84 Sqaurebody 355 swapped

Hello everyone , I know this is a 88-98 Chevy truck forum , but I just recently engine swapped my 84 Silverado with a 355 , it used to start and run fine but now after I start it it’ll die , and when I start it back it runs rough , I’ve checked a bunch of stuff and even bypassed ESC , any tips on what it could be? I’ve added a fuel pressure regulator and gauge , new plugs and wires , I’m just frustrated hope someone can help me , got a car show coming up the 22nd.

95GM said:

Hello everyone , I know this is a 88-98 Chevy truck forum , but I just recently engine swapped my 84 Silverado with a 355 , it used to start and run fine but now after I start it it’ll die , and when I start it back it runs rough , I’ve checked a bunch of stuff and even bypassed ESC , any tips on what it could be? I’ve added a fuel pressure regulator and gauge , new plugs and wires , I’m just frustrated hope someone can help me , got a car show coming up the 22nd.

Click to expand...

Greetings 95GM,

Welcome to the GMT400 forum. Lots of folks in here fix far & wide, but in order to have a chance
of being able to help you, we're gonna need some important details about what's in your engine
bay. Q: Was the engine sourced out of a GMT400? If so, was it a TBI powerplant, or did you
snag a Vortec setup? Is the engine stock, and being run by the matching computer? Or was
it retro-converted to a Carb & big cap HEI setup? What kind of transmission is behind the engine,
automatic or stick? What specific flavor?

The more specific info you can share, the more likely someone who can help you out will respond.

PS: Pictures are the real currency of this forum. Guaranteed a few sharp photos will get more
eyeballs on your thread. Don't be bashful, show us what you have been working on...

A square body going to a show? Yep, pictures are necessary!
Sorry I can't help with the problems, I just dropped in to second the vote for pics! I'll also second the call for more details. We need to know if it's carb or fuel injection. If fuel injection, what type? Where is the timing set at?

CumminsFever said:

A square body going to a show? Yep, pictures are necessary!
Sorry I can't help with the problems, I just dropped in to second the vote for pics! I'll also second the call for more details. We need to know if it's carb or fuel injection. If fuel injection, what type? Where is the timing set at?

Click to expand...

It’s carb , the timing I’ve set to 0° BTC as a starting point , but it ran fine before like about 2 weeks ago but now it’s acting up on me.

Road Trip said:

Greetings 95GM,

Welcome to the GMT400 forum. Lots of folks in here fix far & wide, but in order to have a chance
of being able to help you, we're gonna need some important details about what's in your engine
bay. Q: Was the engine sourced out of a GMT400? If so, was it a TBI powerplant, or did you
snag a Vortec setup? Is the engine stock, and being run by the matching computer? Or was
it retro-converted to a Carb & big cap HEI setup? What kind of transmission is behind the engine,
automatic or stick? What specific flavor?

The more specific info you can share, the more likely someone who can help you out will respond.

PS: Pictures are the real currency of this forum. Guaranteed a few sharp photos will get more
eyeballs on your thread. Don't be bashful, show us what you have been working on...

Click to expand...

It is a 3 speed transmission, a TH350 more specifically, 600 CFM Edelbrock carb , the block is a 70s some block so it’s always been carbed more than likely , it is a HEI distributor using the original distributor and cap to hook up to the ESC , but bypass hoping it would solve the problem but it didn’t.

95GM said:

Hello everyone , I know this is a 88-98 Chevy truck forum , but I just recently engine swapped my 84 Silverado with a 355 , it used to start and run fine but now after I start it it’ll die , and when I start it back it runs rough , I’ve checked a bunch of stuff and even bypassed ESC , any tips on what it could be? I’ve added a fuel pressure regulator and gauge , new plugs and wires , I’m just frustrated hope someone can help me , got a car show coming up the 22nd.

Click to expand...

Here's a few things to check / get the conversation going:

1) Verify that the choke isn't stuck closed or even stuck open. Your description
of the engine behavior matches sounds like a carb with the choke stuck shut --
it starts, but runs rough due to the excessively rich mixture before dying.

