Topic: WHAT DID I WRONG ?
in Forum: C3 Engines
Lifetime MemberIf you pulled 2 wires and it made no difference, those cylinders were not firing correctly in the first place. You still have more problems. Sorry to disappoint you, but when you find it, it will be worth it.
Don't forget to check for vacuum leaks.
this becomes a nightmare.....
put new nut on valverocker , ( end of play + 1 turn ) and .... problem the same , no driving past 3000 rev's..... sh#t.
pulled again valve covers and watched the intake valves working to check the firing order. ( pushing bit by bit the car in gear ) . That seems OK. They work in the same order as my firing .
let engine idle very slow and pulled one by one spark plugs. No very difference.Must pull at least 2 to hear engine noise .
BEST OF THE DAY : removed 6 plugs ( except 5 and 7 witch have to be done from under the car ) to push the car for the above mentioned trial .Afterworths i started once the engine to see the rockers moving and he was idling !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! very bad idle ofcoarse but, YES, running !!!!!!!!!!!!!!!! on 2 plugs....
Now i'm depressed , my god, i stared one hour at the engine smoking a chain of sigarettes and didn't find one thing now to change or try.
What's happen to that engine, he was running so wild !
there are no visible exhaust fumes , but all plugs are dark black.And whatever i do , he's always starting and idling perfect.
Is it possible that static advance is coming in to soon ? That 3000 rpm's make me think.... but why ??? the weights and springs are the same as before.... and without vacuum advance i see the timing marks perfect coming in to less than 36° with reving.
Is that engine than so sensitive to a (unknow) (small ?? ) malfunction ?????? and on the other hand nearly idling on 2 cylinders ???
Anyone have a idee ?????
If all the plugs are black, you are not running out of gas.....
Since you said you put in new points, I assume you don't have an HEI distributor. I left the ground strap off my HEI a few years ago and had the same symptoms you did. Now it sounds like distributor problems. Only thing I can say is to check out the wires inside the distributor very carefully. After 35 years of flexing a wire could be broken inside the insulation.
If that doesn't fix it, you have me stupmed as well. (Excuse the english slang!)
Dave
But what wire do you mean ? There's only the condensor lead and the primary lead. With one broken inside should the engine idle ??? and there's a ground lead under a screw of the vacuum advance.I check that with ohm meter !
What is the dwell at idle and at 3000 rpm?
When you pull the sparkplug wires with a tack hooked up, which cylinders drop less rpm at idle?
See which cylinders show less rpm drop, then look on top of the intake manifold to see if anything there may cause an intake leak, possible pcv valve stuck open, carb base gasket, EGR valve vac. hose, hoses to the tranny modulator?
Maybe set the valves one half turn instead of one turn.
Do you have screwed in studs or pressed in? If pressed in, lay a straight edge across all of them on one head to see if one of them are pulling out, then check the other side.
I plug any vacuum hoses at the manifold to eliminate all other problems from the engine.
I hope I helped you find your problem,and good luck.
Denny
didn't hook up a tach pulling wires , just listening to the engine. but as now seen "running" on 2 cylinders in know better !
Another thought or two. Double check the rocker adjustment. If they are too tight there will be no noise, but the engine won't run well at some rpm ranges.
You may also want to consider a fresh set of spark plugs. They could be too weak to operate with the increased pressure of the open throttle, but fire under lesser load. Watch the brand. Bosch is a good plug for a European car, but is nasty in a Chevy. They usually don't work with our stock ignition. Use the A/C Delco plugs. Make sure the gap is .035
[QUOTE=BelgiumBarry]ok guys , now i'm a bit ,
the car was doing very well but read forums about timing etc. So i played changing :
- breaker points , heavy duty
- adjustable vacuum advance
- Accel kit mechanical advance , sets of springs to choose.
- new spark plugs
tryed a lot of settings but never better than original.Worse !always some pufpufs in acceleration.
so i dicided : back to original , all.
Did that but the pufpufs are stiil there ! I can only accelerate up to 3000 rpm and slowly otherwise there are more pufpufs than rpm's.?????????????? What did i wrong ????????????
On the carb ( a Holley 600 double pumper ) i only adjusted the fuel level in the cowls : raised fuel to bottom sight holes ) and both idle screws optimum with vacuum gauge.I even now returned fuel level in cowls as before ( 1/2 turn of the screw above , first anticlockwise , now again clockwise ) and see the fuel a bit beneath the sight holes.
Just inspected the spark plugs and wonderd : passenger side they are dark grey with spots , driver side black?????????????? ( have a Weiand 8004 inlet , so dual plenum )
i have a perfect idle and engine respond good on gas but not driving.
From the moment i push throtle it is pifpoefpaf....
Pumped all the gas out ( other brand) and refuelled with the one i'm sure it worked OK. No diverence.
Static advance is set again 4° as previous.
Anybody have a idee ????? i'm
[/QUOTE]
Okay, there have been an awful lot of posts on this problem, and all very good ideas. I keep thinking something happened when you did the above as everything was good up until that point. Did you change the condenser when the points were changed? If so, try installing the original and see what happens. I've had these things bad right out of the box.
It's been a long time since I fooled around with a points type distributor, but I think the ground wire flexes when the timing advances with RPM. It may have continuity in the normal condition then flex and part the wire as it advances up around 3000 RPM. This is a hard to diagnose gremlin since the wire may check out OK in the static position then "break" when the ign. is advanced under load.
Following is an article written by John Hinckley, a career engineer at GM and Corvette who finally retired as the Viper plant manager. He has forgotten more than I'll ever know about timing. An interesting read....
Dave
TIMING AND VACUUM ADVANCE 101
The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.
The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.
At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).
When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.
The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.
Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.
If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.
What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.
Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.
For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.