Misfiring again, full tune-up?!

[Drac Morbis]

It was misfiring on cylinder 5 some time ago. A new spark plug, coil, and injector cleaning fixed it. It ran like a race horse for months and months. Now it's misfiring on cylinder 3. The mechanic I use said he'll do a full tune-up this time, all new spark plugs, plus a new coil for number 3. And the usual other stuff.

Is this good? Do I need all the coils replaced?

I don't know anything about vehicles. lol

Thanks!

 

[Gary Waugh]

Make sure he does a compression test on all the cylinders first, you might have a failed head gasket or damaged valves on that cylinder, in which case new coils and plugs are a waste of time & money.

 

[Drac Morbis]

Make sure he does a compression test on all the cylinders first, you might have a failed head gasket or damaged valves on that cylinder, in which case new coils and plugs are a waste of time & money.

Thanks! Is that expensive? Or is it a standard test?

 

[Gary Waugh]

It’s not expensive, just a bit time consuming to remove the spark plugs and then measure the compression on each cylinder. Takes about an hour to run the test on all 8 cylinders. Once you know compression is good then he can look for other faults, but having good compression is the first thing you need to check.

 

[Drac Morbis]

It’s not expensive, just a bit time consuming to remove the spark plugs and then measure the compression on each cylinder. Takes about an hour to run the test on all 8 cylinders. Once you know compression is good then he can look for other faults, but having good compression is the first thing you need to check.

Awesome, thanks! I'll be sure to mention it to him.

 

[texasscot]

It was misfiring on cylinder 5 some time ago. A new spark plug, coil, and injector cleaning fixed it. It ran like a race horse for months and months. Now it's misfiring on cylinder 3. The mechanic I use said he'll do a full tune-up this time, all new spark plugs, plus a new coil for number 3. And the usual other stuff.

Is this good? Do I need all the coils replaced?

I don't know anything about vehicles. lol

Thanks!

I think i've fixed my random misfire/rick condition problem by changing out the injectors. I'd tried cheap ones and got similar but different problems. Just put in the Motorcraft injectors and tested it this morning. It's now a sewing machine. My vehicle is at 295,000 miles. Maybe your injectors are bad. Test the key on fuel pressure at the rail and also at the pump. if the rail value drops quickly and the pump value doesn't, your injectors are probably dripping fuel causing misfires.

 

[Drac Morbis]

I think i've fixed my random misfire/rick condition problem by changing out the injectors. I'd tried cheap ones and got similar but different problems. Just put in the Motorcraft injectors and tested it this morning. It's now a sewing machine. My vehicle is at 295,000 miles. Maybe your injectors are bad. Test the key on fuel pressure at the rail and also at the pump. if the rail value drops quickly and the pump value doesn't, your injectors are probably dripping fuel causing misfires.

Thanks much! What about all new coils as well?

 

[texasscot]

Thanks much! What about all new coils as well?

I find coils fail individually. If I get a misfire attributed to a cylinder I’ll switch that coil around for one of the other ones and then clear codes and run it. If the misfire comes back and followed the coil then bingo.