Hi guys,

I did a tune up on the truck as it was due for some fresh plugs and wires. I wasn't having any misfires or there was no obvious sound or check engine light coming on but the fuel mileage was pretty bad and down to around 10-12 mpg at best. After doing the plugs and wires it sounded good as it did before but no change it mpgs so just tinkering around I decided to check the main ignition coil pack. I connected my timing light to each of the wires coming off of the coil pack one at a time and 1-3 on one side had a continuous flash from the light but on the 4-6 side the #5 wire was flashing but has a pause every couple of seconds, the light stops flashing for a period and comes back on. Is this a normal timing event or is the coil becoming weak? As far as I know and by the looks of it the current coil is still the original one.

Thanks

 

1-3 and 5-4 side

3 4
2 6
1 5
Front

There are only 3 coils in this coil pack, each fires 2 spark plugs at the same time
3 and 4
2 and 6
1 and 5
fire at the same time

So timing light should show 1 spark each RPM, instead of every 2 RPM, and the 5 6 4 side is reverse spark, which might not read well on some timing lights, spark travels from engine to spark plug wire and back to coil pack, i.e. spark is tip to center instead of center to tip(normal)


Drop in MPG can be a few things
New tire size?
Older upstream O2 sensors, 100k plus miles old
Leaking fuel line
New kid in the neighborhood with siphon hose, lol

 

Yes I think it's probably alright still but I know it is old. Iv'e installed magnaflow stainless high flow cats around 5 years ago so I think they are fine. Sometimes on start up I get a check engine light for P01444 and if I run the truck up to 70+ the check engine light comes on for that same P01444. Iv'e heard if the purge flow valve sensor is bad that would cause poor fuel mileage so I just picked one from the dealer today and will install. The O2 sensors were also replaced with the cats back then as well.

Thanks again RonD