Auto Parts: stalls @ driving & sometimes poping noise, spark plug wire, manifold vacuum

Question
i have a 1991 s10blazer 4x4 4.3L v-6 TBI,fuel injected. Every time i am driving usually at 40-50 miles per hour theres always a hesitation on the motor, like a grunting noise or something and it keeps on poping and usually when i barely hit the gas it starts to grunt and i simply dont know what it is, no engine codes, and i dont know what it is, Please help!

Answer
Hi Sergio,

Since testing yourself doesn't cost you anything but time, and your computer is not warning you of a problem via service light (code), here is my suggestion:

You should start by checking the fuel spray pattern. Attach a strobe-type timing light to the coil wire if possible or any other spark-plug wire, aim it into the throat of the throttle body and observe the fuel spray pattern of the injectors as the engine is idling. If the pattern looks consistent and shaped like an up-side-down funnel, check the engine timing, you should still have the timing light in your hand so why not. If that is spot-on then move on to the next test.

Charge the battery fully while letting the engine cool completely. Remove ALL of the spark plugs. Disconnect the ignition hot-wire to the coil and block the throttle WIDE OPEN. Attach the gage, one-cylinder at a time and crank the engine over for a count of five-seconds. Record the results and move on to the rest of the cylinders recording the reading each time. All numbers should be within 15% of each other, if they are not, you have mechanical issues that will need to be dealt with before any other issues are addressed.

'Popping' sounds usually indicate sticking valves. So if all other items checked out fine, attach a vacuum gage to a MANIFOLD vacuum port and record the readings you get at idle. You have to know how to read the results a vacuum gage will give you so if you are uncertain how to decode the data, keep good notes and submit a follow-up question. Record the fluctuations of the needle, the amount of vacuum at the high and low points, when does the needle fluctuate, does the needle fluctuate to more than one pattern, etc. take good notes, a vacuum gage can be an invaluable tool for diagnosing engine mechanical problems.

Thanks for the question, I hope this information is helpful to you.
Fred
www.knucklebusters.us
570-453-0910