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Old 06-18-2012, 09:48 PM   #1
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8.1 Sububan loss-of-power

Experienced a loss of power, then engine died, while coming over Monarch Pass last week. I found a thread where the OP describes nearly the identical occurence.
RV.Net Open Roads Forum: Tech Issues: Suburban 8.1 liter breakdown puzzle (long)

In my case, only filling up with 91+ octane (usually ethanol). Engine/trans temp just under 220 (with a 180 stat). Rig scaled 17,200 at beginning of trip.

No real definitive answers over there.
Anybody have any thoughts?

Thanks
-Joe
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Old 06-18-2012, 11:06 PM   #2
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Sorry no. Our friends in Montrose CO. have same rig and haven't had that problem. But like the thread said it could be vapor lock. I got it once in our Jeep Cherokee coming into Salt Lake. Engine just lost power down to about 30 mph. I stopped at a garage and he knew what it was right away. Asked if I had been using Texaco gas, and I said yes. He said it does that sometimes. Told me to go to Chevron and fill up with premium and let it sit for 45 min or so and then start it up. It was fine after that. Not sure if this is your problem or not, but it might be.
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Old 06-19-2012, 12:26 AM   #3
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Things to try.

Hi, it has been known that some vehicles with a long skinny fuel tank will run out of fuel at the center located fuel pump while on up or down angles. Gas caps that aren't venting properly have shut off engines. Loosen or remove cap to test. Some vehicles have been known for not adjusting for altitude; Disconnect battery power for a few minutes and then drive a few miles immediately after reconnecting the battery so the computer can relearn. [sort of like rebooting a computer]
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Old 06-19-2012, 01:14 AM   #4
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Extra heat from towing on long uphill grades, and high altitude; most common cause = vapor lock.

First, check fuel filter(s) for restricted flow or replace them to rule out this potential, simple cause.

Next, check routing of fuel lines and move them away from exhaust manifold/pipes and other heat sources, if possible. Newer GM pickups and suburban type vehicles often have heat shields in these areas; make sure these have not been removed or damaged.

As a last resort, add an extra electric fuel pump close to the fuel tank, if one is not already installed. In older GM vehicles with large V8s (especially, the "454"), the mechanical fuel pump was mounted low, at the front of the engine block; and it was driven by a push rod off the crank shaft. Often, the fuel line(s) ran right next to the exhaust manifold and along the front end of the tail pipe, both of which are extremely hot. This heat caused the fuel to boil in the fuel lines and fuel pump, making the diaphragm and valves ineffective, and preventing liquid gasoline from being sucked to the front of the vehicle from the fuel tank. This condition is aggravated by higher altitudes, because gasoline boils at a lower temperature than at sea level. This combination of higher engine and exhaust temperatures (due to climbing grades) and lower atmospheric pressure at high altitudes causes gasoline to boil, resulting in "vapor lock".

Adding another electric fuel pump near the gas tank, will PUSH the fuel to the front of the vehicle (as opposed to SUCKING it to the front); and liquid gasoline will push any gas bubbles in the fuel line and fuel pump on through to the carburetor or fuel injectors, thus breaking the vapor lock.

Vapor lock is an old problem, which is mostly compensated for in modern engine layouts. However, it may sometimes still occur under extreme conditions; e.g., towing at high altitudes.
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Old 06-19-2012, 01:59 AM   #5
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I'm guessing that it started back up?

If so, sounds like fuel starvation of some sort. I wouldn't rule out vapor lock, but it's my understanding that vapor lock isn't as easy with a fuel injected engine with a fairly stout fuel pump....which I think delivers something like 40lbs of pressure. Fuel lines are along the frame and are plastic, so not a lot of heat soak to xfer....possible as it gets closer to the fuel rails, but I would think it's a long shot.

How full was your tank? Could be dying fuel pump, pressure regulator.

Reason I ask about how full your fuel tank was, I had a similar exp with my Impala SS years ago when yanking the Safari around with it. Tank had a bit more than a 1/4 tank left, and I took a good grade hill--started loosing power shortly after starting the ascent. Turned out I had fuel starvation. Filled it up and took the hill again, no problems.

As for the temps you mention, those seem a bit high to me. I have the same truck, except with the 6.0L with 4.10s. I have never gone over 185ish for the tranny and never passed 210 for the coolant temp in 97 degree outdoor temps. Though I'm nearly 3k lighter in terms of trailer, I have hauled my 3 ton and some change Safari up some good 2 mile long hauls at significant grade.

