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

11894 Views 60 Replies 5 Participants Last post by  junktrucker, 
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
-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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junktrucker
Ok, WOW I got lucky! So on my way home from the best job a man could ever have (haaah!) I ran into a real bad traffic jam. I decided to double back and hit the autoparts store up for a vacuum guage. Got it. Then, I got home, and my sickly girlfriend gave me a by, so I took full advantage. Backed the valves off one full turn, and it ran like a paraplegic. But it ran just enough that I could run around to the engine and loosen all valves... odd part is that I backed the valves 8* (1/4) turns (2 full turns) until they clacked and shut her down. She still runs PHEW!!! I'm going to have to get back at it tomorrow or as soon as I get a chance... I've got my brothers Sportster stripped down to the frame so we can chop it and put a hard tail on it F* YEAH! We might do that this weekend. Anyway. here's my thoughts.
-Rockers were already way too tight... as far as my math goes, they were 3/4 turn tighter than they should have been.
-If they were this tight... and drove for a long time... I'm guessing the damage is done... Because,...
-I put a piece of paper up to both sides of the exhaust tonight, and the starboard exhaust was hotter and it seemed to flutter more. I noticed this as a fact prior to my valve adjustment... So if anything... and I don't believe, but I may have exacerbated the issue.
-It may be a burnt exhaust valve on at least cylinder 8 likely 6 too at least.
-I'll redo the valve adjustment asap since I don't think the truck was warmed up significantly when I did it tonight, I'll fix the vacuum leak(s) and report back asap.

Oh, and I did notice a fishy looking whitish "tracking" mark on one of my spark plug wire boots... I noticed this when I was putting the wires back on the distributor, and don't know which orientation I had the wires before. I will keep my peeper peeled for this too.
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Zach Smith
Yup, just make sure to follow the steps, and the vac leak and possible leaking wire sounds like some headway.
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junktrucker
Will do. Thanks Zach, You've been a ton of help.
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junktrucker
Ok, so I did a valve adjustment, fixed the vacuum leak at the trans. modulator, and checked the vacuum... Lightly fluctuating between 17.8 and 18.2 Hg In. Went and got a new timing light... It seemed like I had a huge issue with misfiring so I checked it on both of my bikes and the light wasn't flashing at a constant repetition on either of those either. But I still see a misfire on all three with the new light. I knew my Harley was having issues, but the other one has only one cylinder and I can hear it firing steady. My Saturn also has P0300 code... I am no good with wires and electricity so this is not my strong suit, and all my vehicles have this issue apparently. GRRRRR (I really like breaking stuff when I get mad. I have some aluminum auto parts I like taking a sledge hammer to (I use the aluminum for casting projects).)! Anyway, I'm about to drive the truck in a short few, but I can still hear it backfiring...

I have no faith that I've got this one pegged.
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junktrucker
geo1 said:
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
Click to expand...
Ok, so I put that vacuum gauge on a port on the carb, adjusted my distributor, and the highest reading I got was around 25 Hg In. That seemed high so I checked how far advance I was and at idle I was around 38 Degrees advanced.......... uh, so I put it back to 10 degrees... I's there something wrong going on there? BTW I don't know if it makes a difference but this truck is a VIN code "M" meaning this truck is the heavy duty... which from what I gather, this truck has lower compression heads than the C10's of its circa.
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Zach Smith
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
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...
Click to expand...
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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junktrucker
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...
Click to expand...
I need clarification, etc...
"A 5.7 will start running on it's own about 38 degrees base time" Are you saying that with all systems hooked up (vacuum advance, etc) the truck will be at 38 degrees at idle?
"consistent fire"... I should put a plug on a plug wire and watch it fire... if it doesn't I'll let you know.
"consistent fuel" ill have to hook my vac gauge up to it and let you know.
"light flutter and no vac leak" is light flutter ok? and by the vacuum gauge showing steady at idle, does this prove no vac leak?
"i did a compression test a while back and I was getting between 80 and 90 but no more that five off from the one next to it.
"leak down" I have yet to do this.
"relook carb build" ok, sure. but I triple check everything... I could assume again that maybe the float setting would be different for the c30 low compression heads... further, emissions equipment removed. also, the secondary rods, and hanger, were mangled by some donkey before me. I have been wanting to look into this, but with the reving being clean and crisp in park but not on the road, I pushed this one to the side. I'll give it further examination.
"hung/burnt valve" ok, I really didn't want to pull this engine, but I'm starting to believe this is the next step. I do have blue smoke coming from exhaust... intermittent at best.

By the way.. the last test drive I just took... obviously no fixy fixy.
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junktrucker
Ok, so I know I am offloading a lot but I just popped the hood again. I hooked up the vacuum gauge again because I finally read the instructions... it appears this truck is smooth as glass when it comes to vacuum diagnostics.
What do you know! I can see stray sparks at the plugs!!! So very ever so faint that I actually have no lights on around me, and I can't look directly at it, but a very faint spark is visible in my periphery. I can see it on cylinders 1,2,3, and 4! the reason I caught it was because I looked at number one plug wire was touching the header.. concerned, and considering all possibilities I shut my light off and looked... very carefully.
Now the &^%$$ plugs and the ^($%&@ plug wires are brand new. A/C Delco Plugs, and new cheepo wires in the same. (replaced as of this symptom occurred) actually this truck has been like this since I got it.

