PLEASE HELP. I HAVE A 1998 CHEVY SILVERADO WITH A 350 V8 5.7 LITER. WHEN I IDLE AT A STOPLIGHT I HAVE A SLIGHT MISS. I’VE TAKEN ITTO SEVERAL MECHANICS AND MY LOCAL GM DEALERSHIP. I WAS TOLD THAT #5 CYCLINDER SHOWS A MISFIRE AT LOW RPM BUT IT IS NOT AN ELECTRICAL PROBLEM BUT RATHER THAT THE FUEL INJECTOR WAS STICKING. CLEANING THE INJECTOR DIDN,T HELP SO I PUT A NEW FUEL INJECTOR IN LEADING TO THE #5 CYLINDER. I ALSO REPLACED THE SPARK PLUGS AND WIRES, DISTRIBUTOR CAP AND ROTOR BUT NOTHING HAS CHANGED. CAN SOMEONE PLEASE HELP. THANK YOU
Please learn to type without caps lock turned on. Thanks.
Well, if you’re still replacing parts, try the coil. I’d take it to another diagnostics shop; maybe it wasn’t #5 …
Thanks for the reply. I will look into the coil.
I am assuming a compression check has been performed on all the cylinders and the the compression on #5 is adequate and within 20 psi of the others. I would next measure the actual valve motions of both valves for that cylinder. With this many miles on the engine it is possible this is a mechanical problem.
Post the compression results and the results of a leak down test (if performed). Hope that helps.
Did the spark plug removed from cyl. #5 look as though that cylinder was not burining fuel consistantly with the other cylinders. The clogged or sticking injector indicates to me that there is a relation to the misfire. The misfire may have resulted in the malfunction of the injector. It indicates to me that it would lean toward a valve function or should I say malfunction. A leaking valve could cause an injector to fault. A compression test conducted properly would rule out the cylinder and could rule in a valve or head gasket problem.
Remove all the plugs and do a dry compression test, followed by a wet compression test… to narrow it down between the rings or valves. Check for moisture on the end of the plug. Test No. 5 first and place a paper towel loosely over the hole and see if any antifreeze collects on it. The plugs should be OEM AC/Delco. I just realized I’m reiterating what Irakus has stated.
I’d also consider using some well insulated plug wire pliers and take #5 wire off while running, checking
for spark and the strength of the spark. And since you were told it was #5, I’d do all sparkplug wires that way. What we’re trying to tell you is to do all the tests you can
eliminating one problem or the other without changing out good parts.
Now if it were dying at a red light, then the throttle body and idle air control (iac) would need cleaning out with a can of carb cleaner and a toothbrush.
I’m assuming there is no “check engine” light, specifically desinating #5.
Thanks to everyone for your input. The problem was a bad fuel pressure regulator. (Hopefully)
A vacuum test gauge can be used to tell if a cylinder’s valves are sticking, which would cause a misfire. The vacuum gauge is cheap, easy to connect, and the Haynes and Chilton’s repair manuals, usually, have a page (or, two) of illustrations showing causes for different vacuum gauge responses. It could be very useful.
Fuel pressure regulator should affect all cylinders uniformly, so if the problem is narrowed to #5, there is still something at that cylinder that makes it most susceptible to a fuel pressure problem.
I would look for a vacuum leak that affects only that cylinder. For example, a failed intake manifold gasket.