troubleshooting advice

[xray]

I finally got to fire up the engine today and like I expected it was not a glorious roar of inline 6 goodness. More like a dull thud. :sick: Help me troubleshoot...

Here's what I have

L28, reman, compression 160# all cylinders

P79 with very mild cam (specs unknown, but had very little lope when I heard it run)

Previously set up for triple Webers...I have new Z Therapy SUs on an N36 intake

Non-emissions balance tube

Pertronix ignition, known good coil (at least, it worked prior to disassembly), all spark plug wires have 5k resistance (8mm Energy Core wires).

Here's what I've noted:

Turns over great. All electrics work fine

Backfires through the front carb (more like a light puff of smoke) when it fires up for about 3secs

Distributor advance is set all the way to A

No leaks--yet(let's hear it for new gaskets!)

My plan is to retard the timing from "all the way" at the A to a little ahead of midline...Isn't stock baseline supposed to be set at 7 degrees? I presume the Backfire is from a lean condition--I'll need to check the float level and adjust the mixture nut (it'[s already baselined according to Z Therapy at 2 1/2 turns) I'll also have to double-check the spark from the ignition coil, and I'll need to check over theplugs themselves...

I've been wary of the reversed distributor problem some have experienced, so I took care to mark the distributor and engine cover, as well as take pics to ensure it goes back the right way...but what would it look like if it was backwards? The number 1 spark plug wire is at about 7:30 position on the distributor cap, and it then goes anti-CW from there 153624, right?

Any other suggestions? Anything I'm missing?

Thanks,

Steve

[JimmyZ]

Might just be that your timing is waaay off. I'd try twisting the dizzy/crank/retry a few times before going into diagnostic mode.

Do you have a points style dizzy in a box you could try? I haven't played with the pertronix setup so I don't know what the wiring is like. If you could try an old breaker point dizzy you could at least run a wire from the battery to verify that it isn't something in the harness or setup.

You asked and 1-5-3-6-2-4 is right.

Dumb question but I'm assuming you tried a test plug on the block while cranking right? Tried spraying starter fluid? If you haven't either of these should help narrow it down to mechanical, fuel or electrical. With a points type dizzy there is a technique for setting the ignition using a regular light bulb. (Engine not running but being turned by hand)

My error when installing everything in the engine compartment was to switch the wires to the coil and ballast. I had 12V during running and 6V during start instead of the right way. (Killed the coil then realized what I did.) The pertronix setup might just be a 12V/fulltime kind of thing.

2c

[mlc240z]

Steve,

with the pertronix, (which i love) make sure you are bypassing the ballast resistor. that ballast setup was only to restrict the voltage to extend the life of the points.

make sure you use a jumper wire to bypass the ballast to guarantee you are getting 'full' voltage to the pertronix and the cylinders.

you might also want to open the plug gap a little with this setup (since you are getting a bigger spark) for a more complete burn. i tried this with mine and she idles and runs very well.

the backfire sounds like a lean condition in the front carb. try riching it up a little and see if it goes away. not sure about the timing (10 degrees????).

[xray]

The pertronix is installed according to the instructions, so it should be good. I'm testing the primary coil, spark, plug gap/condition and carb float level today, and playing a bit with timing...One step at a time, slowly inching to the finish.

BTW, if baseline fuel mixture is 2 1/2 turns, what is typical for "normal" driving at 300ft altitude?

Thanks for the help so far,

Steve

[xray]

So...I did some work on the car today:

-Float level in carbs normal

-Plugs gapped correctly and wet with gas (leaned it out a bit after seeing that)

-no sparks at the plug wires

-No spark at the coil

-12V identified at the low-tension side of the coil

I noticed the condensor was still attached and wired up to the distributor, which I thought was unusual since the condensor is associated with the points (which were discarded), so I'll remove it. Double-checked the wiring of the Pertronix at the ballast resistor and coil. While the Pertronix may or may not be bad, it would not affect the coil's ability to produce sparking on the high tension side if I'm getting battery voltage on the low-tension side--correct?

I know the coil receives voltage via the tachometer, so since I can see battery voltage at the low-tension side of the coil is it safe to assume the coil/tach circuit is intact? Whether the tach functions or not is yet to be seen...

I think it's narrowed down to a bad coil, but I don't want to miss something obvious. It's strange b/c it's a nearly new coil with no signs of external damage, leakage etc--anyway to test it without getting a big shock?

I enjoy the troubleshooting a good bit, since it involves learning a lot of stuff I didn't pick up in med school, so any advice would be worthwhile.

Thanks,

Steve

[xray]

So...more work on the patient today.

After mulling it over yesterday I just could not figure out how a coil in a sealed container could go bad sitting on a shelf...Recall I initially measured 15 ohms across the primary coil and could not get a reading on the secondary coil. So, I decided to distrust my meter. Borrowed a friend of mine's, rechecked the resiistance and it was normal. 1.5 on the primary, 11000 on the secondary.

Great!

