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engine timing and tuning
#1
All,

recently, I noticed the engine was developing some significant pinging under heavy load (like when you go WOT because you like that kind of thing). Some background: I have points/condenser ignition 302 2bbl. I have ported vacuum which has generally worked pretty well - car has generally run pretty great. I have had one nagging issue where I have to run with the distributor rotated as far as it will go towards water pump. In general it was fine there, but it has bothered me that I couldn't get to zero initial timing. Against water pump was 12-13 deg of timing if I recall. It would generally pull about 15in vacuum at 800 rpm idle.

I went around the engine to check the cylinders and plugs. All cylinders produce between 125 & 135 psi, and all plugs were generally clean and the ceramic was a nice tan color, and gaps were all good at .034.

Since pinging usually has something to do with timing advance, I was curious if I had developed vacuum leak somewhere, so I looked for one. Everything seemed ok (hoses have been replaced in the past year or two). but I checked the vacuum advance module with a vacuum brake bleeder, and found that the line coming off the side of the module (not the axial port) could not hold vacuum.

I changed the vacuum advance module out, and still couldn't get it to run very well. It was rough and irregular. I was frustrated by the inability to get to 6deg initial timing, so I re-stabbed the distributor one cog over. I also put in new points and condenser. The new points actually improved things some too.

With the distributor re-stabbed, the car starts and runs great up to 2k rpm. Now it runs ok with the dist rotation in the mid range, and all the way over to the water pump is too far. Initial timing is around 6degs, and it idles real well, and generally seems normal. Pulls around 15in vacuum (15 seems low to me - should be 18-20 right?). But, when I really put the gas to it, I get a lot of hesitation, and it generally runs badly. it's the 2500+ rpm range that I have the problem.

timing at ~3K rpm is high 20's (thats with both vacuum hoses on vac advance). Seems low... should be over 30 but not more than 36 right? How do I get it there? I remembered I had not adjusted the hex nut inside the vacuum module axial port, so I went out and played with that some, maybe some improvements, but nothing at the high end.

All that to ask, how do i hold the good situation at low RPM, and adjust the high speed advance up to where it needs to be? Seems like I'm almost there, but Im kinda stuck at this point.

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#2
.
plug the distributor vacuum hose and leave it plugged.

rev engine until max timing is reached and tell us what it is.

if you have a tach, tell us what rpm it reaches max timing at.

at idle, advance the distributor 4 degrees and see if the rpm changes and if it still runs smoothly.

retard distributor 4 degrees.

rev engine to 2000 - 2200 rpm or 1.4 throttle then advance timing 4 degrees and check rpm change and if it still runs smoothly.

if the rpms increased with both tests and it still ran smooth, leave it there then set idle then test drive.
.
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#3
Any chance you got some really bad fuel?

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#4
barnett468;255942 Wrote:plug the distributor vacuum hose and leave it plugged.

I'm assuming you mean the axial vacuum port? Should I leave the vacuum port on the side attached?

vozaday;255948 Wrote:Any chance you got some really bad fuel?

I can't rule that out, but I think it's unlikely. Car runs good until I really get into the gas pedal - or perhaps the high RPMS right before transmission shift (I have a C4 auto). When I get there, lots of shuddering/hesitation. Once the load on the engine eases up, the engine runs smoother. Hate to say it, but better chance I screwed something up here

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#5
*****When I get there, lots of shuddering/hesitation. Once the load on the engine eases up, the engine runs smoother.*****
[/quote]

That sounds like fuel starvation.

The pinging is a different issue.

Paul
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#6
Quote:
rocket366;255955 Wrote:*****When I get there, lots of shuddering/hesitation. Once the load on the engine eases up, the engine runs smoother.*****
That sounds like fuel starvation.
The pinging is a different issue.
Paul

oh. that's an interesting thought... Let me run the tests Barnett468 recommends, get those results, and then if it's not clear from that, I'll check into this. I guess that could be a fuel filter? or a fuel pump? I've had to replace the fuel pump in this thing twice and last time was just last year.

The bad pinging I had before does seem to be gone. At least when I'm taking off from a dead start I don't hear the pinging. And when RPMs are up, I get this shuddering...

Thanks for the advice though, I will keep it on the list of things to checkout.

