Drop in 8.1 big block fuel economy--any ideas?

**erikzola** · 01-27-2008, 01:19 PM

I have a 2004 Suburban with the big block 8.1. Has 106K on the clock. I generally do all highway miles and sometimes drive within the real speed limit. I have seen a several mpg drop in economy lately that I can't explain. (I know that an 8,000 lb truck with this motor won't get better than 13 mpg or so but I am around 10 now). I run load range 'E' tires and keep them inflated in the 60-65 PSI range. I have no SES light or codes stored. At 100K I replaced plugs, wires, pcv and fuel sock.

I have read other posts regarding the possibility of bad O2 sensors in other threads but I don't know for sure if that can be a indicator with no code. Are my conditions enough to justify O2 sensor replacement (at a high cost) with no SES light?

Thanks for any suggestions.

**ss~zoso~ss** · 01-28-2008, 04:02 AM

run some fuel system cleaner through it and beat the snot outta it for a day, see if there is carbon build up, Seafoam is a great product, you can suck it in through an intake manifold vacuum line and stall the engine with it, then u let it sit as it eats the carbon from the cylinders then you start it up and it should smoke like a bastard, i did this on my 90 volvo 240 with 200k on the clock and it smoked like crazy, do a search to find out more

**Naf** · 02-12-2008, 10:35 PM

AHHHH!!!!

Its a bit more that just injector cleaner for him...

He has about 106k on the odometer...You need a full day in my books to do the job right...Its starts with a simple engine oil flush...

Then i would turn my attention to your MAF sensor, a good clean with soft hands and WD 40 would do the trick...STAY AWAY FROM THE RESISTORS...If damaged you will have to replace completely...

Then i would pop off the throttlebody and give it a good scrub as well a few squirts of WD40 and carb cleaner into the intake manifold...

Later if you still have the energy i would remove the plugs and replace with Bosche...And the sparkplug wires probably need a good change as well...

This will jump you back to where you aught to be....

have fun

**erikzola** · 02-26-2008, 07:27 AM

Hey Naf thanks for the comments....

At 100K I replaced the plugs and wires and since have added some fuel injector cleaner a few times with no solid results. I will take a look at the MAF and Throttlebody as you suggested and see what happens.