Is there a time element to spark plugs? Or strictly miles? - ZR-1 Net Registry Forums

ram_g · 08-02-2020

My recently acquired '91 now has 13K miles (driven ~250 miles in 4 weeks - probably more than in the last few years, lol). I have no reason to believe the plugs, injectors, etc. were ever replaced. The car drives fine and secondaries work (for now!).

My question is: should I replace the plugs proactively now, or wait till ~18-20K miles ("don't fix what isn't broken")? Do plugs "age" by themselves?

Ccmano · 08-02-2020

While there is no time element, frequent starting and stopping common to low mileage cars can have an effect. I would pull one plug and check it. If it's good leave it. Like you said if it ain't broke don't fix it. For me, worst case, I would simply clean them if there is fouling.
H

Karl · 08-02-2020

Quote:

Originally Posted by ram_g

My recently acquired '91 now has 13K miles (driven ~250 miles in 4 weeks - probably more than in the last few years, lol). I have no reason to believe the plugs, injectors, etc. were ever replaced. The car drives fine and secondaries work (for now!).

My question is: should I replace the plugs proactively now, or wait till ~18-20K miles ("don't fix what isn't broken")? Do plugs "age" by themselves?

If your '91 has the original fuel injectors odds are they will fail when mixed with ethanol mixed fuel.

Might as well leave it alone until the need arises.

ram_g · 08-02-2020

Quote:

Originally Posted by Ccmano

I would pull one plug and check it. If it's good leave it.

Thanks, will do this week.

ram_g · 08-02-2020

Quote:

Originally Posted by Karl

If your '91 has the original fuel injectors odds are they will fail when mixed with ethanol mixed fuel.

Yes, so I gather. For now I've found a source of non-ethanol gas and plan to use that exclusively. I think I'll be needing a plenum pull sooner or later to rebuild the failing secondary vacuum system (down to a 2 second pump interval) and I may consider changing the injectors then.

32valvesftw · 08-02-2020

There should not be a time component that effects plug life, as others have stated the way the car is driven should have more impact. Plugs are easy to do on these cars, #8 requires a little creativity but its really not bad. I changed mine and it made a noticeable difference in the smoothness of the engine. I could actually stand a quarter on the plenum while running after the change. I'm in Houston as well so if you need help let me know. When I changed my plugs I used NGK BKR5E gapped at .045.

Paul Workman · 08-03-2020

Well, actually several things affect the life of plugs, e.g., AF (rich/lean) mix, temperature rating, etc., but b/c everyone's driving habits vary, and so many different heat ranges and core materials are available AND being used, any predictions have a low "ambiguity percentile". (as they say in statistics).

That said, there IS a substantial difference in longevity when e.g., comparing copper core vs. (say) iridium core plugs. The copper core (AC Delco 41-602s) I use would probably last 10k miles or more of mixed driving before the edges on the tip become rounded and the gap increases. Whereas some have reported that 100k miles is not un-common for Iridium core plugs. (For this reason, and others, iridium plugs are often installed in engines where the plugs are hard to get to. I remember the #8 plug on my 95 LT1 Vette I had to access it from under the car! But, that is nothing compared to some cars!)

Pete Polatsidis put me onto the AC 41-602s (copper) plugs because (1) they're cheap (~$2/plug) and (2) they're so easy to change on an LT5 that one can easily afford and install a fresh set every season for way less than a tank of 93 octane and waaaay before they are anywhere close to being worn out! (Pete has run a 10.1 sec 1/4 mile using those plugs when he had his 350 LT5. He's now sporting a 441 LT5 and no doubt running in the 9s, but he'll have to say what plugs he's using in that beast now.)

The comment about differences in wear as related to ethanol vs non-ethanol...was the first I heard of it. But, then I don't run my LT5 plugs to the end of their life expectancy either!

There are several different plugs and heat ranges the ZR-1 community uses. But, for a specific recommendation, your driving application (i.e., habits) would need to be defined, methinks!

ram_g · 08-08-2020

Closing the loop on this thread, I went ahead and replaced the existing plugs with AC Delco 41-801, gapped at 0.050". I'm pleased with the results.

Initially I was going to pull a couple and take a look. The first one, #1 plug, took more effort to remove than I had expected. Turned out that the plug flange seat had some rust. After that #s 3, 5, 7 on the left bank and 2, 4, and 6 on the right bank were no problem to remove, with noticeably less effort and no visible rust on the flange seats. #8 put up a fight - not so much getting the right combination of extensions and swivels - where searching this forum was a HUGE help - but the plug needed a breaker bar to get it loose. Thought initially that someone might have cross-threaded it but turned out it was also quite rusted. Gapping and putting in the new plugs (tiny dab of anti-seize and torqued to 15 lb-ft) was easy for all.

The removed plugs were all ACD FR2LS, no reason to believe they were not factory originals. Condition was actually quite decent - only a couple looked a bit dark but not outrageously so. The gaps varied from 0.038 to 0.042. Oil was on all the threads right up to the seat area. Looking closer at #1 and #8, I believe that at some point in the past both these locations have had coolant drip down into the plug wells, causing the corrosion. There was no sign of active coolant presence or contamination.

I chose ACD 41-801s largely because I got a good deal on a set of 8, lol. A post I had seen on this forum said that Marc H. thought they were a good plug, so that was all I needed! Gapped them carefully to 0.050. After buttoning everything up I swear the car runs smoother at idle and at WOT, but I may be imagining things!

Removed plugs: Top pic is L to R #s 1, 3, 5, 7 and bottom pic is #s 2, 4, 6, 8. Rust on #1 and $8 is visible, particularly so for #8 (in this orientation).

