I recently bought a 98, 12v, 4x4, quad cab, short bed. I have a friend who pointed me in the direction of 12 valves and the 98 quad cab, and i found one online.

its been equipped with the following when i bought it:

#5 fuel plate slid .125" from fuill forward, with the AFC housing all the way forward (checked this)

3KGSK (it will rev happily past 3K rpms)

Larger non-wastegated turbo outlet (unsure of size

It also has a mystery switch, 5 inch exhaust, EGT and boost guages and a scotty II. It is a black truck that had a camper shell from NY if anyone has an idea to whose it was prior to me owning it, id really like to know. I still dont know all thats been done to it, but Eskimo, who has a fairly bombed out 12v truck, did look it over very well.

I recently towed an enclosed race trailer to Ohio from North Carolina, through west va's mountains. It will pull the trailer up the larger hills at about 60 mph at 22~ lbs of boost. I typically ran the rest of the route around 70. While pulling it up there, i saw about 10-11 MPG. After i got back, i replaced the fuel filter and put on a new overflow valve, from what ive read on here. Pulling the exact same route with the same trailer, that probably weighs between 5-7000 pounds, i didnt really see any difference. We had a 15 pass. Van i was following and have a fairly hard time keeping up.

The truck is an automatic, and driving without the trailer to and from work on the highway i was seeing about 15 mpg.


Any ideas on what could be causing the low mileage numbers? The 15 mpg on the highway unloaded is driving conservatively, i was thinking it should be maybe closer to 18? Ive read that towing should reach 12-16 mpg depending on the load.

Thanks- Grant.

 

Id say your stock torque converter is holding you back a lot on getting power to the ground. What is the highest you EGT's usually get? When towing try to keep the Torque Converter locked up. Go ahead and downgear to 3rd with the o/d lockout button right before you hit a big hill and use the RPM's you have and it may do better. They lose a lot of power through the tranny. With what you have done it should be pretty stout, because mine is pretty stout with basically the same stuff. Cant really help you much with the mileage. I also mostly get around 15mpg but i usually cant keep my foot out of it. You have to realize with a load that its going to slow it down some either way. Maybe try sliding the plate full forward for a little more kick. If its like mine it will run a LOT better full forward than it will close to stock. And also your governor lever arm adjustment could be off making it have low power. When i put in my 3k GSK my governor lever arm wasnt hitting the plate right and was really low on power and after i adjusted it, it was running good again.

Eric

 

at 60 or so it will run about 1100* towing at 22 lbs. If speed drops below 55 or so i run with the o.d. off.

Ill check the arm adjustment.

 

635 gives good advice, just be sure your lockup works.

"Pulling the exact same route with the same trailer, that probably weighs between 5-7000 pounds, i didnt really see any difference. We had a 15 pass. Van i was following and have a fairly hard time keeping up.

The truck is an automatic, and driving without the trailer to and from work on the highway i was seeing about 15 mpg."

My truck would pass that van with the same load, at half the boost you need. The trick to having the right power and the right fuel milage is balance. Sometimes the plate and AFC can be TOO FAR forward, not in balance with the fueling requirement at the time. The fuel plate can be out of balance with the RPM you run, wrong diff ratio or oversized tires. Do you get lots of smoke when climbing a hill? Unburned fuel is unrealized power and poor milage. Are your injectors optimized for acceleration (bad), or steady pulling (good), and matched to your fuel plate? I've mentioned fuel plate several times, that could be your problem. Also check for air intake and exhaust restrictions, and set your timing 15 BTDC max for towing.

Self edit: Rereading your post, I get the idea your truck was set up for accelleration without regard for economy. That is a totally different setup from your requirement of steady-state towing with best economy. The clue is that you need 22 PSI boost to climb a hill, I need 11-12 PSI.

 

Im sure the lockup works.

The tires are not oversized and its a 3.55

Up hills, there is no smoke. The only times it will put out any smoke are heavy throttle applications at low speeds.

Any ideas as to what the #5 plate is for? Its listed as the highest powered plate for the 98 automatic on TSTs website. Interestingly it also says it is not recommended for stock automatics. I do not know if i have modified internals in the transmission, it does have a deep hytec oil pan, perhaps its leading into modified components internally. Ill have to check. With all the other modifications done to the truck by the previous owner, it seems maximum acceleration was a main concern. the hitch looks fairly unused as well.

Am i correct in saying that the AFC housing being full forward affects low rpm fueling and the fuel plate is primarily for upper rpm fueling? Also, if there is no visible black smoke while pulling in steady state up a hill, it seems there is complete combustion. I think pulling back the plate to a near stock position may provide some answers, is the stock position in the center of the slotted holes?

 

ur boost sounds really low with that fuel IMO....ur not fueling that much...so umm is ur gov arm properly adjusted? u might not be making proper contact with the plate at all...ooops someone mentioned that already...yep well that may be it then...ur egts sound good unless the probe is in the downpipe

 

"Am i correct in saying that the AFC housing being full forward affects low rpm fueling and the fuel plate is primarily for upper rpm fueling?

Yes. And the more smoke you produce the lower your milage will be.

"Also, if there is no visible black smoke while pulling in steady state up a hill, it seems there is complete combustion. I think pulling back the plate to a near stock position may provide some answers, is the stock position in the center of the slotted holes?

Pretty much, that's a good place to start if the original position is not marked. Another question is Is the plate designed to function properly in the stock position, also, is it designed for economy? I don't know. You could ask TST.

 

question,


When doing the governor adjustment I pulled up the fuel solenoid, but I also had to push the throttle a bit to get the lever to touch the plate. Is this common?

 

Someone please help me out so that I can put my truck back together tonight.



thanks

 

Yes. That is normal to have to push the throttle some to get it to touch the plate. You should be fine. Good luck. If you have any more questions just ask.

Eric

 

Thank-you this is not exlpained in the instructions so I was not sure.

 

No problem. Any luck getting it back together, and if so does it run any better?

Eric

 

Where can I find instructions on gov. rod adjustment, afc housing adjustment and fuel plate adjustmnet. Sorry for these seemingly juvenile questions but I have been a gas engine tuner for many years and this diesel thing is all new to me!

 

go to www.piersdiesel.com and click on tech in the upper left hand corner for the gov lever instructions.

 

Then go to www.tstproducts.com to their tech section for plate adjustment procedures.

Eric