L29 7.4L Spark Plug Gap & Design — Fine-Wire vs Conventional, .035" to .060" Gaps

[deepsiks]

The new IT16TT spark plugs showed up in the mail today. I’m hoping to get them installed this weekend, depending on my plans and hopefully some better weather—it’s raining today.

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[dzynda]

It look like silicate deposits from anti-freeze leaking into the cylinder. video: skip ahead to 0:58

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I'm not losing coolant though, a few years ago I was and found coolant in the oil and thought it had a bad head gasket but found out the lower intake gasket was leaking coolant.

 

[dzynda]

The new IT16TT spark plugs showed up in the mail today. I’m hoping to get them installed this weekend, depending on my plans and hopefully some better weather—it’s raining today.

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Those look nice, you went with the .035 gap? Have you heard of Nology? I have their wires that have a grounding strap on each wire. I also have their coil amplifier and silver core plugs. That truck has a lot more done to it and it is being repainted again. Maybe a waste of money I don't know.

 

[dzynda]

I bought a compression tester but it was a cheap one I guess and wouldn't release the pressure. So I returned it and got a better one today. From Did get cylinder one was 150psi and then cylinder 2 was the same but I'm not sure that I trust it so I'll try to test them all this weekend. I also tried these spark testers to see that I was getting spark. I put one on each wire and it was quite a light show, I can't upload the video. I'm not sure that these are really reliable as for testing if the cap is bad vs pulling the cap. Weird that I tried taking a screenshot of the video and the passenger-side is the three pictures. I couldn't get all of them on in one picture. The driver's side I could which I'm wondering if there is a firing issue? Or maybe I'm over thinking it?

 

[deepsiks]

Roger on the compression test. If cylinders 1 and 2 both showed around 150 psi, that sounds encouraging, but testing all eight with the new gauge will give you a much better picture.

I’m not quite sure what to make of the lights from the screenshots alone. Were the passenger-side testers actually dimmer or less consistent while you were watching them, or did they only appear that way in the pictures? A screenshot from a video may not capture every flash because of the camera’s frame timing, so I wouldn’t assume there is a firing problem based on that alone.

I would take a look at the wires and inside the distributor cap for corrosion, carbon tracking, moisture, or damaged terminals. I’d also double-check that the wires for cylinders 2 and 4 are connected to the correct numbered terminals on the crab cap.

 

[deepsiks]

Those look nice, you went with the .035 gap? Have you heard of Nology? I have their wires that have a grounding strap on each wire. I also have their coil amplifier and silver core plugs. That truck has a lot more done to it and it is being repainted again. Maybe a waste of money I don't know.

The IT16TT plugs come pre-gapped at .040 inch. Hopefully, I’ll get them installed this weekend. I’ll have to check out Nology. For the cap, rotor, and wires, I keep it simple and stick with ACDelco.

 

[dzynda]

Roger on the compression test. If cylinders 1 and 2 both showed around 150 psi, that sounds encouraging, but testing all eight with the new gauge will give you a much better picture.

I’m not quite sure what to make of the lights from the screenshots alone. Were the passenger-side testers actually dimmer or less consistent while you were watching them, or did they only appear that way in the pictures? A screenshot from a video may not capture every flash because of the camera’s frame timing, so I wouldn’t assume there is a firing problem based on that alone.

I would take a look at the wires and inside the distributor cap for corrosion, carbon tracking, moisture, or damaged terminals. I’d also double-check that the wires for cylinders 2 and 4 are connected to the correct numbered terminals on the crab cap.

I hope that I can get the compression test done this weekend. When the truck was running they all looked nice and bright but I agree about visually checking the cap because those are prone to going bad. Thank you

 

[dzynda]

The IT16TT plugs come pre-gapped at .040 inch. Hopefully, I’ll get them installed this weekend. I’ll have to check out Nology. For the cap, rotor, and wires, I keep it simple and stick with ACDelco.

They are expensive I think the wire set is around $4 or $500 They are lifetime and I've had them for at least a decade with no issues. I have Accel 9000 on my other truck, I had AC DELCO wires on this truck but they just don't seem to hold up well. I went with a set of wires from O'Reilly's this time I like the ceramic plug boot. I've used the msd one that have socks on them too.

 

[Carlaisle]

@dzynda The cylinders that are home to those plugs that look like they were salvaged from the wreckage of the Exxon Valdez most likely have broken/seized rings. Valve guides/seals on the L29 are remarkably reliable. I've never actually replaced one other than as part of a full rebuild. Some Marvel or Seafoam might eventually help with rings that are seized but will obviously offer considerably less assistance if they are broken.

