mandingo214

Can someone post an '96 LT4 vacuum diagram? My shop manual has not arrived yet and I am itching to work on the car.

Background: Drove the car, '96 LT4, 1500 miles back to Texas. During part of the trip the SES light came on for a few hundred miles, then back off. When I get it home, I take it in for inspection, and the SES light comes back on. Put my scanner on it, and it throws a P0171, System too Lean (Bank 1), read from an oxygen sensor (not sure which one). Car runs and idles great.

Searching through the forum, I see a vacuum leak could cause the code. The vacuum lines are crumbly, so I would like to replace them anyway.

So I need to know:
1) How to take off the fuel rail covers?
2) Vacuum diagram?
3) Any insights to the job?

I did notice that the line (think vacuum) coming out from under the passenger side fuel rail cover into the MAF? is barely on.

I changed the fuel filter already.

Thanks.

toptechx6

Take a good look at the radiator shroud, typically there is a vacuum diagram there for the engine and emission devices under the hood. The fuel rail covers simply pull off in a straight up direction, once they are off you will understand.
The hose from the right side valve cover that runs to the throttle body is not a vacuum hose, but simply a fresh air supply to the crankcase for the PCV system. The PCV valve is under the opposite fuel rail cover (drivers side).

STL94LT1

There should be a vaccuum diagram on the fan shroud.
Fuel rail covers just pull off.
The vaccuum line in the intake bellows is for the optispark.

mandingo214

The shrouds do snap off easy, and thanks for the vacuum diagram tips.

Unfortunately the only lines that were questionable were the one going back to the evaporator (the rubber connecting part), and the two going to the cruise (not on the diagram). I replaced those and the rest are fine.

Any ideas on my next course of action? I thought about swapping the O2 sensors from one side to the other to see if maybe one of them is bad?

The car really runs well.

toptechx6

The bank 1 O2 sensor is the drivers side, the sensors are the same so swapping them may be worth a try. Without the FSM as a guide the only suggestions I have would be to test the fuel pressure with a gauge,inspect the MAF and and make sure there are no exhaust leaks that might be allowing the sensor to see false air. You could also ohm test the injectors, but it only verifies the condition of the electrical coil, they can still be plugged or have a mechanical problem, good luck.

mandingo214

Thanks for the tips. I read on another thread that a dirty MAF often gives the P0171 code, though I would think it would cause both banks to kick out a code. Regardless, I will clean it first, just with MAF cleaner, before testing the rest, as that should be pretty easy and part of regular maintenance anyway.

I did notice the car has two O2 sensors on each exhaust pipe. I was going to move both from one side to the other, but does anyone know if it is just the first one, closest to the exhaust manifold, that reads the lean condition?

toptechx6

The sensors behind the cats monitor cat condition, they have no input for fuel control.

mandingo214

Cleaned the MAF, and the throttle body while I was there. Drove 10 miles and the SES light did not go off. Should I clear the Code then see if it comes back? I would use my code reader to clear the code, but the Inspection place said when you disconnect the battery to clear codes, you have to drive 50 miles to get all the sensors back "online". Is that the case if you clear the codes with a reader? I want to validate each step, for future reference, so I do not want to do the O2 sensor swap until I make sure the MAF was not the issue. Thanks.

mandingo214

I cleared the code with my scanner, took it for a drive and the SES light did not come on. Took it in for inspection, and it passed, so using the scanner to clear the code, vs. disconnecting the battery, keeps the info online.

Now that I got it inspected, I think my heater core might be leaking. Damn.