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2003 tahoe, update: more bad things

Mark1968

Mark1968

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Update page 2.

Bought this back at the end of september. 4x4 with the 5.3l flex fuel motor. It will intermittently throw codes po171 and po174. Last night the wife was coming home at 3:30 from shopping and got the reduced power message on the dash.

This is what I have now:
p0171 system too lean bank 1
po174 system too lean bank 2
p0300 random/multiple cylinder misfire detected
p1516 manufacturer specific
p0101 mass or volume airflow A circuit range/performance.

I've been doing some reading on them and am making a list of things to check in the morning. Gonna look at the wires on the throttle body, ohm out the injectors and some other crap.

I'd love to get some more ideas from you smart guys on here. Need to get this squared away by monday.
 
Last edited:
Probably going to change the intake manifold gasket too, since a couple of those codes point to that.
 
I would start with that, spray around the intake with carb cleaner and see if rpm changes. The orange gaskets are the updated ones while the greens are the old.
 
Before you change any parts:

1. Check your fuel rail pressure. 60 psi when the engine is off and 55 psi when idling.

2. Check your fuel pressure regulator for fuel in the vaccum line after it has been running for a bit then shut off and left sitting for 30min. Replaxe it if fuel is found in it.

If your regulator is ok and you have less than 53 / 58 psi then your pump / filter assembly needs to be replaced

3. Clean the mass air flow meter with a can of MAF solvent.

4. Check for failed intake gaskets. If they are ok just reuse them on reinstall.

Sounds like low fuel pressure or a vaccum leak to me.
 
I'll check fuel pressure in the AM. T haynes manual says pressure should be 48-55 I think it was on the flex fuel motor.
 
I know the flex fuel motors do have the capability of running a wider pulse width to get ethanol through them depending on the input from the fuel composition analyzer, but 48 PSI is too low no matter how you look at it... It'll run poorly at anything less than 53 PSI in my experience
 
48 psi cold and 44 running. Sounds like either the pump or regulator. I don't like where this is going.
 
Just went through this a few months ago on a friends 05 tahoe. Except the last two you listed, finally found out it was dirty fuel injectors.

Had them cleaned and no more miss fire or lean codes.
 
I would see if you can borrow a FPR from a friend's truck to test your fuel pressure theory. The fuel filter is built into the fuel pump module in the tank on these trucks and is not serviceable.

I'm gonna go out on a limb and guess you're looking at a fuel pump replacement though...
 
The filter on this one is on the frame rail under the driver seat. I think in 04 it moved to in the tank. Called in to a local radio show last night, the host owns a local repair shop and asked him for a second opinion before I changed the pump. He told me to clean the throttle body and maf sensor, both of which were filthy. Clear the codes and run it. All the issues seem to be gone. It had a rough idle on cold days I thought for sure was the intake gasket sucking air and that seems to be gone as well.

Gonna run it for a few days and see what happens. If it comes back I'll probably have a shop change the pump. I hate to pay to have work done, but I've tweaked my neck in a bad way and was really in some pain last night.
 
Update: I took it to a shop. It doesn't fit in my garage and it's too cold to do it outside. They pulled the intake and something fell into the head, which made a whole lot of noise when it was reassembled and started. This resulted in a shattered piston, a beat up head and a decent sized scratch in the cylinder wall.

They want to hone it, replace the piston. Have the aluminum head welded and milled and to be done with it in general.
 
I think they'd be buying at least a low-mile junkyard engine. No way I'd let them do that much work to HOPE that it would repair it, much less not cause more problems down the road.
 
Russell said:
Congrats!!! You just won a new crate engine from GM!

Don't accept anything less.
Click to expand...

yup. No way in hell I'd let them fix it any other way.


FWIW- I have a 2002 with 205K with the same symptoms (rough cold start), replaced the intake manifold gasket on Tuesday night and it's running good again.
 
Tried to contact him yesterday. No luck. Left a message. No phone call returned
 
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