Backfire Causes? Thumping intake sound

[GrassFed]

Howdy all, hopefully you guys that know a hell of a lot more than me will have an idea here. Long story short I've had a lopey type of idle around 1000-1400 RPM as well as excessive vibration at around 2500RPM and beyond that I have been trying to figure out for some time.

In this hunt, I was listening to it from under the hood and heard a thumping type sound from the intake. I opened up the lid and lifted the air filter and sure enough clear as day the same thumping sound. From what I have read this is caused by a backfire and the thumping is the sound of the explosion in the intake manifold working its way out of the front resonator section.

So, thinking maybe my timing was off causing the backfiring I popped the cam cover and aligned the crank to 0 degrees. Everything there looks good to me I attached pictures so you guys can tell me if I'm crazy.

The ignition timing is all electronically controlled so there's not much I can do there.

Is there any way improper valve clearance could be causing the backfire?

Any help is greatly appreciated. https://youtu.be/F37DaeelLKk

Attached is the backfire clip as well as pictures of the timing.

https://youtu.be/F37DaeelLKk

 

[CB3G_GM]

I guess start first with have you done any work on/around the MAF, fuel or ignition components recently?

 

[aontkos]

I'm sure you've already addressed this, but do you have a CEL or any pending codes?

 

[GrassFed]

Howdy guys thanks for the replies. Two of the 3 coil packs are new (Denso) as well as the spark plug wires and spark plugs. I cleaned the MAF a few times now in the past 5K miles. One of the times I foolishly knicked one of the wires inside of it with the straw from the cleaner.

Driveability wise, it feels like it has plenty of power, although I don't have much of a reference as this is the only 3.4 4Runner I've driven.

I have a code for P0420. I thought for a minute that possibly a severely clogged Catalytic Converter could be the cause for the backfiring and the code, although when looking at it with an infrared thermometer the inlet and outlet temps are not far from each other. I have a feeling the code is because of the small leaks at the O2 ports that I have as well as from the two donut gaskets that connect the crossover pipe. I have confirmed leaks via soapy water and a vacuum at these 4 locations as well as the joint just aft of the rear O2.

 

[HiLife]

Did you/can you run a compression test on all cylinders?
Remember to fully open the throttle blades during cranking.

When did you start noticing the pops in the intake? Was it before the coil change and maf sensor clean?

 

[GrassFed]

I ran a compression test and got 210 +-2PSI across all cylinders. For what it is worth it is fresh off of both heads being rebuilt. It has been awhile since I replaced the coils and cleaned the MAF.

Wanted to add this - with me and one other passenger driving up north 4 hours we got hand calculated 21.82MPG. So, it stands to reason that for the most part the engine is in good condition.

Almost every tune up part has been replaced. Everything related to spark minus one ignition coil as well as both O2 sensors.

Another note, fuel trims short and long term are never more than about 5%.

Me and [MENTION=101744]YFZsandrider[/MENTION] have been experiencing similar problems and have been trying to diagnose them for awhile now.

Any help is greatly appreciated. Thank you guys

Matt

 

[YFZsandrider]

Thanks for posting this [MENTION=137023]GrassFed[/MENTION]. I've been talking with a mechanic about the problem I'm having, and he mentioned that he really thinks all signs point to some kind of air leak. Not all vaccum leak, but an air leak after the throttle body. Could be a bad intake manifold gasket or even a cracked head.

 

[CB3G_GM]

Thanks for posting this [MENTION=137023]GrassFed[/MENTION]. I've been talking with a mechanic about the problem I'm having, and he mentioned that he really thinks all signs point to some kind of air leak. Not all vaccum leak, but an air leak after the throttle body. Could be a bad intake manifold gasket or even a cracked head.

A faulty MAF will often act like a vacuum leak. If you don't find any obvious vacuum leaks and based on your description of "knicking" the wire, I would try and track down a known good MAF to test and eliminate it as the problem (even though the problem didn't happen immediately after cleaning).

If you have your old coils as spares I would swap them in (especially the one you didn't replace) to see if anything changes.

And remember the golden rule, go back over everything you've touched recently and make sure its all tight and connected properly. Good luck!

 

[GrassFed]

Thank you for the help guys. I double and triple checked the plug wires and all of that. I could definitely swap the new coils in although I originally replaced them in hopes of helping this issue as I found two of the contacts to be in rough shape. Nothing changed upon changing them out.

Any other ideas guys? I can't believe that none of you have experienced and fixed something similar.

I'm going to look at ways to troubleshoot the MAF sensor and go from there.

Whatever it is, it isn't bad enough to throw a misfire code, although slight misfires can throw a P0420 apparently because the nature of the P0420 code is such that even at 94% efficiency a code will still throw.

Thank you all again

Matt

 

[octanejunkie]

Check your harmonic balancer, make sure the outer ring didn't separate

Anything related to air, fuel or spark will throw a code, or have one pending

 

[LittleCaesar]

My guess is that something is FUBAR with the rebuilt heads, pull off the valve covers and take a close look at everything.....

https://www.yotatech.com/forums/f115/backfire-air-box-133168/index2.html

 

[YFZsandrider]

Thank you for the help guys. I double and triple checked the plug wires and all of that. I could definitely swap the new coils in although I originally replaced them in hopes of helping this issue as I found two of the contacts to be in rough shape. Nothing changed upon changing them out.

Any other ideas guys? I can't believe that none of you have experienced and fixed something similar.

I'm going to look at ways to troubleshoot the MAF sensor and go from there.