The GM trans cooler IMHO is not very good... I put a B&M racing trans cooler and a mag-hytec deep trans pan which could be why I don't see near the same trans temps you are seeing.

Of course if it didn't start back up and/or it did it when you were not at grade, I'd check fuel pump and make sure you are getting the proper pressure at the fuel rails....also a clean fuel filter is always the first step...easiest to do and lowest cost of all.

Edit
I just looked at the link you posted where some folks thought a crank sensor was failing...though it could also cause the issue, your check engine light would be on during and after the event. If your CEL is on, connect a scan tool to verify what error code it's throwing and you've found your culprit. If CEL is not on, then back to my org thoughts.
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Old 06-19-2012, 04:52 AM   #6
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Check GM recall 06083 - crank shaft position sensor:

NHTSA CAMPAIGN ID Number : 07V521000 Mfr's Report Date : NOV 07, 2007
Component: ENGINE AND ENGINE COOLING
Potential Number Of Units Affected : 11974
Summary:
ON CERTAIN PICKUP TRUCKS EQUIPPED WITH AN 8.1L V8 ENGINE, THE CRANKSHAFT POSITION (SENSOR) CAN OPERATE INTERMITTENTLY OR FAIL COMPLETELY. IF THE SENSOR OPERATES INTERMITTENTLY, THE SES LIGHT MAY ILLUMINATE AND THE VEHICLE MAY RUN ROUGH. THE ENGINE MAY STALL, AND IF SO, MAY RE-START IMMEDIATELY OR AFTER A COOL DOWN PERIOD.
Consequence:
IF THE SENSOR BECOMES COMPLETELY INOPERATIVE, THE ENGINE WILL QUIT RUNNING AND WILL NOT RE-START. EITHER OF THESE FAILURES CAN INCREASE THE RISK OF A CRASH.
Remedy:
DEALERS WILL REPLACE THE CRANKSHAFT POSITION SENSOR FREE OF CHARGE. THE RECALL IS EXPECTED TO BEGIN DURING DECEMBER 2007. OWNERS MAY CONTACT CHEVROLET AT 1-800-630-2438 AND GMC AT 1-866-996-9463.
Notes:
GM RECALL NO. 06083. CUSTOMERS MAY ALSO CONTACT THE NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATIONŅS VEHICLE SAFETY HOTLINE AT 1-888-327-4236
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Old 06-19-2012, 08:49 AM   #7
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Joe,

No check engine light?

Have you changed the fuel filter recently? plugged filter=power loss.
Not positive on the Burb. But some gas pick-up's have a "sock" filter on the fuel pick-up that can collapse causing the same symptoms, I'll have to see if the 8.1 has it. Yep it duz.

Any oxygen sensor problems?

A rich mixture will foul the cat converter, causing loss of power especially under load.

On our 454 burb, no light, but a partially clogged EGR valve caused random loss of power, rough idle. Normally does thro a code/light though, P0401-2 or 3.

Bob
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Old 06-19-2012, 09:53 AM   #8
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Monarch is at just over 11,000-ft.

The V8-496 makes 340HP/450TQ at sea level.

The HP loss for altitude, alone, is 120. So, dragging 17k over the top with 220HP gives credence to higher op temps and poor performance. As with the above recommendations: filtration, fuel pressure, and air intake and egress are highest on the list.

Bet that exhaust system was cooking!!

This could be a situation where a number of small "deficiencies" have added up . . not just restrictions in particular places.

Clarification of temps observed would help: Coolant at 220F? Fan Clutch strong? Trans temp was ??

With 17K you have what rear axle gears?

.

.
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Old 06-19-2012, 10:16 AM   #9
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Don't know if diesel is different but I had a similar event on a long (for the East) pull. I felt a hiccup, the engine lost power, running on half of the cylinders, and the check engine light came on. I pulled off at the next exit and checked all around, looking for leaks, steam, broken anything - and found nothing. Checked fluids. I restarted the engine and inspected everthing while I waited for Good Sam to find a shop.

They found one about 20 miles away, and I felt I would do no harm to the engine, so I gently towed myself to the shop. The mechanic read the codes and found the the "pcm" had ordered the shutdown and likely needed replacing. He felt I could make it home - about 200 miles - so he reset the codes and the engine went back to full power.

