| Cracked intake manifold? [message #186755] |
Mon, 08 October 2012 21:52  |
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I'm still getting an occasional pop or BANG which is backfiring but I'm confident it is not exhaust backfiring, it is up front at the engine.
It was suggested to me at Amana that my problem is a cracked intake manifold. If this is the case is there any way short of actually removing the manifold to determine if I do, in fact, have a cracked intake? Engine is 403 with a Patterson rebuilt carb.
Bill Brown - '77 Buckeye Cruiser
Coshocton OH
carguybill@sbcglobal.net
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| Re: [GMCnet] Cracked intake manifold? [message #186756 is a reply to message #186755] |
Mon, 08 October 2012 22:24  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Bill, before you remove the intake, check your carb hold down bolts, and
carefully inspect the gasket under it. Look for signs of combustion gasses
in the area. The intakes on 403,s are not as prone to cracking as a 455,
but it has been known to happen. Very lean mixtures can cause backfire at
the carb, but do not rule out crossfiring ignition wires or a cracked
distributor cap, or for that matter, a carbon tracked cap. You can check
for secondary conductor leaks by viewing the engine bay with the engine
running in the dark. If all this fails to determine the cause, do a wet and
dry compression test to rule out sticking intake valves. Then you can pull
the intake manifold.
Jim Hupy
Salem, Or
78 GMC Royale 403
On Oct 8, 2012 7:52 PM, "Bill Brown" <carguybill@sbcglobal.net> wrote:
>
>
> I'm still getting an occasional pop or BANG which is backfiring but I'm
> confident it is not exhaust backfiring, it is up front at the engine.
>
> It was suggested to me at Amana that my problem is a cracked intake
> manifold. If this is the case is there any way short of actually removing
> the manifold to determine if I do, in fact, have a cracked intake? Engine
> is 403 with a Patterson rebuilt carb.
> --
> Bill Brown - '77 Buckeye Cruiser
> Coshocton OH
> carguybill@sbcglobal.net
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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| Re: Cracked intake manifold? [message #186771 is a reply to message #186755] |
Tue, 09 October 2012 09:01 |
Dennis S
Messages: 3046
Registered: November 2005
Karma: 2
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Senior Member |
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| carguy wrote on Mon, 08 October 2012 21:52 |
I'm still getting an occasional pop or BANG which is backfiring but I'm confident it is not exhaust backfiring, it is up front at the engine.
It was suggested to me at Amana that my problem is a cracked intake manifold. If this is the case is there any way short of actually removing the manifold to determine if I do, in fact, have a cracked intake? Engine is 403 with a Patterson rebuilt carb.
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Bill,
Is the crossover blocked on your manifold?
Dick Paterson once told me that to check for an intake manifold crack, hold open the carb butterflies and, using a good light, look at the floor of the intake for an oily mess. You can even use a soft cloth wrapped on a long screw to wipe the floor of the intake to determine if you have any oily surface.
Dennis
Dennis S
73 Painted Desert 230
Memphis TN Metro
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| Re: Cracked intake manifold? [message #186774 is a reply to message #186755] |
Tue, 09 October 2012 09:29 |
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I did talk with Dick Patterson about this and he suggested I first replace the fuel filter in the carb which I'm going to do this afternoon.
I've found that the easiest way, for me at least, to replace the fuel filter is to remove the carb, so I will look for any signs of cracks and/or oily mess. I will also check out the carb gasket for ominous signs of trouble.
This thing is crazy, I can drive 300 or more miles with no problem at all then, pretty much out of the blue, I get the popping and once on my way from Amana a single BANG. Makes one nervous.
Thanks guys for your help. I'll report back what I find.
Bill Brown - '77 Buckeye Cruiser
Coshocton OH
carguybill@sbcglobal.net
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| Re: Cracked intake manifold? [message #186776 is a reply to message #186774] |
Tue, 09 October 2012 10:09 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| carguy wrote on Tue, 09 October 2012 09:29 |
I did talk with Dick Patterson about this and he suggested I first replace the fuel filter in the carb which I'm going to do this afternoon.