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#7
Results to Barnett468 tests below:

initial conditions
both vac hoses un-hooked and plugged (no vac advance anywhere - all mechanical)
Idles well at 850 rpm, timing ~10deg

Rev to max mechanical timing test:
Reaches about 32 deg timing at 5500rpm
during this test I noticed something that I think is a root cause of the issues. When I get up around 5k RPMs, I noticed that the timing light had SIGNIFICANT gaps in flashing. flashes get faster & faster with revving the engine, until this high speed, then I get erratic drops in flashes - meaning spark dropout. I don't know what the problem is here. I suspect this either is a problem with the capacitor, or I have something shorting the spark out when the distributor gets advanced (either mechanically or via vacuum). Any thoughts on this problem?

Idle tests:
13-15 in mg vacuum (needle stable)
advance timing 4 deg, engine idles just fine at 900-950 rpm
Cannot retard timing 4 deg because the vacuum advance module hits the Air conditioner compressor bracket.
Currently, my min timing is 8-10deg.

RPM's at 2000 test:
Engine runs fine in this RPM range. it's hard to hold there, as a little more fuel and the RPMs quickly get to 3-4k RPMs. I didn't have enough hands to hold the timing light, hold the throttle and and rotate the distributor to advance/retard timing. What I able to do tho was hold RPMs at ~2000, and measure timing. It's very close to 20deg timing in this condition. Seems to run quite smooth at this condition. Spark is regular at this condition (timing light flashes are quick and bright)

So, here are some thoughts:
- I believe something is causing the spark to drop out at high engine RPMs. No idea why. This is consistent with shuddering right before transmission shifts etc. I suspect the condenser as I have had to replace these units multiple times in this car, and they typically create symptoms like this shuddering when they go out. it's not always at high RPMs though.

- I wonder if PO put a performance CAM in this car when it was "rebuilt" I believe 30K miles ago. That might explain why I only have 13-15 in vacuum at idle. It doesn't "lope" though like a harley or anything, it generally idles relatively smoothly.

- My mechanical advance seems to be functioning. I don't know if "the curve" is right. I've only got 3 points from these tests (idle, 2k and 5k). Is 20 deg timing at 2k and 32 deg timing at 5k about right? I'll have to look this up...

Any more thoughts on the issues?
Any suggestions on what might cause my high speed spark to drop out/short out?

Thanks for any suggestions!

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#8
improperly adjusted points, bad condensor, bad coil, old plug wires that are breaking down, cracked cap, moisture in cap, rotor covered in carbon, bad plugs-even one will be enough to cause problems.

I'd replace points with a pertronix unit myself as it is getting harder and harder to find good quality points anymore.

I guess I shouldn't advise you that old wires will shock you when the motor is running and that handling the wires can find the problem sometimes Smile (It only hurts for a moment until you go to HEI)

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#9
Jeff73Mach1;256078 Wrote:improperly adjusted points, bad condensor, bad coil, old plug wires that are breaking down, cracked cap, moisture in cap, rotor covered in carbon, bad plugs-even one will be enough to cause problems.

I'd replace points with a pertronix unit myself as it is getting harder and harder to find good quality points anymore.

I guess I shouldn't advise you that old wires will shock you when the motor is running and that handling the wires can find the problem sometimes Smile (It only hurts for a moment until you go to HEI)

Yep what he said.
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#10
Well, here is my take on each of these:

improperly adjusted points:
brand new and gapped per the book

bad condenser:
2nd new one this week. This is my highest suspicion, but it is a brand new part

bad coil:
New within last year

old plug wires that are breaking down:
Wires are 2 years old. I just pulled each and every one, cleaned & inspected them.

cracked cap:
Cap seems fine. I've had it off multiple times, clean and no visible signs of cracks.

moisture in cap:
cap is clean as a whistle.

rotor covered in carbon:
Clean, has been handled many times thru this process.

bad plugs-even one will be enough to cause problems:
Inspected and gapped each one, have verified strong spark at idle for every cylinder via timing light test.

I'd replace points with a pertronix unit myself as it is getting harder and harder to find good quality points anymore:
Call me stubborn, but that's a $120 option, forces a mod from ported vacuum, and I can't help but feel it's not needed.

I guess I shouldn't advise you that old wires will shock you when the motor is running and that handling the wires can find the problem sometimes Smile (It only hurts for a moment until you go to HEI)
i've learned this lesson already. More dollars to get to HEI, forces more mods in other places in the engine.

HEI and pertronix are "shotgun fixes" (combined in excess of $200)... I'd much rather find the root cause in the original systems here.

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