Rechecked for spark at the output wire...check (Liking not buying a new coil now:laugh:)

Rechecked for spark at the plug wires...check! (woo-hoo! Distributor works!)

So, back to where we thought the problem was---timing. It was a worthwhile exercise excluding air, fuel and spark as we move downstream on the combustion pathway. Even if one has a good idea it's good practice (in cars, medicine and life) to follow a known algorithm to exclude additional problems that may compound the initial symptoms

So I moved the screws a little to the advance side (charging 200--clear!)

Still...asystole:tapemouth

Moved the screw a little more to the advance (chraging 300--clear!)

What was that? Did it fire? Was that automotive VTach??? Still...no pulse :devious:

Advanced the distributor all the way using both screws (charging 360--clear!)

VROOM! Like phoenix from the ashes the car revved up to 3k then...nothing...The tach worked while it revved too, so that's nice...And the cloud of smoke was encouraging.

So, I still have a problem. With the distributor fully advanced it fires up. I got to thinking about when I repositioned the drive gear when reinstalling the oil pump/distributor...was I off? It seems likely given how this came about, so I checked the distributor drive gear tang after manually setting the camshaft to TDC at #1 (picture #3)

I'd like to say that's at the 11:25 position, (pic #1 and 2) but I have my doubts...Is it closer to 11:45? 12:00? Maybe it's off by one groove--that would cause these kind of symptoms yes?...any thoughts? In looking at the pics I think my reference line drawn for 12:00 may be slightly off.

I haven't had much traffic on this thread, but I'm hoping someone with additional experience will chime in and help me out.

Thanks,

Steve

[xray]

So I got it to run at idle after some more fiddling around.

The timing is still max advance, making think the distributor drive shaft is off a tooth, but I would REALLY like some other's input into my prior post---any pics of properly positioned tangs? It looks sorta like that image in the FSM, but some exerienced opinions would be helpful....

I've searched the archives, but can't come up with comparison pics or any definitive thread responses, so chime in here and help me out!

The engine idles at 1500 with occasional pops that I think are coming from the exhaust ( can't see anything happening at the carbs), and while this could be carb related, with the possible timing issue still on the table I'd like to get some advice on what order to proceed...address the distributor drive first then reset timing then tune carbs? Or, is the tang OK and I should focus more on tuning the carbs?

...Need some confirmation, gents. Help would be appreciated.

Thanks in advance,

Steve

[Zs-ondabrain]

I was always under the impression that 12:00 was pointing at the radiator. Picture 1 and 2 are pointing at 3 or 9 O'clock. but not seeing the rotor on the dizzy throws me off.

here's what I do, and you may have done the same but I don't have the time to read everything.....

Piston 1 at TDC compression stroke

rotor pointing at the radiator (12 O'clock 'ish)

1-5-3-6-2-4 CCW

2.5 turns on each carb but only as a starting base line. backfiring is from the carb being too lean, turn it out .5 turns

Pertronics = no ballast risister, 12 and 12 = 12 volts starting and 12 volts running. or so I've been told.

All this is probably been done but I wish I was there to help. A second set of hands and eyes always makes the job easier.

Dave.

[sblake01]

From my experience it looks like the tang is a little too far clockwise. Should look more like this at TDC:

[xray]

Dave, Jimmy, Bart, Stephen:

Thanks for your input...

The FSM places 12:00 toward the cylinder head and block, and on p. EM-31 states the drive spindle should be oriented so its top is "located in the 11:25 am position, at this time, the smaller bowshape will be placed in the front."

I was able to finally do a side-by-side comparison of the drive gear tang orientation, and it appears off (see pics). Tried checking the timing with a timing light, but my old one was non-functional and I finally got a new one today. As a result, the timing marks are off...pretty significantly

The 0* mark on the crank pulley is close to the 12:00 position on the crank pulley as it rotates (viewing the pulley from the front like a clock face), and appears to be about 20* away from the 20* mark on my timing indicator:eek:

So that's 40* advanced, right? :eek::eek:

I have tried readjusting the timing to more retard, but it idles verrry poorly and doesn't fire up instantly like it does with it fully advanced.

My question is this: Is the proper timing simply unmasking the un-tuned (but baselined) carbs, or is this all related to the tang orientation? Sort of chicken-and-the-egg, I know...

I'm thinking I should tend to the drivegear tang orientation first, then recheck timing, then adjust the carbs.

Any thoughts?

[sblake01]

The tang must be in the proper location for the timing marks to be of any use. If not, when you 'advance' the distributor it's still not in time with the engine. In other words, where your distributor drive is now, even when you turn the dist as far as it will go, you run out of adjustment before it reaches the point at which the engine will run properly with no possible further adjustment. Definately get that squared away before you deal with the carbs.

[RandyN]

Good day XRAY,.... I've been working on these L28 over 12 years now, and the distributor shaft is supposed to be at 11:25, we've gotten these engines breathing through triple Mikunis at 270 BHP and 225 Lb Ft, 19 deg of ign timing, with zero detonation........