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Old 03-03-2021, 04:03 PM   #1
Mini-Skoolie
 
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1999 Chevy 350 engine

I am wondering if it is worth rebuilding or replacing my 350 engine and transmission. They have over 185k miles on them. I can already notice it doesn't run correctly or shift correctly. Since the mileage is so high, I was going to either rebuild or replace.

Is there a better built 350 engine today than in 1999? What would generally be the best? I'm just looking for a good quality engine and transmission that is going to last another 185k + miles.

I have a 1999 Chevy 5 window school bus.
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Old 03-03-2021, 04:13 PM   #2
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many of good options out there for both especially if you can do the swap yourself even buying a reman or having yours remanned.
the bonus of using yours is a reman then you can add more HP if you want it and the tranny you can have a shift kit put in it to help with smoother and less notable shift point and so on.
what do you have
where are you located.
i have built many a 350 for all kinds of purchases but i had to pull the 350 out i would look into a 396/400 upgrade
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Old 03-03-2021, 04:39 PM   #3
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Sadly, GM just doesn't build 'em like they used to... And they haven't for quite awhile, say about 10-15 years.

One common problem with the 5.7L Vortec you have is intake gasket failure. Some GM engines of that vintage were also known for what is called 'piston slap', where pistons were undersized and would literally 'rattle' or 'knock' inside the bores as they traveled up and down.

Transmissions are also a crap shoot with GM, and as stated earlier, have been for awhile. You don't state what you actually have, but a 1999 could be a 4L60E, 4L80E, possibly a 4L85E.

One common issue with late-model GM transmissions is that people assume Mercon-Dexron is okay to use in them, and that's not necessarily true of all models. Dexron has gone through a few evolutions, last I knew was Dexron V or VI, which is a pure synthetic and transmissions requiring it will have problems on regular Dexron, as they need additives not present in earlier formulas.

Unfortunately, the 1999 has enough computer controlled crap on it that it really cannot be swapped for anything else unless you shoot the moon and put a full mechanical setup in it, which is not wise, as it will drive the electronics controlling the rest of the vehicle nuts and cause other problems.

However, one common issue with the 5.7L Vortec that a surprising number of people are unaware of is the injection block failures. They are very common, and most people think they need a new engine when they just need a new injection block. These are called 'spiders' because they have plastic legs joining the injectors to the metering block, and the V8 models, they look like, well, a spider.

The plastic lines get brittle and crack over time, and cause fuel pressure issues that can cause any number of problems, including hard starts, black smoke, poor idle, poor fuel mileage, and generally poor driveability. The irony is, this is typically a $400-$800 job that can be done in a day. But if left unchecked, it can and will destroy your engine by diluting oil with unburned fuel. It can also lead to emissions problems.

And these Vortec setups are also known for fuel pump issues. They are like a diesel in that they are very picky about fuel pressure and will not run right if it does have the correct range of pressure.

Easy way to check this is to get a known good fuel pressure tester. Your pressure test port should be on the rear of the engine next to the distributor, and with a cutaway it is best to remove the engine cover and 'dogbox' for easy access. Pressure numbers on a good unit should show 62 psi priming (key on, engine off), and once the engine is running, it should show at least 58-60 psi idling, and should not fluctuate even when revved. These things are picky enough that they will not run right from 55 psi down. And I've heard of a few that flat would not even start with less than 50.

But don't condemn the spider on initial fuel pressure discrepancies. This can also be caused by a weak or bad fuel pump. I have seen them bleed pressure back through the pump into the tank, though much more quickly than a leak in the spider.

And just because it shows normal pressure on prime and idling does not mean it's not the problem. The system should also be tested for leakdown, which was my problem when I had a Safari van with one. System pressure will drop to about 58 on shutdown and should remain there regardless of elapsed time.