2) Step #1 assumes too much fuel is being metered due to the choke mechanism
malfunctioning. At the other extreme, the engine is running rough due to it's
being starved for fuel due to the carb not getting sufficient fuel in order to
keep the fuel level in the carb bowl(s) at the proper level. Q: Do you have a
mechanical or electric fuel pump setup? Is the carb getting both the proper
fuel pressure and volume delivered to it? Is the fuel filter known-good, or
is it possible that the fuel filter is plugged and the fuel isn't making it to the
carb?

3) You replaced the spark plugs. What did the old ones look like? Clean with
slight tan coloring? Or flat black (carbon fouling) wet, or oily? Were you able
to take a pick of all the plugs? (This helps those trying to troubleshoot remotely
move from purely guessing to giving feedback based upon a visual inspection.)

4) Have you verified that the spark plugs are installed correctly? Find the #1
spark plug wire, and run through the firing order clockwise on the distributor cap.
(1-8-4-3-6-5-7-2) You would be surprised how easy it is to mix them up, especially
the #5 & #7 neighbors way back in the back of a dimly lit engine bay.

5) Setting your base timing to 0° is a good, cautious initial setting. The factory timing
settings varied over the years, depending upon compression, camshaft, and even emissions
calibrations. On the old carbureted engines I've seen initial timing set anywhere from
4° to 12°, with 32-34° total at WOT. (initial + mechanical, no vacuum)

Given how much I don't know about your engine from over here, I'd start by adding a few
degrees of timing, and then observe how the engine responds. Essentially you want to add
timing just until you hear the onset of light pinging, and then back it off a degree or two.
(And do yourself a favor, when you find the sweet spot, put the timing light on it and write down
what your engine likes.)

Some will cross check a timing setting by setting for a light pinging at one spot on the rpm band
on say, 87 octane gas, then switching to 89 octane gas and having the pinging disappear completely.
And then running on 89 every day.

DISCLAIMER: I share the above as an old school tuning technique, assuming a reasonably
quiet exhaust and you don't have the ESC in circuit during the tuning effort. (ie: You can't
hear the pinging over the open headers or the knock sensor is pulling the timing out as
you are adding it in.)

In English, 0° initial timing is probably going to lead to sluggish performance. For an unmodified
stock engine, the factory setting is the safest overall compromise. For a SBC assembled from a
unknown spread of stock and aftermarket parts, an optimum initial timing and spark advance
curve can be derived by a hobbyist like those reading this forum, but it takes a careful approach
of making small incremental adjustments followed by listening carefully to the engine, watching
the spark plugs for peppering, etc.

To summarize this whole spark timing thing, you gotta be careful, for the SBC will respond
favorably to more & more timing...right up to the point where we get greedy and we get caught.
If you aren't familiar with the story of Icarus, let's just say that too much timing = flying too
close to the sun. (Wax wings :0)

6) Having just scratched the surface of #5 above, and yet at the same time this writeup becoming
too long for most people to wade through in a forum like this, this is where I need to stop and
ask if you have access to a local mentor who might be able to help you sort this out? If you or
your buddies have a dad/mom/aunt/uncle/grandparent who has a history of successfully tinkering
with cars, reach out to them. You might be surprised when you see that old dormant competitive fire
light up their eyes. 'nuff said. :0)

****

I didn't even bring up all the troubleshooting stuff like air bubbles in the radiator when the engine is
running, low oil pressure, and all that. I assumed that based upon your comments that the engine
is basically healthy, but has decided to give you the business instead of running on your timetable.

Try to verify the 5 steps above, and here's hoping it's something simple that's easily fixed. And
welcome to the old truck hobby. If you are like me, they will provide you with decades of pleasure
in exchange for you figuring out what makes them run well and giving them what they want need.

Best of luck. Hope you get to take your ride to the car show. And be sure to take pictures & share
them so that we can live vicariously through your adventures. It's what we enjoy doing here in the
GMT400 forum.

Cheers --