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#1 |
Registered User
Join Date: Sep 2009
Location: Lloydminster Alberta
Posts: 32
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Truck Doesnt Run Right
My truck is running really rough. The worst at lower Rpm under load. It sounds like it backfires back through the carb and loses power. I put a new air filter in a week ago and its is already black and dirty. When i was driving home tonight it got really bad. I noticed when I stopped that my exhaust manifold was glowing red hot. Im thinking its a exhaust restriction, am i going in the right direction?
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#2 |
sharp as a marble
![]() Join Date: Jan 2007
Location: atlantic beach,florida
Posts: 1,082
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Re: Truck Doesnt Run Right
check the basics first! does your truck have points? are they set correctly? Hows the timing? On start up do you have any smoke? If so what color is it
My guess is that the timing is off. popping back thru the carb would make me think the timing is retarded. And THAT is my .02 worth |
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#3 |
Chemist under the hood...
Join Date: Apr 2009
Location: Fort Erie,ON, Canada
Posts: 617
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Re: Truck Doesnt Run Right
I agree with previous-Did you accidently switch plug wires? I put new plugs and wires in recently and then it ran terrible, backfired etc. I was checking all sorts of other things and it turned out that plugs on 1 and 3 cylinders were switched!
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Current fleet: 2013 GMC Sierra, 5.3L, 4x4 1988 GMC Sierra, 305, Auto 1984 Jeep Grand Wagoneer, 360 V8 1997 VW Cabrio, 2.0L 2017 Toyota Rav4, 2.5L Stuff I wish I still had: 2013 Toyota Matrix [RIP] 1967 GMC 910 Fleetside, 283 V8 [1st Love-SOLD] 1987 Jeep Cherokee Laredo 4X4, 4.0 I-6 [SOLD} 1994 Chevrolet Caprice Classic, 5.7LV8 [SOLD] 1995 Chevrolet Astro AWD, 4.3L V6 (RIP) 1998 Chevrolet Suburban 4x4, 5.7L V8 [SOLD] |
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#4 |
Special Order
![]() ![]() Join Date: Nov 2004
Location: Mt Airy, MD
Posts: 85,859
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Re: Truck Doesnt Run Right
I`m thinking timing,wires,all the tuning stuff,and possibly a clogged PCV valve.Pull it out and see if it rattles when you shake it.
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"BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~ |
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#5 |
Active Member
![]() Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
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Re: Truck Doesnt Run Right
What engine, mileage, and carburetion? Headers?
I've never seen an exhaust glow red hot unless it was headers on a dragster after a race. I'd be concerned about that. Restricted exhaust can cause rough idling and loss of power so I'd check that out too. There's several issues that can cause idling rough so I'd start with the basics as mentioned above. Once you've eliminated the ignition, carb issues, then you may be looking at worn cam, burned valves, timing chain. Last edited by 68gmsee; 12-18-2009 at 10:26 AM. |
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#6 |
Registered User
![]() Join Date: May 2008
Location: Granbury, TEXAS
Posts: 250
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Re: Truck Doesnt Run Right
Have you changed anything recently? Something has changed. I have seen headers glowing red once when I rebuilt an engine and on the initial start up I ran the engine for 20 minutes at 2500 rpm for the cam breakin. The timing was set at about 10 degrees after TDC (way retarded). I have also seen timing jump with a worn out timing chain and it jumped a tooth on the cam gear. Made the timing way retarded.
I would suggest putting a timing light on it and making sure of initial timing set.
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Mine is chopped, has a clutch, and a big block. |
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#7 |
Registered User
Join Date: Dec 2006
Location: Porter Ranch, CA
Posts: 978
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Re: Truck Doesnt Run Right
Sounds like a bad piston return spring on #5 cylinder...
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#8 |
Registered User
![]() Join Date: Jul 2007
Location: Toppenish, WA
Posts: 15,514
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Re: Truck Doesnt Run Right
Five good posts with honest advise and one smart #$*.
