 Rapidfire plugs .040 gap, air filter, fuel filter, 02 sensor, MAP sensor, TPS, new 98' style 350 muffler and tailpipe (3")

Problem: Off idle hesitation! If you mash it, the truck will almost diesel and die, sorta like that for 5-10 seconds, then it will pick up and go. At cruising speeds (55mph), the truck will shudder in overdrive. When climbing a hill from a dead stop, it takes forever to develop RPM's.

I'm having a hunch that it's either a plugged cat, or the fuel pump is on it's way out. I'd like to do a fuel pressure test, but am unsure of what to look for pressure-wise.

This truck is a daily driver, I got a heck of a deal on the V305, and I just want it to run right. Any information would be of great assistance!

Red

 

I can almost gaurantee that your engine is pretty lean, especially at high demand times like you mention. Find out what your pressure is and get a adjustable regulator to bring it up. Of course, make sure the fuel filter is good. I run mine at 16 1/2 lbs of pressure and it works good (slightly rich at idle). I also have a Fastchips chip.

I just took a 10 hour one-way trip last week and got 17 mpg on the way down, and 18 coming back. That's at 80+ mph most of the time. My truck is 2wd, 1/2-ton long bed with 4L60e and 3.42 rear.

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'93 2wd truck
408 sb, vortecs, 454 TBI, Comp Cam, dual exhaust

[This message has been edited by SCRA rules! (edited March 13, 2001).]

[This message has been edited by SCRA rules! (edited March 13, 2001).]

 

Thanks for the reply.

Will the stock pump be capable of putting out more PSI if I get an adjustable regulator?

I was really watching the tailpipe today - 1/4 throttle, shudder in overdrive, let off the gas.. a hint of black smoke rolls out. Get on the throttle right after and it pushes the rest out. Rich? Weird.

 

Good God man are you kidding with that mileage??? I have a 91 Ext cab, SB, 350 TBI, 700r, and 3.42s. I can't get 18 out of it running 65. Bump it up to 75 and it's more like 16!!

 

Rig, I don't understand the black smoke deal, but your symptoms scream lean at high demand. Are your ignition components in good shape? Where's your base timing at? 4-6 degrees advanced would probably be good. Your stock fuel pressure should be around 11 or 12 psi. With my stock pump, I could only go up to about 15. I now have a Walbro inline pump. If you have the Holley 1741 adapter plate, make sure your TBI is positioned to the front, not the rear. Don't ask-it don't work!

As for the mileage, I was kinda surprised too! My old stock 350 with 160K miles got about that much on the freeway, even hit 19 once. This was my first long trip with the 408. It has about 15K on it now and usually gets about 13 mpg with 60% freeway driving. The truck has 188K miles now. I have a Trans-go shift kit and IROC GM converter. I'm guessing the motor is close to 350 hp with the TBI setup, but should be around 400 with a good carb setup and better intake (has vortec performer now). Compression is 9.2:1, cam is Comp XE268, Thorley headers (it wants Hooker SC 1 3/4), and GM 5.7" PM rods.

In the next year or so, it will no longer be a daily driver and then it will begin a new, computer free life, as well as receive an S&W 4-link rear frame kit (making it a short bed), rack & pinion steering, 6-speed manual, etc... Oh yeah-that 17 mpg I got was hauling my old complete 350, a window a/c unit, 6-foot dresser, and some other odds and ends.

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'93 2wd truck
408 sb, vortecs, 454 TBI, Comp Cam, dual exhaust

[This message has been edited by SCRA rules! (edited March 14, 2001).]

 

Sounds like you are running too much fuel to the engine. Is it a 305 or 350 t.b.???? Sounds like a 350, 650 cfm???? My car had that exact same problem when I put the holly tbi on it. I sent it back because it wasn't worht the $300.