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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: greenmonster on September 06, 2010, 09:12:38 am
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I have a misfire that I can't track down.It is from idle-2500.It makes a puffing sound from both sides of the exhaust.It feels like a dead cylinder,but it moves around.I put a vacuum gauge on it and it is steady at about 20in.Any ideas would help.
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True duals
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Yes,true duals.
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Are your header bolts tight??
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Yes they are tight.I just switched headers 2 weeks ago,but I have had the problem for months.
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common diagnoses tried yet? wires, plugs, cap, rotor? Got a temp gun? point it to each cyclinder at header and see if one reads much lower. These temp guns (usually w/ a red laser) are very cheap. I use it for a lot of things.
At night, no light, idling, pop hood, any sparks from wires?
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I put a full tuneup on it,and it didn't help.I even tried a different distributor that a friend had.
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Try a compression test.
btw sgt
"At night, no light, idling, pop hood, any sparks from wires?"
I did this and my wires were glowing blue.
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I done a compression test 2 months ago,and it was fine.
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If the symptom wasn't there 2 months ago, the test would be good......
If this started since then, the test is needed
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It's been like this for 6 months.It was running great,then one morning it started acting this way.
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Fuel filter good?
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I replaced that too.I pulled a plug and grounded it out and the spark is orange.Is that normal for hei.
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It should be blue. Where did you ground it to?
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You have 12 volts going to the distributor?
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I have 12.34 volt with key on and 14.59 volts at idle.
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Where did you ground it to?
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A bolt on the a/c bracket.
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A bad ground from the bock to the frame or body can cause it not to but hot enough. What I do sometimes is grab the treads of the plug with a jumper cable and put the other matching end to the neg side of the battery and test from there.
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I'll try the jumper cable thing and let you know how it goes.
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The spark is still orange even with it grounded to the battery.
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Tell you the truth I have a miss my spark is blue. If you ground is good and you changed all your distributor parts I'm lost
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What kind of HEI? Do you still have ESC hooked up? External or internal coil?
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As far as I know it is factory from 1975.I don't know what esc is but the coil is in the cap.
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ESC wouldn't be on a 1975 that is the first year for the HEI. ESC started in 1981.
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Is that voltage reading you gave of the battery or the wire going to the distributor? What kind of a plug are using to ground against the frame to check for spark or are you using that tester from Harbor Freight? Did your truck come with a governer?
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The volt reading is from the dis.I am using a ac delco plug gaped at .035.
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20 in of vacuum is quite a bit. Has this engine ever been rebuilt? I'm thinking either fuel pump or maybe the strainer/sock in the fuel tank is clogging something up. What's fuel pressure like?
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When i bought the truck about 3 years ago the guy told me it had a fresh top end.I just put a new fuel pump on it when it started acting up but i never tested the pressure.It is just a cheap replacement pump.
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I think there's anything but a cheap replacement pump that's mechanical unless it's a race pump.