07 Suburban LTZ Performance

[Mike]

Im looking for ways to improve the towing performance of my suburban. I tow a 25 foot camper that weighs around 5500 lbs. I find that Im always having to 'punch it' to accelerate, evening going down hill. Uphill starts and driving into an incline are brutal too. I find that my RPM gauge is always around 5k. It will ride it out like that until i let off the gas. Normal driving (without towing) seems ok. Towing my boat isnt too bad but thats only about 1000 lbs. I used to tow a different camper weighing 3500 lbs and it wasnt really noticeable. A friend was pulling a 7000 lb camper with a ragged out 1999 chevy pick up and didnt have as much trouble as Ive been recently having. I used to tow the 3500 lb camper with my 03 TB LT EXT with little trouble. I would expect the 5.3 suburban to do much better than the I6 TB.

I dont know is it is related but, after towing yesterday, my wife noticed an odd odor coming from the truck. Today I got a low oil warning. The oil was changed last month. I've put less than 1000 miles on it since the oil change. Oil life indicator says 78% oil life left. I have checked tire pressure on the trailer and the brakes (not engaged/stuck). I plan on keeping the vehicle for another 2-3 years so I need to do something to improve the performance. I'm not looking to spend thousands on upgrades but will entertain reasonable, moderate cost (hundreds ) suggestions. I also wonder if its possible that there is an underlying issue.

Any suggestions/thought?

Thanks in advance!

Mike-

 

[BO TIE SS]

Have you tried Marshall at PCM of NC yet?

 

[Mike]

Have you tried Marshall at PCM of NC yet?

Thanks for the reply but I dont know what any of that means. Is Marshall a member here?

 

[RayVoy]

The first thing you need to do is check the oil. You've checked the oil life, but the oil level needs to be checked on the dip stick.

Your truck is designed to tow the weight you are towing, but it needs to be properly equipped.
Do you have have the TOW MODE switch? You should have it. Operating this switch will change the way the transmission shifts, helping with the driveability.

From your description, it sounds like the engine may be getting hot. Do you know if the truck has the factory tow package, which includes a couple of additional fluid coolers?

The other thing you should check, is the rolling resistance of the trailer. Having to "punch it" going down hill does not sound right. Could you be towing a trailer with a brake applied, or dragging?

 

[Mike]

The first thing you need to do is check the oil. You've checked the oil life, but the oil level needs to be checked on the dip stick.

Your truck is designed to tow the weight you are towing, but it needs to be properly equipped.
Do you have have the TOW MODE switch? You should have it. Operating this switch will change the way the transmission shifts, helping with the driveability.

From your description, it sounds like the engine may be getting hot. Do you know if the truck has the factory tow package, which includes a couple of additional fluid coolers?

The other thing you should check, is the rolling resistance of the trailer. Having to "punch it" going down hill does not sound right. Could you be towing a trailer with a brake applied, or dragging?

I DO have the tow switch. I used it and it seemed to make the whole situation worse. Oil was 2 quarts low. I'm still not sure how that happened. Oil was still clean when I was checking it before adding more. As far as I was told by the dealer, this vehicle had all the options except 'cooled' seats. They also said that the vehicle had just had the tranny flushed and filter changed, as well as all other scheduled maintenance. The only other issue I can link to this is, the idle is sometimes rough. Every 10 seconds or so, you get that feel like you have a miss. I never notice this while driving. All seems to be smooth while driving. And normally, my gas mileage is in the 15-20 range. I towed 63 miles and burned a little over a 1/4 tank.

I dont know if this helps.....

Thanks for the help thus far!

 

[RayVoy]

Ok, I could look up the RPO (build code) for the towing package; but, I see you have a 4x4.

The 4x4 trucks came with one of two transfer cases. The trucks with the tow package have the 2 speed transfer case and the trucks without the tow package use the single speed t-case (they all have the tow hitch receiver on the rear).

Check the 4 wheel drive switch, do you have a 4 LOW position?

I'm not suggesting you use 4 low, that would not be a good idea, but the trucks with 4 low have the additional cooling.

These trucks have great engines and they have a lot of towing power, however, GM built them to give good gas mileage numbers, so you have a rear axle ratio that gives good mileage and not great towing ability, changing the rear ratio to a lower ratio will help, but it is expensive.

