Home » Public Forums » GMCnet » Backfiring
| Backfiring [message #310964] |
Sun, 27 November 2016 01:22  |
davidlive
Messages: 143
Registered: November 2011
Location: Simi valley, Southern Cal...
Karma: -1
|
Senior Member |
|
|
My project coach, which i'm trying to only keep running barely, the engine isn't running the best,
started backfiring though the carburetor, but the engine starts up easily ?
(it started doing this after i parked it from a 1 hour drive)
it has a newer distributor (Hei) , i suspect the timing is off, but the mark has fallen off the front of the engine, so idk how to check that, other then that, i've pulled the cap to make sure there was no moisture under the cap, i did pull a spark plug and it was black, which would confirm the incorrect timing.
I plan on replacing the plugs, wires and cap. would there be any suggestions at which brand/model to use ?
and any suggestions at where to look for the reason for the backfiring though the carb ?
Thanks David
78 Royal #749
74 #136
Oversteer is when you hit the wall with the rear of the car, understeer is when you hit the wall with the front of the car. Hp is how fast you hit the wall, and torque is how far you take the wall with you when you hit it.
|
|
|
|
| Re: [GMCnet] Backfiring [message #310965 is a reply to message #310964] |
Sun, 27 November 2016 02:18  |
 |
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
|
Senior Member |
|
|
David,
Here's the $16.00 fix:
Tiny URL: https://tinyurl.com/hnrlgvw
Full URL:
http://www.ebay.com/itm/68-74-OLDSMOBILE-442-CUTLASS-W-30-TIMING-COVER-TAB-POINTER-BRACKET-CLIP-350-455-/161246841691?hash=item258b0
f8b5b:g:ElMAAOSwf05XPH-Q&vxp=mtr
Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of David Morrison
Sent: Sunday, November 27, 2016 6:22 PM
To: gmclist@list.gmcnet.org
Subject: [GMCnet] Backfiring
My project coach, which i'm trying to only keep running barely, the engine isn't running the best, started backfiring though the
carburetor, but the engine starts up easily? (it started doing this after i parked it from a 1 hour drive) it has a newer
distributor (Hei) , i suspect the timing is off, but the mark has fallen off the front of the engine, so idk how to check that,
other then that, i've pulled the cap to make sure there was no moisture under the cap, i did pull a spark plug and it was black,
which would confirm the
incorrect timing.
I plan on replacing the plugs, wires and cap. would there be any suggestions at which brand/model to use ?
and any suggestions at where to look for the reason for the backfiring though the carb ?
Thanks David
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
|
|
|
|
| Re: [GMCnet] Backfiring [message #310968 is a reply to message #310965] |
Sun, 27 November 2016 05:48 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
|
Senior Member |
|
|
Recheck the firing order.
The firing order picture of the distributor cap in the GMC manual is wrong.
That little plastic indicator that Rob pointed out is readily available. Dick Paterson also had a bunch of them on his table at one of the GMCMI rallies.
That said, you could mark where the distributor is now and slightly change it to see if it makes anything better.
Finally check the spark plug wire routing to see that there is plenty of separation between wires. Then run it in the dark, looking for a spark jumping between wires or to ground.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
|
|
|
|
| Re: Backfiring [message #310969 is a reply to message #310964] |
Sun, 27 November 2016 07:06 |
Chris Tyler
Messages: 458
Registered: September 2013
Location: Odessa FL
Karma: 7
|
Senior Member |
|
|
To clarify, is it backfiring at idle? Or when you rev it?
If its backfiring at idle its probably retarded. Bump the timing in smalll increments.
Also, where is your vaccuum advance hooked up to?
Check to make sure the advance weights are not stuck as well.
Last, if you are changing the plugs, it would be a good idea to do a compression check. An engine that has sat around may have rusted up the valve seats and could also explain the problem.That may or may not improve with it running a while.
76 Glenbrook
|
|
|
|
| Re: Backfiring [message #310976 is a reply to message #310964] |
Sun, 27 November 2016 08:35 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
|
Senior Member |
|
|
Concentrate on the left rear cyls. Many GM engines gave been ruined by a 5-7 to 7-5 wire swap. Essy mistake to make.
