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94 K3500 Sierra needs a new mill.

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I have a surprisingly rust free 1994 K3500 Sierra with a full size bed, duallys, a cab bigger than some apartments I've rented and a bad 454 under the hood. I plan to use it here on the ranch as well as pulling gooseneck trailers over the road occasionally. Probably including a flatbed with a backhoe on it occasionally.  But I'm wondering what I should do about this bad engine and was hoping to get the opinions of some folks who know more about these things than I do.  The existing engine is (or was) a L19 engine 7.4L(7.4N),V8 (TBI) (MARINE) 7.4N(L19) according to the VIN decoder I used.  It's geared 4.10 with a 4L80-E with OD.  I know there are some little differences between the 454s by model year and intended use and I'm trying to find out what they are and how to shop for them.

 I'm not above buying a core to have rebuilt, or even another whole junk truck for the donor parts I need to put this together.  I'm pretty handy with a wrench and a soldering iron but my training as a machinist a few decades ago tells me that I'm better off having someone else do the machine work now.  

Would something out of a motor home be more reliable for me? Is there a difference in the way they are made within the same model years?

Would it be worth my time, for the sake of power and efficiency, to get a whole truck with a vortec in it and swap out the ECU?

Are there questions I should be asking that I haven't?

Are there any sites online that might already have answers to these questions that I haven't found yet? 


Edited by Kineticarts
More questions.
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What is bad about the current engine?


Can it be rebuilt or is there a window in the block with a rod hanging out??


To make your life simple it would be the easiest to find a 454 with another truck or RV from 1991 to 1995 to make it a drop in and go unit.


Swapping to the newer stuff would be more involved that just the engine/computer. You'd need to upgrade the fuel system for port fuel injection and possibly even need to swap the dash/cluster to make the PCM talk with all of that.

They changed the interiors and all the wiring stuff in 1995 and more so in 1996 with the vortec engines.

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Cam asked:  "What is bad about the current engine?"

Well the first indication was how hot it seemed by the radiator after even a short run. Then a blowdown test gave some really radical readings on most cylinders, and no reading on #7. Confirmed the readings with a cranking compression test none of which were above 85lb so I figured the thing wasn't even worth putting the new plugs in. It starts and runs well enough to haul things around the property here but I don't want to leave town in it.  It's a new truck to me and I'm a little leary of even driving *into* town in it after finding this.  I've already had the 4L80 rebuilt and put a new set of leaves on the LR corner so I feel like I'm pretty committed to this project. I think the truck is just a good fit to a guy my size. It takes just one butt shift to get comfortable in the saddle and the tailgate is just at the right height for a workbench,,, so there it is!

Then Cam asked: "
Can it be rebuilt or is there a window in the block with a rod hanging out??"


Not on this one! But back when I'd grown tired of only being able to rent apts smaller than the cab of this truck I joined the National Guard. After leave after basic, on the way back to GA to complete the electronics training I'd signed up to get, my in-line 300 ford did that to me in the middle of a dark and stormy night. In the light of my BIC I was having trouble finding the source of all that oil but I found the window in between the three bosses of the right motor mount. I dropped the pan, pulled about half a camshaft out of the bottom of it and tied the rod that'd lost it's cap off to the motor mount with a strip of rag threaded thru that conveniently located window and drove onto base six or seven hours later looking and feeling my best, but still made it to formation on time!

  Then came the logic and rationality I came here for. To which I respond by trying to explain my own logic on this. YMMV

Most of the miles (or considering my plans for this, the hours) I rack up on this truck will be local stuff, building fence, pulling crap out of the woods, running to the hardware store or supply house for whatever, which may include 4300 lb of MDF or as much gravel as I can haul in one trip. But occasionally I'll be a few thousand miles from my usual stomping grounds pulling 20 odd thousand dollars worth of custom built furniture or some priceless horse flesh to places that only exist for the weekend. These are "gotta do" situations for groups of people who really can't afford to do these things they love. I'm their infrastructure guy.    So if it were just for getting to today's jobsite or running fence on the property here, putting a $700 used mill in the thing would make sense. If it went down,the tow charge wouldn't be catastrophic. But if I'm 1500 miles away pulling a custom adapted trailer it's a different story.
  I'm going to have an engine rebuilt by someone who's eyes I can expect to look into at the grocery store sometime this year. I'm just looking for some guidance on what engine to have rebuilt.

Somehow this editor has gotten stuck in "overwrite" mode. Suggestions anyone?

  From what I read on wikipedia, the Vortec 454 offers 20% more horsepower and 8% more torque with better fuel economy than what was in this truck originally. I've built a career out of turning whatever you have into whatever you want so I'm not skeered of the work involved to remodel  an instrument cluster.  If the PCM speaks OBD2 I could just ignore the cluster and use the app torque to get what I need to know.


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9 hours ago, Kineticarts said:

Well the first indication was how hot it seemed by the radiator after even a short run.


Remove the plastic cover above the radiator, clean out the debris/bugs etc between the radiator and condenser. Should help cool it down.

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  • 2 weeks later...
On 7/15/2020 at 8:46 AM, Super 8 said:

Remove the plastic cover above the radiator, clean out the debris/bugs etc between the radiator and condenser. Should help cool it down.

