For poss. lack of a better term: Decarbonization time! '99 Discovery 2 w/ 120k miles. Fairly well kept vehicle but I suspect previous lease owners used cheap gas. I have also been guilty of this.
I only get 9-10 MPG around town and maybe 14 MPG freeway. She runs a little rough on a constant basis, just an engineshaking here and there which isnt alarming just feels like a common V8 misfiring.
I want better MPG and I want to keep this vehicle for 200k+ miles. I've been told to decarb but who is qualified to do this (I live in the Los Angeles area southside), what exactly do I ask for (so a mechanic doesnt just clean the injectors) and how much should it cost?
I also might need to get the Magna Cor? wires. I currently have what appear to be thin light grey spark plug wires (cheapos, maybe autolite?) Should I replace these as well as the dist. cap and plugs and maybe even the O2 sensors? Anyone know where to get these parts cheap enough?
Also- is it OK to use Jiffy Lube for oil changes? Am I ok w/ non-synthetic Vavoline and a low grade oil filter?

 

You could do it yourself if you search on this forum for 60k services, and perform everything on that list. Yeah, the thin grey wires are OEM wires, I would chuck those things. The wires are probably your problem, are you getting any codes? Replace all of your wires and plugs first, then do induction cleanings. Search on this forum for using seafoam, it will describe how to do an induction cleaning. If you do that, and do everything else on the list, it will run like new again.

Get the advice of someone that has put synthetic in their old truck. Most everybody that frequents this board runs some sort of synthetic, but at your mileage you may want to transition first with a good blend.Just be sure to flush your engine first. And I wouldn't suggest anything less for an oil filter than a K&N 3001 filter. It has anti-flowback valves and all that good jazz, and it is an extra long filter so it holds more oil.

I think your main worry would be breaking loose alot of established old crude and opening yourself up for oil leaks, so all of this should be done gradually, or you may put that old engine in to shock!

Edit: Oh yeah, magnecor all the way, they are great wires. I recommend topping them with plat +4 or +4 fusion.

 

magnacor 8mm FTW (for the win)

fuel additives to clean carbon

an engine flush to clear buildup

if you are throwing codes, you may need more than just o2 sensors

and if your mechanically inclined or have the money to throw at it, drop the oil pan and clean out the uptake tube

 

When faced with troubleshooting a vehicle, particularly when the history is unknown, I adhere to Occam's Razor which when paraphrased dictates that all things being equal, the simplest solution tends to be the right one. Problems like the one you are describing can be caused by several issues. The trick is to try to eliminate the simpler and less expensive possibilities in a progressive fashion. With luck you'll stumble onto the problem before you've spent "real" money. I'm not sure what you mean with the term "decarb". It could mean doing something as easy as adding a can of BG44K to the gas to try to clean deposits, or as complex as removing a cylinder head to have it blasted with walnut shells. I'd certainly start with good spark. Plugs are cheap, plug wires are easy, if not as cheap, and progress in that fashion. When you feel like you've ruled out the affordable parts of ignition system and seem to have good spark, move to the fuel side. It can really be helpful to commit your plan to paper and check items off as you go. This can be a black hole for money in a shop, so try to do what you can yourself. You might actually solve the problem, and if not, you've narrowed it down for the tech. Good luck.

 

Here is a list you need to work off of if you want to keep the old girl happy.

This is the parts list for a 60,000 mile service the way I do it.
1 Oil filter, K&N 3001
1 Air filter
6 Qts of engine oil
12 Qts of ATF
7 Qts of 80/90W gear oil
2 Qts of Brake fluid
2 Qts of synthetic Power steering fluid
2 Gallons of OAT, orange coolant
1 Bottle of Lucas Power Steering additive
1 Bottle of Lucas Transmission additive
1 Can of Spray Carb. Spray
1 Can Of Brake cleaner
8 Spark Plugs, I use Bosch Platium Plus 4's
1 Set of Magnacor 8mm plug wires
1 Serpentine belt if not yet replaced
2 Bottles of SeaFoam


60,000 Mile Service or Major Service for High Mileage Used Vehicle just purchased
Bleed the brakes
Flush and change the power steering fluid adding one bottle of additive
Service the tranny adding one bottle of additive
Flush the coolant system
Do an engine flush before changing the oil
Do an induction cleaning
Clean the throttle body
Add fuel additive to full gas tank
Change both of the diffs fluid
Change the t/case oil
Replace the plugs and wires
Replace the air filter
Lube all the drive shaft grease fitting including the 2 slip shafts
Do full inspection of brakes, hoses, bushings etc.

