Strange Spark Plug issue

[Purv-Dawg]

I've been trying to eliminate any potential causes of pinging so I changed back to the plugs that allegedly were original equipment but it barely runs, backfires, and has no power. Does anyone have any insight into this? I've asked multiple people over the last twenty five years, trying to get some insight and no one has any answers.

My vehicle is a 1989 GMC C1500 5.7l. The plugs that every cross reference tells me are original equipment are CR43TS. They do not work for my application. I spent two years trying to figure this out twenty years ago and found out by dumb luck that the problem is those plugs. Although everything I read tells me it's not the plugs. It runs just fine on R43TS and R44TS plugs but I was trying to eliminate potential causes of pinging.

The only difference I know of is that the "C" in the recommended plugs stands for commercial. That tells me nothing. I can visually see that the electrode is larger on the commercial plug but most people swear by them on these trucks.

Any insight is welcomed.

[ralmo94]

I don't have any insight, but both cr43ts and r43ts both cross to the same NGK, both appear to be projected type, same heat range. I usually get NGK copper myself for everything, that's just me.

[Purv-Dawg]

I know a lot of people get good results with NGK plugs on these trucks and they are finicky about which plugs are used. I just can't be totally sure of false knock without eliminating anything other than the original plugs. I'm going to unplug the knock sensor tomorrow and see what happens. I emailed ACDelco and asked them for insight but I'm doubtful they will have any.

[ralmo94]

If you just unplug it you will get a cel and probably retarted timing if not disabled in tune. Do you have hardware to rewrite?I didn't see elsewhere that you posted?

[Purv-Dawg]

Initially I was using the stock ecm. Now I'm using EBL II and it's significantly worse now than it was originally.

[PlayingWithTBI]

Initially I was using the stock ecm. Now I'm using EBL II and it's significantly worse now than it was originally.

Maybe a little more history would help. Have you done the normal tuneup like, cap, rotor, wires? How old is your ignition coil and distributor? What heads are you running? What is your fuel pressure? Have you done very many VE Learns yet? Maybe your SA tables aren't dialed in?

Low fuel pressure, or lack of flow, can cause lean pops. Loose exhaust or a rattling Cat can cause KCs too.

Edit: How about throwing a WBO2 on it and logging with your WUD?

[Purv-Dawg]

I have other issues I do need to address understanding how to customize my spark tables to reduce spark knock but the plugs themselves have nothing to do with the EBL system. This issue has persisted for twenty five years back to when the vehicle was totally stock and the tuneup is fresh.

I'm going to have to wait until I can buy a WBO2 kit and hopefully that won't be a lot longer. The vehicle is drivable normally but I live in an area with tons of minor foothills and I'm getting spark knock when climbing them and I haven't figured out how to completely eliminate false knock yet to rule them out.

What's caused my biggest confusion is which strategy to take to reduce knock. I've gotten lucky with my intuition but many settings in tunerpro are confusing, just don't give quite enough information to understand, or appear to conflict with and change other settings that on the surface appear completely unrelated.

I've done enough VE learns to get it dialed in close enough to be nearly acceptable. My primary issue is pinging when climbing hills. The first half of the life of thus truck was spent in the flat lands of Georgia so this was never an issue but now it is with a 2.73 rear gear and 32 inch tires in different terrain and I'm not a formally trained mechanic and i have health issues that cloud my thinking so I'm very slow in finding the obvious.

I changed the ignition coil and distributor about five years ago to a Davis unified 12620BK and a Pertronix D3002 coil. I'm running an EDL3702 cam with the stock heads which I'm reasonably certain are 193's.

I've been looking for rattles and I'm not finding anything yet.

[ralmo94]

a 2.73 rear gear and 32 inch tires in could equal pinging when climbing hills. original open throttle spark map wasn't designed for that much load. Probably need a couple degs out of high kpa on main map?

[PlayingWithTBI]

I have the EBL Flash-II on my 88 5.7L too. I guess what I'm getting at is, I find it curious that your plugs are causing your issue(s). I've run ACDelco plugs in different heat ranges, NGKs in 2 steps cooler range, now I'm running Accel 416S "header plugs" (long reach with Gasket Seats instead of Taper Seats). I have not seen a lot of differences with spark knock.

In the EBL you have "SA-Launch Mode" which adds spark based on MAP vs RPM. I was getting KCs at low RPMs until I noticed it was adding more spark while my SA tables are fairly aggressive for my aluminum heads. Can you data log and trap SA before and during KRs? Then maybe lower Launch Mode by 50% to see if KCs go down. If you're running too lean, you'll get more KCs too. Watch your O2 voltage too.