Your transmission selector should have a M (manual) position as well as the D (drive) position. When I tow, I use the M position and the +/- paddles. I keep the transmission in 5th gear, which prevents the PCM from shutting down 4 cylinders and it keeps the rpms in better place on the power band. When I approach a hill, I "paddle" down into 4th gear and if the hill is real steep, I might go to 3rd. Climb the hill and I'll pop it back up to 5th.

This procedure has the same effect (at highway speeds) as lowering the rear axle ratio. I've reduced the engine to wheel ratios resulting in more power at the rear wheels. However, it won't help when starting on a hill, only a gear change will help that.

 

[Mike]

Ok, I could look up the RPO (build code) for the towing package; but, I see you have a 4x4.

The 4x4 trucks came with one of two transfer cases. The trucks with the tow package have the 2 speed transfer case and the trucks without the tow package use the single speed t-case (they all have the tow hitch receiver on the rear).

Check the 4 wheel drive switch, do you have a 4 LOW position?

I'm not suggesting you use 4 low, that would not be a good idea, but the trucks with 4 low have the additional cooling.

These trucks have great engines and they have a lot of towing power, however, GM built them to give good gas mileage numbers, so you have a rear axle ratio that gives good mileage and not great towing ability, changing the rear ratio to a lower ratio will help, but it is expensive.

Your transmission selector should have a M (manual) position as well as the D (drive) position. When I tow, I use the M position and the +/- paddles. I keep the transmission in 5th gear, which prevents the PCM from shutting down 4 cylinders and it keeps the rpms in better place on the power band. When I approach a hill, I "paddle" down into 4th gear and if the hill is real steep, I might go to 3rd. Climb the hill and I'll pop it back up to 5th.

This procedure has the same effect (at highway speeds) as lowering the rear axle ratio. I've reduced the engine to wheel ratios resulting in more power at the rear wheels. However, it won't help when starting on a hill, only a gear change will help that.

My 4WD switch has 2, Auto, 4 arrow up, 4 arrow down, and N. It wont stay in the N position. The shift selector does not show an M.

Thanks for your response.

 

[BO TIE SS]

Thanks for the reply but I dont know what any of that means. Is Marshall a member here?

Marshall is a vendor here and does tunes on the PCM. He could probably tune you PCM to tow better. He can explain it better and make other performance suggestions.

http://www.pcmofnc.com/

 

[marshall@pcm]

Replied to your PM, Mike.

 

[navigator]

..... Every 10 seconds or so, you get that feel like you have a miss. I never notice this while driving. All seems to be smooth while driving.

I have a 2007 Suburban LTZ also. Mine does the funny idle as well. From what I have read, it is pretty normal especially for the ones that came from the west coast to deal with emissions. MIne was originally from Wa.

I'm going to clean my throttle body to see if that helps. It runs great outside of the idle.
Mine also uses a little oil. I've read lots of feedback about some 5.3s using oil and some use no oil.
When my OLM read about 50% I had to add a quart. We haven't driven it hard, mostly short trips, no towing.

 

[MDBT]

...Oil was 2 quarts low. I'm still not sure how that happened. Oil was still clean when I was checking it before adding more...

You have a 5.3L with AFM, that's how. Keep an eye on that oil level and if you continue to use oil at a significant rate you'll need to look into the TSB's for the model.

 

[gmcman]

Are you using a K&N filter? Reason I ask is if you are, oil can coat the MAF. You can't really compare an I6 TB to a 5.3 burb....torque is higher with the 5.3 naturally but you have that motor in a land yacht, no offense, I like the suburban.

The I6 is a great motor and is no slouch, I6 TB to 5.3 TB is another story. You could be crippled with a tall gear ratio along with the added weight in the suburban, what is your gear ratio?

Have you changed your plugs? 5K lbs is a fair amount of weight, a 6.0 or 8.1 would be better suited for that vehicle but the 5.3 does work.

Could be tires or brakes, I agree having to give it the beans downhill raises a brow.

 

[gmcman]

Thought of some more....how old is the fuel in the tank? Have you verified fuel pressure?

Have you checked the vacuum? Is the needle steady?

Exhaust backpressure test can rule out a bad cat.

If you get around to the plugs, would be good to perform a compression test, (dry and wet) just to be sure you don't have a weak cylinder.

 

[Mike]

Thanks for the replies. I have been very busy with work (heating and a/c) due to the warm weather. My last tow went better using the Tow switch. I'm not sure what happened the last time I thought I was using it......

I'd still love to upgrade the performance a little though. Will the PCM upgrades make a noticeable difference?