mopar!

i got a 2000 jeep cherokee and im getting around 10mpg, and have been for sometime. i changed the plugs couple of years ago but i think the coil pack is original at 140k. could it be a weak coil pack?

i have no cel, new O2 sensors, new MAP sensor, new air intake temperature sensor.

anything else it could be? my guess is still weak coil pack.

VTJeep

Bad coil/coil pack should account for some/all that poor mpgs.. Looks like you've hit the other likely culprits..

mopar!

well thats why im kind of on the end of my rope. im thinking im gunna change the plugs and coil pack and if that doesn't fix it then im just gunna assume i get bad gas mileage. ha

BrofessorXJ

Cracked header as well give that a good look over. Mine was cracked and I was getting around 10mpgs.

ZINGGG

When you replaced it, what kind of improvement did you see? I'm getting around 10 with a cracked manifold and I'm gunna throw in a Borla header pretty soon here and hoping to see a small improvement.

There's a lot you can do to help mileage. All new fluids (oil, differentials, transmission, coolant), clean the throttle body, run seafoam through the gas tank and brake booster vaccuum line, change out spark plug wires (with some 8mm wire), distributor cap and rotor, all new filters (air, fuel and oil)

mopar!

well i got a 2000 with the coil pack and all of my fluids have been replaced within the last 10k miles. but i will check into the manifold idea. thanks guys!

tjwalker

Usually a bad coil pack will result in misfires.

Are you "calculating" your gas mileage by taking miles driven divided by gallons consumed? Don't try to extrapolate your mileage by the amount of miles you get to a tank of gas. That technique is not particularly accurate. Do the math.

I'd recommend fresh NGK copper plugs for your 01. Be sure that you confirm the gap is .035 before installing them.

BrofessorXJ

I put on a new APN header, 99+ intake manifold, and 703 injectors at the same time and it jumped up to about 15-16mpg's with mixed city highway driving. more power and throttle response is crisp. I press down the pedal and it's there right away.

Honestly I wouldn't waste money on a Borla header, APN is a knockoff and they run for $150. Love mine.

So cal eh? I'm up in the San Fernando Valley. 96XJ sport as well.

ZINGGG

I've done the injectors already, no change in mpgs really. Still sits around 10. So my headers are next. Thanks for your input though, i'm definitely considering the APN manifold. Haha yeah orange county. You aren't too far away. As soon as I get everything fixed that I need to, I'll be looking for some places to wheel, maybe you can point me in the right direction.

Not meaning to thread jack you, but yeah, your coil isn't going to be contributing to your gas mileage really at all. Use all the above pointers. Cracked manifold is a huge suspect

BrofessorXJ

Ineedparts.com is where I got my apn. It says it won't fit the 99+ because of the newer intake manifold but it will with a little grinding on the underside of the 6th intake manifold runner.

541_halseth

Can i ask when you added the roof top camper because i can tell you, my roof rack alone is automatic 2 mpg decrease. That may be your killer. If you were watching you MPG before it with 31's you might of noticed it around 15-17. It doesnt get much better than that with lift and tires.

mopar!

Yes i calculate it properly by gallons ive used by miles driven. Not a rough estimate from my gas gauge.

And the rooftop camper is off. If it was on i dont expect the same mileage.

volaredon

plugs a couple of years ago?Youre due for replacements again.

cruiser54

My thoughts exactly. How many miles has it been?

rrich

I don't know why people think the engineers that designed the motor were crazy. They put in junk plugs because the kid at the parts house sells what he wants so he can get his commission.

The underhood label tells you what YOUR engine was designed to use. MAKE, NUMBER AND GAP.

A defective coil pack doesn't always make you feel a misfire - no typical "thump thump thump" The coil rail fires 2 cylinders at a time - companion cylinders, so the engine still is in balance. The main symptom is poor performance - lack of power and poor mileage.

To test - run at 2000 RPM for 2 minutes, go under with an infrared thermometer - measure the 2 pre-cats outlets - both should read around 400 degrees each, a bad coil rail will read lower on one, and about 700 degrees on the other.

Be sure to use a QUALITY coil rail - Chinese junk like Autozone and O'Reileys sells won't last long. NAPA Car Quest, or the dealer has real ones. The difference in cost is only about $10-20 (except the dealer), but the difference is 1000 miles vs. 100,000+ miles.