[PlayingWithTBI]

a 2.73 rear gear and 32 inch tires in could equal pinging when climbing hills. original open throttle spark map wasn't designed for that much load. Probably need a couple degs out of high kpa on main map?

Agreed, I was hoping that was a typo and he actually has 3.73s,

[Purv-Dawg]

I think that changing the plugs fried my ignition coil. You have any suggestions for a new one? The pertronix was fine I guess but I'd like it to last longer than five years like this one did.

[tayto]

sounds like you got a bad plug or cracked one installing it 25 years ago. millions of people run stock ac delco plugs and have no issues with them, including myself. do you check&set the gap on your plugs or install them as is? pertronix is known garbage i would run stock stuff here. i have never used davis stuff but have heard its OK.

[Purv-Dawg]

sounds like you got a bad plug or cracked one installing it 25 years ago. millions of people run stock ac delco plugs and have no issues with them, including myself. do you check&set the gap on your plugs or install them as is? pertronix is known garbage i would run stock stuff here. i have never used davis stuff but have heard its OK.

I'm starting to think I understand what's going on. I suspect that the larger electrodes on the commercial grade plugs increase resistance just enough to destroy coils that may already have enough mileage on them to finish them off. Which is exactly what appears happened this time. Maybe the coil should be replaced when installing these plugs the same way a weakened battery will destroy a new alternator. I went through four alternators in three months on a Mustang when I was a kid. I just assumed I was getting poor remanufactured parts because they were from AutoZone, which is often a legitimate thing. Since they had lifetime warranties it wasn't a big deal to swap them out.

[Purv-Dawg]

a 2.73 rear gear and 32 inch tires in could equal pinging when climbing hills. original open throttle spark map wasn't designed for that much load. Probably need a couple degs out of high kpa on main map?

I've had to reduce the spark tables down to 12 degrees in the cruising speed range to get the ping down enough while climbing after dropping down out of overdrive. The locked torque converter only worsens the problem and I have added about 15 degrees of retard when it's locked.

I'm going to replace the rear gear within the next couple of weeks but I'm trying to decide on a 3.42 or 3.73 ratio. My main goal has always been to get the best fuel mileage possible so I will likely try the 3.42's. I just don't want to be pissed off at myself for being unable to either stop the ping or decreasing my fuel mileage to the point I don't want to drive it any distance. Power is great but this engine has serious limitations without more modifications than I can afford. These are the main reasons I've stuck with the stock heads, which most people consider garbage. If I dropped a pile of cash on a set of summit racing heads it would still cap out at around 330 horses unless I change the intake, injectors, etc. It would be far less expensive to swap to an LS and it would still get better mileage.

I never intended to increase my tire size as much as I did but I found that there are tons of people who buy brand new jeeps and want wider tires. I don't understand the logic but they sell brand new sets of wheels with tires for considerably less than a set of new tires on the original wheels. I got sick of replacing the original hubcaps every few months. The jeep wheels do require adapters and about an hour of grinding out the ring that prevents them from fitting the spacers but it's not difficult. Although I wouldn't advise an inexperienced person to to it.

[Fast355]

I've had to reduce the spark tables down to 12 degrees in the cruising speed range to get the ping down enough while climbing after dropping down out of overdrive. The locked torque converter only worsens the problem and I have added about 15 degrees of retard when it's locked.

I'm going to replace the rear gear within the next couple of weeks but I'm trying to decide on a 3.42 or 3.73 ratio. My main goal has always been to get the best fuel mileage possible so I will likely try the 3.42's. I just don't want to be pissed off at myself for being unable to either stop the ping or decreasing my fuel mileage to the point I don't want to drive it any distance. Power is great but this engine has serious limitations without more modifications than I can afford. These are the main reasons I've stuck with the stock heads, which most people consider garbage. If I dropped a pile of cash on a set of summit racing heads it would still cap out at around 330 horses unless I change the intake, injectors, etc. It would be far less expensive to swap to an LS and it would still get better mileage.

I never intended to increase my tire size as much as I did but I found that there are tons of people who buy brand new jeeps and want wider tires. I don't understand the logic but they sell brand new sets of wheels with tires for considerably less than a set of new tires on the original wheels. I got sick of replacing the original hubcaps every few months. The jeep wheels do require adapters and about an hour of grinding out the ring that prevents them from fitting the spacers but it's not difficult. Although I wouldn't advise an inexperienced person to to it.

With 32" tall tires, I would go no taller than 4.10 and probably 4.30 or 4.56. 700r4 with 4.10s and 32" tall tires is 1,800 rpm at 60 and 2,100 rpm at 70. I had a buddy that had a 91 RCSB 4x4 on 33s. It had the stock 350 and 3.42 gears. The only place it ran well even in 3rd gear was downhill and the truck would not even pull overdrive.