Engine/Transmission (1998.5 - 2002) Should I be worried?

[strehl]

I've noticed a slow steady drop in milage for about a year now. I was getting 20-22 and now I'm down to 14-16. At first I thought it was just something that happens until a couple of weeks ago. I had to lay into the throttle hard to get onto the highway and when I looked in my mirror all i saw was black smoke. The truck is basically stock except for a 4" exhaust, fass, and K&N filter. The slushbox is starting to get tired but I don't think that has much to do with it. injector cleaner didn't help. what should I look for? I get an overboost code thats it.

 

[RacinDuallie]

Might be time to start thinking of freshening up your slushbox..... When your in gear and apply some pedal, does the tach swing up near 2000 rpm's? If yes- slushbox time... .

 

[ROADWARRIOR]

It may be your MAP sensor, or MAP sensor connections. I have read they can drop your mileage, power and produce excessive smoke when they go bad, plus you have an overboost code. I would also clean the IAT sensor and make sure your air filter isn't plugged up. I am assuming your fuel pressure is good. Check out these simple things first and see what happens.



Dan

 

[strehl]

my tach will swing up to about 2300 so i know i need a new slushbox but i cant afford one right now. I'm ending up putting all the money I've been saving up into diesel to get me to work. Where is the MAP sensor and IAT sensor. I'm not very familiar with this engine yet.

 

[UMPRacer]

Here is one to ponder on!

Maybe nothing is wrong with your truck at all. Your tires have worn, which reduces the diameter of the tire so it doesn't go as far anymore as it once did, (per revolution). Also as your tire diameter changes so does your gearing! Put new tires on and I bet mileage will go back up!

 

[strehl]

Maybe nothing is wrong with your truck at all. Your tires have worn, which reduces the diameter of the tire so it doesn't go as far anymore as it once did, (per revolution). Also as your tire diameter changes so does your gearing! Put new tires on and I bet mileage will go back up!

Sorry it has new tires

 

[Cummins Pilot]

Maybe nothing is wrong with your truck at all. Your tires have worn, which reduces the diameter of the tire so it doesn't go as far anymore as it once did, (per revolution). Also as your tire diameter changes so does your gearing! Put new tires on and I bet mileage will go back up!

Tell me your joking right????

 

[ROADWARRIOR]

The MAP and IAT sensors are on the driver's side of the block back toward the firewall. There is a 24valve diagram on this site someplace, do a search for it. You may also consider getting a repair manual, it has helped me a lot over the years.



Dan

 

[UMPRacer]

Pilot!

No I'm not kidding/joking. Sorry! I race and change gearing many nights by putting smaller tires on the rear of the car. It can change 300 to 600 rpms.

I know it may sound crazy but its true.

 

[CumminsAholic]

You're right, it does change the gearing. BUT, the speedometer isn't read off of the tires, so the tire diameter doesn't change how fast the speedometer says you're going. I. E. If you put 44" boggers on a truck and went 55 on the speedo, you'd actually be doing a lot faster, probably 70, the speedometer doesn't self correct for the change in tire size. Hope this helps.

Corey

 

[UMPRacer]

Aholic

Yes you are correct, However, if your speedo reads exactly 1 mile. With the 44" tires on there you probably went 1. 5 miles actually. My point exactly,in reverse of this. When tires wear down gas/fuel mileage will change due to distance covered on the road and gear change due to tire diameter. .



Same principle people warn you about when you look at a used truck that has been lifted with larger tires. Mileage on that truck is more than reads on the odo.



Unless speedo was corrected!

 

[WestTN]

Tires don't wear down that much. Not to account for a 35% drop in fuel mileage. But that 2300 rpms on takeoff indicates a possible torque convertor problem that certainly can reduce your mileage. Way back in the 70's, some torque convertors internal fins were not properly furnace brazed and could flatten out after being subjected to heavy loads. Thereafter the vehicle would act like it was pulling a heavy load when nothing was actually there. In other words it wasn't converting torque any more. You really need to have that checked.

 

[strehl]

Tires don't wear down that much. Not to account for a 35% drop in fuel mileage. But that 2300 rpms on takeoff indicates a possible torque convertor problem that certainly can reduce your mileage. Way back in the 70's, some torque convertors internal fins were not properly furnace brazed and could flatten out after being subjected to heavy loads. Thereafter the vehicle would act like it was pulling a heavy load when nothing was actually there. In other words it wasn't converting torque any more. You really need to have that checked.

I know that is affecting my milage but will it affect it that much. And would that make it randomly smoke?? I'm curious if I have multiple problems.

 

[CumminsAholic]

Yes, your theory is backwards, BUT... The Speedo Isn't Read Off The Tires. It doesn't matter how small (or big) the tires are the speedo will still read the same, so unless he's calculating his mileage with a gps or distance wheel tied to the truck he wouldn't notice the difference as the speedo & odometer say the same mileage no matter what the tire size. I don't know how to explain it any better, just like you said, a speedo doesn't read more miles for oversize tires, it also doesn't read less miles for undersize tires. So he won't notive the mileage change for the smaller tires because it doesn't change. Hopefully this helps you understand what I mean.

Corey

 

[UMPRacer]

Corey

So he won't notive the mileage change for the smaller tires because it doesn't change.



I give up! nice chatting with you!

1. Back to my original post. I said nothing about the speedo!

2. You are right about the speedo not changing and he would not notice.

3. So what does he do, he comes on TDR and asks for help not knowing.

4. I suggest tires cause I know it makes a difference on mileage and gearing.

5. Just trying to help.

Have a great weekend I'm going racing!

 

[CumminsAholic]

HE WON'T NOTICE THE CHANGE!!! Why do you think Cummins Pilot said you have to be joking???? YES, IT AFFECTS MILEAGE, but he won't notice it because his odometer says he's going the same distance, worn tires or not. Sorry for trying to help you understand something so people don't laugh at you, or say you have to be kidding. I dunno how to explain it any simpler, maybe somebody else can. He wouldn't have asked for help if he didn't notice the mileage change, so yes the tires make a difference, but it won't be noticable.

Corey