Spark Plug help / recommendations

MorrisGray · March 28, 2019

I was hoping some of you might give me your thoughts and recommendations for which plugs to buy... ?

I have a 2002 Silverado 5.3L v-8 Vin code T

The manual list Denso PTJ14R15

and NGK PZTR5A15 AND the manual list a .060"gap.

When I go to local auto parts websites there is no help for these part numbers and I am unsure of what plug and what plug gap I should use. I currently have a misfiring truck that runs like crap. Looking to replace the plugs, and possibly all of the coils, maybe the spark plug wires. My truck sits for months at a time unused but did run good before all this happened. Initially I thought it was bad ethanol gas from sitting unused but have used a lot of SeaFoam and have run through three tanks of pure gas. When I discovered possible coil failure could be the problem I started reading about issues that could cause the misfiring. Plugs are relatively cheap and I thought maybe I would replace them anyway and if that doesn't fix the problem take it to a shop for evaluation. I am not equipped with any specialty tools or knowledge to know much about what I am doing. I can change plugs if my standard sockets and wrenches will fit in the tight spaces and I can plug in new parts but don't want to buy parts I don't need either. My truck only has 70k miles on it. I have a friend coming over with a code reader to see what it might show but I don't believe it will tell you exactly what part to replace, just what the general symptom is and possibly which cylinders are misfiring. Could be fuel injectors too?

Someone who tuned my truck years ago put in Denso TT16 plugs or something like TT but definitely 16 was the number.

I do have long tube headers and a cold air intake but no power mods on the engine otherwise.

Any and all help or suggestions are welcomed. And thanks in advance for any assistance.

avalonandl · March 28, 2019

DENSO PTJ14R15 replacement spark plugs

AC Delco 41-983

Brisk GR17LP-5

NGK 5146

NGK PTR4B-15

AC Delco are at most Napa etc.

diyer2 · March 28, 2019

If the scan tool tells you what cylinders are misfiring, swap the coils with a non misfiring cylinder.

If the same cylinders misfire after swapping coils maybe injectors.

If the misfire changes to the cylinder that the coil was swapped to maybe bad coil.

I guess you have no idea how many miles are on the plugs?

Change them.

The gap is preset from the factory but checking it is good idea.

There are a lot of plug choices. Just look at rockauto,com.

LH Lead Foot · March 28, 2019

All of these are good spark plugs, but get iridium plugs, whether NGK, Denso or ACDelco. But as you indicated, you are experiencing misfire(s). Let's start their first.

Kent-Moore or OTC sells a spark plug tester that has an air gap that forces the coil to produce at least 25,000 volts or 25kv for short. ACDelco for years had such a device called ST-125. "Spark Tester" Model #1, 25kv voltage air gap. Many type and brands can be purchased. They come with an alligator clip for ground and a spark plug wire tip. One, buy one, engine off, disconnect a plug wire (Twist first, then twist and pull to remove) and install the spark tester & clip to ground. Start engine and look to see if there is spark or no spark. It works like a "Go / No-Go" gauge. If there is spark, yes, it could be the spark plug as long as engine mechanical is ok.

Begin...Compression check during cranking with fuel relay & fuse removed. Make note. Move to next one and repeat. They all should be within 10% of each other. Next...Do a running compression test. This is the compression gauge in the hole, un-plug coil, start the engine, make note of reading. It will be much lower than a normal test that's accomplished at 175 - 225 RPM of the starter. At idle, the intake air will be adjusted for anything below programmed desire idle speed of 750. The reading is lower because of volumetric efficiency. The faster the engine turns, the harder it is to get atmospheric gases into the cylinder. The ability to fill the cylinder is volumetric efficiency. Note all reading from the running compression test and they too should be within 10%. At any point, you find one that is really low, it could be a broken spring or valve train issue like collapsed lift with AFM or called Displacement on Demand. It has to be checked as you cannot tune an engine that has little or no compression in one cylinder. If you are lucky and all cylinders have good compression, running or not, what did the spark test find? If one spark test fails, switch plug wire. Now it spark with tester, you need wire(s). I would suggest ACDelco inductance wires as shown below. Actual wire wrapped around arimyd core and test at 1,000 ohms per foot as compared to 10k-12k per foot.

