# What Spark Plug for 98 5.7l Vortec



## Mtank (Nov 17, 2012)

Hey Guys. Recently had my truck in the shop to diagnose some misfires/general rough performance. They replaced the crankshaft sensor and said cylinder 5 was misfiring and it would be a good idea to throw some plugs in it. 

I told them I would do that job myself and purchased some autolite double platniums because they werent the most expensive, but not the cheapest either.

After installing them and driving the truck for a day, the performance seems even worse than before I took it to the shop. Ive heard that these motors dont run well on certain types of plugs and it has been suggested to me that I try a "better" plug. 

Is there any validity to the plug statement? if so , what plugs do you guys recommend for this motor? Thanks!

-Matt


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## DAVE (Nov 17, 2012)

I would use a/c delco plugs but I doubt that the misfire is caused from the spark plugs. When the shop recommended spark plugs it was probably because they were worn and that would be the first step in correcting the problem but by no means the final solution.


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## Mtank (Nov 17, 2012)

well I pulled the plugs again today and 2 on the right side of the motor were extremely fouled for being in only 2 weeks and they also had oil on them. the other side had no oil but had an even coating of black carbon. any idea what may be going on?


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## GoldDot40 (Nov 17, 2012)

How many miles on the motor? You need to have a compression test done on all 8 cylinders. My guess is that those 2 will have low compression. This could be from one of several different scenarios. From bad valve seals, bad rings, cracked pistons, cracked head, etc etc. Compression test 1st....get it diagnosed properly and go from there.


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## Lick Skillet (Nov 18, 2012)

how many miles are on the truck? have you had the intake gaskets replaced yet? a/c delcos run great, been ran in my truck since new and im at 250000 now mines a 98 gmc z71. also check your distributor make sure that it isnt loose may need a new coil and cap. new wires even!


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## cuda67bnl (Nov 18, 2012)

Crank it up and open the hood in the dark. My money says you'll see what looks like fireworks where your wires are shot.


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## bilgerat (Nov 18, 2012)

cuda67bnl said:


> Crank it up and open the hood in the dark. My money says you'll see what looks like fireworks where your wires are shot.



Yep, AC Delco plugs and a good set of wires wouldnt hurt


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## Napi (Nov 18, 2012)

I'm guessing the plug wires/distributor cap aren't getting fire to those plugs. I bought an '88 chevy new. I changed the plugs at 120,000. If I hadn't already bought the new plugs, I would've put the old ones back in. They looked pretty dang good!


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