roguecoxnet

I have a random knock and engine runs like crap. It idles but I knew something was wrong. Pulling plug wires and had no change in rpm when pulling both 5 and 7. So checked spark at the wire and I have spark.... Well when I leave 5 and 7 unplugged at the cap the engine doesn't do that random knock that comes and goes. So I think it's firing randomly and causing a jolt.

1987 350 TPI
-Cylinders 1-8 all have 190 psi compression
-fuel pressure good
-newish wires, cap, Ngk iridium plugs (5 and 7 got brandnew Ngk iridiums today)
This has me stumped. I have 90lb injectors cuz it's turbo but I don't want to believe those suckers would go out.... Expensive....

#5 plug was clean and 7 was alittle black. I know I have 2 cylinders out but my question really is will a engine knock hard randomly or is the motor prob trash? I never heard of that. Engines fully forged and I put a ton of money into it.

bigal55

iTrader: (1)

Did this problem occur after the engine had been running fine or is this a new build and had this problem from the first time running? Sounds like 5 and 7 cylinders are dead, need to find why. When you pull the wires from the cap, your problem with knock goes away? Sounds like cross fire between 5 and 7 wires, check to see they are not burned and separate them so they do not run together from the distributor to the plug. Also, you didn't switch 5 and 7 at the plug end by mistake, easy enough to check. Inspect your cap inside around the terminal area for arcing, could be cross fire within the cap. How's the rotor look? If all this checks out ok and you think you might have a couple bad injectors, swap the 5 and 7 injectors with the 1 and 3 to see if the problem moves with the injectors, if not, you can rule out poor fueling to those cylinders. Next would be to remove the valve cover to check the valve train. HTH!

TTOP350

iTrader: (8)

My vote for 5-7 got crossed.

roguecoxnet

ThAnks I'll check. Order is right. I'm going to switch injectors tonight. I have FIRST fuel injection intake. Pulled valve cover everything good.
The problem is new. Ran great. I appreciate the help.

roguecoxnet

Found wires that were bad. Fixed now. Thank you! Spark plug Wire holder clamp caused a cut in wire 5 and 7. Had to remove to see once it buzzed me.

bigal55

iTrader: (1)

Glad to hear you got it fixed! Also, thanks for responding with the results, too many posts go dead after the solution is found.