John Lebetski
Woodstock, IL
77 Eleganza II
|
|
|
|
| Re: Backfiring [message #310988 is a reply to message #310964] |
Sun, 27 November 2016 12:01 |
davidlive
Messages: 143
Registered: November 2011
Location: Simi valley, Southern Cal...
Karma: -1
|
Senior Member |
|
|
I will check the firing order, and I'm going to get that timing tab (thank you), but to clarify
the backfiring though the carb, is at idle and reeving the engine, and the engine ran ok before i parked it after i drove it for 1-2 hours when i moved it from a house to storage, and i found the backfiring when i went to start it after about a month in storage.
Thanks David
78 Royal #749
74 #136
Oversteer is when you hit the wall with the rear of the car, understeer is when you hit the wall with the front of the car. Hp is how fast you hit the wall, and torque is how far you take the wall with you when you hit it.
|
|
|
|
| Re: [GMCnet] Backfiring [message #310990 is a reply to message #310988] |
Sun, 27 November 2016 12:12 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
|
Senior Member |
|
|
The back firing through the carb. indicates it must be running lean.
Suggest you remove the top cover of the air cleaner and see if the choke is
on strong enough.
Also advance the timing without the marker by rotating the distributor
clockwise few degrees.
On Sun, Nov 27, 2016 at 10:01 AM, David Morrison
wrote:
> I will check the firing order, and I'm going to get that timing tab (thank
> you), but to clarify
> the backfiring though the carb, is at idle and reeving the engine, and the
> engine ran ok before i parked it after i drove it for 1-2 hours when i
> moved it from a house to storage, and i found the backfiring when i went
> to start it after about a month in storage.
>
> Thanks David
> --
> 1974 G-M-C Painted Desert #136
> "Oversteer is when you hit the wall with the rear of the car, understeer
> is when you hit the wall with the front of the car. Hp is how fast you hit
> the wall, and torque is how far you take the wall with you when you hit
> it."
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
|
|
|
|
| Re: [GMCnet] Backfiring [message #310992 is a reply to message #310990] |
Sun, 27 November 2016 12:36 |
sgltrac
Messages: 2797
Registered: April 2011
Karma: 1
|
Senior Member |
|
|
Could also be a fuel supply issue.
Sully
77 eleganza 2
Seattle
On Sunday, November 27, 2016, Jim Kanomata wrote:
> The back firing through the carb. indicates it must be running lean.
> Suggest you remove the top cover of the air cleaner and see if the choke is
> on strong enough.
> Also advance the timing without the marker by rotating the distributor
> clockwise few degrees.
>
> On Sun, Nov 27, 2016 at 10:01 AM, David Morrison >
> wrote:
>
>> I will check the firing order, and I'm going to get that timing tab
> (thank
>> you), but to clarify
>> the backfiring though the carb, is at idle and reeving the engine, and
> the
>> engine ran ok before i parked it after i drove it for 1-2 hours when i
>> moved it from a house to storage, and i found the backfiring when i went
>> to start it after about a month in storage.
>>
>> Thanks David
>> --
>> 1974 G-M-C Painted Desert #136
>> "Oversteer is when you hit the wall with the rear of the car, understeer
>> is when you hit the wall with the front of the car. Hp is how fast you
> hit
>> the wall, and torque is how far you take the wall with you when you hit
>> it."
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>
>
>
> --
> Jim Kanomata
> Applied/GMC, Fremont,CA
> jimk@appliedairfilters.com
> http://www.appliedgmc.com
> 1-800-752-7502
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
|
|
|
|
| Re: [GMCnet] Backfiring [message #310994 is a reply to message #310992] |
Sun, 27 November 2016 13:44 |
Hal StClair
Messages: 971
Registered: March 2013
Location: Rio Rancho NM
Karma: -12
|
Senior Member |
|
|
Not to try and cry wolf but with the quality of our present gas you might have a fuel induced problem. If you ran the engine with old gas prior to the last trip you might have a valve that is stuck and a guide that is galled. I've seen it happen way too often with the lousy fuel we have to use. If the ignition tips don't work a quick compression check should tell the tale.
