So I just had my tranny oil/transfer case oil/ rear diff oil/ brake job and spark plugs done this last week. All but the plugs were done at the dealer (gapped to .028.) A few days later I noticed at a warm, non-moving, idle an intermittent popping noise. Similar to the clunk of a bad strut mount but sounds like popping pop corn. It seems to feel strongest on the floorboard on the driver side where the tranny/tc would be. There are three to four pops that are clearly heard (not obnoxiously loud, and can only be heard while in the car.) After a few pops it will then come and go at idle. In the pattern of 4-6 pop at startup and then goes away, 30 seconds go buy a few more come... exe exe. It is only able to be replicated after the car has ran for 5-10 minutes and the only time I feel/hear is when i am at a idle or stopped. Whether the clutch is engaged or not engaged, in gear or neutral. This wasn't a problem until the above work was done and I am just baffled at what it could be. I am going to run it by the dealer tomorrow and see what they say, but i figured it would be best to throw it up on here to see if anyone else had an idea. I have ruled out low fluids due to the gears shift as easy as ever, and there isn't the notorious TC whine. Also it isn't the exhaust pop either. For that is notable whether in the car or outside the car. The only way to hear this is to be sitting inside the car. I have put my head above the motor while it was happing and no noise can be heard (had the wife sit in the car.) Like i said, there is no noise when the car is moving, only when it is at a idle. There is no rpm change or vacuum loss as well. Hopefully someone has some ideas or possible issues. Going to grab another set of stock iridums today to rule out bad plugs, but this doesn't seem like plugs do to me still having a full/strong power band to 7800, and no reflected idle changes. Thanks for your guys help and take er easy.

 

Sounds like misfiring.

1. Make sure the coil packs are set correctly.

2. Make sure the coil packs are sitting tight on the plugs.

3. Check the gap on the plugs.

4. Make sure you tighten the plugs back to the correct torque specs (18 +/- 4 ft-lbs).

 

Yeah. I'd definitely say it's ignition-related as well, but only if there are problems at high rpms to go with it.

The only other thing I can think of is maybe an exhaust leak? Have you tried listening behind the car with the wife sitting in it?

 

I haven't thought to try and check for a leak... I tend to agree with you on it not being a ignition related problem due to me not having and issue with my power band or basic driving. Exhaust leak would be plausible due to the clunk feeling being where the tc/tranny are. Just move it over a inch and that is where the DP meets the cat delete. I will jack it up tomorrow and see if there are any noticeable holes. Maybe since it only happens when it is warmed up it is causing it to expand and create the leak. Worth a shot at least. thanks for the input.

 

No problem, let us know what you find!

 

Ok so here is what I found... Checked for the exhaust leak and didn’t see anything visually. The pops do seem to be coming from the dp. Detonation maybe? So I figured I would check the SES light out to make sure nothing new has popped up, knew one cause for it was the cat delete. The scan found that I am running lean (wish I had that A/F gauge now.) So I took the car to the dealer to a tech I trust and he hooked the Mitsu scan tool up to the car. My O2 sensors are registering as they should (both at around .8-.9 low and high end) Was told this is normal since I am running without the cat. But then he went to another menu and he saw that I was at 12.5% fuel correct (highest value possible) The number that was changing was around 9.9% and he said I want both those numbers as close to 0 as possible. Not sure if that holds for a tuned car due to, but he said it still shouldn’t have been so high. He stated this is common with a car running lean due to a vacuum leak. This was all done at idle. He said I could have a vacuum/boost leak, bad fuel pump, or MAF. I figure I can do the boost leak test myself, but would probably have to take it to a shop for the rest to be tested. I pulled the plugs and have some pictures of them on my home PC that I will post up later for you all to take a gander at. Since the plugs are only a week old not sure if the whiteness on them is due to the lean issue, or just standard plug wear. There isn’t a lot of color, just a little bit on the side electrode, and no whiteness on the center. I figure I am about to park the car for awhile until I can find a shop I can trust to do an inspection, or until I figure just what is going on. Hopefully no damage has been caused. Anyone know of some good places in Indianapolis, IN that would be trust worth for an Evo?

