No drop in idle RPM after pulling #1 spark plug wire

lep · 01-26-2008, 06:13 PM

Recently, I replaced a fuel filter in the engine compartment and after installing the new one, the bowl never seemed to fill up when running. In addition, it seemed that one of the cylinders is not firing (for example, at idle). Interestingly, I alternated through each cylinder and pulled the spark plug wire when at idle. After pulling the wire for cylinder #1, nothing changed. There is incredibly spark at #1, and no reason why the dwell or timing were drastically changed to prevent #1 from firing. I think what is happening is that either the fuel hoses have lost their integrity (seal) or the fuel pump is failing. One thing is certain: if there was less fuel getting to #1, then pulling the spark plug wire and not noting a drop in RMP could mean there is not enough fuel there in the first place. With such a strong spark to #1, I doubt that the timing is so far off that it would not result in an RPM drop when the wire is pulled.

What could possibly be happening if RPM does not drop when I pull the #1 cylinder plug wire? Do I need to install new fule lines, get an electrical fule pump, etc.

lep

Scott Douglas · Scott Douglas's Garage

I'd check the idle jet first. Sounds like it's plugged up.

lep · 01-27-2008, 09:40 AM

thanks - will give this a try.

Jim Chambers · 01-27-2008, 10:10 AM

Could also be a badly fouled plug in the #1 hole. If fuel is the problem it will be carb related, not fuel line or pump. The clear plastic fuel filters never seem to fill completely.

lep · 01-27-2008, 08:32 PM

Today I remobed each idle set screw and inserted a spray hose from a can of 3m carb cleaner -- then cleaned out the idle inlet. After that, it ran like a charm.

Thanks for the tip.

lep · 02-02-2008, 02:00 PM

Thanks for all the recommendations. The most important observation was that the idel jets were clogged. After unscrewing each idle jet screw and spraying carb cleaner inside the jet hole, here was noticeable improvement.

I am also going to use an electrical fuel pump in addition to the manual - which has been recommended by some.

Last, someone said the shelf-life of today's alcohol based gasolines are essentially 72 hours. Thus, I believe that taking a Porsche out for a Sunday cruise will result in gummed up carbs, etc. It was recommended to me to use a product called "Stable: for the gas.