Ok, havent been on here in a long while and havent posted in an even longer time. Been very busy with work. Anyway to business. I got a little problem with the truck running rough like it is missing. No CEL cylinder 5 is weak but fires 1 has fire but like it has no power. All the rest of the cylinders are strong. A time ago it was 5 with no power and spark and 1 was weak with spark. Now it will act up or run rough from what I can tell from accelerating normally. if i creep up on RPMs it wont miss but if I accelerate normally as soon as it goes into overdrive it runs rough. Ohmed the coil coil appears to be good.Got good even compression on all cylinders. Got me stumped any help would be greatly appreciated on this.

 

spark plugs/cylinders 1 and 5 share the same coil in the coil pack, they are a matched pair, both are at TDC at the same time, one on compression stroke the other on exhaust stroke.

There are 3 coils in the coil pack
[3 4]
[2 6]
[1 5]
front

OHMing a coil will tell you if it is bad, but not if it is good, one of the issues when dealing with low ohms.

Each coil in the pack is hooked up to the spark plugs in series, so one spark plug sparks from center to point the other from point to center.
(One reason you need to use Double Platinum spark plugs if you want them to last longer)
This can cause a weaker spark on both plugs if a spark plug wire is going bad.
Or it could just be the coil pack is starting to go bad

 

Thanx for the reply ill try switching wires and inspecting 1 and 5 plugs and see what happens. will keep updated.

 

5 has a dead cylinder and i checked compression on that cylinder 138 psi. I'm starting to wonder if its a weak injector because over the past few weeks the problem goes away and comes back as intermittent as can be. changed the wires and no change. Also think it could be a cracked plug. Also thew a new coil at it still the same. Any suggestions please?

 

Spark plugs are not expensive, I would buy one, matching what is in the others, and put it in #5.

You can use an OHM meter to test at least 3 of the injectors, including #5.
Ford uses 14ohm injectors, so set OHM meter to lowest scale, like 200 or 1,000, and test 3 injectors, I think 11-18ohms is the "good" range.

The reason you need to test at least 3 is because like compression test the test equipment and the conditions will change the numbers, so if 2 are 19ohms and #5 is 19 ohms then 5 is OK, your meter is just a bit off, if you tested it by itself you might end up replacing a perfectly good injector.

If 2 are 13ohms and #5 is 19ohms then you know replacing #5 is not a waste of money, may not be your problem but it could be.

If #5 has compression of 138psi and number #4 and #6 were 165psi then I would suspect #5 has a valve issue, if #4 and #6 were 140psi then #5 compression is good, it was test conditions or gauge that is off.

3.0l vulcan should be in the 160-170psi area, testing with all spark plugs removed and a good battery to get crank up to speed for the testing.

 

This problem is getting deeper now #1 and #5 are dead the rest are firing. The coil was switched and the wires for those plugs were switch with brand new ones still the same.I feel like the answer is just there i cant figure it out. Could it be a cam or crank sensor going bad? Please help!!

 

Ok now for some findings. Injectors for cylinders 1 and 5 arent working either due to their failure or the wiring controlling them. I have heard mention of a "noid" light to test the injector circuit. How to employ it and if there is a diy for it. Im getting there. Any thoughts?Thank you in advance.

 

1 and 5, of course, are a matched pair so use the same coil in the coil pack.

If you have tried a new coil, then the problem will be in the wire from the Computer controlling that coil, or in the computer itself.

The CKP(crank position) sensor or the CPS(cam position sensor) can't cause that kind of issue.
CKP either works or is doesn't, once computer knows when #1 is at TDC from CKP tone ring it calculates the rest, for spark and injectors, if CKP sensor wasn't working there would be no spark and no fuel..........so not start.
CPS helps with spark advance but not the actual firing of the spark, it's main purpose is to time injectors with intake valves.

On the coil wiring connector there are 4 wires, one is 12volts when key is on, the other 3 are used by the computer to Ground one coil in the pack, and then unGround it to cause that coil to spark.
I would use an ohm meter and see what those 3 wires show, key on and key off.
I am not sure of what they should show??
But if the 1 wire for coil 1/5 has a different reading than 3/4 and 2/6 coil wires then that is the problem, broken wire or broken computer.

If injectors on 1 and 5 are also not working then it looks more like a computer issue.
Try to get OBDII scan to see if there are any new or old codes.

A Noid light hooks between injector and its wiring plug, so you need one with Ford connector, the light flashes each time computer Grounds the injector.
All injectors get 12volts when key is on, the computer Grounds injector to open it, so similar to the way the coil pack works.

 

Ok number 1 injector is bad 5 can only be tested without taking off the upper intake manifold. im gonna assume its bad too and will replace. The only thing that has bothered me is that the computer never threw codes for the injectors or cylinders. I read all the time about lean codes misfire code high o2 but nothing from the computer and all the time getting it scanned and no codes!!

 

How did you test #1 injector?

 

noid light

 

Noid light tests the computer and wiring, not the injector
Put an OHM meter on injector, should be about 14ohms

If computer is not setting codes and there is a problem like missing then you probably have a bad computer.

disconnect MAF sensor and start the engine, should get a CEL and a code for that.

 

another problem i was experiencing was the radio randomly choosing tracks on it`s own

constant pre-ignition in all cylinders , turns out the edis coil was leaking EMI heavily

the external plastic coil casing was no longer containing the EMI interferance

try an aftermarket edis coil to see if the problems continue , might just be the coil itself

 

Solution:Changed out injectors 1 and 5 cylinders were bad replaced them this morning. I even tested them out off the vehicle 12 vols with a pigtail injector connector and both dead. Runs better tham before. Thanks RonD for everything! Case closed

 

Good work

Thanks for the update

 

Check the Fuel Injector.

 

About 5 years to late

 

I was on my way to work this morning and my truck just stopped running. When i first started the truck i let it warm up for about five minutes or so. I was around a mile and a half from my house when it stopped running. I got under the truck and let my Dad turn the key to the on position, My fuel pump is definitely coming on. Pluse it's not that old. Sounds like it isn't getting any fire.Some one please point me in the right direction!!