I cleared that out and in the process soaked the passenger side exhaust manifold and noticed why the new doughnut gasket didn't help the noise more than it did. #4 has a longitudinal crack in it which I suspect made it seem hot up front too.  Thanks for the advice, there was a little collection of stuff but the mill still has much bigger issues internally.
    So anyway, I've picked up a 1998 Sierra C3500 from a Ford guy who got it on special from a friend who had a tenant abandon it on his property. The Ford guy wanted the bed and cut it off the frame along with big chunks of the frames top flange. Then he priced the remainder of the beat up C3500 as if he just wanted it off his property, I was glad to oblige and now have a nearly complete 98 C3500 with Vortec 7400, Four good spare tires, a NV4500 that seems to be in great shape,  A 4:10 posi rear just like mine (I think), and no doubt, a lot of surprises!
     The engine turns over easily and my el-cheapo compression gauge reads between 50 and 68 LB on a cold engine with all the plugs out. Most reading at 60. The fuel tank is out and judging by the plugs and wires (one of which was missing?) I suspect the injectors need replaced too, so I haven't tried to start it yet. I'll do a static blowdown on it tomorrow to get some more data on it to guess at. It just got too hot outside the garage door to do it this afternoon and I had plenty of other paying work to keep myself busy with. Keeps me from playing with my truck and the forum here too!
     So it seems I'll be blending a 94 K3500 and a 98 C3500 together into a Frankentruck with the 94 frame, body, bed, axles and 4l80 trans and the 98 Vortec and misc, parts to fill out the bill.

    The 94 fuel tank is good but a bear to change and the fuel filter on the rail doesn't look like it'll come out leaving the fittings intact. The 94 fuel pump is a known good pump and delivers 12 lb like it should, but that's not enough pressure for the Vortec. I was thinking of adding an in line pump when I replace the filter to kick the pressure up for the Vortec. The tank from the 98 is missing the pump and is full of crud but I'll keep it to install when the 94 pump goes out. Good idea? Bad Idea?

     Looking at the manifolds on the Vortec this afternoon I noticed some cracks between the ports but I didn't see anything like on the 94. Does it seem like a good idea, for the sake of efficiency, to put some long tube headers on it to help it eat highway while pulling a heavy trailer?  If so does anyone have recommendations on tube diameter, length, and/or manufacturer?  I'm a bit of a greeny for a guy with a 454 and want to keep the cats and emission controls operational.  I found one outfit that has some bent up of Stainless to fit a Vortec 7400 in a motor home and is 50 state compliant, but I don't know if they'd fit a vortec in my 94 K3500. Suggestions?

      I'm also wondering if anyone has a recommendation on reprogramming the parameters on the PCM after I decide what this beast will be?

  Thanks for reading and your comments and questions are appreciated.  Enjoy!

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  • 5 weeks later...
  • 1 month later...
On 8/27/2020 at 2:21 AM, KINGENGINEMAINTENANCE said:

Drop in a replacement 454 and use it on the farm and around town. Hauling long distance get you a duramax! I had an LLY stock on 285s to haul car trailer and it would tow a full size pickup on a trailer with ease. Really opened my eyes to the power of a turbo diesel V8 with 500 "torquepower!" Peace be da journey!

Thanks for the suggestion but it's just not an option for me at this point.  The goals of the whole of my life demand I spread my money a little thinner this year. ?

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But back to the main thread, I have given up on the idea of putting the whole Vortec thing into the 94. Just too much wiring that I don't have time to learn about and do. But my research seems to indicate that if the block and heads of this 98 C3500 with a Gen VI 454 I picked up for a pittance from a Ford guy who seemed to only want it off his lot are in good shape, I could jack up the intake manifold of the Gen V in the 94 K3500 and slip them underneath it with very minimal hassle.   According to "CHEVY BIG-BLOCK ENGINE PARTS INTERCHANGE: THE ULTIMATE GUIDE TO SOURCING AND SELECTING COMPATIBLE FACTORY PARTS" (available on Scribd.com) The short deck block intakes are interchangeable between Gen V and GenVI, mostly. Has anyone done this before?
    Today's issue is while checking out the 98 to see how it runs, I've noticed that the fuel pump I've hacked onto what's left of the truck will quickly reach 60 lb pressure I can't get the fuel pressure test port to read over 52 which may explain why it's impossible to start. When I try to start it it sounds like the distributor has a plug wire/ plug mismatch problem, and the app Torque reads a P1345 fault which seemed to support a distributor problem.  But after chasing my tail all the way down behind the intake to lose one of the cap mount screws I didn't find any problems with distributor timing or wiring errors.
    Both of the theories of why I can't get the 98 to start and run in order to get it heated up to the point I can get a decent compression check seem to need some additional info from a Scan Tool, which I don't own yet. (at least according to the info presented on Alldatadiy.com, which I'm using for a reference on these matters)   Does any or all this sound familiar to anyone? 

   Which scan tool should I buy?  I don't want to spend any more than I have to but I want to work on my GM vehicles. I'v got a 99 Blazer to get back on the road as my daily driver after I get this Hauler/Tractor working well again.

  Maybe I should be asking this in a tuning forum on this site?

Edited by Kineticarts
It's Saturday night and I like bourbon?
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