Suburban 8.1 Liter Breakdown Puzzle

OpenTrackRacer · May 12, 2009

I had an incident over the weekend with my 2005 8.1 liter big block Suburban which was quite disturbing. It was the first and only time the vehicle has let me down in 30,000 miles.

We went camping in the mountains for the weekend which entails a climb to 8,500 feet. I was towing my 32' 9,000 pound travel trailer. I've done this run before and had no problems in this Suburban (towing and not towing) and dozens of times in my previous Suburban (also towing and not towing). It was very hot at the base of the mountain... 95 degrees.

After an uneventful run up the hill I suddenly started slowing. This was about 30-40 minutes into the climb and around ten miles from the summit. At first I thought the transmission was slipping but as we slowed to a stop I felt the brake pedal harden and noticed the tach was at zero RPM's. All the other gauges were good including water temp and transmission temp. I was low on gas but still had at least four gallons in the tank. I tried to restart the engine and it sputtered and died. I let it sit for about a minute and then it started up. I continued on and it did the same thing a few miles further up the road. Again, it took a bit of trying and sitting to coax the engine back to life. This time I limped a few hundred yards further and off into the first available turnout, where it died again. I let it sit and took a quick look around. I noticed a strong smell of unburnt fuel from the tailpipe. After about five minutes, the engine started right up. I got a "high engine temperature" warning but the temp instantly went down as the coolant started circulating again. The air temperature at this point was down to about 70 degrees and the elevation was around 8,000 feet.

I made it another mile or so and crested the summit. I continued down into town with no further problems. I fueled up and went to the campground. I drove around all weekend and then back home with no issues whatsoever.

I checked for codes when I got back and there were none.

One other related tidbit... my Dad drove his Chevy 6.0 liter powered motorhome up to the campground the next day in similar conditions (on a different route). His engine also lost power and stalled near the top of the hill. He had a full tank of fuel and continued to have problems at the campground (which is at 7,000 feet). His also ran fine on the way home and he had no further issues. His did throw a code that indicated a lean condition. No one else that also drove up to the campground had any issues including another 8.1 liter powered Suburban and a 8.1 liter powered motorhome.

So, what do you folks think? Mass airflow glitch? Fuel pump?

Thanks!

Mike

Draenor · May 12, 2009

Strange condition. Being the 8.1, I still go towards the crank sensor.

By smelling the unburnt fuel, your not running lean. How is your air filter? Is it an aftermarket oil'd one?

OpenTrackRacer · May 12, 2009

Nope, definitely not lean. That kind of casts doubt on fuel pump issues in my mind. The symptoms lead me more towards the MAF or TPS. It could also simply be the computer getting confused with the temperature and air density changes.

I've had CPS problems before on my Jeep and the symptoms were quite different. Still, it's a possibility. How do you diagnose it?

Two other things I forgot to mention... It seemed to me that the Suburban was having more trouble than before getting up some of the grades. It's been a year since the last time I towed the trailer up this road but that was the sense I got. Also, I seemed to use an excessive amount of fuel going up the mountain (which could be another indicator of running rich).

The air filter is stock and in good shape.

svensk · May 13, 2009

Sensor, or faulty MAF. Since you made this trip before something is obviously failing.

Draenor · May 13, 2009

Nope, definitely not lean. That kind of casts doubt on fuel pump issues in my mind. The symptoms lead me more towards the MAF or TPS. It could also simply be the computer getting confused with the temperature and air density changes.

Its hard to tell. In this case;the cooler temps are hitting the MAF, causing the IAT to drop. It then tells the ECM to compensate, by using more fuel, which is what it is supposed to do. The MAP on the other hand could be taking the decrease in pressure and subtracting MAF reading to a point where the ECM is getting no reading,causing the engine to shut down.

What I am not getting is why the O2s are not seeing the excessive fuel not pulling back the fuel trims or the ECM should be advancing the timing to compensate too. You would have to be looking at the inpur of the sensors to get a better feel on whats happening or not happening.

