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badbob85037
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Aug 13, 2013, 3:06 PM
Post #1 of 23
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350 NO POWER, BACKFIRES
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I'm new here and this will be my first post. I have owned a 1974 Chevy K-10 truck since 1982. Ihave replaced everything at least twice except the transmission, transfer case and the power brake booster. Its been in two wreaks, one a roll over and neither my fault. In all that time it has never been to a shop. But this time I AM AT A LOSS. .I have rebuilt the Eldebrock 600. Distributor looks ok. Replaced intake and carborator gasket. It has fuel pressure the dwell is set to 29 degrees and the timing chain shows no slack. At idle (900 rpm) I have 20" of vacuum. The timing is all over the place covering around 10 degrees. When driving under a load it is backfiring through the exhaust and has no power. Compression test, all within 10 pounds, 160-170 psi. I'm out of ideas and would be pulling my hair out if I had any to spare. And one last thing. Yes I have checked the power brake booster for leaks. If anyone has any ideas throw them out there. I'm to the point I only know what's right without a clue as to what's wrong.
Thanks
the new guy
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badbob85037
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Aug 13, 2013, 4:19 PM
Post #3 of 23
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Re: 350 NO POWER, BACKFIRES
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A stock Delco. There is about .120" of up and down movement in the shaft but not enough to cause the timing to be jumping around like it is. I'm going to replace it anyway. At this point I'm willing to try anything.
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Hammer Time
Ultimate Carjunky
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Aug 13, 2013, 4:23 PM
Post #4 of 23
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Re: 350 NO POWER, BACKFIRES
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Dwell is a measurement taken on cars using points. That truck came with an HEI distributor and has computer initiated ignition timing. The backfiring indicates and ignition issue. You might want to try a different ignition module.
Double check your firing order too.
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Tom Greenleaf
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Aug 13, 2013, 9:47 PM
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Re: 350 NO POWER, BACKFIRES
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Did I miss something? GM HEI began in model year 1975, vacuum advance used. Stock 1974 was separate points and condenser, most replaced with a "uniset" along the way - same stuff just attached to each other. Dwell adjusted by Allen screw thru door in cap while running. 29 is close enough as it will rise as they wear, spec is 30.
Motion of advance could rub wires inside distributor.
Manifold vacuum of 20Hg seems too high unless this is below sea level or wildly advanced timing. Bouncing timing? IDK, is timing light picking up well?
Seemingly tight timing chain isn't convincing me just yet. Measure the degrees it can turn one way then they other. More than 5 degrees you could get problems. More than 7 you will get problems.
You can also watch dwell change while revving engine. Really shouldn't move that much.
Either or any distributor I still suspect that is source for backfire so far,
T
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Hammer Time
Ultimate Carjunky
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Aug 14, 2013, 2:41 AM
Post #6 of 23
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Re: 350 NO POWER, BACKFIRES
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My mistake. I thought they dropped points before that.
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Tom Greenleaf
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Aug 14, 2013, 4:59 AM
Post #7 of 23
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Re: 350 NO POWER, BACKFIRES
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TMK and there were exceptions, American Iron about universally started EI with Mopars (1973), Ford (1974) , GMs (1975) throw in AMC! You got what ever powerplant they bought from others. Breaker points from imports was not as well defined by model year or for where cars were destined. Some rare so called American stuff had CDI or whatever "Perma- Tune" was exactly much earlier.
My eyesight stinks up close so miss things posted. This should still be mostly all 1974 GM truck 350 w low power and a backfire so blaming ignition first.
Vacuum hose routing could be an issue. Dwell meter and timing light may not be reading properly. Points could have excessive metal transfer, condenser marginal(?) and IMO vacuum reading at idle too high indicating usually timing too far advanced which would cause backfires, low power but also excessive knocking not mentioned.
Geez - it's old now so open book and just start ruling things out,
T
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Hammer Time
Ultimate Carjunky
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Aug 14, 2013, 7:02 AM
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Re: 350 NO POWER, BACKFIRES
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Chrysler was '72
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badbob85037
Novice
Aug 14, 2013, 9:55 AM
Post #9 of 23
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Re: 350 NO POWER, BACKFIRES
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Does this make sense? Last night, if I can believe my eyes I saw sparks grounding on the distributor body under the cap. When checking for vacuum leaks the engine would straighten up when shooting the starting fluid in the area of the distributor. When I stopped the spray the engine would keep running straight another few seconds. It still does it after changing the gasket and both head and intake are true. Could it be nothing more than a bad ground? I'll let you know as soon as I get off my lazy butt.