I'll check spark/ etc. tomorrow I guess
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Zach Smith
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:D 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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junktrucker
I'm glad you've stuck with me Zach. I had it in the back of my mind that you meant dieseling, but I didn't want to type it out loud hehe. I was considering tossing a video on Youtube to show what the light flutter looked like. But like I said, it's minute... .2 to .4 Hg In. And it is slow, I would say it drops and raises between the two twice per minute. so four movements @ .1 to .2 in either direction... Very hard to see. And when it comes to valve issues diagnosed by a vacuum gauge, I've seen videos that show A much larger and more "fluttery" movement. Say 1 full Hg In in either direction.
Come to think of it, I need to check vacuum on a different port, because when I pulled the vacuum for the electric choke (and left the hose to hang), it dropped to 5 Hg In and was a completely steady reading.
I also just watched a video about "induced crossfire". I am going to guess this is a problem for me since my engine bay is not tidy at all, and I'm using zip ties to keep things where they belong... but zipping two plug wires together is no good from what I see now. I'll honestly say I never knew that.
As for good pressure on the oil filler, I'll look at that tomorrow and the like with the compression. (I say tomorrow, but life takes me on many random and unforeseen journeys).

So "Tomorrow"::::

-Straighten out plug wires
-Watch spark with inductive lamp... if not steady watch with plug in plug wire boot near ground and look for intermittent firing
-Recheck vacuum on different port
-Compression Test
-Leak down Test (if I can figure out how)
-Post video of vacuum test if requested.

*added

-check fuel pressure
-check oil filler
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Zach Smith
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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xPosTech
junktrucker said:
Ok, so I know I am offloading a lot but I just popped the hood again. I hooked up the vacuum gauge again because I finally read the instructions... it appears this truck is smooth as glass when it comes to vacuum diagnostics.
What do you know! I can see stray sparks at the plugs!!! So very ever so faint that I actually have no lights on around me, and I can't look directly at it, but a very faint spark is visible in my periphery. I can see it on cylinders 1,2,3, and 4! the reason I caught it was because I looked at number one plug wire was touching the header.. concerned, and considering all possibilities I shut my light off and looked... very carefully.
Now the &^%$$ plugs and the ^($%&@ plug wires are brand new. A/C Delco Plugs, and new cheepo wires in the same. (replaced as of this symptom occurred) actually this truck has been like this since I got it.

I'll check spark/ etc. tomorrow I guess
Click to expand...
You can visually enhance the spark arcing from wire to wire or to ground by using a spray bottle of water in the garage with the lights off or at night. The finer the spray the better. Just mist the area you want to check. Ideally you want no arcing at all while misting.

This creates a worse case condition for checking the condition of the plug wires. If there's no arcing with the mist there won't be any when dry.

Ted
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junktrucker
xPosTech said:
You can visually enhance the spark arcing from wire to wire or to ground by using a spray bottle of water in the garage with the lights off or at night. The finer the spray the better. Just mist the area you want to check. Ideally you want no arcing at all while misting.

This creates a worse case condition for checking the condition of the plug wires. If there's no arcing with the mist there won't be any when dry.

Ted
Click to expand...
BRILLIANT! I was wondering of a way to enhance that arcing visibility. I am gaining mad repertoire from this new crew of bad @%$es I have chosen to associate myself with!
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junktrucker
Zach Smith said:
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?
Click to expand...
I am going to assume that the pressure at the filler would tell me if there is good crank case pressure, and if not good pressure, maybe a bad head, valve issue, piston issue... and so should I check the pcv port as well?
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junktrucker
negative pressure at the left bank (even side) and positive pressure on the right bank (odd side). 1 Hg In vacuum left .5 psi on the right.
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junktrucker
scratch that, pcv was causing vacuum... I'm getting a minute positive pressure from both banks. about .5 psi
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junktrucker
Ok, I know for an absolute certainty that my plug wires are... I cannot speak those words on this forum.... and there is about a hundred of them I can use! I routed them all away from each other... Not touching anything metallic in the engine bay. Even near the cap I isolated them from each other. And what do you know? I can see stray arcing coming through the wires all over the place! I picked up a bundled area where I zip tied them in a fashion that kept them a quarter inch away from the one next to it. and saw arcing there! I caused this arc to be stronger visibly with a bit of misting too. I also noticed where #2 plug wire was draped across a RUBBER COOLANT HOSE and saw arcing on it as well! RUBBER!? (I'm guessing the antifreeze passing through that line caused enough static electricity to charge the surface of that rubber hose and thusly accepting or donating electrons). I can still see arcing at the plugs too (spraying a mist at that location didn't help since it actually formed water on the surface of the plug and thusly completing the open circuit). However, I know that, and with all other adjustments in mind, the spark plug isolation indeed helped reduce misfiring. I went out for pizza and beer in the truck and it barely stumbled when I got on it. I know that all of my wires are getting spark to the combustion chamber because I unplugged each one at the cap and could hear and see (timing light and vacuum gauge) that there was a swift change in engine performance. AND WOW WHAT A JOLT! I put on a "chemical safe" rubber glove and the arc jumped right through it and made me convulse just a little. I mean, I know I'm at around 30,000 volts but WOW! That was painful! Anyway, am I dealing with an under insulated plug wire set, spark plug, other, or an overcharged H.E.I. system? Maybe a bad ground circuit? If it is bad plug wires, I am going to absolutely flip the freak out on the manufacturer! That is if I can find who made them... I know what store I got them from though... GRRR!
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junktrucker
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?
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Zach Smith
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?
Click to expand...
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 :D
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