I've found that the easiest way, for me at least, to replace the fuel filter is to remove the carb, so I will look for any signs of cracks and/or oily mess. I will also check out the carb gasket for ominous signs of trouble.
This thing is crazy, I can drive 300 or more miles with no problem at all then, pretty much out of the blue, I get the popping and once on my way from Amana a single BANG. Makes one nervous.
Thanks guys for your help. I'll report back what I find.
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Try replacing the ignition module with the spare AC Delco one you are carrying in your coach.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Cracked intake manifold? [message #186804 is a reply to message #186755] |
Tue, 09 October 2012 19:55 |
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I did pull the carb and replaced the filter. Also looked into the ports - found some carbon build-up but no oily stuff. Called Dick Patterson and he told me where to look for cracks - in the web between the secondary ports. I do have a hairline crack at this point which extends down ~ 1/2". Dick told me that this is not a problem and is, in fact, what one would find on 98% of all manifolds.
Tomorrow I will get my new carb to intake gasket from my NAPA, button the thing up, replace the module with my spare and hope for the best on our trip this weekend to Indiana University vs OSU football game.
Thanks again for everyone's help.
Bill Brown - '77 Buckeye Cruiser
Coshocton OH
carguybill@sbcglobal.net
[Updated on: Tue, 09 October 2012 20:04] Report message to a moderator |
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| Re: Cracked intake manifold? [message #186829 is a reply to message #186755] |
Wed, 10 October 2012 06:59 |
mschultz
Messages: 113
Registered: September 2010
Location: Maple City, MI
Karma: 0
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Senior Member |
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I just pulled my manifold off my 403, yesterday. I read in the blue pages that the cracking was not as prevalent in the 403. I also think that up here in Michigan maybe it does not get as hot. Anyway, I was pleasantly surprised that the underside was not that torched and the turkey tray did not have much carbonized oil. No cracks. Unfortunately, I get to go a bit further, as #8 has no compression. As the King said, 'off with their heads'. I did however this summer have a major back firing affair. It came on over a long period of time. at first just now and then, and finally dead by the side of the road. As it turned out, the aftermarket cheap distributor cap allowed the screws that hold the grounding wires for the ignition module to strip. Worth a quick check. Once this shorting happens it is likely to destroy the module and or coil. An easy switch and you should always carry spares anyway. So, what everyone else said, I agree with and am just offering my experiences. Good luck
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| Re: Cracked intake manifold? [message #187338 is a reply to message #186755] |
Mon, 15 October 2012 12:36 |
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OK, as promised, here is, hopefully, the final report.
I replaced the fuel filter as suggested by Dick Patterson and it needed to be replaced. I identified a slight hairline crack on the web between the secondaries which Dick Patterson said it typical, in fact, routine. But I still had the occasional backfire on our ~300 mile trip this weekend.
However, before I started on our way back I replaced the ignition module as was suggested here by many knowledgeable GMCers. I'm happy to say that with the module replaced that I had no, repeat NO, backfiring on the 300 mile return trip.
Thanks to all who spoke up here with your suggestions.
Bill Brown - '77 Buckeye Cruiser
Coshocton OH
carguybill@sbcglobal.net
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| Re: Cracked intake manifold? [message #187349 is a reply to message #186755] |
Mon, 15 October 2012 14:34 |
GeorgeRud
Messages: 1380
Registered: February 2007
Location: Chicago, IL
Karma: 0
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Senior Member |
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As Dick so wisely quoted Smokey Yunick ( one of my personal heros) at his wonderful presentation at Amana, 90% of carburation problems are ignition related!
Glad to hear the coach is running well once again.
George Rudawsky
Chicago, IL
75 Palm Beach
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