08-02-2020	#2
Ccmano Join Date: Jun 2006 Location: Sparks, NV Posts: 2,852	Re: Is there a time element to spark plugs? Or strictly miles? While there is no time element, frequent starting and stopping common to low mileage cars can have an effect. I would pull one plug and check it. If it's good leave it. Like you said if it ain't broke don't fix it. For me, worst case, I would simply clean them if there is fouling. H __________________ 90'ZR-1 #1461 Red/Black Ported Intake, Degreed Cams, OBX Headers & Exhaust, Fidanza FW, Secondary Delete, Custom tune, C6 GS Wheels. Sold 08 C6 Z51 Crystal Red Metallic Sold Vararam Intake, Tune, Sold 05 C6 Z51 Red/Black Sold 90'ZR-1 #1723 Black/Gray Sold but not forgotten 91' Z51 L98 White Vert. My First, you always remember your first. Sold.

08-02-2020	#6
32valvesftw Join Date: Jun 2015 Location: Texas Posts: 530	Re: Is there a time element to spark plugs? Or strictly miles? There should not be a time component that effects plug life, as others have stated the way the car is driven should have more impact. Plugs are easy to do on these cars, #8 requires a little creativity but its really not bad. I changed mine and it made a noticeable difference in the smoothness of the engine. I could actually stand a quarter on the plenum while running after the change. I'm in Houston as well so if you need help let me know. When I changed my plugs I used NGK BKR5E gapped at .045.

08-03-2020	#7
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,493	Re: Is there a time element to spark plugs? Or strictly miles? Well, actually several things affect the life of plugs, e.g., AF (rich/lean) mix, temperature rating, etc., but b/c everyone's driving habits vary, and so many different heat ranges and core materials are available AND being used, any predictions have a low "ambiguity percentile". (as they say in statistics). That said, there IS a substantial difference in longevity when e.g., comparing copper core vs. (say) iridium core plugs. The copper core (AC Delco 41-602s) I use would probably last 10k miles or more of mixed driving before the edges on the tip become rounded and the gap increases. Whereas some have reported that 100k miles is not un-common for Iridium core plugs. (For this reason, and others, iridium plugs are often installed in engines where the plugs are hard to get to. I remember the #8 plug on my 95 LT1 Vette I had to access it from under the car! But, that is nothing compared to some cars!) Pete Polatsidis put me onto the AC 41-602s (copper) plugs because (1) they're cheap (~$2/plug) and (2) they're so easy to change on an LT5 that one can easily afford and install a fresh set every season for way less than a tank of 93 octane and waaaay before they are anywhere close to being worn out! (Pete has run a 10.1 sec 1/4 mile using those plugs when he had his 350 LT5. He's now sporting a 441 LT5 and no doubt running in the 9s, but he'll have to say what plugs he's using in that beast now.) The comment about differences in wear as related to ethanol vs non-ethanol...was the first I heard of it. But, then I don't run my LT5 plugs to the end of their life expectancy either! There are several different plugs and heat ranges the ZR-1 community uses. But, for a specific recommendation, your driving application (i.e., habits) would need to be defined, methinks! __________________ Good carz, good food, good friendz = the best of timez! 90 #1202 "FBI" top end ported & relieved Cam timing by "Pete the Greek" Sans secondaries Chip & dyno tuning by Haibeck Automotive SW headers, X-pipe, MF muffs Former Secretary, ZR-1 Net Registry

08-02-2020	#1
ram_g Join Date: Jun 2020 Location: Houston, TX Posts: 183	Is there a time element to spark plugs? Or strictly miles? My recently acquired '91 now has 13K miles (driven ~250 miles in 4 weeks - probably more than in the last few years, lol). I have no reason to believe the plugs, injectors, etc. were ever replaced. The car drives fine and secondaries work (for now!). My question is: should I replace the plugs proactively now, or wait till ~18-20K miles ("don't fix what isn't broken")? Do plugs "age" by themselves?

08-08-2020	#8
ram_g Join Date: Jun 2020 Location: Houston, TX Posts: 183	Re: Is there a time element to spark plugs? Or strictly miles? Closing the loop on this thread, I went ahead and replaced the existing plugs with AC Delco 41-801, gapped at 0.050". I'm pleased with the results. Initially I was going to pull a couple and take a look. The first one, #1 plug, took more effort to remove than I had expected. Turned out that the plug flange seat had some rust. After that #s 3, 5, 7 on the left bank and 2, 4, and 6 on the right bank were no problem to remove, with noticeably less effort and no visible rust on the flange seats. #8 put up a fight - not so much getting the right combination of extensions and swivels - where searching this forum was a HUGE help - but the plug needed a breaker bar to get it loose. Thought initially that someone might have cross-threaded it but turned out it was also quite rusted. Gapping and putting in the new plugs (tiny dab of anti-seize and torqued to 15 lb-ft) was easy for all. The removed plugs were all ACD FR2LS, no reason to believe they were not factory originals. Condition was actually quite decent - only a couple looked a bit dark but not outrageously so. The gaps varied from 0.038 to 0.042. Oil was on all the threads right up to the seat area. Looking closer at #1 and #8, I believe that at some point in the past both these locations have had coolant drip down into the plug wells, causing the corrosion. There was no sign of active coolant presence or contamination. I chose ACD 41-801s largely because I got a good deal on a set of 8, lol. A post I had seen on this forum said that Marc H. thought they were a good plug, so that was all I needed! Gapped them carefully to 0.050. After buttoning everything up I swear the car runs smoother at idle and at WOT, but I may be imagining things! Removed plugs: Top pic is L to R #s 1, 3, 5, 7 and bottom pic is #s 2, 4, 6, 8. Rust on #1 and $8 is visible, particularly so for #8 (in this orientation).