I have a 01 D/A with 80K, owned since new. Around 50k the cooling system began blowing water out the overflow. Made several appointments to have it checked out and every time I picked it up they said it was fixed. Well, 25k later and 2 months worth of visits plus 1 month to fix they find a bad head gasket. The left head was replaced. During the time from 50k to 75k I noticed that the truck began losing power and would not pull very well. IE. Began jumping out of overdrive pulling 6k loads on a 6% grade. Having to push 3/4 pedal trying to maintain 65mph on 6% grades until the tranny jumps to fourth gear before the speed begins to recover. I see the same issue now even pulling 2500 lbs. And when trying to pass with plenty off room, I have to go full pedal to get any additional speed on level ground. The truck just does not seem to have the same torque or power. It almost seems to be down a cylinder or 2.To top that off the fuel mileage pulling 2500 lbs. is 8mpg.(And that's with the speedo corrected.) Empty the best I get is 13.8 and thats driving 65 most of the time. When I bought the truck it use to get 18 to 19 mph. Ever since I had the cooling system problem this thing is not right.


I had the dealership look at the truck and they are telling me that it is due to the LT265R16E tires I am using.(recently installed 6k miles ago.) I know that changing the tires will have some issues however CANNOT believe that it would have this type of effect. the diameter of a 265 is only 4% larger than a 245. Need help.http://www.dieselplace.com/forum/smileys/Cry.gif

I would highly doubt that the tires would have anything to do with it. I think possibly they may have missed something when you started having issues and overlooked a minor problem. I can not see the MPG issue being caused by anything that you have done and the load you are talking about is not severe enough to cause it. I would make them take it and fix it and then refuse to take it back till it is right, like when you bought it. I know that over time performance does go down but I would think that much.

Glad to see you made it over here...


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As I said before, DmaxAlliTech would be the one with all the answers...


The rest of us (myself included) do our best to make educated guesses...http://www.dieselplace.com/forum/smileys/Big Smile.gif

Probably a dumb question but how old is your fuel filter? My truck began losing power at 6K miles and a new FF fixed it quick. Also are you getting any smoke on medium to heavy acceleration?


I have had 276/75/R16 tires on my truck from day one and I get anywhere from 16.5 mpg city to 19 hwy. The problem is NOT the tires, they're only 3% bigger in diameter than stock.

I agree with Fred.The 285's I'm using have still allowed over 20 mpg.


The problem lies elsewhere.

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Thanks, I changes the filter when I got the truck back from the head replacement. It has about 200 miles on it.

Have you had your injector rates checked ? At 80k, and after everything else you have had checked, I would suspect a fuel rail/fuel injection problem. Just a thought. http://www.dieselplace.com/forum/smileys/Geek.gif

Here's what the service ticket said " Customer Req. check engine Says Truck has no power Unable to duplicate customer concern Refer to bulletin 01-03-0108 Refers to tire size. Checked fuel pressure, ok. Check PCM and TCM for codes none found at this tme. Checked Turbo, Boost 27 PSI under load ( I'm not sure what load they used for a load) Off 14 PSI. Checked fuel injectors Respond to comman at 160 MPA( I don't know what this means) Truck has new filter. Called TAC Case 7278332. Power is a subjective view. No problem found no repair made at this time.


My complaint was I had very poor towing performance, Lacks power and torgue while pulling 4000 lbs and 2500 lbs. Truck jumps out of overdrive on 6% grade before speed recovers. This is in response to 3/4 to almost full fuel pedal. When passing takes excessive time to go from 60 to 70 when towing same.

where are you at? from the info given it sound like two things.
1 they (the dealer)are rooling you under the bus.
2.not all the info is 100% accurate to preformance issues.
fuel psi (160mpa) is relating to the fuwl psi comand
at idle. with the tech 2 you can ramp up fuel psi.
160 mpa is the metric form of 23,000 psi. this is commonly used to see if the injection system will hold
psi. if it does not than the tech will go into another diag.document to help.with no codes its hard.
hows the air filter?
Are there any other symptoms?
diesel engine preformance is not that hard.
you say the trans is droping out of overdrive?
What do you mean? do you feel it or do you shift it?
any smoke?

