Engine boggs @3500 after sparkplug replacement gapped at .045 - Diesel Place : Chevrolet and GMC Diesel Truck Forums
 
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Old 11-22-2018, 06:41 PM   #1 (permalink)
2001burb
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Engine boggs @3500 after sparkplug replacement gapped at .045

Hey guys,

I am hoping someone can give guidance here. I have a new 8.1l suburban 2001. I just added a throttle body spacer and replaced my plugs and wires. I gapped them at .045 with Ac delco 41-993 iridium plugs. I used taylor thundervolts 82225.

The engine runs great up to 3600 rpms. Then it is bogging. I have two guesses as to the problem.

1. The spark plugs are not firing properly at that rpm.
2. The air to fuel mixture is off due to the new throttle body spacer. Airaid PowerAid TBS Throttle Body Spacers 200-512-1.

I have removed all the plugs and wires to check for damage. They all look fine. I was under the impression gapping at .045 was supposed to make the 8.1s perform better at high rpms.

It also could be the throttle body spacer is making the air much more dense at high rpms.

More background info. I just cleaned the MAF. which is a Delphi and looked like it was replaced recently. I also scrubbed and cleaned the throttle body. I started the truck and it ran fine after cleaning the throttle body and before putting it on.

I am also In the process of getting a custom tune from diablo Lewis. I am hoping he will be able to help me with air/fuel mixtures and that will resolve the issue. Otherwise I will replace the plugs with standard .060 gapping to see if that fixes it.

Anybody experience this or know which direction I should head in?? Thanks and I will try to upload the video I took.

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Old 11-22-2018, 11:34 PM   #2 (permalink)
2001burb
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Problem solved. Well figured out my idiocy.

There is a rev limiter when in park/neutral. Took it for an drive and no problems.

Happy Thanksgiving everyone

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Old 11-23-2018, 12:44 AM   #3 (permalink)
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Happy Thanksgiving!

Glad you figured it out!

I hope you got the throttle body spacer for free, otherwise you wasted your cash. It does absolutely nothing on the 8.1L engine, except lighten your wallet, it's been proven again and again and again.

When you did your taylor wires, did you put heat shields on at the plugs? The 8.1 puts out plug melting heat to the point Accell makes these with ceramic heat shields to keep from nuking them.
https://www.ebay.com/itm/ACCEL-9065C...XVDY:rk:2:pf:0

I hope you did the 180* tstat at the same time as it makes a massive difference, especially with towing.

No clue on who Diablo Lewis is , but the tried and true tuners for the 8.1L platform, with thousands of well done tunes both, are Westers and Black Bear.

Last edited by Drakito; 11-23-2018 at 12:48 AM.
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Old 11-23-2018, 12:53 AM   #4 (permalink)
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Thanks drakito,

Unfortunately I did pay for it. Oh well.

I re-used the stock heat shields. Hope they pan out. Otherwise I will have to upgrade to ceramic.

And the 180 thermostat is the next and probably last mod I do. As the next thing I do is forced air and I'll have to do it right. And a system will run more than what I paid for the whole truck.

But dreams do come true!! Lol
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Old 11-26-2018, 05:06 PM   #5 (permalink)
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I feel you there! My wants are far, far more than what I can afford!
Stock heat shields on stock manifolds is totally fine. I've seen far to many people take them off and throw them away when they put new plugs in.
The ceramic ones are needed if you put headers on.
A solid tune from Blackbear or Westers, e-fans, headers, muffler, the tstat and you will have a significant increase over stock in both torque and power.
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Old 11-27-2018, 09:25 PM   #6 (permalink)
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Agree with the throttle body spacer. Have no effect on engine.
You mentioned a forced air induction. Where do you put the intake tube through the core support. I have been away from this forum for a while, and was wondering if something had come out.
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Current Rigs:
2006 8.1L GMC 3500 Allison 6 speed 4X4, Reg Cab longbed single rear wheel, 4.10 locker.
265/75R16 Michelin LTX A/T-2. 180 Tstat and plug mod.
Air Box opened. True dual exhaust with an H pipe, two 3inch Glass Pacs
72 Chevy Custom Deluxe fully restored. The actual truck I had in high school.

Past Rigs:
2000 Chevy 2500 Reg Cab 454 3.73 gears. Gone Oct/2001
2001 Chevy HD 2500 Reg Cab 4X4 8.1 ltr 4.10 gears. Gone 12/2003
2004 GMC 3/4 Regular Cab 4X4 Dmax. Gone 4/2005
2005 Chev 3/4 Regular Cab 4X4 Dmax. Gone 9/2006
2005 1/2 ton Silverado 4dr 4X4 Gone 3-2007
2007 1/2 ton Silverado 4 door, Gone 6/15/10.
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Old 11-28-2018, 08:23 AM   #7 (permalink)
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Raylor has come out with a 2.9L Whipple based supercharger. It costs dang near $9K with intercooler, upgraded injectors, etc.
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Old 12-15-2018, 11:19 AM   #8 (permalink)
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I made an aluminum heat shield in front of my battery from the inner fender to the core support, top to bottom. It keeps hot underhood air from going back in front of the core support and into the air inlet between the inner and outer fender. Also remove every inside sound deadener fin inside the airbox, it helps flow. Then add a 2 1/2" round air inlet tube (epoxied in place)below the original inlet, and also make the original inlet larger. Then radius the air outlet to the MAF and use the left over epoxy to radius the exit also. Buy a K&N air element. Mark where you need to open up the inner fender to match and use a piece of foam rubber about 1 1/2" thick with matching holes to seal the whole thing to the inner fender. Next carefully remove the MAF inlet and outlet screens (that raises the flow by nearly 25%) and works great. Remove the Helmholtz resonator and "divot" from the air crossover too. I use a Superchips tuner on the street/tow setting. Stainless worx Headers 1 7/8" (2" work better if you don't do much towing) and dual 3" Dyno Max Super Turbo muffs. You can use dual 3" tailpipes, or do what I did and construct a dual 3" inlet to single 4" outlet "Y". That will minimize the drone. I used a Dyno Max universal 4" (with slip section in the middle) Diesel tail pipe. The single 4" pipe flows 23% less than 2 single 3" pipes, but since the exhaust gasses are much cooler after the headers, head pipes and mufflers, the flow is not compromised. Don't forget to do the manifold mods inside, it is a BIG deal, if done correctly, if not, then the gains will only be about 60% of what the full mods do. Recircuit the PVC to pull from the front corner of the manifold, and add a baffle under it. Use Amsoil in the engine, rear end, and transmission too. Its pricey, but the difference in fuel mileage is worth it. T-body spacers will NOT do anything with or without manifold mods. Boring and flowing the T-Body helps if you have done the FULL manifold mods, otherwise not.

I gained about 50+ RWHP, several miles per gallon, and cut the oil consumption by 65-70%. I have been doing these mods and perfecting the method for over 6 years, and have a flowbench and complete machine shop at my disposal. I also will not argue the merits or usefulness of these mods, here or anywhere else. This is not arrogance, as I have done lots of trucks and know these mods work.
P.S. my sign off line is also not arrogance either, it means: If you are not that wonderful, don't tell anyone that you are. Then others won't expect much from you. TIMINATOR
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Last edited by OkDually; 12-15-2018 at 11:50 AM. Reason: rpi
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