Whatever it is, it isn't bad enough to throw a misfire code, although slight misfires can throw a P0420 apparently because the nature of the P0420 code is such that even at 94% efficiency a code will still throw.

Thank you all again

Matt

If your issue is caused by the same culprit that plagues my 4runner, then it will still be present after replacing the cats. I had a p0420 code and replaced both cats after trouble shooting the o2 sensors, and doing some tests on the cats.

I also thought it might be a MAF sensor issue... so I swapped it with another sensor off a '04 camry(same MAF part #), and it didn't change a thing.

 

[GrassFed]

Your P0420 was ultimately resolved after you replaced the catalytic converters though? Which ones did you go with?

Of course, I was hoping that I could fix the exhaust leaks and run some witchcraft cleaners through them before having to bite the bullet and shell out the $ for CARB approved cats(CA Emissions)

Thanks for the reply little caeser, I'm going to have to pull those off and check it out. This was a gut feeling of mine but am trying the least invasive stuff first. I wouldn't be surprised if I found my culprit after taking those off and measuring clearances and inspecting cams etc.
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[YFZsandrider]

[MENTION=137023]GrassFed[/MENTION] replacing the cats cleared my p0420 code, but nothing has fixed my idle issue. I replaced both cats with Walker. I've had them on for a little over 6 months and am super happy with them. They have a 5 year warranty and 90 day satisfaction guarantee as well.

 

[LittleCaesar]

Your 0420 was ultimately resolved after you replaced the cars though? Which ones did you go with?

Of course, I was hoping that I could fix the exhaust leaks and run some witchcraft cleaners through them before having to bite the bullet and shell out the $ for CARB approved cats(CA Emissions)

Thanks for the reply little caeser, I'm going to have to pull those off and check it out. This was a gut feeling of mine but am trying the least invasive stuff first. I wouldn't be surprised if I found my culprit after taking those off and measuring clearances and inspecting cams etc.
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Let us know. Sometimes it is the little things. There isn't much tolerance for mistakes.

Some time ago my friend's dad rebuilt a semi stock 350 and put it in a 2nd gen Camaro. I remember it backfiring through the carb something fierce. I believe it was the cam being incorrectly set; it was removed, new cam, and all was good. It wasn't a DD though.

 

[YFZsandrider]

Sorry, my post was a little incomplete... yes, replacing the cats cleared my p0420 code. I found a good mechanics video on YouTube where he showed a couple ways of trouble shooting bad cats. With the vehicle at full operating temp, he held the throttle at about 2500-2800 rpm, then used an infrared thermometer to measure temps on the cats. A functioning cat should read a temp of about 100 degrees hotter at the exhaust pipe just after the cat. Mine were the opposite, 100 degrees hotter just before the cat. A proper cat will burn the exhaust inside and have and higher temp post cat. Mine were plugged, hence the higher temp from back pressure, just before the cat.

Anyhow, replaced both cats with Walker and they work great! They're stainless steel, according to Walker. Haven't seen a spec of rust on them, though I do live where we don't get any snow.

 

[GrassFed]

Thank you for the heads up on the Walker Catalytic Converters as I'll be in the same boat if after I get the rest of this stuff situated I still have the code. Exhaust leaks, and proper combustion first to give my old CCs the best chance possible.

Well to anyone that isn't up for a, "What color wheel should I get?" discussion then stay tuned you might just appreciate this ongoing project.

Well yesterday I ran it for about 3 minutes, just long enough to get it into the driveway and then proceeded to start taking the plenums and valve covers off. After however long it took me to do that, I checked the valve clearances. Hopefully the engine was cold enough to warrant proper checking of the clearances.

I'll upload the picture, but the long and short of it is that most of my exhaust valves were about 4 thousandths too tight. NOT good. One of my intake valves was about 3-4 thousands too tight as well. I checked out everything else made sure the Cam caps were still torqued to spec and that the lobes weren't wiped. I couldn't find anything too out of the ordinary besides the fact that my valves are not set at the correct clearances.

When I got everything back together and fired it up in the morning, it was definitely missing. Hooked the scanner up to it and sure enough #2 misfire. Took out the plug to check it out, everything good and best of which it was dry. After this I put a stethoscope to the injector and then to a good injector and sure enough hardly any sound was coming from the #2 injector. Injector also Ohm'd Ok at 14.3.

Part of me wonders if this wasn't part of the problem to begin with and then got worse once I start working around that area and wiggling it moving it around etc--or maybe just pure good luck..

Link of video and picture of the clearances. Until next weekend.

Thanks for taking the time and if you stayed around long enough here are some engine-internal goodies for those interested

https://www.youtube.com/watch?v=MLqbMNHvyXc

 

[YFZsandrider]

So you're getting a new injector to replace that one?

 

[GrassFed]

I reckon I'll get a new one and swap it in and then go from there. Valve adjustment is still going to happen one way or another. Unfortunately, it's not a job where I can save a whole lot of money upfront as the valve shim kits aren't cheap and I won't know which sizes I'll need until I take them out and measure them -then compensate to get the correct clearance.

I would love to get this thing squared away and have a nice smooth engine like everyone else seems to brag about with the 5vz-fe.
Mine vibrates through the floorboards like crazy at about 2500RPM.

Until next time

Matt




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[LittleCaesar]

Well Matt I guess just keep us abreast of how it all turns out. I myself need a valve adjustment, for #4 has become a little noisy (loose I think).

Get the correct clearance on the valves and a new injector and it sounds as if you should be good to go.