If your wire swap did not work, check with key-on, engine-off, coil disconnected. Using a test light or DMM, one wire should be hot or B+. It passes thru the coil, hot all the way back to the PCM. It simply grounds the control wire, turns on the coil, then turns off when spark is timed ready. Their where 3 coils for years and I can not tell which one you have. Denso, Melco and Delpi. Melco & Denso coil primaries because their is an electronic module between the "IC" terminal and the primary windings. The secondary canon be measure because they use a diode. All coils are internally grounded through the harness, but Melco & Denso are also grounded thru the case to ground. A permanent magnet is part of the frame to reduce size and increase out put. So, take a coil in, if bad, to match it at the parts store.

No Check Engine Light? The crank sensor tells the PCM which two cylinders is on top, but only the camshaft sensor will tell the PCM which cylinder needs spark. So, P0300 = mis-fire, P0307 = cylinder number 7. This will turn the CEL as soon as it happens for 50 seconds or continuous mis-fire. You will the correct cylinder number only after 80 seconds of continuous mis-fire after the PCM matches the cranks speed learn stored in it's memory.

Injector...If your purchase a "Noid Light", it will blink showing it is turn on & off. Use a long screw driver on the injectors body, place in fist with the handle in ear. You will hear it click. It can still be blocked as a tiny filter is in the top body of the injector, but fuel pressure remains available to all.

As for bad fuel, ethanol causes no issue unless you got a tank of E85 in a vehicle without the capabilities of running on & recognizing E85. Sea Foam has it's critics, and I am one. It will not open a clogged injector unlike "Berrymans B-12". Use "Eagle Eye" brand of fuel stabile in the tank for long term storage. Guess the tanks current volume and gallons remaining, then add twice the normal amount for long term (6 months or More) just like a snow-blower, boat motor, weed-eater in winter, etc.

Tools, DMM, test light, good spark plug socket with u-joint built in SnapOn best (You snap off a plug / used a little anti-seize on each plug, compression tester with release valve, noid light kit (Take photo to ID the correct one), long screwdriver / mechanics stethoscope can be purchased at HF. Parts at RockAuto. Fuel stabilizer sold a parts stores, Lowes, Home Depot, Menards and small engine shops every where.

Hope this helps.

ASE Master Tech since 1978 / Retired

For plug wires, see below.

swathdiver · March 29, 2019

15 hours ago, MorrisGray said:

I was hoping some of you might give me your thoughts and recommendations for which plugs to buy... ?

I have a 2002 Silverado 5.3L v-8 Vin code T

ACDelco 41-962

Stick with GM OE or ACDelco Professional. Plug in your VIN here:

https://parts-catalog.acdelco.com/catalog/catalog_search.php

txab · March 29, 2019

https://images.oreillyauto.com/parts/img/documents/acd/41-110.pdf

If you'd like to use iridium then 41-110

Double platinum 41-962

All with .040 gap. Originally the set gap from factory was .060 on OEM, about 2005 GM issued a bulletin to go to the .040 because of misfire and a couple of other issues

Iridium has a long life, but only slightly longer than Plats. I think on rockauto.com it shows DPs lasting 3x longer than copper and Iridium 4x longer. In an older, high mileage vehicle the double plats will do every thing you need, plus you should save a buck or two per plug.

You'll notice most part # checkers no longer list Iridium for these older models. The PDF is why

Beware of counterfeit plugs if buying on Amazon or Ebay

Edited March 29, 2019 by txab

MorrisGray · March 29, 2019

To all of you... Many Thanks for the replies and advice and opinions.

I am going to get new plugs first and try that.

I swapped coils after unplugging wires to see which cylinder was dropping the rpm or not. Changing the coils did not change the effect so I swapped plugs and then the problem followed the plug so I believe at this point it is the plug or plugs that are bad. I don't know why they would have gone bad as I haven't put many miles on it in the last few years or ever as I only have 70k total since new purchase in 2002.

If new plugs don't correct my problem I will proceed with other testing or take it to a shop.

And again, many thanks. Nice to find a helpful and active forum.

