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Thread: Pop / backfire through the throttle body?

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Posts: 1-10 of 12
2014-03-05 01:37:28
#1
Pop / backfire through the throttle body?
I installed my vintage Stillen K&N filtercharger on my P10 which otherwise is completely stock. After the installation, the moment I started her up and gave her a rev I was greeted by a pop back through the intake. I dismissed it as a fluke and it ran great with no issues for a week. This past Sunday I was sitting at a light, it turned green and as I feathered the throttle to pull out I got another pop with a stumble. Hmmm? Today I stopped to back into the driveway of our babysitter and again, pop and stumble.

It has no other drivability issues and has been running great otherwise, and as you can see it only happens occasionally.

Two things I've noticed that may be related. The first week I had the car I changed the cap and rotor, I noticed a tiny bit of oil on the rotor and it does appear I have oil seepage in the area below the distributor. I believe this is a failed distributor o-ring and I very well may have more oil in the cap/on the rotor.

I also noticed that I'm getting exhaust gases OUT of the breather I installed on the AIV/PAIR valve. This seems to indicate and issue with the valve itself or the vacuum controlling it. I doubt this is related, although worthy of a mention and needing to be addressed anyway.

This weekend I am going to...

1- Check the timing
2- Pull cap and check for oil seepage
3- Check all hoses and vacuum lines in the AIV/PAIR valve circuit

Other suggestions welcome, please. Thank you in advance. Time for a glass of red....
Last edited by SE-RMonkey on 2014-03-05 at 01-58-52.
2014-03-05 01:49:54
#2
Where is your timing at? Norm when cars pop thought the intake it has too much timing
2014-03-05 01:57:57
#3
Originally Posted by Dave_SR20
Where is your timing at? Norm when cars pop thought the intake it has too much timing


Oh, good thought! I futzed with the timing about a week prior to installing the filtercharger, and I believe I'm at approx. 17 degrees advance but I will add that to my list of things to check. Thank you Sir.
2014-03-05 02:03:56
#4
I have seen/heard this before on several occasions and timing could be one of them (was one of the issues at the time of the occurrence). When we had a popping through the intake, it turned out the exhaust cam was installed just slightly too tight, so when cranked over, it through a rocker and not allowed the exhaust valve open. This inadvertently caused a "backfire" through the intake once the valves were open (caused by the cylinder charge ofcourse) and not allowing the "explosion" out the exhaust, but out the partially open (on the way to closed) intake valve.

It may not be the case for you, but I would also pop the valve cover off incase you don't find anything a miss. The FSM is a good place to check for timing and as well, @Kyle has a writeup on here (which I used in conjunction with my FSM to confirm my timing settings).

Also, to check, you can adjust the distributor advanced/retarted and see if it soothes the noise. If this happens, it will most likely point to timing and you won't have to pop the valve cover to check right away!
Good luck! P.S How is your friend doing BTW??
2014-03-05 02:14:34
#5
Originally Posted by Boostlee
I have seen/heard this before on several occasions and timing could be one of them (was one of the issues at the time of the occurrence). When we had a popping through the intake, it turned out the exhaust cam was installed just slightly too tight, so when cranked over, it through a rocker and not allowed the exhaust valve open. This inadvertently caused a "backfire" through the intake once the valves were open (caused by the cylinder charge ofcourse) and not allowing the "explosion" out the exhaust, but out the partially open (on the way to closed) intake valve.

It may not be the case for you, but I would also pop the valve cover off incase you don't find anything a miss. The FSM is a good place to check for timing and as well, @Kyle has a writeup on here (which I used in conjunction with my FSM to confirm my timing settings).

Also, to check, you can adjust the distributor advanced/retarted and see if it soothes the noise. If this happens, it will most likely point to timing and you won't have to pop the valve cover to check right away!
Good luck! P.S How is your friend doing BTW??


I'm going on Dave's advice and checking the timing first. Something tells me I may not have had her in timing mode last time I checked it and now that I'm "talking" through this I noticed the idle seems a bit high since then.

My buddy, thanks for asking. Actually just got off the phone with my wife and she asked if hiswife had called us but she hadn't. They thought he might come home as early as yesterday but we haven't gotten any updates. I'm going with "no news is good news" at this point, I don't want to be a pest but I'm going to call his wife tomorrow to see what's up. And anyway, their dog is stinking up my house!
2014-03-05 13:55:38
#6
Before you even started talking about the distributor I was leaning towards it not really being a backfire, and instead being a pop from the ignition system. Usually the high voltage coil wire gets loose on one end and eventually a spark pops it off with a bang and the car dies. But yours stumbles and then recovers, which makes me think it is an ignition issue somewhere else, possibly in the distributor. Then you started talking about oil in the distributor and I'm pretty sure that's where the issue is. Not positive, but I'd look there first. The CAS does not have enough adjustment on a factory setup to cause real backfires. That takes a stand-alone or similar.
2014-03-05 14:55:26
#7
SE-Rmonkey hasn't messed with the cams so I'd rule out the exhaust cam being too tight-
2014-03-05 15:16:27
#8
Originally Posted by Storm88000
SE-Rmonkey hasn't messed with the cams so I'd rule out the exhaust cam being too tight-


I think you missed my (many) points
2014-03-05 15:46:18
#9
Originally Posted by Boostlee
When we had a popping through the intake, it turned out the exhaust cam was installed just slightly too tight


and how did I miss that?
2014-03-05 16:18:43
#10
Originally Posted by Storm88000
Originally Posted by Boostlee
When we had a popping through the intake, it turned out the exhaust cam was installed just slightly too tight


and how did I miss that?


My point was never that it is a re-installation/installation issue with the cams (they were notably never removed), but there are several different scenarios which can cause this issue. Also, overtorqing the cam is not the only reason one can lose or have a rocker become dislodged from it's place.

Also, as mentioned, I pointed to timing and gave him several other options incase timing/the distributor checks out and he is still scratching his head .

You just gotta read between the lines a bit my friend and stop taking my statements out of context. If you read the entirety of my posting you would have seen that
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