Hey Guys,

Having an issue with a 2011 Chevrolet Suburban LT (5.3) with 198,800 miles. Here is the whole story;

My wife called me one day about a month ago while driving to say that the oil pressure gauge in her Suburban wasn't working. On the way home that day, I picked up a new oil pressure sending unit to replace it. As I began working on that issue, I was unable to gain access to remove the sending unit behind the rear plastic guard with the tools I had. After a lot of swearing and internet research, I decided that I would just pull the intake manifold for access. Completed the oil pressure sending unit replacement, replaced the intake manifold gasket with a new gasket, torqued everything to spec, fired her up, and the oil pressure gauge began working as designed. Took the vehicle for a test drive, and my true frustrations began.

Upon test driving the vehicle, I could feel a shudder at about 50 mph, but only if I was "coasting" and began to ease back into the gas. This caused a code, which initially was a P0300 code. At first, it was just a soft code (flashing check engine light that went away) but then later turned to a hard code (solid illuminated check engine light). As I had used one of the smaller, cheaper FelPro gaskets for the initial intake manifold gasket replacement, I decided that a good first step would be to install one of the thicker gaskets. Did that, took it for a test drive and got a P0300 code again but also a P0305 code. I then found where some of the EGR tubes were cracked... replaced them, replaced the spark plugs, replaced the plug wires, cleared the codes, and took her for a drive and got nothing for 40 miles. Once the vehicle cooled off, I left to run an errand and got another soft code that was a P0305. I then thought maybe it was a coil issue... moved the cylinder 5 coil to cylinder 2 and the cylinder 2 coil to 5, cleared the codes and went for a test drive. Still got a P0305 code. I then figured maybe it was a fuel Injector issue.... pulled the rail, swapped the cylinder 5 injector with the cylinder 8 injector, put it back together, cleared the codes and went for another long drive with no issues. Next day, my wife drove the vehicle and it started having a P0305 code again.

At this point, I was getting frustrated with it and decided I would take it to the small town dealer where my wife has had the vehicle serviced since it was new. They kept it for a week but were unable to figure it out either (they didn't charge me so no harm no foul). Once I got it back, I then figured I would dig a little deeper into things. I had already used a bore scope to look in the combustion chamber and the top side of the valves when I replaced the intake manifold gasket to the bigger gasket. Having seen nothing, I figured I would start with a leak down test... did that and found everything within spec. I then completed a compression test and found it looked good. At this point, I really just am not sure where to look. My scanner doesn't do live scan data but I can see the data from when a code is thrown and the only thing that looks odd to me is that the fuel pressure is consistently running in the low 40 psi range when the codes are thrown and with my limited knowledge and research I thought it was supposed to be higher.

Any thoughts on where to go from here would sure be appreciated. I've started wondering if it might be a lifter issue but with good compression and a good leak down test I just wasn't sure. Also, I get it... I know the thing has almost 200,000 miles on it and many people would just go buy a new one but up until this point we have had very few issues over the past 14 years and we would like to keep it running.... plus the idea of a new car payments versus no car payment just make me cringe and I would like to pay my truck off at the end of next year before we jump off into another big payment on a newer Suburban.

Thanks for any insight!!!

 

Welcome to the forum. Since you mentioned that it was displaying low fuel pressure, I would put a gauge on it and just see what it really is. I think it's supposed to be in the 60 PSI neighborhood.

 

Did you ever get this fixed?

 

We got it fixed - but it was nothing quick or easy. It ended up being a lifter on cylinder 7 that was intermittently collapsing and causing a faint shudder that was throwing the codes. I pulled the heads, replaced all of the lifters, put her back together and she has been riding like a champ since June.