 

Any shop with a dyno and/or wideband can tell you if you're lean or not at idle and throughout the normal rev/load ranges.

I've never tuned a stock ECU, so I have no idea if those correction values are ok or not.

If it were fuel, I'd suspect a pop from a late ignition caused by aggressive cams and too much fuel, not stock cams and a lean situation. Unless maybe you are so lean that the clunk is from a lack of ignition rather than a late ignition?

 

jbrown I am going to pick your brain here because you have been so helpful so far with troubleshooting and I appreciate that. The lean issue aside because that could be unrelated to the popping noise. Not saying they don't go hand in hand at this moment, but the popping noise did show up after the dealer did the fluid changes. Is there any known noises that the transfer case and tranny make that show there is a problem? Outside of whining and grinding gears? If the incorrect oil, or not enough oil was put in would that in any way cause a popping noise? Whether it be idle or driving in general. Aside from that because I don't think that is the case anymore but wanted to clear the air before killing that issue.

Now you stated that it could be lack of ignition. This has “sparked” my interest. Since I did change the plugs (kept stock IGR7A-G) and it seems to keep coming back to an ignition related issue so I am really swaying towards checking that stuff out. Would possibly a coil on plug or one of the plug wires be going? Would that in turn cause a lean issue with an intermittent popping sound/feel? If that is plausible would I just check the resistances on those to see if they are ok, and also get a spark light to check for correct spark to troubleshoot those?

FYI: I did run a compression test and got 175-180 for each cylinder so I am ruling out anything valve or piston related at the moment.

Once again thanks for the help troubleshooting this, and will get those pictures posted once I get them resized for the 100k limit

 

Well you said the car was standing still. If you smoked a transfer case, but the car was still driveable, it would pop, but only when turning (been there, broke that) Aside from that, low or incorrect fluid could cause whining, but again, only while moving.
I meant a lack of ignition in the combustion chamber that is instead happening in the exhaust manifold because the unburned fuel is ignited by the hot manifold. This rarely happens in a lean situation, I would suspect it more if you were too rich at idle. If you were either excessively rich or lean I would expect the car to stall occasionally or at the very least have a rough idle.

Anything related to the plug wires or coils should effect more than the idle, but they are easy enough to get to that metering the wires shouldn't be tough. I've never metered the stockers, but I would expect them to read somewhere between 2-20kohms for the short one and triple that for the long one.

That's a good start, didn't even consider that it could be a sticky valve or damaged valvespring. Wouldn't know how to test for that without a lot of effort.

 

Nope, so far at idle... it has progressed to being noticeable when the car is slowing down. But most the time it is doing it at idle. And of course no whining noises to note, at least yet : )...

Haven't had a hard time starting, nor has it stalled on me yet. The idle is starting to be affected by the pops now. Drops to around 700-750 then back to 850 -900 when the pops disappear. This just started today. About to park the car for the next week, and if none of the troubleshooting for the plugs work I already have a date scheduled with AMS in Chicago to take care of a few things. (Headwork, Cams, AFR Gauge, tune.) So I may just have them put their brains to it at that point. I will report back after I test the wires, and let you know if anything comes of that. Once again thanks for your helpful insight and inputs. Let me know if you think of anything else.

 

Any news??

 

Well after taking it to AMS the noise is GONE!!! Lean issue has been solved, and it now runs better than ever thanks to the guys at AMS. It seems the maps I was running with the UTEC were causeing the issues. As far as the popping noise they could not produce it, and yet to know what exactly that was. But it is gone and that is all I care about. Since the 272's have been installed and car has been tuned the car has never ran better. JBrown thanks for your help with troubleshooting. Thanks

 

glad you got it worked out man!