Hal
"I enjoy talking to you. Your mind appeals to me. It resembles my own mind, except you happen to be insane."
1977 Royale 101348,
1977 Royale 101586, Diesel powered,
1974 Eagle Bus 45',w/slideout,
Rio Rancho, NM
|
|
|
|
| Re: Backfiring [message #310997 is a reply to message #310964] |
Sun, 27 November 2016 14:39 |
davidlive
Messages: 143
Registered: November 2011
Location: Simi valley, Southern Cal...
Karma: -1
|
Senior Member |
|
|
Firing order is correct, I don't think bad fuel is a problem as I don't have the fuel tanks installed I use a 5gallon gas can, only thoughts on the fuel is its just 87octane
So far wire brushing the plugs, (I do plan on replacing later on) but cleaning them should help,
So far the result on the compression check is
Cylinder
1 - 125
3 - 130
5 - 130
7 - 135
So the left side is good, now to check out the right side
78 Royal #749
74 #136
Oversteer is when you hit the wall with the rear of the car, understeer is when you hit the wall with the front of the car. Hp is how fast you hit the wall, and torque is how far you take the wall with you when you hit it.
|
|
|
|
|
|
| Re: Backfiring [message #311000 is a reply to message #310964] |
Sun, 27 November 2016 15:10 |
davidlive
Messages: 143
Registered: November 2011
Location: Simi valley, Southern Cal...
Karma: -1
|
Senior Member |
|
|
The right side
2 - 140
4 - 125
6 - 135
8 - 120
Cylinder 8 is the lowest at first I got a reading of 100but I rechecked it after the rest and I got a steady 120
78 Royal #749
74 #136
Oversteer is when you hit the wall with the rear of the car, understeer is when you hit the wall with the front of the car. Hp is how fast you hit the wall, and torque is how far you take the wall with you when you hit it.
|
|
|
|
|
|
|
|
| Re: Backfiring [message #311005 is a reply to message #311000] |
Sun, 27 November 2016 16:20 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
|
Senior Member |
|
|
Sir, your pressure readings do not indicate a leaking valve issue. So probably electrical. The video indicates the backfire is not random but is probably isolated to one cylinder. First check cc firing order. 18436572. Check inside the distributor cap for carbon tracks which will cause crossfiring. Also start the engine in the dark and look for wires sparking and crossfiring. I have seen a foulded plug backfire.
davidlive wrote on Sun, 27 November 2016 16:10The right side
2 - 140
4 - 125
6 - 135
8 - 120
Cylinder 8 is the lowest at first I got a reading of 100but I rechecked it after the rest and I got a steady 120
C. Boyd
76 Crestmont
East Tennessee
|
|
|
|
| Re: Backfiring [message #311006 is a reply to message #310964] |
Sun, 27 November 2016 16:34 |
davidlive
Messages: 143
Registered: November 2011
Location: Simi valley, Southern Cal...
Karma: -1
|
Senior Member |
|
|
After I read your post c Boyd, I pulled one spark wire at a time from the cap, and it appears to be cylinder 5 right next to the do wiring , when I disconnect it stops backfiring but oh course misses
78 Royal #749
74 #136
Oversteer is when you hit the wall with the rear of the car, understeer is when you hit the wall with the front of the car. Hp is how fast you hit the wall, and torque is how far you take the wall with you when you hit it.
|
|
|
|
| Re: Backfiring [message #311010 is a reply to message #310964] |
Sun, 27 November 2016 20:33 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
|
Senior Member |
|
|
Triple check that wires 5 and 7 are not swapped.
John Lebetski
Woodstock, IL
77 Eleganza II
|
|
|
|
| Re: Backfiring [message #311011 is a reply to message #310964] |
Sun, 27 November 2016 21:07 |
davidlive
Messages: 143
Registered: November 2011
Location: Simi valley, Southern Cal...
