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

11898 Views 60 Replies 5 Participants Last post by junktrucker, Nov 15, 2017

junktrucker

Discussion Starter · Nov 7, 2017

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
-HAVE NOT REPLACED DISTRIBUTOR
-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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Zach Smith

· #16 · Nov 7, 2017 (Edited)

junktrucker said:
BTW, what's my vacuum at idle (Near 0 at WOT I believe)?
I should sign off for the night, and I'll pick up at my earliest convenience. It's the only vehicle I WANT to drive this winter... not that it is necessary that it runs, but I hate it when the things I've got don't play their roll.

15-18 for vac, should be steady (not bounce)...and no on feelers...GMs valve adjust procedures suck...always off (for 5.7 and 4.3)...just warm engine, pull v covers, run engine... (You will lose some oil and make a bit of a mess if you don't have modified v covers for this) back off valve till "clacks" slowly tighten till clack goes away...do this for all valves (16 times) shut down engine ,let cool. Turn all valves 1/2 to 3/4 full turn (do ALL the same). Replace valve cover, check oil. Unless you have solid lifters...

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Zach Smith

· #17 · Nov 7, 2017

You can get an idea of what is happening by checking your plugs...what do they look like?

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Zach Smith

· #32 · Nov 9, 2017

How did you do valve adjustment, feeler gauge way or 1/2 to 3/4 turn way? As to the balancer...if its never been replaced...likely enough.

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Zach Smith

· #35 · Nov 9, 2017 (Edited)

Yeah...well as long as we arnt hitting valves...turns by hand, no hard spots or tinks, when you tried to start it? Hydraulic lifters bleed as they sit...allowing slack. They are probably cranked way to tight now. I would do the factory adjust now, then see if I could start it...then, do it the way I said earlier....
1.Warm engine
2.pull valve covers
3.start engine, making sure all is clear
4.roll adjuster back until valve starts to clack...
5.roll adjuster forward slowly until clack goes away
6.do this for all valves
7.shut down engine and let cool
8.roll another 1/2 to 3/4 turn on all adjusters, staying the same across all adjuster's either 3/4 for all or 1/2.
9.start and check
10.assuming all is well replace valve covers.

Another option... Do a compression test and back off low cylinders.
Or back all of them back, the last 3/4 turn adjust you made...but I think (with what you just explained to me, that you did) (I should have numbered steps as I did for you this time, so I'll take part blame for not laying it out well) the first option, though the most tedious is probably the best.

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Zach Smith

· #37 · Nov 9, 2017

Your truck, your job, but I suggest going the long rout at this point...

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Zach Smith

· #39 · Nov 9, 2017

I meant go ahead with the factory setup (feeler gauges), that should allow it to start...prob have some clack though, then go forward with valve adjust procedure that works. I.e. the feeler gauge way should get you close...then get it right after that.

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Zach Smith

· #42 · Nov 10, 2017

Yup, just make sure to follow the steps, and the vac leak and possible leaking wire sounds like some headway.

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Zach Smith

· #46 · Nov 11, 2017

No 10 degrees... Should be, reliable... Maybe not best, but reliable... A 5.7 will start running on its own about 38°...base time...Do we have consistent fire? Consistent fuel? If so and you have a light flutter and no vac leak it may be time for a compression test, then leak down...then focus on the specifics of the leak...may be able to "fine tune" valve adjust...or you may be stuck with a hung/burnt valve...or relook the carb build...unless you are SURE of this...

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Zach Smith

· #47 · Nov 11, 2017

Zach Smith said:
No 10 degrees... Should be, reliable... Maybe not best, but reliable... A 5.7 will start running on its own about 38°...base time...Do we have consistent fire? Consistent fuel? If so and you have a light flutter and no vac leak it may be time for a compression test, then leak down...then focus on the specifics of the leak...may be able to "fine tune" valve adjust...or you may be stuck with a hung/burnt valve...or relook the carb build...unless you are SURE of this...

My carb skills are decent but, not ne'er as good as say, my dads', I do remember some float setups and other tricks for these stock(ish) carbs as they like to lean at throttle and such by factory settings, but I would rather someone with more experience walk with you on that if needed... I still call my dad when I'm dealing with them (very reputable carb tuner)...I'll call some boys up, that may be able to guide in that if you have any questions about the carb setup...in the mean time, do the compression test, and make sure we have good steady fire...

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Zach Smith

· #50 · Nov 12, 2017

With the timing... What I was saying is depending on health and compression and such, a 5.7l with no computer advancement (just base timing) at about 38° will run by itself..(diesel) as in when you cut the ignition, it continues to run...more advance... More it diesels...until you overcome that arc anyway... Light flutter COULD be a sign to look into valves (also light flutter is not easy to see from this side of net, so just covering base's) Glad you found some plug arcing as that could do the trick

the vac gauge steady at idle IS a Good sign, Yes...I know you tested compression earlier...but I would like to see how it is now..80-90...kinda low...even for low comp heads. Makes sense with blue smoke...does the crank case (when you open the oil filler) have some pretty good push to it? Start with wires...let's go from there...

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Zach Smith

· #52 · Nov 12, 2017

Sounds good, I think for now...we can forget the 2 on the list...and sounds like you're flutter is very minimal...and not of concern.

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Zach Smith

· #60 · Nov 15, 2017

junktrucker said:
Every last one of those plug wires. Each and every last one, I can see arcing coming through the insulator... I did a test where you ground a wire and run the other end across the plug wire, and I can see arcing coming through the insulator to the wire, and the entire length of the wires. I can also see arcing at the plugs. I looked at the wires and they say "Made In USA" and "Suppressor" and "ISO" something something. Can plug wires really be that cheap? Am I loosing it? Are the plugs to blame? Did I do something? Is it something else? Is it normal? Sorry, but wtf, over?

Sorry bud, you got lost in shuffle, glad some other boys stepped in...yes, they can be that cheap, parts quality is terrible these days...and I'm glad to see just a hair of positive pressure on both sides of rocker covers...that's what we want...too much usually indicates something like blow by...vacuum usually indicates something like intake leak... Try another wire set...you could try to hunt down a set of Packard wires for the truck...they are OE, and seem to work nicely, or go high quality.... Porcelain... You could also run shields...basically... Just make the leaks go away lol... Also they have little "help" kits with wire separators... A decent investment in my book. When you get the leaks gone...dial that ol girl in on the road dyno with the screwdriver in your pocket

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