I will come back after new plug installation to follow up with results, may be a week before I get it done though.

sefiroxx · March 29, 2019

https://images.oreillyauto.com/parts/img/documents/acd/41-110.pdf

If you'd like to use iridium then 41-110
Double platinum 41-962

All with .040 gap. Originally the set gap from factory was .060 on OEM, about 2005 GM issued a bulletin to go to the .040 because of misfire and a couple of other issues

Yep, remember the iridium to platinum switch. Came time to replace the plugs on my 01 Suburban, and was convinced by the sales guy to go iridium. Got home, found the gaps did not match the FSM so I reset them. MPG tanked quickly, and after so much time, about to do the retune, ran across the TSB showing the gap change. . . Eerrgh

LH Lead Foot · March 30, 2019

Yes, spark plug gap is important, but usually, newer spark plugs for sometime now, come out of the box with a sleeve over the anode and cathode to protect gap change during handling. I alway think of the "Samsonite Luggage" commercial where they gave a large caged gorilla a suitcase. He banged it around for sometime, they took it out and still worked! Yeh...But all parts are subject to being dropped, bang around, and hit the floor at the shop. Yes, It was one of 4 jobs I had working for GM with one, going to warehouse distributors to look at "alleged" defective parts. Crazy what I saw in boxes.

Back to spark plugs. Under normal circumstances, iridium are pre-gapped. but I would check all visually, but gap can be different for iridium from platinum. So keep this in mind. The combustion chamber is a harsh environment and a spark ionizes gases and cause metal transfer from negative to positive. Iridium is one of the hardest metals known to man and found in the earths crust all around the earth. Thought to be a result of the meteor that hit the "Ukacatan peninsula" when most all dinosaurs where thought to have died because of a nuclear type winter, plus the dust in the atmosphere rained down and block the sunlight for decades.

Too much info, but that's the instructor mode coming out... Sorry!

Look at the top insulator for tiny black line from under the wires boot. Coils will produce as much voltage as possible to jump as gap, under load is the most stress. This is carbon tracking. If found, the plug & wire both need changed. There is no way to get rid of it.

All plugs are not created equal, as plugs with an iridium button welded on both anode and cathode will cost the most, but last the longest with coil over plug / or coil near plug. Carefull gapping the plug as the iridium button can be broken off and as stated, check for updates & TSB's.

I include a photo of the spark plug spark tester. As a dealer tech, we fight the clock all day, so quick, accurate results help with the process of elimination. I hate the idea of parts in a wheel borrow next to the vehicle, even if my wallet could afford it. At the dealership, we did not have that luxury. Yes, the parts where there, but you would get fired in a NewYork minute.

I hate guessing the problem, but the accurate locating the "Root Cause" is very important, rewarding...and many times requires one part.

(Just for Fun!) I used the example of an "Automotive Court of Law".

(Q) Sir, was this relay bad? (A) Yes. (Q) Can you prove it? (A), Well, no, I just move the BLK one from the fuel pump location and replaced it with another BLK one from the horn location...and it worked. (Q) Can you say you guessed? (A) Well, yes. (Q) Can it fail or possible create the same problem? (A) I guess so. (Q), What would be the best practices to determine the relay is actually defective? (A) You would install four jumper wires from the relay center, to the relay, then using a DMM, check it for voltage drop using the circuit turned on, with the meter lead on terminal 30 and the other lead on 87, then repeat until you see a high voltage reading...say 1.5 or higher. A low reading of less than 0.050 is best in the real world, but just real low. (Q), So, you did not properly test the relay in question, but guessed. (A) Well, NO!) (Q) Will it fail and come-back? (A) Possibly. (Q), So how long before it fails? (A) I don't know. (Q) How much will it cost the customer in time, money, loss of vehicle use, etc. (A) I don't know. (Q) So, you guessed? (A) yes, I guessed the relay was bad without knowing for sure by skipping the testing using voltage drop.

(Statement) Sir, you are a technician and you guessed, therefore you are guilty of guessing, wasting time, money and perhaps sold a part that was not the "Root Cause"? (A) YES! YES!

(Judge) I have heard enough, Mr. Technician, I find you guilty of guessing and not testing using "Best Practices" with voltage drop...Therefore, I sentence you to jail and compensate the customer! (Judge) Bailiff, Take this technician to jail!

Ok, a little dramatic, but drives home my point for proper testing. Just a little exercise in jocularity! Have some fun with it.

Otherwise, there would be a lot of dented fenders & broken windshields is you get mag and frustrated. I guess, taking a break, thinking with a beer will help.

Yes, many things should be serviced as a set, plugs, wires, etc.

The diagnostic flow chart includes a section called "Diagnose by Symptoms". It still includes the use of a simple spark plug tester. Simple, but effective.