Alright so decided against my better and I bought a 383 crate engine. Got it all wrapped up now can’t find anyone to tune it. Any suggestions? Know a tuner said can’t do it nothing obd1, another said same thing. Not many choices here in North Dakota
It picked up a surge at idle now and dies randomly when put in gear. This is my family hauler I need all nine seats to get us around. Thank You for any help.
Greetings BigIron002,
Welcome to the GMT400 forum. This space is full of enthusiasts for this generation of GM's
work/play vehicles. There's plenty of folks who can share their own hard-won experience derived from
doing similar things to their rides.
The thing is, I am only aware of the details of your drivetrain that you share with us. And speaking for
myself, I hate to guess (especially in public) when other people's tiime/money are involved, so don't hesitate
to share any/all details that might help us help you.
****
Let's define the problem in front of you.
* First of all, the OBD1 TBI setup does not
directly measure the amount of
air ingested into your engine. Instead, your computer is filled with VE (volumetric efficiency)
data organized into tables describing how much air was drawn by the stock engines on GM dynos
while undergoing various speeds and loads. (aka: Speed Density FI)
Depending upon your real time RPM + MAP (Manifold Absolute Pressure) + TPS
(Throttle Position Sensor) sensors, your computer will index into the factory
data tables, infer the amount of air drawn in, and then end up with the correct amount of time (in milliseconds)
to pulse your fuel injector...for your
stock 350 drawing in air based on the
stock heads & camshaft.
(Note: The above is an oversimplification, for other sensors are used to help further accuratize the
fuel delivery, but it's close enough to support where I'm going.)
* Second, in terms of physical displacement, the
383 is only
33ci larger than your
350. That's just
9.4% larger in terms of gross displacement. IF you were using the same stock heads & cam, I would
bet that in pure Open Loop mode (ie: running just off the factory tables) that your engine would run
a little off (lean stumble, etc) *until* the O2 sensor warmed up, you went into Closed Loop, and then
with the help of the O2 sensor influencing the short/long term fuel trims in the right direction, then
given how much the system is allowed to locally add/subtract from the factory defaults, again I wouldn't
be surprised that in Closed Loop operation the 383 would end up running pretty decent. (See attached
to explain the translation of OBD1 vs OBD2 fuel trim terminology.)
* So far so good, but a lot of times when someone steps up to the 383 solution, better breathing
cylinder heads & larger camshaft are included to make the most of the physical displacement increase. With
these upgrades, the engine is able to ingest more air than the TBI setup is able to retune itself to.
In this case, there is a variety of fixes, as
@Drunkcanuk listed previously:
From cheapest to most expensive.
-Get a chip burner, start data logging and burning chips.
-Switch to a EBL Flash 2 ECM, they take your stock ECM and modify it to allow it to be tuned.
You would still have to tune it yourself or get someone. A few here have gone this route.
-as @Sean Buick 76 said, switch to a completely aftermarket fuel injection system.
Since you indicated that "you wanted to put hands on it", to me it sounds like having your existing
TBI computer modified so that you can dynamically tune it yourself (EBL
Flash 2 ECM) might actually
be the best fit. Sure, the aftermarket FI systems automagically tune themselves, but not all of them
include highly desirable safety net features like an operational Knock Sensor.
Here's a link to the EBL web page: (
EBL for TBI systems)
****
To summarize, it's not like you have upgraded from a 4.3L V6 to a 7.4L big block. You've added <10%
of physical displacement plus an unknown cylinder head & camshaft upgrade. If you could tell us which
383 crate motor you purchased we might be able to figure out where your stock computer is flummoxed
and why. And if you have the interest in learning this for yourself, then investigate which self-help method
is the best fit for your situation. And we've got some serious talent in here that's already been down this
path with their own rides, and should be able to add valuable insight as to the tuning process.
One last thing. A lot of people will tend to cr@p on the late '80s TBI setups, just like others just can't say
enough bad things about the '60s-'70s Quadrajets. For me, in both cases the more I study what the
engineers were trying to accomplish, the more impressed I become with what they did with what they had
to work with, technology-wise. Especially with the built in self-diagnosis features they included back then.
(That today's 2024 aftermarket don't do...but then again a lot of these systems are "for off-road use only.")
As a matter of fact, I'm not trying to disparage the aftermarket stuff. Some people get great results from
using them -- others not so much. And I'm not trying to steer you any particular way, but instead would
have you explore all possible solutions and then decide which way you want to proceed. If this was a pure
toy I know that I would push towards the self-help tuning/learning experience...but if you need this *now*
in order to move precious cargo (family) then maybe paying someone to put the 'right-now' fix into your
engine bay is the better answer.
****
And we're always about more detail/more photos. If you could tell me all the times that the current (stock)
TBI setup gets it right (ie: all warmed up, cruising down the highway) vs when it gets it wrong (cold engine,
dies when going into gear or stumbles away from the stop light during Open Loop operation) ...then the
better we'll understand the problem that you are trying to solve.
Hope this helps. Safe travels!
