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5.7 SBC Surging on acceleration and under load in gear only.

11897 Views 60 Replies 5 Participants Last post by  junktrucker
Ok, so I am new here, but I am not new to this truck. I have a 1985 Chevy Scottsdale C30. This thing is a pig, and acts accordingly. I've been all over this truck since I got it a year ago and my head has been itching over it so much that I've developed a balled spot. That said, the title explains it. I can't get this thing to surge here in the driveway, at all... period. and the only way I can test my "fixes" is to drive outa my subdivision to the local stretch and romp on her, which is where she decides to conform to her true nature; a no good, fumbling, bucking, squealing pig that wants to do anything BUT what I ask from her. Here's what I've done so far.
-New Mechanical fuel pump
-Cleaned out the gas tank
-Rebuilt Carburetor
-plug wires, and plugs
-oil change
-checked timing.... over and over again.
**cant find a true VIN CODE M Emmisions label for this truck.
-New coil, cap, rotor, ignition module
-Tested pick up coil... Checks out ok.... hmmm...
-Checked timing slack by watching rotor when turning crank by hand... no sign of significant slack.
-Drilled out fuel mixture screw covers... adjusted and adjusted... and adjusted.
-Checked vacuum advance mechanism for operation... yeah, it does.
-egr... oh yeah, the egr is there, but all ALL other emission stuff removed by previous owner.... pfft, fool.
-A/C system removed as well
-Cheap reman 63amp alternator put in place. tested yesterday at local dumbnut parts store... they say its fine.
-New PCV valve... yeah, I went there.
Now, my thing is, when I stomp the gas. it acts like it starts to rev up, the rev disappears and reappears several times, but not consistenty. the harder I push the gas the more pronounced it is. but it doesn't change a bit. It just does not like more than half throttle at all. and I'm lucky to get half throttle most of the time.
Please get me outa the pig farm. it stinks in here!
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1 - 10 of 61 Posts
Can you do a vacuum test and post back, you covered everything else,darn truck
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And is there any backfiring in carb?I had a 84 carbed truck , similar problem,head gasket was leaking between two cylinders,and only when I got on it
Modulator I think,get your connections tight,any line with vacuum at idle will work
So unburnt fuel igniting in exhaust, tailpipe black and sooty?
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Lifters adjusted too tight,valves not seating 100%?a bad vac line should make you run lean and bit higher than normal idle,a lifter adjustment might be a problem,odd, but stuff happens
It was in another thread, but what if you're harmonic balancer spun?and you're timing is retarded, just throwing ideas out there,but do tighten up that vacuum line
Spun,meaning the outer layer slipped on the inner layer,Wich is separated by a rubber like membrane,that deteorates over time,so the line on the outside ring for the timing lite is off
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So from the start, vacuum line repaired?now time the motor by ear, keep advancing,bit by bit,at operating temp,shut off and restart,until it bucks on the starter,then back off a bit,or with vacuum gauge,stop at highest reading
One way to check tdc, take bolt out of balancer, keyway will be straight up @ 0 or180,then check rotor pointing at no1,or no6 @180 out, another idea, before bolt removal,use breaker bar on bolt,go back and forth,see how much timing chain stretch you have
1 - 10 of 61 Posts
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