99 Grand Caravan-Poor Gas Mileage

[Mcooper]

My '99 GC has been getting terrible gas mileage - 12-13mpg! I noticed it idles kinda rough. What should I try to get better mileage? The van has 78,000 miles and I change the oil religiously every 3000 mi.

I have BF Goodrich Traction T/A tires with 6000 miles and I keep them inflated properly. The tranny seems to be operating smoothly and I replace the air filter yearly. Should I change the fuel fiilter, spark plugs and wires?

If I do change the plugs, how the heck do I get to the 3 rear spark plugs? They are tucked away pretty good on the back of the engine.

[Mcooper]

The GC has the 3.3L engine.

[Stretch58]

My 2000 gets about 22-23 MPG on straight 87 octane. When using E10 Ethanol it is a little less. Mine has 111,000 on it. I would pay for a check at a qualified shop to see what the problem is before changing a bunch of parts. One thing I did do at 100K was I had the Intake system cleaned, replaced plugs & wires, replaced fuel pump,water pump and belt tensioner. At 85K I had the trannie flushed on a BG machine at a local dealer. Also flushed radiator and brake fluid(was filthy).
Stretch

Originally Posted by Mcooper

My '99 GC has been getting terrible gas mileage - 12-13mpg! I noticed it idles kinda rough. What should I try to get better mileage? The van has 78,000 miles and I change the oil religiously every 3000 mi.

I have BF Goodrich Traction T/A tires with 6000 miles and I keep them inflated properly. The tranny seems to be operating smoothly and I replace the air filter yearly. Should I change the fuel fiilter, spark plugs and wires?

If I do change the plugs, how the heck do I get to the 3 rear spark plugs? They are tucked away pretty good on the back of the engine.

[neon_rt]

Interesting thing, the BF Goodrich Traction T/A tires.
About 10,000 miles ago I put the same tires on my '00 GC (3.8l).
They must have a very high rolling resistance because my mileage went down 3mpg (from 24 to 21). They have better handling than the last brand of tire I had, but I will probably go back to the other brand, given the price of gas.

[Mcooper]

neon_rt,

I have been getting the poor mileage for close to 10 months now. It has been steadliy decreasing but it actually got a little better once I put the tires on. My previous tires were Continental and they wore out after 25K. I will never buy Continentals again.

I do not think it is the BFG tires. I put the same tires on my '97 Maxima last year and my mileage did not change.

[neon_rt]

I was only suggesting a minor reduction in MPG from the tires.
I've had two '00 GC's, one with the 3.3l and one with the 3.8l.
The 3.3l started running rough at about 80K miles. I took it in for a tuneup and it restored the mileage and it ran smooth again. The plugs were in really bad shape and probably contributed most to the problem. I had "MotorVac" treatment done as part of the tuneup. They remove and soak the injectors, clean the TB and PVC and do a de-carbonization of the intake manifold and cylinders. At this mileage it is suggested to replace the 02 sensors as part of the tuneup but I did not. It could be that you need a tuneup and 02 sensors. Lazy 02 sensors will cause the mixture to be rich and eventually plug up the CAT, causing more loss of performance and mileage (loss of $ too).
I hope you can fix this soon b/c gas is so expensive.
My GC with the 3.8l didn't have the tuneup problem until about 120K miles. I really like the 3.8l, when I trade this van in, I will only consider buying one with a 3.8l. I consistantly get better MPG with the 3.8l over the 3.3l and having the extra power is nice too. My Brother in Law just got a '05 GC with a 3.3l 180hp. My '00 3.8l is only rated 180hp. Apparenty horses were bigger in '00 b/c I caught up to him the other day on the road and blew is doors off going up the hill (1 mile, 6%). Actually I probably cheated a bit, I have an aftermarket exhaust on mine (made a noticeable difference).

[Mcooper]

Thanks, dude.

I am going to take the ol' family truckster in for a tune up. I will inquire about the "MotorVac." I will report back with the post tune up results. Thanks again, neon_rt.

[RIP]

Couple more thoughts. (1)You could be loosing compression on a cylinder or two. Have them do a compression check to confirm. (2)Hows the wear on the brake pads and shoes? Are they worn evenly? How fast are they wearing down. You may have one or more brakes dragging. Is the parking brake releasing completely? It doesn't take much drag to effect mpg.

You can change the passenger side spark plug by loosening the alternator and pushing it aft. You have to go under the van and reach up through the cavity next to the exhaust to get at the other two. Not exactly easy but, not that bad once you get in there. I've read some remove the throttle body to get at it from the top. To me that opens the door to too many things going wrong.

[Mcooper]

RIP,

Excellent suggestion about the brakes. You might remember I posted last week about uneven wear in my front brakes. I just changed the front pads and lubed the guide pins and bushings. Maybe I will wait to get the tune up until I use a couple of tanks of fuel. I will monitor the mpg's for the first few tanks since the brake pad change.

To be continued.

[RIP]

I remember now. Did you ever notice the van pulling left as you went down the road? You may or may not have depending on what position the pins bound up at. Either way, as I said, it doesn't take much to effect mpg. Hopefully you "killed two birds". Let us know. Cheers!

[neon_rt]

With a negative scrub radius (most FWD), a dragging left brake would make a slight pull to the right. The pivot point on most FWD is on the outside of the center of the wheel. This makes most torque steer and uneven braking self cancelling.