On that one, with the engine and related components warm, it didn't drop right away. It didn't even show a drop within 5-10 minutes. Two hours later, it had dropped to 40, bottoming out at 20 before another hour passed. With the system cold at 3 am, I reprimed it without starting the engine and I could watch the pressure drop on the gauge, 1-2 psi every other minute or so.

The symptoms displayed can be (but not limited to):

Black smoke from exhaust, especially on startup or acceleration
Spitting, sputtering, unevenness at idle
Hard start (excessive cranking)
Worse fuel economy than usual
Engine oil smells like fuel

The key indicators I observed were:

Hard starts that were helped by opening the throttle (you should never have to touch the throttle to start a fuel-injected engine)
Black smoke from tailpipe on startup
Uneven idle / spitting, sputtering that cleared on acceleration

Essentially, when these lines crack and leak fuel, they flood the intake, drowning the cylinders in fuel on startup. And because the injection spider is inside the intake manifold, the only way to know is to check the fuel pressure for static pressure, fluctuations and leakdown.

And this could be part of what's causing your transmission to act up. A flooding engine will bog and surge, which can confuse the transmission control software. A bad throttle position sensor can also cause this.

So if you have a check engine or service engine soon light on, check the codes. A P0420 indicates a catalyst problem, potentially an end result of this problem. Other codes that can indicate this would be Bank 1 or Bank 2 Rich Mixture / Too Rich, or Random Misfire / multiple cylinder misfire codes (generally P0300-310). An intake gasket failure might cause skipping / stuttering from coolant entering the cylinders, and could also cause a lean code on Bank 1 (left side) or Bank 2 (right side), even a specific cylinder misfire. The Vortec ignition distributor has also been known to wear or strip its drive gear and jump around, altering ignition timing.

Yours could have one or more of these issues. There could very well be nothing wrong with it that $1000 won't fix. Cheaper than a new engine and trans, and as much electronic control as there is on a 1999, it's cheaper to fix small problems before they cause big ones.

One more thought, there is a marine intake for the 5.7 used in Mercruiser and other boats that can physically replace the crappy plastic intake / spider setup, but some modifications are necessary. I doubt the injector wiring will mate up without modification, and the intake will have to be modified to accept an EGR valve. You could just ditch the EGR, block off the tubing and reflash the PCM to turn off the Check Engine light, but I don't recommend it. Bypassing emissions controls is often more trouble than it is worth.
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Old 03-03-2021, 04:59 PM   #4
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yeah i dont play with much new stuff anymore and when i heard 350 chevy i got excited and didnt even think about the computer mess.
but a full rebuilt long block and short blocks are still available or the OP could have his rebuilt with all the aftermarket upgrades to fix the original problems.
but you have a good point CW about the stuff that could be checked and fixed to keep the motor alive for another 100,000?
i dont know where i was at when i was thinking 99 was an all mechanical?
yeah i do? in the shop building drag strip motors.
sorry OP i got lost for a minute.
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Old 03-03-2021, 05:05 PM   #5
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It's okay, JollyRoger... I only know these things because I had a Vortec 4.3 (essentially the 5.7 missing two cylinders). Honestly, 350s had few, if any problems, before the arrival of the PlastiCrap I speak of. They're still good engines, just a little higher maintenance than they used to be.
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Old 03-03-2021, 05:18 PM   #6
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. I updated my post. I have a 1999 Chevy 5 window school bus
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Old 03-03-2021, 05:25 PM   #7
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So it sounds like my best option really is to just rebuild the engine and transmission? I wasn't sure if I could buy a new engine from Summit or Jegs and just drop it in.

