Vortec heads on stock TBI 350

someotherguy said:

Hearing from someone who has already "been there, done that" is often very valuable information and what forums are great for.

However, it also assumes the installation is correct and there are no other issues besides insufficient this or that which can be solved with different this or that.

Richard

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However the problem is with the tuning being thrown off so badly the normal diagnostic methods do not really apply because you will be chasing problems that do not exist except in the programming, fuel delivery and commanded EST timing. Unless he paid big money for the GM intake to keep the EGR, the EGR is not even OFF in the tuning and the ECM is still altering fueling and timing for its presence.

I have made them run well enough to drive as long as you do not stab the throttle by increasing the base timing to 8-10 BTDC and maxing out the OEM fuel pressure regulator which will not even allow for fuel to return out of the return line. The OEM pump opens its internal bypass valve around 15-16 psi.

I'm getting the impression, at one time it ran OK but, now it's not. If so, I'm leaning towards fuel pressure and maybe timing too. An EP381 pump from a 96 Vortec, an 18LB spring, and an AFPR (Adjustable Fuel Pressure Regulator) will help. With mine set up that way, I can run 15 - 20 PSI which can help OP dial it in for acceptable VE. Proper tuning is definitely the way to go after the components (heads, exhaust, fuel, timing, etc) are matched to each other.

Don't overlook the year of the truck , if it's the stock fuel pump, the little hose in there could be rotted away and full of holes, this causing the same symptoms and wicked drop in fuel pressure.

L31MaxExpress said:

Having actually run a Vortec head TBI, it is time to load the parts cannon on all items he mentioned. The stock fuel pump and injectors are pretty much maxed out with the TBI heads. The pump capable of 70 psi works beautifully at 18 psi and was the same pump GM put into the 94-95 30 psi TBI systems. Either the fuel pressure needs to increase or it needs 454 injectors. Also it needs a chip that is remapped appropriately. Otherwise its a lean running, cannot get enough to drink, undriveable mess, that tends to spit fire into the air cleaner if you stab the throttle.

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The symptoms you just described are exactly what is happening with my truck. I’ve looked into a chip from Western garage in Calgary Alberta, and a common theme seems to be the vortec fuel pump and 18 psi regulator spring.

OBSlates said:

The symptoms you just described are exactly what is happening with my truck. I’ve looked into a chip from Western garage in Calgary Alberta, and a common theme seems to be the vortec fuel pump and 18 psi regulator spring.

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I haven’t looked into scanning it yet, or the timing

someotherguy said:

Hearing from someone who has already "been there, done that" is often very valuable information and what forums are great for.

However, it also assumes the installation is correct and there are no other issues besides insufficient this or that which can be solved with different this or that.

Richard

Click to expand...

It could be dis or dat, but could also be the udder thing. lol

your ecm was designed to work with tbi heads. it won't work ok with something else.
backfires can be caused by leaking valves.

It sounds lean to me, maybe from the better flowing heads, but it could also be clogged injectors, manifold air leak, bad O2 sensors, etc. I always recommend a compression and leakdown test to confirm basic engine health before spending money on high flow whatevers.

Jeeze, this thread is making me not want to put my heads on. I’ve had a set of Vortec heads sitting in my closet for almost 5 years. However, L31MaxExpress has usually been on top of his stuff so that’s giving me hope. Haha

I’m planning on upgrades for my ‘91 K2500 in the future. I’m going to have the bed off in the next few weeks for exhaust upgrades and cleaning/painting the frame.

Is there any negatives to going ahead and doing the Vortec fuel pump now with the engine being stock? I have a set of fresh Vortec heads, a ‘93 LT1 camshaft and lifters, and I’m planning on buying the GM Vortec intake to retain EGR, cruise, etc.

I know I’ll need the bigger pump later, and since the bed is already going to be off, I’ll go ahead and do it now as long as it won’t affect the stock setup.