hey guys im new here..i have a 99 4x4 suburban that has been giveing ne fits for along time.poor performance and gas milage runs ruff doggie .it has had everythang under the sun replaced ignition fuel system its been checked checked and rechecked no codes no issues just runs like crap..my first question is does anybody know if the flattop pistons could be screwing up the computer system on this truck.. i just wonder if the rise in c.r is messing up thangs pleas help thanks

 

Did someone rebuild your engine?

 

I'd imagine, he mentions flat tops and a raise in compression...

FYI these are stock Vortec 350 pistons:

 

yes i was completly rebuilt

 

Have you tried running 93 octane?

 

i have tried 89-91 cant get 93 in my area i have tried messing with the distributer..i dont get much results idk..no check engine lite it runs like crap idles really low like 475rpm and it surges at low rpm acceleration its just a piece of crap lol

 

we just took a trip i started out with a mix of 89-91 in the tank it ran sum better but got 13.4mpg we ran 175mi interstate onlits a 42gal tank i put 15 gal of 87 in it then tan 230 miles threw hills and hollers of ky it got 12.7 i put 17 gal of 87 in it ran 183 mile interstate back home and got 15..but it soes seem to performe just a little bit better with the higher octane just worse on mpg

 

Turning the distributor won't do anything. The timing is controlled by the computer on them.

 

My take? Your compression is too high for the fuel available and your computer is tuning down the hell out of the motor trying to compensate for that Compression and possibly engine knock.

 

Had a similar problem on my 99 3/4 ton 4x4. CRC mass airflow cleaner! Truck runs like a champ now! Still only get bout 10 mpg. But Frank has 3" body lift n 37" Mickey Thompson Baja claws lol

 

i thank back about a 8 months ago we tried a maf sensor but i cant remember now been a long battle..i am really wondering about the c/r and the pistons i get two opinions some say its the prob and others say no way so idk..all i do know is a got a friend that has the excat same vehicle all stock original and his runs decent for a 7300lb vehicle and gets 17.5mpg on highway, i have seen it first hand..mine idles rough runs ruff gets 15at best and has to down shift to 3rd gear to hold 70mph on a small rolling hill..my dad has a 95 ext pickp 2wd we can put a large boat behind it equalling out the weight difference and it will run circles around mine and is smooth as silk

 

also when its hot it starts hard like advanced timming but no matter were i set the timming it still does it