I would definitely like to go old school on the engine and transmission and just drop in something from the 60s or 70s. I have 2 engines just rebuilt sitting on engine stands waiting to go into my 66 GMC truck and 67 Chevy wagon.
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Old 03-03-2021, 05:57 PM   #8
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as CW mentioned the computer mess will be a nightmare to go old school especially if you have the hydro boost brake steering mess.
a reman will not come with the plastic air intake and all the other plastic BS that if it isnt giving you problems right now it will.
as well as the all the vaccum mess.
so if a rebuilt motor is in your future then while it is out is the time to replace all the vaccum lines and change the air intake from the plastic to aftermarket.
sorry gotta run need to go look at aproblem with a supercharged thunderbird that just pulled in my driveway.
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Old 03-03-2021, 06:02 PM   #9
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Quote:
Originally Posted by Jolly Roger bus 223 View Post
as CW mentioned the computer mess will be a nightmare to go old school especially if you have the hydro boost brake steering mess.
a reman will not come with the plastic air intake and all the other plastic BS that if it isnt giving you problems right now it will.
as well as the all the vaccum mess.
so if a rebuilt motor is in your future then while it is out is the time to replace all the vaccum lines and change the air intake from the plastic to aftermarket.
sorry gotta run need to go look at a problem with a supercharged thunderbird that just pulled in my driveway.
It's a Ford. At least they circled the problem.
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Old 03-03-2021, 06:04 PM   #10
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Quote:
Originally Posted by Ivanhggs View Post
So it sounds like my best option really is to just rebuild the engine and transmission? I wasn't sure if I could buy a new engine from Summit or Jegs and just drop it in.

I would definitely like to go old school on the engine and transmission and just drop in something from the 60s or 70s. I have 2 engines just rebuilt sitting on engine stands waiting to go into my 66 GMC truck and 67 Chevy wagon.
No, your best option is to have the vehicle properly diagnosed to see whether the engine and transmission really are the problem. Read back through my post and you will see several known common issues with these that could be much cheaper than an engine or transmission rebuild / replacement. And dropping in something old school will create ten problems in eliminating one or two.
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Old 03-03-2021, 06:18 PM   #11
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really.
i grew up with ford for work and chevy to play. at least chevy polishes there turds with a bowtie to sell them? oh how cute it has a bowtie?
the OP mentioned he had old dodges which were Bad A.
in my opinion anything with a computer involved can and will cause motor/engine problems that dont exist just because a sensor fails and is telling the computer it failed so we do this type of mess?
they have made them where only the specific dealer can work on them and even my local ford and chevy dealer stocks parts and parts books for anything in the last 10 years?
when i asked my local parts stores to pull there books out from under the counter and let me find what i want they look at me wierd cause some didnt even know the books were there.
sorry OP i got on a little rant but i will shut up now
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Old 03-03-2021, 06:43 PM   #12
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I think I may have confused you guys. What I am meaning to say is, my bus has very high miles on it. I want to either rebuild or replace the engine. I want to start out with no miles on my bus. This way I can enjoy it for several years before I have to replace or repair it. I was just curious what the better option would have been. Replace the old engine and transmission or rebuild them. Either way, i would rather it was done. Thank you Jolly and CW
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Old 03-03-2021, 06:48 PM   #13
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Quote:
Originally Posted by Ivanhggs View Post
I think I may have confused you guys. What I am meaning to say is, my bus has very high miles on it. I want to either rebuild or replace the engine. I want to start out with no miles on my bus. This way I can enjoy it for several years before I have to replace or repair it. I was just curious what the better option would have been. Replace the old engine and transmission or rebuild them. Either way, i would rather it was done. Thank you Jolly and CW
I get where you're coming from, but it simply may not be necessary. Vortec or no, the 350 has a long history of the ability to be patched up with zipties and baling wire to limp it home when it is in trouble, and otherwise runs a long time without issue. I really think you're setting yourself up to spend a lot of money that isn't necessary and might be better spent on a few simple fixes with the rest going into your build.

I would say the transmission is more likely to give up than the engine, pending proper diagnosis of course. To illustrate, I saw a Chevy 1500 with a 305 that had 375k on it, and was driven to a junkyard during Cash For Clunkers. Nothing wrong with it, just some misguided yokel taking advantage of a government program.