Here's what I think: Although the engine and tranny heat gauges were not reporting higher-than-normal temps, the module itself overheated. This may be due to my Bully Dog tuner giving me enough power that I did not shift down from OD and this caused the problem. I uninstalled the Bully Dog at the mechanic's shop and came home without it, careful to downshift on most hard hills. Interestingly, I got better-than-expected mileage on that last tank.

As the codes are no longer readable, I'm not sure what the dealer can do for me at this point. I think I will just continue on for a while.

Pat
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Old 06-19-2012, 10:17 AM   #10
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GM fuel pump problems

I have a 8.1 and the same fuel pump in the tank. The first fuel pump failed at 34,000 and replaced the crank position sensor at the same time. $1,000. Second fuel pump went out at 65,000. Same low power indication and would not start reliably. Quoted $1,200, but GM Mr Good Wrench warranted (after I had the original paid receipt sent to me on the road) free. Check the output pressure from the pump. These pumps are notorious for going bad.
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Old 06-19-2012, 10:35 AM   #11
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Quote:
Originally Posted by pmclemore View Post
Don't know if diesel is different but I had a similar event on a long (for the East) pull. I felt a hiccup, the engine lost power, running on half of the cylinders, and the check engine light came on. I pulled off at the next exit and checked all around, looking for leaks, steam, broken anything - and found nothing. Checked fluids. I restarted the engine and inspected everthing while I waited for Good Sam to find a shop.

They found one about 20 miles away, and I felt I would do no harm to the engine, so I gently towed myself to the shop. The mechanic read the codes and found the the "pcm" had ordered the shutdown and likely needed replacing. He felt I could make it home - about 200 miles - so he reset the codes and the engine went back to full power.

Here's what I think: Although the engine and tranny heat gauges were not reporting higher-than-normal temps, the module itself overheated. This may be due to my Bully Dog tuner giving me enough power that I did not shift down from OD and this caused the problem. I uninstalled the Bully Dog at the mechanic's shop and came home without it, careful to downshift on most hard hills. Interestingly, I got better-than-expected mileage on that last tank.

As the codes are no longer readable, I'm not sure what the dealer can do for me at this point. I think I will just continue on for a while.

Pat
Turbocharged diesels are -- from the factory -- best configured (by design). Monkeying around with a tow vehicle op parameters should be left to those who tow for a living.

"Tuners" "chips" and the rest are for the children. Ask the vehicle to live a long time in the most reliable manner and stock configuration is what one will find with most who work light duty pickups for 300k to 1.2m miles. (The details of what brand, what configuration, etc, are beside the point for general purposes).

Some (mild) engine mechanical timing advance may be beneficial for a post-2000 TD, but extra fuel delivered to the engine to "up" the HP is almost always a bad idea.

Gas motors traditionally benefitted from better exhaust systems than OEM (when properly studied), and occasionally better air intake (the trade off being noise and poor filtration versus stock).

Better gearing (numerically higher) is the "real" answer for most complaints of poor towing performance (with 3 and 4 speed transmissions) on a heavy combination.

17k ascending 11k is never going to be fast, easy or without the possibility of problems (that might not otherwise surface).

The "order" for performance is:

1] Vehicle spec
2] Climate
3] Terrain
4] Operator (use & skill)

For this thread one can see that 1-3 are all in contention as to what constitutes the sharpest edge.

Big block gas motors are like kilns . . slow to heat, but long in cooling off. The underhood temps must have been impressive on that climb. A maximum performance call to the engine room.

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Old 06-19-2012, 08:24 PM   #12
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Quote:
Originally Posted by ROBERTSUNRUS View Post
Hi, it has been known that some vehicles with a long skinny fuel tank will run out of fuel at the center located fuel pump while on up or down angles. Gas caps that aren't venting properly have shut off engines. Loosen or remove cap to test. Some vehicles have been known for not adjusting for altitude; Disconnect battery power for a few minutes and then drive a few miles immediately after reconnecting the battery so the computer can relearn. [sort of like rebooting a computer]
Every time I take the gas cap off, I get that suction sound. (btw, I just replaced the fuel tank vapor solenoid thingamajig)
I'll try disconnecting neg, tnx
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Old 06-19-2012, 08:41 PM   #13
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I had a 454 Motorhome that did the same thing...it was a carb motor so it was easy to tell that fuel starvation was the problem, just pumped the pedal for a squirt and the big block would perk up. I was chasing bad filters and pumps...

The give away at the problem...about :10 after parking I heard a "BOING" as the fuel tank lost the suction and re-expanded from it's sucked in state...a dirt dauber nest in the charcoal vent...
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