A rod knock is pretty hard to mistake. It's unlikely to explain your "tick". An exhaust leak is always the first place to look for such a noise. If it cannot be found there, the valve train is the most likely culprit. How many miles are on your engine? GM did have some soft cams in these engines, but very few. Much more common is for the retaining clip in the lifters to fail. It typically goes around 150k. If you make it well past that, they seem to last pretty much indefinitely, so almost certainly a manufacturing defect. Need to pull the lower intake and put your eyes on them for all of 60 seconds to confirm. If luck is on your side and you drive with a delicate foot you can limp along like that for a long time, but it is not advised. It'll work right up until it doesn't.

I wouldn't worry about my fuel pressure dropping over a period of hours. If it drops over a period of minutes and you still have the OEM injectors they're almost guaranteed to be the issue.

If you need to keep this truck running for a while, just swap out those gnarly spark plugs on a regular basis. They're not doing you any good caked like that.

 

[dzynda]

@dzynda The cylinders that are home to those plugs that look like they were salvaged from the wreckage of the Exxon Valdez most likely have broken/seized rings. Valve guides on the L29 are remarkably reliable. I've never actually replaced one other than as part of a full rebuild. Some Marvel or Seafoam might eventually help with rings that are seized but will obviously offer considerably less assistance if they are broken.

A rod knock is pretty hard to mistake. It's unlikely to explain your "tick". An exhaust leak is always the first place to look for such a noise. If it cannot be found there, the valve train is the most likely culprit. How many miles are on your engine? GM did have some soft cams in these engines, but very few. Much more common is for the retaining clip in the lifters to fail. It typically goes around 150k. If you make it well past that, they seem to last pretty much indefinitely, so almost certainly a manufacturing defect. Need to pull the lower intake and put your eyes on them for all of 60 seconds to confirm. If luck is on your side and you drive with a delicate foot you can limp along like that for a long time, but it is not advised. It'll work right up until it doesn't.

I wouldn't worry about my fuel pressure dropping over a period of hours. If it drops over a period of minutes and you still have the OEM injectors they're almost guaranteed to be the issue.

If you need to keep this truck running for a while, just swap out those gnarly spark plugs on a regular basis. They're not doing you any good caked like that.

Thank you and I appreciate everyones responses. The truck has 312k on the clock, I don't know much history on it other then what a car fax told me which wasn't much. It does have a Jasper sticker on it but I've identified that is for the 4l80e. I've owned the truck since fall of 21 so about 5 years I didn't really drive it much until March of 23 when my duramax went into the shop then one of my other obs 454 burnt up on me. I still think it was a squirrel or something that got into the wiring but idk. I drove it for a few months that then thought that I had a bad head gasket because I found coolant in the oil. I replaced everything and was having a difficult time getting it to run correctly. I replaced the distributor, plugs, wires and it was good. There are no cats on it well they have blown out basically that exhaust system was on my other truck. I do have all 4 oxygen sensors on it. I'm going you keep an eye on the oil consumption it's not a lot. I'm not losing coolant, I'm thinking the tick is in the valve train. It kind of goes up if you give it a little gas and it say flutters down as you let off, if that makes sense. I've pulled the valve covers thinking a broken or bad rocker or bad lifter. I could see anything but I could be over looking it too. Here are some old pictures the truck kind of sat over a year or so as I slowly cleaned everything and fixed it. I flushed the oil a few times and coolant also to try and make sure it was cleaned out. I've probably put 12k miles on it since the intake gaskets have been done and it idles smooth at 700 or 800 rpm the timing is about 20° which I thought was supposed to be zero. I'm just trying to give all the information that I know, thank you all again for the input. I really appreciate it.

 

[deepsiks]

I have a set of NGK Rutheniums to go into my 383. That being said the ignition system on it will fire just about anything.

Hi @L31MaxExpress , I finally had a chance to look into those plugs. Which NGK Ruthenium plugs did you go with? I see that the Ruthenium HX line comes in two different electrode designs: DFE, which looks very similar to the opposed fine-electrode design of the Denso IT16TT and is recommended by NGK for naturally aspirated applications, and PSPE, which is aimed more toward turbocharged and supercharged engines.

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Will this be your first time running them? I’m also curious about what led you to choose the Ruthenium plugs and whether there was a particular benefit you were looking for. I’ve been reading more about the different electrode designs lately, so I’d be interested to hear your thoughts and how they work out for you.

 

[deepsiks]

I’ve run into a bit of a delay. When I tried to remove the existing spark-plug boots, I found that they were bonded to the plugs so tightly that I doubt the wires will come off without being damaged. Reusing compromised wires would pretty much defeat the purpose of installing the new plugs, so I ordered a fresh set of ACDelco wires along with some spark-plug boot protectors.

ACDelco 748G/GM 19171857 spark-plug wire set — the GM OE set for the L29

DEI 010552 Protect-A-Boots — for some additional heat protection around the plug boots

Everything should arrive in about a week. Once it gets here, I should be able to install the new IT16TT plugs, wires, and protective sleeves together without drama. This time, I’ll be sure to use a good amount of dielectric grease inside the boots so they don’t bond themselves to the plugs again — or at least less likely.