Another way to look at it is this -- The $6500+ you'll likely spend rebuilding / replacing the engine / transmission would likely replace everything that is much more likely to need replacement, such as springs, shocks, steering / suspension components, radiator, alternator, etc. And I'd be willing to make a wager that all of those will fail long before that 350 will.
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Old 03-03-2021, 07:11 PM   #14
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I see what you're saying. That makes good sense too. More or less I'm going to be getting to those items as well. My last trip almost ended in disaster. Heater hoses blew, radiator started to leak, engine would overheat, transmission didn't want to shift all of the time.

While the engine and transmission are out, I can address everything else. I may even install a new heater core just to be on the safe side
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Old 03-03-2021, 07:26 PM   #15
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what is your symptoms sir?
we need to know how its feeling in your opinion?
that mileage on a well maintained motor isnt scary.
why do you think its tired?
and i am not a fan of computer stuff but you could also if also obd 2 then swap an LS engine into it as well. the caddy cts versions have the higher hp engines.
but you need torque and horsepower so choose and or build the correct motor.
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Old 03-03-2021, 07:43 PM   #16
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The guy i bought the bus from didn't seem like the type to take care of things. The tranny slips from time to time. Over heating was a big issue. Sometimes it's really hard to start. The A/C unit is bad.

I am totally ok with a new/ rebuilt engine. I have cash set aside just for this. I was originally going to spend $15k on a school bus. I got this one for $5k. The new engine and tranny will get me places without too much worry. Everything else is just small stuff I can do anytime.
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Old 03-03-2021, 07:50 PM   #17
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I see where you're coming from, but you might do just as well with good used units from a reputable salvage yard, and some even install what they sell. The 350 is pretty generic from model to model, even through its evolutions from carb to TBI to CSFI. You might just luck out and get a clean 70k engine and trans from a wrecked Suburban 2500 that will work in your '99 for half to one-third the cost of of new / reman. Case in point:

When I bought a police Impala that turned out to have a shot engine, I found a replacement 3800 from a clean one-owner Buick that had 46k original miles. $1850 installed and I never looked back. That car NEVER saw a tow truck from the time I bought it in 2016 to the time it was totaled in 2018, I put over 40k on it, and I still had a bit of a leadfoot, I've calmed down since then.

*EDIT / UPDATE* I found a 97 350 from a 2500 pickup with 40k for $1000 near me. Shop around if replacement or rebuild are really necessary.
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Old 03-03-2021, 08:14 PM   #18
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where are you located?
only trying to help?
lkq pick your part is almost nationwide and will bring it to you if need be.
engine and transmission if needed.
if this vehicle is new to you and you said the previous owner wasnt the maintenance type and you say the motor feels lazy and the tranny slips sometimes?
why not try some basic maitenance with the engine like plugs,plug wires,dizzy cap and rotor. tranny fluid and filter change.
try the 200$ refresh before you go the 3-4000$ route?
all the stuff as mentioned before like vaccum line or cracked intake manifold or any EPA stuff could be clogged and holding it back.
if you have an android phone.
they dont support apple yet.
BFX products has an OBD 2 scan tool that links to your phone for 20-30$
you cant change parameters but you can see everything the computer sees and you can clear check engine lights and watch the parameters while driving down the road while trying to clear the check engine light the 60 or whatever miles and you can set a custom screen to display what you want to see.
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Old 03-03-2021, 09:27 PM   #19
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Thanks you guys. That info was really fantastic. I'll look into those suggestions.
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Old 03-10-2021, 05:16 PM   #20
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I tend to buy a used engine of the same type and year and rebuild that, so that I do not have the vehicle out of service for long. However if you do not need to drive it for a bit I would pull the current engine and trans and rebuild or have them rebuilt by a local shop that has a good reputation. Or do it yourself but have a machine shop do the machining on the block and heads.
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