81 bronco 300 straight 6, front 3 not firing??

[RumpRanger98]

So lately my dads 81 bronco hasn't been running like it should, he had cams redone i think 6 months ago and he said it ran great, but now, When we pull the wires off numbers 1,2,3 there is no change to the motor at all. new plugs, wire, cap, rotor... not sure what could be causing this? seems to run decent.

sorry wasnt really sure where to post this.

 

[feellnfroggy]

strange as it may seem,,, I was sold an Excell Chrome high performance coil to use with this set up at a local auto supply store. I placed my hand on the coil and found it to be unusually warm, so I put old coil back on and tried it. No other changes were made nor alterations. This fixed the problem. The motor immediately began to function full force again. ( wierd huh )

Someone on wiki asked about a v-8 that wouldnt fire on back four. This might be an option for you. Other than this I have no idea. Post in the 6 cyl section, they might have more insight. (Or have a mod move it)

 

[lil_Blue_Ford]

Did you check compression in the motor?

Have you pulled any of the plugs?

Have you verified that the plugs are actually firing? (cap or wires could be messed up even when new, rare, but possible)

 

[feellnfroggy]

When we pull the wires off numbers 1,2,3 there is no change to the motor at all. new plugs, wire, cap, rotor.

have you tried the screwdriver test? Put a screwdriver in the plug wire and hold it 1/4 inch from the block. Be careful. If you have spark then you might not have even fuel distribution. Check the lower intake runners. look for excess gum up.

 

[RumpRanger98]

theres spark to each plug, plugs have been pulled, they are a day or 2 old.

it is carburated. is there something that could of caused the front 3 to all of a sudden not be recieving enough fuel?

compression was checked and all in proper spec, dont know the numbers but thats what i was told.

i almost feel like the new cap and rotor he put on could somewhat be defective.


The thing that really gets me is when we drive it around it seems to run fine, goes up hills etc. I feel like its not running tip top and have all the power it should. I find it hard to believe it can run like it is on 3 cylinders.

 

[feellnfroggy]

It might not be running on 3 cylinders, it might just be running on 3 weak cylinders, If you have spark I am thinkin like others have said maybe a compression problem, on a scale of 1-10 (10 being same as before) how different does it run now?

 

[RumpRanger98]

according to the book the wires are all to the correct plugs from the dist cap. the compression was checked and all came out good, there is no low compression and nothing is really high either, all within range of each other, i dont know exact numbers but i know its good.

when we pull the front 3 plug wires there is zero change in the motor, of course have not driven it like that, but it seems to affect nothing even when revving.

as to how it ran before and how it runs now i cant say because ive never drove it.

Thanks for the help guys

 

[akalogan]

have you checked timing?

 

[PaleBlue90]

check timeing, check the dizzy, check the coil, check the plug wires, they could be crossed or are cross arcing.

what i mean by cross arcing is on my chebbie, i had 2 wires that would lay on each other and it would cause 2 out of 8 to not fire

 

[RumpRanger98]

timing was checked. I will check the wires out today. I know the wires are new, but I have heard stories of them sometimes being defective and causing voltage leak/ arching.

Thanks again

 

[PaleBlue90]

timing was checked. I will check the wires out today. I know the wires are new, but I have heard stories of them sometimes being defective and causing voltage leak/ arching.

Thanks again

np, good luck and keep us posted

 

[lil_Blue_Ford]

One way to check to see if they are arcing is to open the hood an fire it up at night and look for sparks jumping around the engine compartment.

Also, check the grounds, there should be a negative cable attached to the motor, if the cable is bad it could be causing weak spark.

 

[Nhaz]

One of the first things I do when I get another car is Add a ground wire from the block of the car to the fender/firewall sometimes neg battery terminal. Just in case there is bad ground to the engine.

I don't even look to see they they are bad. I don't buy new vehicles most of mine are generally crap so I assume its going to have bad grounds.

With a vehicle from 1981 bad grounds are a good place to start.

 

[feellnfroggy]

Play with the wires some more and switchthem around, SOmetimes the book isnt always accurate with trucks that old. Someone could have swapped in another motor at some point with a different year crank and changed the firing order. Nhaz is right about grounds too.

 

[lil_Blue_Ford]

Play with the wires some more and switchthem around, SOmetimes the book isnt always accurate with trucks that old. Someone could have swapped in another motor at some point with a different year crank and changed the firing order. Nhaz is right about grounds too.

Hey now, I was the first to mention the grounds, lol.