Karma: -1
|
Senior Member |
|
|
I've done that, and i replaced the cap and rotor, and it's still doing it, I started replacing the plugs, which the old ones were autolite 87's which i believe are non-hei plugs gapped about 40 avg, and put in a/c delco hei plugs gapped at 60, the wires i got were crap from autozone, so i have to exchange them, one wire kept falling off the cap, another wire was missing the crimp piece in the boot .... so i'll get another set tomorrow and hopefully make it out in the tomorrow evening to see if that's helped.
I have a gut feeling telling me that's not the issue, and i'm left confused at why the #5 would be backfiring, tomorrow i plan on checking the engine ground and grounding the distributor directly too, maybe there's a issue there.
Thanks David
78 Royal #749
74 #136
Oversteer is when you hit the wall with the rear of the car, understeer is when you hit the wall with the front of the car. Hp is how fast you hit the wall, and torque is how far you take the wall with you when you hit it.
[Updated on: Sun, 27 November 2016 21:08] Report message to a moderator |
|
|
|
| Re: [GMCnet] Backfiring [message #311012 is a reply to message #311011] |
Sun, 27 November 2016 22:31 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
|
Senior Member |
|
|
David,
Once more for everyone: Set GMC plugs to 0.038"-0.040". More and you'll
overstress the HEI module, possibly leading to premature failure.
As you've already found, it's difficult to identify problems like yours.
But if you've truly refined the problem to #5 cylinder, you're almost
there. You reported the compressions on the right cylinders, but not the
left -- what's #5 compression? I fully expect it to be low. And if so the
earlier hypothesis of a sticking valve is probably correct. Even if it's
not significantly low during the cranking-speed test, it may still stick at
idle, giving the intermittent problem you've seen. It may clear itself up,
but a dose of Marvel Mystery Oil may be needed too.
JMHO,
Ken H.
On Sun, Nov 27, 2016 at 10:07 PM, David Morrison
wrote:
> I've done that, and i replaced the cap and rotor, and it's still doing it,
> I started replacing the plugs, which the old ones were autolite 87's which
> i believe are non-hei plugs gapped about 40 avg, and put in a/c delco hei
> plugs gapped at 60, the wires i got were crap from autozone, so i have to
> exchange them, one wire kept falling off the cap, another wire was missing
> the crimp piece in the boot .... so i'll get another set tomorrow and
> hopefully make it out in the evening to see if that's helped.
>
> I have a gut feeling telling me that's not the issue, and i'm left
> confused at why the #5 would be backfiring, tomorrow i plan on checking the
> engine
> ground and grounding the distributor directly too, maybe there's a issue
> there.
>
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
|
|
|
|
| Re: [GMCnet] Backfiring [message #311013 is a reply to message #311011] |
Sun, 27 November 2016 22:34 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
|
Senior Member |
|
|
Did you replace the coil recently?
On Sun, Nov 27, 2016 at 7:07 PM, David Morrison wrote:
> I've done that, and i replaced the cap and rotor, and it's still doing it,
> I started replacing the plugs, which the old ones were autolite 87's which
> i believe are non-hei plugs gapped about 40 avg, and put in a/c delco hei
> plugs gapped at 60, the wires i got were crap from autozone, so i have to
> exchange them, one wire kept falling off the cap, another wire was missing
> the crimp piece in the boot .... so i'll get another set tomorrow and
> hopefully make it out in the evening to see if that's helped.
>
> I have a gut feeling telling me that's not the issue, and i'm left
> confused at why the #5 would be backfiring, tomorrow i plan on checking the
> engine
> ground and grounding the distributor directly too, maybe there's a issue
> there.
>
>
> Thanks David
> --
> 1974 G-M-C Painted Desert #136
> "Oversteer is when you hit the wall with the rear of the car, understeer
> is when you hit the wall with the front of the car. Hp is how fast you hit
> the wall, and torque is how far you take the wall with you when you hit
> it."
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
|
|
|
|
Goto Forum:
Current Time: Wed Sep 25 13:18:09 CDT 2024
Total time taken to generate the page: 0.00920 seconds
|
GMCforum
Search
Help
Register
Login
Home
