1991 suburban is missing bellow 35mph

[apisraelson]

My 1991 suburban is missing bellow 35mph at higher speed it runs fine it has new cap, roter, plugs and wires,
dose anyone have any ideas what is going on.
thank's.

[Ryan685]

Was it missing out before you replaced the cap,rotor & wires etc?

Take each spark plug out (again) one-at-a-time and look at them. You need to know what cylinder is not firing and why. There are many possibuilities. For instance, a bad injector on that one cylinder will cause it to not get fuel. Once the engine gets above a certain rpm you just don't feel the miss but it's still there. If one cylinder was low on compression, it would also miss out as you describe. A leak-down test would determine the condition of the engine. A leak-down test is different then a compression test. Leak-down testing will determine where the leaking compression is going. Valves, rings, head gasket etc. If you or someone can do a leak-down test on the suspected bad cylinder. That cylinder's piston is brought up too it's compression TDC (4-stroke, intake-compression-fire-exhaust) An air fitting is screwed into spark plug hole. The leak-down tool measures psi of air lost in percentages. I think 6% is bad for any engine but some people like to see double digits in loss before they start to spend money.

[apisraelson]

It turned out to be a durty injector. It runs good now.