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Username Post: L03 TBI Missing at low throttle around 50mph cant get to bottom of it        (Topic#369697)
Chevyman Sheffield England 
Posts: 2

Reg: 10-05-22
10-07-22 02:53 PM - Post#2848216    

Cant believe I havent joined this forum earlier!

Ive got 2 Lt1s, 2 L03s, a 502 gen 6 bbc and a 433 gen 4 bbc.

Im pretty handy with these things and carb tuning but my L03 TBI is causing me grief. Car is a 93 caprice station wagon.

Engine is stock, timing 8adv, replaced plugs and wires thought maybe leads breaking down.

Issue is at light throttle at about 50mph it starts to miss its quite harsh, but if i step on the gas a bit it pulls itself through. No engine light, starts every time, can drive anywhere in it, engine is strong no smoke, sits just below half on temp gauge when warm. I dont want to just throw money at replacing parts unless I have to.

I do find 99 octane fuel reduces the problem when Im not running 95 but its still there this top gear low throttle missing. My gut tells me its possibly a little too advanced because as soon as I get on the gas a bit it picks up well, but then 8adv is hardly radical? EGR system still in place, everything stock, anyone had this or got any ideas? I dont even want to retard it as everywhere else in the range it drives/runs so well



Valued Contributor
Posts: 3376

Loc: Lake George, NY
Reg: 11-11-15
10-07-22 04:42 PM - Post#2848221    
    In response to Chevyman Sheffield England

Is this a 4sp auto trans, if so this could be the torque convertor "shudder" in lock up, it can mock a light load misfire. This can be a tough diagnosis. Have you driven the truck and watched o2 activity on the scanner, a skewed sensor can cause this as it drives the ecu to the lean side. No quick answer here.

Frequent Contributor
Posts: 2448

Loc: Orlando Florida
Reg: 07-09-18
02-28-23 06:11 AM - Post#2855170    
    In response to Chevyman Sheffield England

A vacuum leak will show up at idle and low speeds like you are mentioning. It will be worse when under some type of load. You will need a scan tool to monitor fuel trims and also check for misfire counts.

That GM OBD I system has great data points and you must have a proper scan tool to diagnose the issue.

People fear change because it threatens what they know, or what they claim to know.

Super Senior Member
Posts: 6625

Loc: paradise
Reg: 09-05-03
03-04-23 10:18 PM - Post#2855346    
    In response to Chevyman Sheffield England

uh, if you cant scan and read real time data. your gonna throw money at it.

70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails.


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