I am located in Sanford, North Carolina. The dealership is Central Chevrolet in Sanford.


The air filter is new.


I do not see any other symptions except poor towing performance (lacks power and torque) up grades and when passing on level ground. I say this because I used to pull the same weight up the same grades before the cooling system problem and would compensate for the grade with slight pedal and would gain speed in overdrive. Never felt under powered. Now I feel the need to start pushing.


When approaching grades pulling 4k loads at 60 mph the speed begins to decrease very rapaidly so I respond by slowing pushing the fuel pedal to compensation. I continue until the tranny shifts out of overdrive in an attempt to recover; however, the speed never recovers until the speed drops to 50 mph and the tranny shifts to third and the RPM's are screaming. Then the truck just hold in third with the RPM's at the red line.


I pulled 10,000 or 12,000 lbs. today up the same grades and the speed kept dropping until I hit 40 mph with the pedal throught the floor. I just can see a tire that is 4% larger than stock causing this problem. Hell, if this is 300hp and 520 ft lbs. torque I would need double that to pull the max load for this thing.

whats the trans fluid like?I know my questions aer a little stupid but trying to cover basic things first.

well, I think we can rule the tires out of the equation. Some things are unclear to me. Did the lack of power start at the time of you loosing coolant or after the head was replaced? Other than that, start with the basics, like was stated before. Make sure your filters are clean. You made no mention of any abnormal smoke or check engine lights on. Something is indicating power is down as now it is kicking out of overdrive. I assume it didnt do this before or not as bad?

patrick


The transfluid appears to be ok. Does not smell burnt. No SES light, no codes. No smoke. I do see white or blue smoke but only if it is around freezing, start the truck, let it idle for 20 minutes, then drive off and it will smoke white or blue for 1/4 to 1/2 mile. That has been going on for 50k and not fixed to date. Well, the temperature is staying above freezing now so I guess I'll have to wait until next year to get this fixed.http://www.dieselplace.com/forum/smileys/Ermm.gif May be a stupid question, but I'm trying to think out of the box here. If I had a plugged tranny filter would it cause or send a signal to the engine to reduce power? Could the tranny be tell the ECM ( or what ever controls the engine) to reduce power?


dmaxallitech


The power problem started after the coolant leak somewhere between 50,000 and 75,000 miles. I thought since they found a head gasket leaking that it was the reason my power was down. Well the cooling problem appears to be fixed after 25k however the power problem is still there.

dmaxallitech.


No, I never had a power problem until after the coolant leak. I am using how the truck use to pulll as compared to now. There's a huge difference.

Also, the engine uses about 1.5 quarts in 3,000 miles. The dealership said it's normal but take these guys with a grain of salt now.


Also, sent an Engine oil sample off today. Will be the end of next week before I get the results.

If it's only when you are towing it is possible that there is something wrong with the flash of the stock settings on the computer in TOW/HAUL Mode and yes the tranny will change the power of the engine if it detects slippage or it will go into "Limp" mode.

demaxallitech


I' not using the tow/haul mode. It does not make any difference on the condition.

What about finding a chassis dyno and generating some real numbers? Saying it is low on power is "subjective" and gives the dealership an out when they won't or can't find a problem. The local dealership here seems to have a favorite saying:"Could not duplicate problem."


You might want to try a different dealership. John Kennedy sent me a PM recommending three in Charlotte. I realize that is about 2 hours drive for you, but I bet there is somebody competent in Raleigh, if you have lost confidence in your local dealership.


Good luck.

I remember reading somewhere of a similar problem. Turned out to be a leaking injector sleave or something like that. Sorry, but I can't recall what forum I read it on. Maybe the Diesel Page. Call GM technical assistance and ask them about this problem.

I though about this also. I've found a dyno at a local community college. They are trying to determine if they can rent it to me. Should know something in a couple of days.

I do see white or blue smoke but only if it is around freezing, start the truck, let it idle for 20 minutes, then drive off and it will smoke white or blue for 1/4 to 1/2 mile. That has been going on for 50k and not fixed to date.





