| Author |
Message |
Terry Springer (Tspringer)
Member
Username: Tspringer
Post Number: 286
Registered: 4-2002
| | Posted on Tuesday, October 01, 2002 - 10:51 pm: | |
Im having this same problem as well. I am also still getting a good bit of exhaust smell in the engine bay area, so I suspect an exhaust leak around one of the CO tubes on the front exhaust header. However, it could be plugs (im using Champion) or carbs?
How would an exhaust leak cause such popping on deceleration? |
Hans E. Hansen (4re_gt4)
Junior Member
Username: 4re_gt4
Post Number: 208
Registered: 4-2002
| | Posted on Tuesday, October 01, 2002 - 1:16 am: | |
NGK 5 series?? Highly respected 'Carlo' in Seattle told me that he has seen the 6 series cut a piston like a laser. Told me to use the 7's, which I have had zero problems with on my 27 year old car. Maybe you have a mixture prob?
PS - Don't hold me accountable for the plug advice. Just relaying what a professional F-car mechanic told me. |
Mitchell Le (Yelcab1)
Member
Username: Yelcab1
Post Number: 420
Registered: 11-2001
| | Posted on Monday, September 30, 2002 - 11:24 pm: | |
Those of us who are unlucky enough not to have the factory tool for plug removal have to do with Sears and Snap on tools. So, for me a 13/16 plug socket, a flexible extension and a 3" or 6" extension depending on front or rear bank. |
david handa (Davehanda)
Junior Member
Username: Davehanda
Post Number: 249
Registered: 5-2001
| | Posted on Monday, September 30, 2002 - 8:33 pm: | |
How about using the tool provided in the factory tool kit? Always worked for me... |
Sean Higgins (Sean_higgins)
New member
Username: Sean_higgins
Post Number: 6
Registered: 9-2002
| | Posted on Monday, September 30, 2002 - 8:11 pm: | |
LOL that's my problem then. My 13/16 is too fat to fit down the sleeve. I'll have to look into getting a different one. Thanks! |
Erik R. Jonsson (Gamester)
Junior Member
Username: Gamester
Post Number: 53
Registered: 3-2002
| | Posted on Monday, September 30, 2002 - 12:39 am: | |
13/16 plug wrench, has to be a thin wall. I successfully use a Snap On thin wall deep 12 point, with a 3" extension. |
david handa (Davehanda)
Junior Member
Username: Davehanda
Post Number: 246
Registered: 5-2001
| | Posted on Sunday, September 29, 2002 - 10:45 pm: | |
Stacey, is it wise or recommended to just but the hotter plug in the cylinder that is giving you trouble? Or this even something to worry about? |
Sean Higgins (Sean_higgins)
New member
Username: Sean_higgins
Post Number: 5
Registered: 9-2002
| | Posted on Sunday, September 29, 2002 - 7:44 pm: | |
I mean this things sounds like a volkswagon. It's that bad. What size socket does it take to remove the spark plugs? I have deep well sockets and nothing seems to fit, maybe they aren't deep enough. |
Gordon Hollingsworth (Gordonh)
New member
Username: Gordonh
Post Number: 7
Registered: 5-2002
| | Posted on Sunday, September 29, 2002 - 6:41 pm: | |
A carb 308 will pop a little on deceleration when the motor has been run long enough for the header and muffler to get good and hot IF the cats have been removed, AND the air injection is still operating. I think what happens is that the added air causes the rich mixture to burn in the "bypass" pipes and muffler. The fuel cutoff with a closed throttle with electric fuel injection is a better design. |
magoo (Magoo)
Advanced Member
Username: Magoo
Post Number: 3161
Registered: 2-2001
| | Posted on Saturday, September 28, 2002 - 4:45 pm: | |
Stacy, You are correct the No. 5's work best for me and I don't get fouling in city driving and short trips. |
Sean Higgins (Sean_higgins)
New member
Username: Sean_higgins
Post Number: 3
Registered: 9-2002
| | Posted on Saturday, September 28, 2002 - 12:19 pm: | |
I forgot to mention that it has a single distributor conversion. Don't know if that makes a difference or not, in what might be the cause. |
stacy o'blenes (Stacy)
Junior Member
Username: Stacy
Post Number: 58
Registered: 8-2001
| | Posted on Saturday, September 28, 2002 - 12:01 pm: | |
Sean,
I had the exact same problem. I cleaned up and converted the distributors to crane xr700, new wires, and new ngk brp6evx plugs. The thing ran like a dream for a couple weeks until one day I got stuck in traffic. It started missing with occasional backfire (nothing like before). This recrrence was due to a fouled plug. It happened a couple more times before I switched to ngk bpr 5's and it runs great again with no more fouling. It was the same cylinder that fouled each time and I suspect I have a bad valve seal.
Bottom line is it sounds to me like an ignition issue. However you should also check your plugs. You may have some oil fouling from worn valve guides/seals.
THe ngk 5's are hotter than recommended but it seems from this site that some people have had the same experience as me with the 6's and have switched to 5's (magoo where are you?) I just can't justify hauling the engine out to go after those seals yet.
|
Burnell P. Curtis (Burnell)
New member
Username: Burnell
Post Number: 47
Registered: 4-2002
| | Posted on Friday, September 27, 2002 - 9:29 pm: | |
Sean,
My 75 308 GT4 popped just as you described. I found that the floats were set wrong. Adjusting them solved my problem. Installing 60 idle jets replacing the 55s also helped the idle.