Now what is needed to correct your current issue would be, the Magnacors, plugs, Plus 4's, an engine flush and decarbon it then start looking at replacing your 02 sensors.
What octane gas are you burning?

 

You can decarb the engine yourself in your driveway. Just buy a can of Seafoam at AutoZone and follow the directions on the can.
I wouldnt flush the engine, you could break loose all that sludge and clog your oil pickup and cause lifter noise.
Switch to a full sysnthetic oil, it has more detergants than conventinal oil and will clean the engine as you drive. But it wont do so fast that the filter wont be able to handle it so it will not clog anything.
Buy your own filter and take it to Jiffy Lube and have them put it on for you. They have sysnthetic oils too.
Once you pick a brand suse only that brand of oil. Rather it is Mobil 1, Valvoline, Castrol...it doesnt matter, just stick with it.
I buy my filters at Wal-Mart, they have Mopar filters and it seems to have a good anti-drain back valve and it is half the price of a K&N filter.
You want to good ant-drain back valve. When the truck sits over night all the oil in the filter drains back out into the oil pan and when you start the engine in the morning the engine runs dry longer than normal because it has to pump the oil back into the filter before it goes through the rest of the engine.
So instead of the engine running for 5 seconds without oil it runs for 10 seconds without oil.

 

No at-home decarb will really work, to do it right you need to rebuild the heads and replace the valve guide seals, springs, etc in the process. If you're planning on keeping it for 200K+ then you may want to look at this as an option. Rebuilt heads are fairly reasonable and performance heads only a little more. If your head gasket hasn't gone yet then it's also a good chance to do both at once. Read up on the rover V8 on the RPI site to see some of their advice. It's a case of do it early and things will really last.

 

So, there are differences of options, bottom line, dealers have been successfully decarboning engines for the last near 20 years.
Seafoam will do the job pretty well along with a few other things but don't follow the directions on the can. Some years ago they sitch the directions so that now it states to use 1/3 of the liquid in the tank, 1/3 in the crank case and the rest for the cleaning. They did this because too many people were concerned about the smoke caused from the treatment.
I will PM you and walk you thru the best way to get the best results.
As for the engine flush, believe me, if you have the average mileage of a 99 then a flush will help the engine.

 

By 'really work' I mean remove it all. By all means do as many treatments as you can tolerate I believe you should have the carbon cutter valves in that, if not it's something to think about adding when you rebuild eventually.

Having taken many engines apart I can tell you that some carbon deposits just won't come off with solvents, only mechanical removal works. They'll build up over time it's normal. The looking in the valve cover at the colour of the components trick that RPI talk about on their site is a good way to judge where your engine is currently at wear wise. You'll probably do more good flushing and then only running a high quality synthetic oil than the other treatments though.

Oddly the one problem endemic to other engines that nobody mentions here is clogged injector nozzles, how often should you do a proper injector cleaning (I'm talking pressurized solvents etc) to keep those in good shape? They'll absolutely affect the engine performance. Especially if you're not in an area that you can run a clean fuel all the time.

 

Go onto the bg cleaner website, chose locate a shop at the bottom of the pageand then choose fuel/induction servce. From what I have read, this is the best solvent cleaning possible for your engine- if that is how you choose to go. Many people have claimed to get improved gas mileage afterwords. I called around my area and got quotes from about $100 to $150. I decided to do it myself with seafoam due to the cost and I wasn't experiencing engine problems anyways. I did finally buy some bg induction cleaner and 44k to do myself soon.