Are you sure this only happens when its freezing... just wanted to make sure since maybe because when its cold is the only time you let it set to idle (warm up) for a extended period of time.


I personally think you have injector issues.. I would go do another dealership and tell them of your power loss.. Fom what you have written this has not been checked yet..

Well I do see some smoke when it's around 50 F but not as much and only the first time the turbo boost. During the summer I do not see it at all.


Ya, I said this to the tech and he did not agree. I think your right or it's compression loss.


Thanks for all the comments

How about a Thicker than required Head Gasket..........


Does GM not make three for these engines ????


If a thicker one was installed on the one side then lower compression would be present on one bank.........


Do a compression test............I would start there at this point http://www.dieselplace.com/forum/smileys/Confused.gif


GOOOOOD LUCK !!!!!!!





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Tony, I thought of that scenario, but not sure if its something to be related.. The new head should not change the requirements of the needed gasket. the difference in the 3 different gaskets are so minute that I doubt it would be any loose. Just a few thousands. I know when I did Hoots truck, we went with a thicker head gasket on one side, ( I think just one side, cant remember) from the measurements we got when measuring piston height. I have to kind of lean on slightly an injector issue, but its hard to say. I wish I had the truck here to look at it first hand

A/Cman,
I have been suspecting a similiar concern. I pull a fifth wheel that weighs approximately 9500#. I have recently noticed power loss. Pulling trailer, pedal to the metal and doing good to maintain 65 -70 mph. It was recommended to me to change the main control filter on the Allison (19800miles). I have replaced ($7.92) along with a new air filter. I will not pull the trailer until tomorrow but in the daily commute pedal response has been grrrrreeeaaatly improved. I will reply Sunday night with the new results. All indication thus for have been positive.http://www.dieselplace.com/forum/smileys/Approve.gif

tpcobb, What is th main control filter on the allison? I have a new fuel and air filter.

Dmaxallitech


The fuel pressure regulator was disassembled around 45k to look for injector tip wear. It was noted on the service ticket as being ok. The electrical solenoid was replaced to correct idle surge. Is it possible to put it back together incorrectly? If so what's the symptons?


Also, what compression values should I see? New engine? average? Minimum? And variation between cylinders?

The minimum compression in any one cylinder is 2069 kPa (300 psi). There should not be more than 345 kPa (50 psi) difference between a suspect cylinder and the average compression of all 8 cylinders.

The fuel pressure regulator was disassembled around 45k to look for injector tip wear.


???http://www.dieselplace.com/forum/smileys/Confused.gif???Edited by: tanner

The fuel pressure regulator was disassembled around 45k to look for injector tip wear.


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Thats what I was thinking too!


There should be no disassembly of the regulator, just replacment, and thats only usually done for a lopey idle concern.

Yes, that is correct. Before I had the power problem, I had a lopey idle. They said GM made them inspect the tip for wear to determine if the problem with the lopey idle was wear of the tip or bad solenoid. They only replaced the solenoid.


Will disassembling the fuel pressure regulator cause problems?


I wish I could find a service department that could fix this thing so I would not have to ask all these questions. Edited by: A/Cman

Will disassembling the fuel pressure regulator cause problems?





You dont disassemble the FPR it isnt a servicable part you replace the whole unit.

tpcobb,*What is th main control filter*on the allison?**I have a new fuel and air filter.
The main control filter is the screw on filter located on the drivers side of the transmission. This filter is scheduled to be changed at the first 5000 to 7500 (See owners manual)and then at regular scheduled intervals with tran. oil change. 25K if pulling often under extreme condition or 50K for normal everyday driving (See owners manual). The internal filter is to be replaced when overhauled. If you have not changed, I would highly recommend it as would several people on this site. As for as my trip this weekend, pulled trailer 190 miles. Set cruise on 70 and pulled with no problems, except for slowing down and having pass other RVers. I have come to the conclusion, that my truck pulls just fine. I beleive my expectations have grown.http://www.dieselplace.com/forum/smileys/Cool.gif