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The old 12 Valve is getting a little tune up...

1549 Views 24 Replies 11 Participants Last post by  DEMON76
I just dropped my truck off this afternoon to get a much needed tune up. It's a 98 CTD 12 valve Quad cab 5 speed with 105K miles. I needed to have the KDP done as well as a new serp. belt and a new fuel solenoid boot installed. I recently replaced the fuel filter, rubber fuel lines, lift pump and a bunch of other crap.

Now I'm having a 4K spring kit installed, the fuel plate will get a little grinding, I'm having a 4" Magnaflow exhaust installed with no cat and a straight through muffler, having the timing set as well as adjusting the valves and the injector pump timing. He'll also turn up the injector pump and see how much power I can get out of it before I start eating up the stock clutch. I'm looking for a balance between decent power and reasonable EGT numbers, I know I can take it higher but I don't want to be past 1050 - 1100 when towing if at all possible.

Can't wait to get it back and feel the difference, she's been feeling very sluggish lately. :)
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dont forget the fuel overflow valve. thats usually the culprit before the lift ppump on one of those goes out. the old 12v lift pumps lived long lives 200k was average and even then you could keep it as a spare most the time
I replaced the overflow valve when I replaced the lift pump. :D I spent 2 or 3 weeks searching for killer fuel issues until I found the real problem... a stuck fuel sending unit and an empty fuel tank.
I am just curious - what are you paying the shop for all of this work? (if you don't mind me asking!) I have a 97 12v and I am looking at doing a lot of the same work so I am curious.
I wanted the exhaust before I had it tuned so they agreed to install it for free if I bought it from them and the price was right. He's also going to tackle the KDP, new front seal and new belt while he's doing other things. He has to pull the fuel solenoid so he's putting the boot on as well.

I don't know enough about the mechanics of a diesel to starting doing things like setting the injector pump, engine timing or the gov. spring kit.

I've provided him with the KDP kit and he's providing the new belt, the solenoid boot, the gov. spring kit, the 4" magnaflow exhaust system and a couple other small things plus all the labor for about $1200. The guy working on it knows more about the old 12 valves than I will ever know, when he started talking about setting the engine timing to within a 1/2 degree I knew it was over my head.
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Your going to be kind of wierded out when you first drive your truck after you get it back. When I put the 3200 rpm spring in my first gen the sound of 3k rpm tripped me out! The timing takes some getting used to as well. With that exhaust kit you'll be able to hear your exhaust whether you want to or not!! :flipoff2:

This is that black 98 12v you bought a while back right? Nice to see people taking care of their Cummins! rattle on :smokin:

I was told that I might not recognize it when I get it back, it was running very sluggish and conservative... Even towing I've never seen a hint of black smoke out of her. I have a feeling that anything he does will be great.
Yup like he said there, with a 4k governor spring you;ll need to upgrade the valve springs to 60lb HD springs. or you'll be tempting a valve to float and kiss a piston.
You guys were worrying me but I called and he's including all of that in the price, he really knows more about the 12 valves than I can dream of... and he's rebuilding his 12 valve track truck that used to run mid 11s.
Well I picked up the truck today and WOW is all I can say really. :eek: I'm still a little uneasy about getting on it because I'm still running a stock clutch with 100K miles but it's an obvious night and day change from before. It's like a new truck and is so much faster it's a bit scary to drive. :D
You didn't mention the air cleaner. The stock one is a big restriction when you start pumping more air.
I put the typical BHAF on it when I bought it a year ago, I need to get one of those slip over pre-filters but she's getting plenty air on the input side.

The truck is running great, I'm just a little worried about the clutch so I'm taking it easy. She's not slipping yet but I can't imagine it'll last much longer. I haven't towed anything yet but my EGTs are at least 250 - 300 degrees lower at highway speeds and I'm getting getting the boost up in the 30 - 32 psi range when I stomp on it. Can't really get the EGTs past 850 but I haven't hooked up to a trailer yet, we'll see what happens then. The only problem I have right now is my fuel pressure, I'm 99% sure it's a bad gauge and I'm going to check it tomorrow to make sure. I built my own fuel gauge with parts from Grainger but I had to use a different valve from what I wanted. I think the valve is regulating the pressure even when it's fully open because the truck is getting plenty fuel but the pressure is reading about 10psi lower than it should.
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It all sounds good. Why are you worried about the fuel pressure on it if it is running well? I guess you must have a snubber in the gauge somewhere...

While you are plumbing things it is nice to have a fuel bleed valve on the pump. I put one at the front of the pump where you tap for fuel pressure. I sure makes it easy to bleed the air if you need to...
I'm worried because I just went through a metric ton of BS with the fuel system replacing all sorts of crap when it turned out to be a stuck fuel gauge and an empty tank the whole time. All new hoses, overflow valve, lift pump, etc etc all because the fuel tank was empty which believe it or not will cause the truck to stop running. :D

I just want to make sure I didn't mess anything up when I did all that, I installed the gauge and I would like to be able to monitor it correctly.
You shouldn't really need to worry about fuel pressure with that mechanical pump, they're pretty reliable and pretty strong. but if you put a guage on it with out a good snubbing device the pulses from the pump will rapidly destroy the bourdon tube in the guage, even if its a fluid dampend needle. then your guage is NFG with bad readings.
Very good point, when I first installed it everything seemed normal but after a few months it seems to be off. I guess I'll leave it alone for now.
That won't last long.... Then you will be doing a clutch job :smokin:
I hope that can wait a couple months, I travel a lot so I really don't drive it that much plus when I'm home I use the Jeep a lot. This really is my tow rig so as long as I can baby it and still tow my TJ I'll be ok... for a little while at least. :D
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