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Author Topic: Random exhaust "Pop"  (Read 202 times)
psychohamster
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« on: October 21, 2018, 07:47:02 PM »

Actually my engine does run very good. I have a habit of listening to an idling engine exhaust note and smoothness. When started cold, like sitting overnight, at idle the exhaust is smooth with a steady exhaust pulse but once up to operating temp it gets a random "pop". It isn't a steady 1 - 2 - 3 - POP, but random like every 6th then 10th then 7th pulse,but not when it's cold. I've searched online for answers and it appears this is something all vehicle makes and models experience, even non turbo diesels. Many claim this is normal and others really like it but I can't imagine someone walking onto a dealers lot and hear that on a new car and find it acceptable let alone the factory just ignoring it. I figure it must be a fuel issue rather than an ignition related cause. If it was ignition wouldn't it happen all the time and at a steady pace? Thinking it is fuel leads me to focus on a an injector or maybe the cold start injector.
Anyone know, think they know or even a good guess? Thanks.
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ReelDeal
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« Reply #1 on: October 26, 2018, 04:53:45 PM »

How loud is the "pop"? The idle is up when it is cold. Have you tried increasing the hot idle speed to see if that helps?

T
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psychohamster
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« Reply #2 on: October 27, 2018, 12:14:02 AM »

Overall it does run pretty good. When I start it cold it takes about 1 second of cranking to fire but once it's warm it is just a tap of the ignition.
Once started I go to the exhaust tip and listen to the cadence of the idle and when dead cold it is as smooth as can be. Once it is warm it makes an intermittent "pop/gurgle" type of sound and it feels like it's stumbling slightly when moving. It still bucks slight;y when I'm cruising in second and third at a steady 2000 rpm although it was worse before I put in the new o2 sensor. I am leaning toward a dirty #1 injector or maybe a leaking cold start injector. I am just puzzled at the fact it runs perfect when dead cold and only burbles and stumbles when warm/hot. Why would it act up only once it's warm/hot? Logically a dirty injector would act up at all temps. I've also contemplated a bad temp sensor giving my ECU a faulty hot/cold signal/reading hence the need to check my electrical readings for all the related components to eliminate the guess work. I think it might come down to getting someone to scope the engine with the right equipment and know how to figure it out. It's got to be something because I can't imagine Toyota putting something in their showrooms with this type of issue. I just don't want to do an expensive parts chase.
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ReelDeal
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« Reply #3 on: October 27, 2018, 04:37:05 PM »

I assume there are no codes, that would be too easy. Do you have a wide band to check the A/F? Sounds like the ECU is creating a bit of a lean/rich condition due to bad sensor feedback or maybe something as simple as a bad plug wire.

I think it is electrical though. I'm an old guy. Back when the earth was cooling off good and we all had carburetors, we had a saying: "When you think it is the carburetor, check the ignition". We didn't have OBD's then, we had a Sun Scope and could watch what was happening electrically on each cylinder. I would check the spark plug wires with an Ohm meter. Check the coil, igniter, etc. I would check all of the pins out on the ECU as per the FWM. Then I would fire it up and pull each spark plug wire off of the cap and check the spark color and gap jump. Check the RPM drop on each cylinder when the wire is removed completely and see if they are relatively equal.

Valves set properly? Sticky valve? Hold a playing card next to the tailpipe and see it sucks in when the stumble occurs. That could mean you have a valve sticking.

Good luck!
T
« Last Edit: October 27, 2018, 04:41:47 PM by ReelDeal » Logged
psychohamster
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« Reply #4 on: October 27, 2018, 08:27:54 PM »

The last code I got was a few weeks ago (#5) and it was the second time it came up in 6 months so I replaced the 02 sensor and it did help. I've done the plug wire trick by pulling them individually while its running and it's fine. I always seemed to get shocked when I do it that way so many times I'll use a timing light and clip it down at the plug boot and check the light blink.
I reset my valves about a month ago but the new engine has less then 10,000 miles on it so I'm hard pressed to think it is an internal mechanical condition even though I initially thought my plug was fouling due to a bad intake valve seal. I've also done a compression test but not a leakdown, it was good.
Overall the truck runs very good. It starts fine and pulls hard without any throttle hesitation, but this little "glitch" just shouldn't be there. I'm inclined to think I might have an ignition problem like you mentioned but the bottom line for me is why only at temp and not when it's cold. A bad/dirty injector shouldn't be effected by that. It could turn out to be as simple as a bad distributor cap or as complicated as an ECU. If and when I find it I will definitely pass on that info. To many times you search for a thread on a site that goes into a lengthy discussion and then just ends because I guess they corrected the problem and abandoned the conversation leaving you slack jawed and shaking your head in what they found/did from that point on.
I think I'll concentrate on the ignition at now since it will probably be easier to diagnose and check then a fuel issue. I'll start with the basics and work my way through as far as I am able. Hopefully it is something simple, stupid and cheap.
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ReelDeal
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« Reply #5 on: October 28, 2018, 08:19:14 PM »

Ok. It is something only affecting the #1 cylinder. You say that you are now convinced the plug is fuel fouled and not oil fouled. If it was oil, then your choices are valve stem seal, or worse, broken oil ring on the piston. A broken oil ring would still give you good compression and leak down numbers, but would foul the plug and burn oil like a diesel. Let's hope for fuel/spark. The easiest fix is new/plug/wire/cap. If that doesn't work, pull the injectors and send to Osidetiger or RC Fuel Injection or other shop that specializes in injector rebuilding and cleaning. Most shops over a 1 day turn around and cost between $60-$100. You will get a chart with before and after specs and spray patterns. It has got to be one of the above issues. Anything else would affect all 4 cylinders IMO.

T
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