 

[AuroraGirl]

Hello fellas, since we are on this subject and I've searched and haven't found anything. You all seem very intelligent and I'm stumped but I'm trying to figure this one out. This is about plugs and spark, I have what looks like melted plugs. It's a 97 L29, I was having issues getting it to run right after replacing both intake gaskets. I replaced the distributor, cap and rotor also and it still wasn't running well. I ended up bringing it to a shop and they got it running better by replacing the cap, rotor, wires and plugs. It was actually a bad wire that had a 90° boot that I didn't see was bad. They used ngk plugs and 350 wires that didn't fit right so I replaced them with a better set from O'Reilly. I left the plugs, I've fixed the exhaust, cats are blown out so open. I've replaced the O2 sensors and I've noticed that it's injectors are not holding pressure now after a few hours of sitting. It's also had a tick pulled the valve covers and rockers all look OK. It idles fine and runs fine, it's hard to hear the tick over the exhaust manifold leak on the driver's side. I'm trying to get a bracket from Kral auto parts to eliminate the manifold leak.
The oil pressure is 60 when started and after not long drops, it's around 20 at idle and 40 while accelerating. I've tried 5/30 and I've tried heavier oil it always does the same thing. I have been driving this as a daily since last October because I have two trucks that are being painted (don't get me stated about my paint guy taking forever) and my duramax fuel pump went out which I'm trying to fix.

After putting I'd say 6,000 miles or more on it, oil changes checking everything and coolant everything looked good. The truck started running poorly so I pulled the plugs and this is what I found. Some look melted, I've never in my life seen that and have no idea why.

severe carbon tracking on the plugs,you arent using any dielectric interface on the boots to the porcelain

 

[AuroraGirl]

I’ve run into a bit of a delay. When I tried to remove the existing spark-plug boots, I found that they were bonded to the plugs so tightly that I doubt the wires will come off without being damaged. Reusing compromised wires would pretty much defeat the purpose of installing the new plugs, so I ordered a fresh set of ACDelco wires along with some spark-plug boot protectors.

ACDelco 748G/GM 19171857 spark-plug wire set — the GM OE set for the L29

DEI 010552 Protect-A-Boots — for some additional heat protection around the plug boots

Everything should arrive in about a week. Once it gets here, I should be able to install the new IT16TT plugs, wires, and protective sleeves together without drama. This time, I’ll be sure to use a good amount of dielectric grease inside the boots so they don’t bond themselves to the plugs again — or at least less likely.

go ot harbor freight, and buy coolant hose pick set from icon. Then use a large pick to start the boot removals use a q tip to smear the dielectric grease os it doesnt end up between the metal contact and that. or use molykote.

also , smooth porcelain is better if you can find it but not a big deal

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you can use the clear stuf but if you want better stuff, molycote

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HERES an improvement to dielectric grease IF You want it

 

[dzynda]

severe carbon tracking on the plugs,you arent using any dielectric interface on the boots to the porcelain

I'll get some on them thank you.

 

[dzynda]

I’ve run into a bit of a delay. When I tried to remove the existing spark-plug boots, I found that they were bonded to the plugs so tightly that I doubt the wires will come off without being damaged. Reusing compromised wires would pretty much defeat the purpose of installing the new plugs, so I ordered a fresh set of ACDelco wires along with some spark-plug boot protectors.

ACDelco 748G/GM 19171857 spark-plug wire set — the GM OE set for the L29

DEI 010552 Protect-A-Boots — for some additional heat protection around the plug boots

Everything should arrive in about a week. Once it gets here, I should be able to install the new IT16TT plugs, wires, and protective sleeves together without drama. This time, I’ll be sure to use a good amount of dielectric grease inside the boots so they don’t bond themselves to the plugs again — or at least less likely.

The suspense is killing me. lol

 

[deepsiks]

The suspense is killing me. lol

Me too!

 

[dzynda]

Me too!

Those are pricey dang, I was looking at the twin tip ones .04 gap #4511 about half the price of the IT16TT. In my current situation a more affordable plug may be better. Idk

 

[deepsiks]

Those are pricey dang, I was looking at the twin tip ones .04 gap #4511 about half the price of the IT16TT. In my current situation a more affordable plug may be better. Idk

Not so bad, I got the for $9.21 each at https://www.sixityauto.com/denso-47...for-it16tt-it16tt-tune-up-kit-3056104713.html

 

[dzynda]

Not so bad, I got the for $9.21 each at https://www.sixityauto.com/denso-47...for-it16tt-it16tt-tune-up-kit-3056104713.html

O OK thank you, they are $15 each at the parts store.