As the other five said, go to the basics and one by one go through them. I'm with 68 Chop Top in that I would check the timing first as it may be late. If it has points check the gap to make sure it is right and then check and set the timing. Along with that check the vacuum advance. A vacuum advance with a ruptured diaphragm will also cause a vacuum leak which will lean out the mixture which will cause hot exhaust along with the retarded timing. Go through the firing order and make sure that each plug wire goes to the correct plug. On a small block V8 it is usually 5 and 7 that we get crossed up because they are beside each other and fire one after the other. If the engine is a six with a single barrel check to see if the body of the carb is tight to the base by gripping it with your hands and twisting back and forth. Some times the screws holding the body to the base come loose enough to let this happen. I'd probably just replace the pcv valve and be done with it as they are under five bucks most places. Also take a serious look at the hose going between it and the carb as I have seen a lot of them crack and leak over the years. Also check the other vacuum hoses on the engine for cracks or leaks. If those steps don't cure things. I would suggest doing a compression test to make sure that all of the cylinders have good and even or near even compression. On a compression test you have to pull "ALL" of the spark plugs and prop the throttle wide open to get best results. Pull the coil wire or disconnect the power wire from the hei too. I was taught to and taught all of my students to let each cylinder hit five times. Then write down the results and go to the next cylinder. You are looking first for even compression and then having the compression at or near factory specs. If you don't own a compression gauge and don't want to buy one you can rent one at Autozone through their rental deal. If it ran good before you swapped air filter elements my guess is that the timing is off or that there is a vacuum leak and that is what I would check first. |
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#9 |
Registered User
Join Date: Nov 2002
Location: Charleston, South Carolina
Posts: 1,370
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Re: Truck Doesnt Run Right
I immediately thought timing. Retainer may have loosened up and timing changed as you drove. Go simple first. Good luck!
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2006 Silverado CCSB, 1939 Ford Sedan, 1962 BelAir Wagon, 1976 Vega Panel Charleston, South Carolina |
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#10 |
Registered User
Join Date: Sep 2009
Location: Lloydminster Alberta
Posts: 32
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Re: Truck Doesnt Run Right
I have done some work to my truck recently. The head has been redone with new seats and reground valves. I rebuilt the carb and changed spark plugs, checked the points. Also checked timing at 4deg before TDC. Removed the in carb filter and replaced with a inline filter. Ran new vaccum lines.
Everything ran really good after doing all the work untill a few weeks ago it started running ****ty. Im not sure about the timing being off as sometimes it runs good. It only seems to backfire at low rpm well under load. Anywhere from 1500 to 2500 rpm. Does anyone have any more ideas? Also about the exhaust manifold, its a factory manifold, and at was glowing bright red. I would think its a exhaust restriction and its unable to dissipate heat. |
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#11 |
Senior Member
![]() Join Date: Aug 2004
Location: Centennial, CO
Posts: 2,951
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Re: Truck Doesnt Run Right
The hot manifold could be a restriction, but I'm thinking combustion after the exhaust valve. Either late timing or leaking exh valves.
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ClusterTruck: 68 C10 Bought in 89, wrecked in 03. Slow low $ rebuild started '17. 6.0 & TKO http://67-72chevytrucks.com/vboard/s...d.php?t=788602 93 K1500 Short Step, 350, NV4500, EBL flash ECU. Vortec heads & roller cam someday... 05 Jeep Wrangler Unlimited. 3” lift & 6-speed 02 E320 the insurance total “free car” 13 Tahoe LTZ |
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#12 |
Registered User
Join Date: Mar 2007
Location: San Pedro River, SE Arizona
Posts: 734
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Re: Truck Doesnt Run Right
There is a lot of good, practical advice above. Given the work done on the engine and the onset of trouble, odds are that it is a vac leak (= lean mix) or a timing issue (late fire?) so take the odds and start there. There seem to be literally hundreds of timing/vac/ign component problems for every exhaust restriction issue, so unless you have had the exhaust apart recently or maybe have a really tight rodent nest WAY up in there, get out the timing light. If timing is off, follow the leads noted above. If problem persists once you are certain that the timing is correct and there are no vac leaks, the diagnosis would become much more specific as noted in some of the other comments. Good luck.
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CCCC 67 Sting Ray Coupe 327 4sp; 68 K10 Suburban 327 4sp; 69 K20 Lifted 383 4sp; 69 C80 Fire Truck 478 V6 5sp/2sp; 69 C20 Longhorn 327 4sp; 70 C30 Wrecker 350 4sp; 70 C30 Flat Bed 350 4sp; 71 C20 LWB 350 4sp; 72 K5 Blazer 350 4sp; 72 C30 Flat Bed Gooseneck Hauler with sleeper 350/TH400; 72 C20 Longhorn 402 4sp; 52 Mack LTL Supercharged Cummins 5sp x 3sp; 01 Dodge 5.9 HO Cummins 6spd; 02 Safari Trek 2430 8.1 Vortec on Workhorse Chassis; 03 Silverado 2500 HD 4wd Duramax/Allison Moved but still in the family 70 C20 Custom Camper 350/TH350; 72 K5 Blazer CST Highlander 350/TH350 Recently sent to new homes 72 C30 MoHome 402 4sp; 72 K5 Blazer Conv 350 4sp; 75 GMC 6000 Aerial 350 w Allison; 72 GMC 3500 Utility 350 4sp; 70 GMC 3500, 350 4sp |
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