This is puzzling.

wil_derby · August 14, 2009

I had the almost same issue about 3 weeks ago. However I had been at altitudes of over 11000 feet with no problem and as soon as I got into the 100 degree ambiant temps and an altitude of only like 4000 feet the truck was wanting to die, the more fuel I tried to give it the lower the rpm. I would let off from the throttle and the rpms would come up. When I crested the hill the problem stopped and I was able to continue. On the next hill the issue came back, however this time it died. :0\ I had just talked to a buddy who had had this issue in his shop a week before and he was told to hit the bottom of the fuel tank, I know sounds kinda wierd, and I thought B.S.. So i continued to look for any obvious issue, I didn't see anything unsual and I attempted to start is MULTIPUL times. it would try to start and when it did start it would idle at less than 500 rpm, and as soon as I would touch the throttle pedal it would die. So as a last resort I climbed under the truck and hit the bottom of the tank a few times with my hand. I then got in the truck and >>>>VAROOM<<<<< fired up, first time, no key cycling, just went straight to the start position and it started right up. I was still a little doubtful of the fix, but I continued on. The very next hill it did it again. This time I went attempted to start it a couple of time with the same non-start issue, so this time I went straight to the tank, three good whacks, went back in>>>>>>VAROOM<<<<<. HOLY CRAP!!! THe amibient air temp was still in the 100's and nothing else had changed, the altitude was about the same. The only thing that varies from my issue is that I did NOT have a raw fuel smell. I'm pretty sure it was the fuel pump. I had over a half of a fuel.

I continued to drive the truck another 30 miles with NO other issue. The next day I drove it 340 miles without even a hiccup. I was gonna tear the tank out as soon as I got home but desided to wait until it did it again, guess what......3 weeks and 500 miles later.... nothin'. :0\

My question is to the GM tech's, or anyone that might have knowledge of fuel pump issues in this application. Is htere a known problem with the contacts in the fuel pump in the primary tank in the 8.1 liter Suburban/Avalanche platform? I tested the fuel pressure today and it was 63 psi, the needle was fluttering a little bit, about .5 lb over and under 63 psi. Is that exceptable?

Before anyone says anything about a fuel filter, dont waste your time, its a non-serviceable filter, i.e. it's in the tank with the pump.

well thanks in advance.

Wil

Sweathog62 · April 1, 2012

This is an old post but has anyone ever resolved this issue. I too have had this happen. Going into Estes park out of Denver. Within the same 3 mile section of the road. Coded lean but seems to restart after a few minutes. Is it a computer calibration.

8.1HD/ALLISON · April 2, 2012

Sounds like fuel pressure is in range. Im wondering about the elevation/ air density change. Thats a tough one, would like to make that run with a scan tool to monitor engine paramters.

Sweathog62 · April 2, 2012

The wifey reminded me that it also pulled the same stunt out of Cody heading west on that real long 3-4% grade... I did have a scan gauge hooked up and it did give two codes. I believe one or both were related to the MASS. Real strange for sure. And, yes, I do agree it has something to do with the altitude so I am told. Going on a drive up to elevation caused the need for the computer to recalculate... NOT a great feeling when you been driving 750 miles and the things go to idle and then it dies on you.....

Thanks for the response!!

PS-This is a stock 2004 city truck with 88K miles on it.... Other than blowing out a tire - it's a heck of a unit!!

8.1HD/ALLISON · April 3, 2012

Next time you make that trip, stop about half way altitude change and shut truck off for a minute. Restart and see if it acts up. Don't know if that would prove anything but it might get the maf sensor back on track? Not sure if it has a certain amount of tolerance in the parameters. Or even better get a new maf sensor and try it.

ChevyTech77 · April 3, 2012

This is a fuel system/quality issue, plain and simple. Hitting the bottom of the tank does nothing else than shock a poorly running fuel pump back into running again. Fuel pressure isn't the only thing you need, you need volume too. ESPECIALLY when pulling heavy loads up a steep grade and drinking fuel in the manner that only an 8.1 can.

Sweathog62 · April 4, 2012

Very interesting comments 8.1 and tech 77. Yes, the beast does go through the fuel when pulling. I've often wondered if the 4.1 rear end would take off some of the stress, but when you are putting that volume of fuel through it it likely will have no impact. The sensor, pump, outside temp, tank level, all seem to be tied together. Lucky for me the road speeds in Estes are relatively slow and I've managed to find a pull out. I'm out of Oklahoma City, so I'd be surprised if we don't hear some comments from those living in and around the Denver area. This would seem to be a hot topic for them.

Thanks for the comments!!

ChevyTech77 · April 4, 2012

Taller gear would just make it eat fuel faster due to the higher engine speeds. That engine has more than enough grunt to pull the 3.73 gear, I wouldn't change it personally.

Sweathog62 · April 4, 2012

Great advice!! Ask me how I just saved at least $1,500 dollars today...!! LOL My goal is to drive this city truck for about 250K miles and let GM and Dodge continue to sort out all this diesel issues and then cash in my lifetime saving to buy another truck... Heck, it may be cheaper to drop the alley and duramax into the beast!!

Thanks again for your comments!!