MikieG1971

Today driving across Tn and Ar and Ok, I noticed some sputtering and hiccupind and backfiring. My car is a 96 LT4.
In 6th gear running around 70 and 1600 rpms, I noticed that when rolling on throttle the ignition was choppy feeling, not smooth. If I put it to the floor, it would really backfire before spooling up.
Within a couple hundred miles I noticed this sensitivity to low rpm range was beginning to happen in all gears. When taking off from a dead stop the car would sputter and die before accelerating,
By the time I got home to tulsa it hardly wanted to move itself from a start. As I turned into the driveway, it gave up the ghost.
I really feel like this is ignition or vacuum related.
Last year around 7000 miles ago, I replaced the opti, all sensors, ignition module etc.
What are your thoughts?

grandspt

I would first check fuel pressure using the shop manual as a guide. It is very important that the system not only reaches about 42-45psi with ignition on (engine off), but also holds pressure when the ignition key is turned off. My new Delphi pump was defective and caused stumbling, hard starting, pinging and poor idle. It had fuel pressure but apparently no volume because it would not hold pressure when the ignition key was off. It dropped to zero psi immediately.
If the fuel system including fuel pressure regulator and fuel filter check good than you may have an Optispark that is bad.
To me the fuel system is easier to diagnose. My Optispark gave out and threw no codes! But the Optispark caused poor idle and high RPM breakup.
Good luck!

MikieG1971

Fuel had crossed my mind. I have never done anything to the fuel delivery system. Not even changed the filter.
Come to think of it, ever since I owned the car 1.5 years, when ever leaving a stop light under casual acceleration, it would hiccup.
Yes, there are no check engine light or codes present. I think fuel delivery is a very good place to start looking.
Any other ideas or experiences are welcome.

Krusty84

Could be fuel but low RPM stumbles under moderate to heavy load sounds like ignition to me too. Get some dielectric grease and check/re-grease all of your plug wire connections before you go delving into other stuff. If one of the wires wasn't seated properly and backed off a bit, it can/will have the same symptoms.

I had a 2 month long issue with this when I first bought my LS swapped '84 and I was chasing my tail trying to find a vacuum leak. It would stumble at low RPM under load but would clear up and run great in the upper RPMS. One day it got real bad and I limped the car home. I popped the hood and immediately noticed the #3 plug wire just resting on the tip of the plug. I fixed the loose connector inside the boot and it snapped back on and it immediately fixed the issue.

MatthewMiller

It could be a lot of things. First thing: tomorrow go out and cold-start it and drive it for a few minutes. See if it does it from cold. If not, does it start misbehaving after it warms up (~10min, depending on outside temps and how hard you drive it)? If that's the case, then you're probably having a sensor problem. I'd look at O2 sensors and Coolant Temp Sensor in the water pump first. Although in a stock 96, a dead O2 sensor should throw a CEL/code. If you can datalog, do that and see if anything looks flatlined. You may be experiencing a dying coil or Ignition Control Module, too, and heat is making it worse.

Kevova

Codes? OBD2 should have picked up misfire information. A scanner would be handy, There is a ALDL gizmo that ties into a phone app. Most auto parts stores will read codes for free.

MatthewMiller

For whatever reason, the OBDLink ALDL scanner that I have has a hard time connecting my 1996. It works beautifully with every other (later) OBD2 I use it with. Sometimes it works on the Vette, sometimes not. But there seems to be something different, maybe just about the power supplied through that port in the early OBD2 setup.