Once in November, and then twice in the past week, my suburban has the SES light come on. I went and had the codes read all three times, and each time it was
P0172 - rich bank 1
P0175 - rich bank 2
P0305 - Misfire cylinder 5

Here is the history on the vehicle.

172,000 miles
Two new fuel pumps in past 18 months
Last time replaced was in June of '08, at
which time I also replaced the catalytic converter as well.
New OEM spark plugs in December.
When I replaced the plugs, number 5 was a little darker
than the others, looking like it was running rich.

Autozone said my MAF may be bad if both codes (P0172 and P0175) set
at the same time.

Anyone have any thoughts on this?

Thanks in advance.

Smittygj

 

Maf is a possiblity although I rarly see them go bad on thease trucks. Also the usually set a lean code not rich. You need to check fuel pressure. You would be looking for it to be to high. And you also want to see how quickly it drops when the key is turned off it is possible that #5 is stuck open.

 

Could have a small peice of crud cause #5 injector to stick open just a little too long.
Get a quality injector cleaner or find a shop with the equiptment to clean your injectors

 

I have seen the fuel pressure regulator fail internally several times on these. It will suck fuel through the vacuum hose, which plugs into intake right above cyls 3 & 5. W/engine running pull vacuum hose off regulator & wait a few seconds. If fuel starts coming out of regulator vacuum nipple, your regulator is bad.

 

170K + I'd consider repalcing the poppets and injectors and while your there the regulator, try not to be to freaked out by all the carbon build up under the manifold from the EGR.
As for the MAF it might be a good idea to pull it out and clean it first as it is probably got a fine coat of dirt and debris from the high mileage that and its a good idea to check the air intake snorkle for any thing that may have gotten past the air filter while it was off i.e. a leaf a chuck of foam from the air filter (this happen to me and the engine would run fine but sometimes just dive and nearly stall)
Turns out while putting the air cleaner on I caused a protion of the foam ring to tear off and it got sucked up into the cold air intake and was blocking air flow at the MAF, but it would fall away and the engine would run fine until it got sucked up against the MAF again..

 

Brain fart. We are talking 5.7 ,not 5.3. Internal regulator leak is 5.3 problem.
Injectors are 5.7 problem.

Im surprised nobody yelled at me!