What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

New AC Delco Plugs and now I get slight misses

jeff in co

jeff in co

1/2 ton status
 Premium
Joined
Nov 14, 2003
Posts
2,198
Reaction score
446
Location
Colorado Springs
I've changed all kinds of parts already, plug wires, cap, rotor, O2 sensor, etc. but never the plugs.

My mileage has been around 11 mpg so thought I would just throw in some new plugs for the heck of it.

Picked up some stock, AC Delco plugs for the 89' 350 engine and pulled out the Bosch platinum plugs that have two prongs on them.

When I pulled off the air cleaner, I noticed one of the injector wires was pinched between the tb unit and air cleaner housing. After changed the plugs, I adjusted the injector wires so they wouldn't have any interference issues.

Put everything back together and drove the truck around. After it warmed up and sitting at a stoplight, I got a few sputters (or mis-fires). It didn't happen too much but it certainly was noticable. Drove some more and each time I stopped, a few more random sputters.

Thinking it might of been a pinched injector wire, I cut out the bad wire and soldered the connections real good.

Drove the truck around and the misses are still there.

Is it possible the truck ran better with the Bosch plugs?

This is a replacement block but don't know about the heads. I think the block is from an early 80's vehicle if that makes a difference. The guy at Autozone said the 89' had vortec heads and the earlier engines did not so maybe I have the wrong AC Delco plug in there.

Any thoughts? It did run better before any plugs were changed.....:dunno:
 
1989 did not have vortec heads. Maybe he was confused with swirl port heads??? Do you have a part number for the plugs he sold you?
 
The vortec head guy was from a different store (advanced auto) but I did question him on that too. I told him I though vortec began in about 96'.....he said the intake part was vortec in 96' but the heads were earlier. He pulled up the part number for an 83' blazer and it had a different part number than the 89'. We looked at both plugs (89 and 83) and looked almost identical. Just don't know.

The plug's that O'Reilly's gave me were CR43TS gapped at 0.035
 
The CR43TS is the right plug. How are your plug wires? Could you have damaged one when changing the plugs? Did you double check that you did not screw up your ignition sequence?
 
Are you sure you didn't crack a plug when you installed the new ones, they are pretty fragile. Also make sure your plug wires are good and you didn't seperate the internal connection or damage the ends. You can check the resistance of each, and you should feel them "click" onto the plug.
 
Keitha said:
The CR43TS is the right plug. How are your plug wires? Could you have damaged one when changing the plugs? Did you double check that you did not screw up your ignition sequence?
Click to expand...

Wires are about 3 months old, AC Delco. I might of damaged a wire but the likelyhood would be pretty slim. I took my time and didn't need to yank/force anything.

I would think if I got a wrong wire crossed, the truck would barely run. It runs pretty smooth 85% of the time, just some misses ever so often at idle.

I'll throw the old plugs back in tonight and see if there is any difference. Maybe I just got a bad plug in that bunch somewhere.....:dunno:
 
jeff in co said:
I would think if I got a wrong wire crossed, the truck would barely run. It runs pretty smooth 85% of the time, just some misses ever so often at idle.
Click to expand...

lol, I've driven about 15 miles with crossed plug wires. It will run.
 
DokWatson said:
lol, I've driven about 15 miles with crossed plug wires. It will run.
Click to expand...

OK, that was actually amazing! For experimental purposes -- I did switch two of the wires and it ran "fairly decent" although a little rough. Just goes to show you the truck can run pretty good even if the wires are crossed. I would have never know that.....thanks!

But, that was not the problem. I checked all the wires from my manual and they were all correct. I pulled out the new AC Delco ones and re-installed the old, Bosch +2 plugs and it now runs much better. :dunno:

So the old plugs are better than the new AC Delco.....I am guessing I must of just gotten a bad plug in there somewhere. I'll return and get a new set.

The block and heads are painted blue and the block was from 83' so I'm guessing that the heads may also be from 83'.
 
Yeah you may have had a bad plug. As much as I don't like Bosch platinums I have had engines run good with them :dunno:

I'll like to hear how it works out. Sucks you have to do it twice tho.
 
I've yet to see an issue with AC's... and I do hundreds of V-8's a year... MR43T and LTS's in bulk...

not that you couldn't have a cracked insulator or something... just wanted it to be known from a source who sees/does a f*ckton of em... still the best plug on the market hands down..

I'd be much more likely to suspect a cap issue.. been seeing that a bunch the last couple years...
 
The best plug i've found to run is an NGK V-power plug. I'v been using them for 20+ years and VERY happy with them. They look the same as they did when I put them in after 3 years of use.
 
new ac plugs are now made in Mexico and look slightly different from the USA ones. There were still some old USA on the shelf so I bought several packs. I was told that they are now discontinued. New stuff is Mexico.
 
so that means they're sh*t?

how many spark plug jobs do you guys do a week? huh? AC plugs don't look a damn bit different then they did 10 yrs ago....
 
check the gap on one of the old plugs. If you have a high output ignition system its possible that the gap was widened a little from what the factory setting is. it may run better that way
 
I brought back the AC Delco plugs last night and picked up the Bosch +4 plugs. I figured that the older Bosch +2 plugs worked in this engine so I'd try the +4's.

Slapped them in last night and test drove. Solid as a rock on the idle. Drove it this morning too, very smooth idle without any sputters.

So basically, I think I got a bad set of AC Delco's. I only went with the Bosch because this was not the original 89' block/heads and for some reason it was doing good before on the same type of plugs. Glad it's fixed!
 
You must log in or register to reply here.

Latest Posts

Top Bottom