350 TBI

[Morella]

On the 350 TBI engine, I'm not getting enough fuel in the low and mid range, and it keeps getting worse. This started after the vehicle was stored for 2 years. It runs fine wide open, so it's not likely the fuel pump. It's electric. It's not the computer either...I hooked up my laptop and it's getting the correct inputs from the sensors and attempting to lenghten the pulse width. It's getting knocks and low O2, and lots of block learns, which, in plain English, means that it's not getting enough fuel and is trying to correct for it. An exhaust sensor verified the lean condition.

Since it's not sequential, there's no rail to check. Can you clean the injectors somehow? Is that likely the problem? They're awful expensive just to throw at the problem. Can you soak them? Take them apart? Swap the wires, if they're the same? We've tried putting lots of injector cleaner in the tank. Also, it seems like more fuel in the tank makes it run better. We had someone else replace the pump...could they have left a vacuum leak? Again, the good WOT performance makes me doubt that, but is there a place where that would be likely to happen? I don't want to drop the tank if I don't want to.

This stuff is just too new for me. I'm an old lady. Maybe one of you young folks or pros can help. I'll take any advice.

[Morella]

Oh, and more....

When I start it cold, it runs well for a few seconds and then starts surging. It will sit there surging for a few minutes, then die. As it warms up, it gets worse. It used to be that the IAC would bring the idle up a little when I turned on the A/C, and it no longer does that...not at all.

I couldn't see how to remove the injectors. There is a torx fastener in the middle, but it only moves a little, and I don't want to round it out. There are more of them, but they take they take the whole EFI unit apart.

[Riff Raff]

TBI is just an electronic carb. The injectors are where the venturi used to be. They maybe dirty. You could try cleaning them by taking the TBI unit off the manifold turning it over and spraying them. Or you could used the type that hooks inline and runs a whole can through the unit. Or you could try both.

Have you checked the fuel filter? If it is clogging, it will restrict the fuel flow. But at wot there is more fuel being pushed through the filter.

[Morella]

Have you checked the fuel filter? If it is clogging, it will restrict the fuel flow. But at wot there is more fuel being pushed through the filter.

That's why I didn't suspect it. When the filter gets clogged on any other car, you don't notice it until you go WOT.

I tried looking through the manual, and there are too many expensive tools to buy, almost as bad as the 2004 box. I guess I could take the EFI unit apart and try to clean it. This is where, as usual, a parts book comes in handy more than a service manual.

I have a Quadrajet that is tempting to try to stick on there with a rubber hammer.

It's an extended cab model truck with power everything and R134 cold air, and those plush seats, and I hate to let it go, but if I can't fix it, I'll have to sell it as-is, or try to trade it for a pre-1980 truck that I can understand. I could probably fix it, but with my back the way it is, I can only work about 15-30 minutes on cars. I went to some Chevy truck forums and even printed my Excel spreadsheet from the ALDL for them, and no one could come up with an idea that worked, so it won't be a cake walk.

Funny...I called Tony, and at first he thought I was talking about our big truck, the Volvo 680, even after I said that it was the pickup truck. He wanted to know why I would want to sell our only source of income. haha It's not even halfway to the end of the warranty yet. I think he was letting the sound of his wheels drive him crazy.

[kshearsedriver]

Have you checked the fuel pressure regulator? I don't remember exactly but I'm pretty sure you should have 15-17 PSI. Then the regulator adjusts the pressure to the injectors via vacuum.

[Haroldfromhell]

I had an s-10 with the tbi that would run rough because it was losing electrical contact where the little white plugs are on top of the tbi unit, i took them apart and tweaked them so they fit tighter on the post and worked great from then on, I think GM has a replacement kit for that also!

[LMS]

Are you sure the throttle position sensor is reading correctly?
When you hook up the computer you should see a nice steady increase in reading as you slowly move the sensor, it should not jump around or stay low then shoot up suddenly.
You might also want to change the fuel filter anyway, the wide open throttle may seem fine but really be lower then normal.....worth a try.