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No Spark While Cranking

4K views 5 replies 4 participants last post by  rperryman 
#1 · (Edited by Moderator)
Please help. I have a 1976 Silverado with a 1968 Chevy 427.

The previous owner reported that the engine had been refurbished with a mild cam, high compression heads, Holley 750 cfm Double Pumper, and HEI ignition.

The truck doesn't get driven very often, but the last few times that it was used drivability got progressively worse.

I mistakingly concentrated on the carburetor since my exhaust exhibited symptoms of an overly rich mixture. I was able to get the idle smooth but suffered from the effects of too lean a mixture.

I moved to checking the ignition system and found the spark at the plugs to be visually weak, just barely noticeable. During these cranking evolutions I used another vehicle's battery in parallel with the truck to keep voltage up.

The battery (Duralast Gold,less than six months old), at rest, reads 12.5 to 12.7 volts. While cranking, voltage drops to 11 volts. The voltage at the distributor feed reads 10.5 volts during cranking.

Coil checks done: .7 to 1.O ohms (tach terminal to battery terminal on distributor cap);


tach to distributor center terminal infinite ohms; ground terminal to distributor center terminal (coil in cap) 12.5 k ohms, (coil removed from cap) 8.7 k ohms. This coil is relatively new, one year or less.

New pick up coil and ignition module.

No. 1 TDC verified with a compression gauge and physically checked with a screw driver through spark plug opening.

All plug wires checked with shortest wire reading 6k ohms and longest at 9.1 k ohms. Spark plugs, R43XLS, are gapped at .045 inches.

Start circuit wires checked, grounds cleaned, and suspect power wires under the hood repaired.

On subsequent try with another vehicle's battery in parallel, a couple of distributor adjustments, disengaging the truck's battery lead to distributor primary and running a jumper from assist vehicle to distributor battery terminal (maintaining 12.5 volts during cranking) I was able find a spot that gave a nice bright spark pattern from no. 1 plug that was out of it bore and against a ground point.

I installed the plug and tried again to no avail. Pulled no. 1 and 3, set against ground points and tried again for sparks with none present. Can anyone suggest where I'm going wrong or what I'm over looking. Any help will be most appreciated.
 
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#2 ·
what you didn't mention testing is: for full batt V present on the solonoid and the "R" wire from the solonoid to the dist which is hot while cranking

really need to test for 12V+ at the dist with the motor running...
not while cranking....
a worn starter motor will most definitely pull down the V even when cold and alot more when hot....
your probably getting a "false" spark impression (as demonstrated by jumping the ign with another batt direct)
yes the HEI needs 12V plus at idle and above
 
#3 ·
Doc here, :pimp:

I edited your Composition To address each issue as it was presented to help identify the steps performed. Hope that's OK with you..

First, you didn't say, but I will assume you are now in a "No Start" Situation..would That be a correct assessment?

If that's the case..lets do (go back to) basics first..(in some cases a second time)..

Remove the Dizzy Cap, Bring up #1 TDC , Compression, BOTH Intake and exhaust Valves closed..Timing marks aligned..If you can't coordinate these you have a mechanical problem (Timing chain or mis aligned cam installation)

If you don't have a piston stop, you can use a Soda straw in the #1 plug hole as you bring it up to TDC..

Then "Rock it by hand" until the straw moves ONLY down by turning the Crank either direction..This is TOP DEAD CENTER..(and a soda straw won't damage anything should it get hung on something..)

Check your valves..are they slack? should be no pressure at TDC..This is good.

Now look at the rotor..Mark with a straight edge the exact center of the #1 plug tower on the base off the Dizzy..Do the rotor and mark line up...If not put them that way..(either by advance / retard or resetting the Base unit)

If you have that..your Static timing is fine..If not correct as needed.

NEXT, Pull all 8 plugs..Do a Compression test..should read 125 to 150 PSI + / - 10 % all the way around..If it is consistently low, (like 75 PSI) all the way around..the chain has jumped..If some are low, and some aren't..check valve adjustment. The lows may be slightly over adjusted.

If good, Install all 8 plugs..F.O. 1 8 4 3 6 5 7 2..Direction of rotation is Clockwise. Verify 5 & 7 are NOT reversed! This error is performed by Pros and Novices alike..and When queried, say "Yeah it's all good" up to 3 times..after a month of troubleshoot and a ton of parts thrown at it ..I hear back..Gee..5 and 7 were reversed..HAND over HAND them to be sure!

NEXT, Retest your Coil..IT should be..DVOM set to OHMS , R X 1 scale, Calibrated to 000, One probe on the "Batt" terminal, the other to the Tach terminal..It should read LESS Than an ohm..But more than 000, Outside of that range toss it..

Next do the Secondary..Set your DVOM to R X 10 k or higher or auto range..and with one probe on the carbon element of the rotor pickup, the other on the "BATT" terminal Should read between 6,000 and 30,000 OHMS..outside of that range, toss the coil.

These tests will not detect the integrity of the internal windings of the coil (Internal Arc~Over) You need a running engine and Oscilloscope to test that, should you suspect it, substitute it with a known Good coil.

Inspect the Rotor..(Especialy if new..) Place your meter probe on the Tower tang and the other on the pickup tang..move the spring arm up and down..It should not "jump" around on the meter as you do this. If so, toss it..the spot where it is injection molded in the center has separated..(NAPA just had a bad run on these..)

NEXT, Remove you module..Take it to the auto parts store and have it tested..Just because it is new has no bearing on if it is good..the out of box fails on those is 1 in 3 or 5...It may have been on the way out when you installed it. These modules are very Heat sensitive..Did you clean off all the Heat sink compound And generously apply (not sloppy) new compound? If not , if it hasn't by now, will fail..VERY soon.

If you need a new one..TEST it SEVERAL times before you leave the store to heat it up..and be sure it is functional. Once you leave the store , it becomes your problem, and can put you in a troubleshoot "Spiral" ..with the mindset.."It can't be bad..It's new.."When installing ANY module remember the compound!

NEXT, Test the magnetic pickup..Measure across the Pickup with your DVOM at R x 1, I think it should be about 4,000 ohms on pre 75's and more on later models, look at your spec's to be sure..short test, just pass a magnet in front of it..It should "jump" on the meter..Anyway, If good..

NEXT, Check and Verify that that the Stock 1968 Resistance wire has been removed from the system..If there it will run like "crap in a can"..If at all..make sure that wire is direct feed (no resistor) from the "Run" position of the Ignition.

NEXT, Verify the "R" or "I" terminal is connected from the solenoid and parallels into the "BATT" wire on the HEI..make sure there is full Battery voltage when cranking..If not..It won't start.

You have a weekend of testing ahead..But somewhere on this list, you'll find the problem! Print it out and use it as a check list, then post us back with the results!

Good Luck!

Doc :pimp:
 
#6 ·
I'd like to give thanks to everyone that offered help with engine, especially Doc. This reminds me of the teamwork I experienced 20 yeras in the Navy. My truck is running and I've been able to address carburetor adjustments with much better success.

Several things were creating my no start dilema and going back to the basics was the best thing that I could have done. The biggest issues were timing, worn starter, dirty grounds, and high resistance in the starting circuit. I'd recommend Doc's approach to anyone that is met with a frustrating ignition problem.
 
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