Engine miss

[Jim-n-Texas]

I have fuel (35# at the rail), new fuel filter, new injectors -- I have spark (new rotor, cap,plug wires and plugs) -- I also have a miss (at all speeds) -- in the process of cleaning all connections on the FI system - don't know where to go next. Ideas?(or experience?)

[Pomorza]

Jim,

What kind of miss? Is it a miss fire as in the engine, (poor firing, hesitation type thing) or is it in the intake (like a popping noise). Both are never good but if its the latter (popping in the intake) you maybe running lean. Remember just because you have propper fuel pressure does not mean you have propper volume of fuel entering the combustion chamber. With old FI system like the one in 76s (I have one) the electronics tend to fade over time and lean the heck out of the mixture.

To really understand how the old L-jet fuel injection works on Z's I've included a link (TADA). Its of an old manual I found someplace on the net when I first got the car. I used it constantly when I had the old L-jet system to make the car run better. I finally had it set and running the way I wanted and then the wiring finally started taking a crap:mad:. Go through it and see if you've done everything suggested. For reference, throwing parts at a miss with these cars rarely ever fixes them unless you know exactly what the problem is. (I learned that the hard way)

Hope that helps

Jan

Edited August 17, 2012 by Pomorza

[Wade Nelson]

Start by checking vacuum. That will give you an indication of the health of the valves, rings, mechanicals.

http://www.classictruckshop.com/clubs/earlyburbs/projects/vac/uum.htm

Chances are VERY good you simply have a vacuum leak somewhere, and that unmetered air is what's causing your miss. One very fast way to find it is to smoke the manifold, using a tool only a shop will have --- a smoke machine, that pressurizes the intake manifold to 1-2psi with smoke.

Pull off all the rubber boots between the air cleaner and the throttle body, clean, and inspect using a bright light to find cracks in the bellows, etc.

See if you can get rid of the miss (a lean miss) by adding faux fuel.

If not, attempt to identify the cylinder misfiring -- pull plug wires, or find a shop with an old-tymey "Engine analyzer" --- oscilloscope. 30 seconds to show which cylinder has the problem.

Modern vehicles (OBDII) all do misfire detection automatically, and report it to scan tools, so finding a guy who knows how to use a scope (and has one) may be a challenge. Ask around, ask one shop what OTHER shops might have a engine scope.

http://www.governmentauctions.org/uploaded_images/engineanalyzer-778764.jpg