Burnell |
Paul (Pcelenta)
Junior Member
Username: Pcelenta
Post Number: 128
Registered: 7-2002
| | Posted on Sunday, September 22, 2002 - 8:13 am: | |
my 78 definately doesn't run lean...It has no cats,airpump and an euro ansa system (loud)...I find that when the car is initialy warmed to operating temp it doesn't pop at all...after driving all day I will get more poping...I have found that frequent spark plug changes fix this and reduce poping....the car will only run well on NGKs...being a former P-car guy I put a set of Bosch plugs in and it poped like mad on even the most minor decell on brand new plugs...changed to the NGKs and it stopped. |
Richelson (Richelson)
Member
Username: Richelson
Post Number: 823
Registered: 12-2001
| | Posted on Saturday, September 21, 2002 - 12:19 pm: | |
My 308 pops from time to time. Mainly when I am on a hill sloping down. The car will get much leaner due to the angle and cause it to pop. |
Bruno (Originalsinner)
Member
Username: Originalsinner
Post Number: 553
Registered: 5-2002
| | Posted on Friday, September 20, 2002 - 7:21 pm: | |
At high revs on a downshift it is not unusual for exhaust to pop.All the time is no good. |
Sean Higgins (Sean_higgins)
New member
Username: Sean_higgins
Post Number: 2
Registered: 9-2002
| | Posted on Friday, September 20, 2002 - 7:12 pm: | |
Thanks for all the responses. I'll have a lot to check this weekend. Thanks again to everyone. |
Edward Gault (Irfgt)
Intermediate Member
Username: Irfgt
Post Number: 2004
Registered: 2-2001
| | Posted on Friday, September 20, 2002 - 3:33 pm: | |
If your car is equipped with an air pump, a defective diverter valve or a broken vacuum hose to it can cause the backfire. |
'75 308 GT4 (Peter)
Intermediate Member
Username: Peter
Post Number: 2022
Registered: 12-2000
| | Posted on Friday, September 20, 2002 - 2:05 pm: | |
It can be a few things:
-Running lean on some cylinders.
-Vacuum leaks in the carbs (which in essence can cause a lean condition with all of that extra air going into the intakes).
-Exhaust leaks (either the donuts, a holed muffler, or worse, cracked headers).
-Anything in the ignition system (bad wires, caps, condensors, extenders, etc...). |
Drew Altemara (Drewa)
Junior Member
Username: Drewa
Post Number: 62
Registered: 2-2002
| | Posted on Friday, September 20, 2002 - 8:49 am: | |
Sean,
I've had a similar problem on a carbed 308 and Boxer. Both required two very minor fixes. On the 308 the car would pop at idle. The mechanic blew out the weber jets and it was perfect. He also said that if you red lined it a couple of times this can sometimes clean out the webers a bit (in additions to cleaning the plugs).
On the Boxer, I had a pop on deceleration. Initially the mechanic suspected that there may be some air leaking past a worn weber throttle shaft. It turned out the distributor advance mechanism was sticking and he cleaned and lubed this and its been perfect for 3 years.
Good luck |
Mike Fisher (Mikef)
Junior Member
Username: Mikef
Post Number: 112
Registered: 11-2001
| | Posted on Friday, September 20, 2002 - 8:24 am: | |
Sean,
Check for water in the spark plug wells. I opened the engine cover to check the oil at a gas stop and all the rainwater ran down the front bank of the engine. About five minutes later down the highway it started to pop & crack. Thought I had got a bad tank of gas. I had to replace three plug extenders as they had arced through. That big flat deck holds a lot of water and dumps it all down the front of the engine if it is opened when wet. I guess the rubber seals around the plug wells can't be 100% effective. |
Henry D. Chin (Hanknum)
New member
Username: Hanknum
Post Number: 22
Registered: 2-2002
| | Posted on Friday, September 20, 2002 - 1:21 am: | |
It sounds to me you have an exhaust leak, check the donuts |
jeff ryerson (Atheyg)
New member
Username: Atheyg
Post Number: 32
Registered: 8-2002
| | Posted on Thursday, September 19, 2002 - 11:34 pm: | |
You may have a valve out of adjustment or a broken spring or some other valve condition |
magoo (Magoo)
Advanced Member
Username: Magoo
Post Number: 3143
Registered: 2-2001
| | Posted on Thursday, September 19, 2002 - 9:30 pm: | |
Sean, There are many things that could have that effect from electrical to emissions. I would start with emissions controls, if you still have them hooked up, and go from there. |
Sean Higgins (Sean_higgins)
New member
Username: Sean_higgins
Post Number: 1
Registered: 9-2002
| | Posted on Thursday, September 19, 2002 - 8:47 pm: | |
I have a 1978 308 that suddenly started popping. Under exceleration it sounds good, if I lift off the gas it starts popping, like a backfire in the muffler. It also pops if I stay on the gas at the same position, say like 3000 rpm for about 5 seconds. I thought mabye the fuel mixture was too rich, but I'm not sure. Like I said it started all of a sudden. I don't have a choke that works and it does pop a little until it gets warm, but NOW once it gets warm it pops like pop corn in a microwave! Does anyone have any other ideas as what could be causing this. I thought maybe it was running on 7 cylinders, but it runs great at idle and when I get on the gas, just when I let off or staying stactic on the throttle.
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