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Hammer Time
Ultimate Carjunky
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Aug 14, 2013, 10:02 AM
Post #10 of 23
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Re: 350 NO POWER, BACKFIRES
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Let me understand this................
You see sparks so you spray starting fluid in that direction?
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Tom Greenleaf
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Aug 14, 2013, 12:29 PM
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Re: 350 NO POWER, BACKFIRES
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That would end all the issues for good! What are you doing, looking thru the little door that adjusts the points?
If you meant OUTSIDE you need to toss cap and rotor and wires if new or not may have a problem? Can't recall - is coil near by? They can arc also or anything carrying secondary voltage,
T
T
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Discretesignals
Ultimate Carjunky
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Aug 14, 2013, 1:03 PM
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Re: 350 NO POWER, BACKFIRES
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" I didn't figure out the backfiring issue, but I sure did find out where the spark plug wires were leaking."
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Hammer Time
Ultimate Carjunky
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Aug 14, 2013, 1:52 PM
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Re: 350 NO POWER, BACKFIRES
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Gee, I don't think I'll do that again
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badbob85037
Novice
Aug 14, 2013, 2:51 PM
Post #14 of 23
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Re: 350 NO POWER, BACKFIRES
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I wrote "shooting the starting fluid in the area of the distributor." With the window to the distributor closed I sprayed the starting fluid along the seem between the head and the intake. If the intake, that grounds the distributor had a bad ground could the starting fluid improve the ground if it was sprayed between the intake and the head? My mother wasn't a player for the WNBA that would slam dunk my head on a concrete half court.
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Hammer Time
Ultimate Carjunky
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Aug 14, 2013, 2:53 PM
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Re: 350 NO POWER, BACKFIRES
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Of course not. You hit a vacuum leak.
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badbob85037
Novice
Aug 14, 2013, 3:16 PM
Post #16 of 23
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Re: 350 NO POWER, BACKFIRES
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The intake and head are true. I replaced the gasket 3 days ago. I doughty the vacuum leak would be in the same place twice exspecially with the vacuum holding a study 20 inches.
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Hammer Time
Ultimate Carjunky
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Aug 14, 2013, 3:20 PM
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Re: 350 NO POWER, BACKFIRES
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Whatever you say
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Discretesignals
Ultimate Carjunky
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Aug 14, 2013, 4:10 PM
Post #18 of 23
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Re: 350 NO POWER, BACKFIRES
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Is that BBQ sauce on that guy's lip in the picture. eekk
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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badbob85037
Novice
Aug 14, 2013, 4:12 PM
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Re: 350 NO POWER, BACKFIRES
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You say you volunteer your time and knowledge but after your response to me and reading a few other post your all about ridiculing and belittling all who have a problem, especially when they have some basic knowledge of automotive. My profession isn't automotive and I never claimed it was but I have turned a few wrenches in my days. "What ever you say" isn't the answer I would expect from any 'professional', no matter what his line of business is. Drop me from your membership. The 'problem is resolved'.
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Hammer Time
Ultimate Carjunky
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Aug 14, 2013, 4:19 PM
Post #20 of 23
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Re: 350 NO POWER, BACKFIRES
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If you're going to say stupid stuff, then I'm going to call you on it. I told you that you had a vacuum leak and there is really no other explanation. The mixture got richer when it sucked in the starting fluid and straightened out the idle. Believe me, my reply was holding back on what i really wanted to say to you.
If you want your account closed, i can gladly take care of that for you.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Discretesignals
Ultimate Carjunky
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Aug 14, 2013, 4:30 PM
Post #21 of 23
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Re: 350 NO POWER, BACKFIRES
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When I read starting fluid being sprayed around the engine with sparks jumping around, I'm not going to waste my time.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Double J
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Aug 14, 2013, 8:38 PM
Post #22 of 23
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Re: 350 NO POWER, BACKFIRES
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Had a new 1974 Olds 98 that came with HEI
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Tom Greenleaf
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Aug 15, 2013, 12:52 AM
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Re: 350 NO POWER, BACKFIRES
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Double J. Olds especially noted for coming out with things early. Had mechanical ABS (how I don't know) on a '68, Regency 98? 4 piston 'Vette front brakes bought OE from orig owner - go figure?
OP - If you are not happy there's a whole web out there. Using starting fluid to find vacuum leaks or arcing is plain suicide. You could have used plain water in a spray bottle. Seems all the "wrenching" didn't sink in much did it?
T
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