I have a weak spark from my distributor.

[jakedachef]

Hello,

My truck has a Windsor 5.0 v8. I have spark to all plugs but the back 4 plugs have a weak spark. I think this is the reason that my truck bogs down when i go to accelorate (if i go to pass and put pedal down). I origionally thought it was a transmission problem but it shift and accelorates just fine when i only put the pedal down about half way. Also everywhere I look it says that I should have a rotory distributor and coil, but i actually have an electronic distributor cap. I actually have 2 4plug caps on my distributor. Please give me any advice that you can. I dont know if it is the caps going bad or the what?

 

[Dan Whitaker]

You do not have a distributor. All 1996-2001 V8 Explorers/Mountaineers have D.I.S. (distrubutorless ignition system) What you are referring to as your caps are called coil packs. It is possible one of the coil packs is going bad.

 

[jakedachef]

Oh ok

I have heard the term coil pack before but wasnt sure what it was. I guess that explains why i cannot find a distributor for my truck.

 

[Explodr94]

Coil packs are easy to test with a Multi-meter. There is primary resistance which is the plug on the side and secondary resistance which is going from top to bottom or 1-5, 2-6, and 3-4. The primary resistance is less than 1.0 Ohms. The secondary resistance is 6.5 to 12.

 

[SoNic67]

There is no "weak" spark, only "spark" or "missfire". Spark cannot go just half way...

Missfires would trigger a code and Check Engine Light.

 

[deweyville65]

I'm sorry, but I beg to differ with the statement "there is no weak spark". If the coil does not build to its full capacity, for what ever reason, then the spark will still be there, but weaker than otherwise if it builds to full capacity. The coil may be putting out only 25,000 volts instead of 45,000 volts. I dont know what the Explorer coils are supposed to put out, that figure is for reference only. All I know is, my 96 will jump spark from the coil a good 2" to my hand. I found that out the hard way.

 

[IAmTodd]

How are you measuring this 'weak spark'? Your hand?

You have spark, so your coils are ok. The coils are mixed side to side and front to back so it's unlikely both coils have failed. Cleaned your MAF lately? How's the fuel pressure? Any pinging?

 

[deweyville65]

IAm Todd, would you please explain what you mean by the coils are mixed. I personally am not having any trouble with mine. I am afraid I am "old school", and not up to date on all this new technology. In my post about spark being weak, I am used to only one coil, of which I know there are different output voltages. Please PM me if you would prefer. I have a 96 4.0 if that makes a difference.

 

[IAmTodd]

I've swiped Section's drawing for this.

There are two coil packs. The way OP makes it sound is that oil coil is feeding cylinders 3,4,8,7 and that it is not supplying energy to spark. In the picture above you can see that they are not isolated like that.

As said above, new coils really only have two states, they either spark or they don't.

 

[koda2000]

I don't know how you are measuring spark and determining that certain cylinders are receiving a "weak spark". With coil packs it is certainly possible that one or more coils are going bad, but as described above you can test individual coil packs by measuring primary and secondary resistance. You can also switch the coil packs around and see if the problem follows the coil pack.

Question: Have you replaced your fuel filter lately? If the fuel filter is starting to clog it could produce the symptom you described at WOT. I had this happen to me once. The truck ran perfectly until you floored it to pass, then it fell on its face

 

[SoNic67]

I'm sorry, but I beg to differ with the statement "there is no weak spark". If the coil does not build to its full capacity, for what ever reason, then the spark will still be there, but weaker than otherwise if it builds to full capacity. The coil may be putting out only 25,000 volts instead of 45,000 volts.

The voltage of the spark is related to the electric arc - plug geometry, distance between electrodes, pressure in chamber... Let's say that based on your conditions, you need 15kV to ignite the spark. If your coil is not capable of generating that voltage (let's say only 14kV), then NO SPARK will be generated. At all.
If your coil can put out maximum 18kV (with no plug attached), the spark will ignite at 15kV (in your conditions) and the voltage will be limited to that value while arching.
There is nothing "in between". Just "fire" or "missfire".
Like the pull on the trigger on a gun. You have enough pull or you don't...

 

[jakedachef]

I don't know how you are measuring spark and determining that certain cylinders are receiving a "weak spark". With coil packs it is certainly possible that one or more coils are going bad, but as described above you can test individual coil packs by measuring primary and secondary resistance. You can also switch the coil packs around and see if the problem follows the coil pack.

Question: Have you replaced your fuel filter lately? If the fuel filter is starting to clog it could produce the symptom you described at WOT. I had this happen to me once. The truck ran perfectly until you floored it to pass, then it fell on its face

Yes I have. I replaced it about a month ago.

 

[jakedachef]

I don't know how you are measuring spark and determining that certain cylinders are receiving a "weak spark". With coil packs it is certainly possible that one or more coils are going bad, but as described above you can test individual coil packs by measuring primary and secondary resistance. You can also switch the coil packs around and see if the problem follows the coil pack.

Question: Have you replaced your fuel filter lately? If the fuel filter is starting to clog it could produce the symptom you described at WOT. I had this happen to me once. The truck ran perfectly until you floored it to pass, then it fell on its face

Also my fuel filter was very very badly clogged and I was wondering if my problem might also have something to do with the fuel pump being harmed by this blockage. I know for a fact that a pump can gradually die, it happened on my dads truck and thats what a mechanic told us.

 

[koda2000]

if your fuel filter was badly clogged it's likely the sock on your fuel pump is also clogged. at any rate, there must be a lot of crud in your tank. i'd pull the tank, clean it out and put a new sock on the pump. if there's any question about the pump this would be the time to replace it, otherwise you'll be dropping the tank again.

 

[jakedachef]

I just replaced my fuel tank (brand new) and my "sock" was clean. So there isnt any crud. IDK what else it could be with fuel system. I even used carb/injector cleaner.

 

[waskly]

I'm sorry, but I beg to differ with the statement "there is no weak spark". If the coil does not build to its full capacity, for what ever reason, then the spark will still be there, but weaker than otherwise if it builds to full capacity. The coil may be putting out only 25,000 volts instead of 45,000 volts. I dont know what the Explorer coils are supposed to put out, that figure is for reference only. All I know is, my 96 will jump spark from the coil a good 2" to my hand. I found that out the hard way.

spark or no spark, if its weak or w/e it still wont spark in the engine and you get a miss fire. spark plug wires carry resistance.

 

[ShortyzKustomz]

Sounds like more of a maf or other sensor problem...imo

 

[waskly]

fuel tank or fuel pump? regardless if the sock or in tank filter is clean, the pump it self can be worn.

 

[budwich]

get some obd run data on fueling and air during one of your "stomps" and compare to normal running.... you will likely find a direction to look there after.

 

[AgInternational]

weak spark exists

I'm sorry, but I beg to differ with the statement "there is no weak spark". If the coil does not build to its full capacity, for what ever reason, then the spark will still be there, but weaker than otherwise if it builds to full capacity.

Sonic67 and IamTodd,
You can test for weak spark and it does happen. Just use an adjustable spark tester and open the gap wider than the specified plug gap. If the spark wont jump the gap at a certain distance, there is not enough voltage coming from the coil, meaning a "weak spark".