Yellow Spark No Start

[Frank Enstein]

My Wife's 94 Astro TBI 4.3 bucked twice so we thought maybe fuel so we topped it up.

Fired right up so taking the girl child to work it just shut off.

Get it home tried starting fluid. Nope! O.K. so it's gotta be ignition right?

Pulled doghouse, Popped the coil wire from the cap, stick a spark plug in it and sparks-ish.

Jumps a 1/4" gap but orange/yellow crappy spark. So I grab the Hynes manual and do the tests.

So according to the crappy manual it runs now. Not so much in the real world.

I'm going on the most usual suspects starting with grounds.

If anyone has any brilliant ideas before I fire off the parts cannon please speak up!

I'm about broke this week (more than usual!) so I really don't want to spring for a module (3 years old) and a coil (original I think).

Thanks in advance,

Frank Enstein

 

[Schurkey]

My Wife's 94 Astro TBI 4.3 bucked twice so we thought maybe fuel so we topped it up.

Fired right up so taking the girl child to work it just shut off.

Get it home tried starting fluid. Nope! O.K. so it's gotta be ignition right?

Pulled doghouse, Popped the coil wire from the cap, stick a spark plug in it and sparks-ish.

Jumps a 1/4" gap but orange/yellow crappy spark.

I'd rather use a spark-tester calibrated for HEI. And either it jumps the spark-tester gap reliably, or it doesn't. 1/4" gap isn't really enough to test HEI.

Have you tested/inspected the plug wires/coil wire?
Distributor cap carbon-tracked? Burnt carbon button? Rotor have "punch-through" where the insulation fails and the spark grounds to the distributor shaft?

Fouled plugs?

Timing light showing correct initial timing?

What is the cranking compression pressure on all six?

"I" would want to know the fuel pressure, and whether the injectors spray.

And, as always, connect a scan tool to verify all the sensors and computer outputs--IAC, EGR, etc. 'Course, you're not going to get all that info until the engine runs, but verify what you can.

So I grab the Hynes manual and do the tests.

Not impressed with Haynes manuals.

 

[Frank Enstein]

Me either. With 280k on it I'm thinking timing chain. Ugh!
It was running fine except for an occasional "hiccup" or stutter that I couldn't find when I drove it.

 

[Frank Enstein]

I feel like a complete noob.

The rotor was burned through and I didn't catch it. (Momma's van is white Blue Astros are cursed!)

I put it in new 172000 miles ago. It should still be good right?

But I dodged the timing bullet chain for now.

 

[Schurkey]

Glad you found it. Do you have a way to measure spark voltage? Excess plug gap, wide rotor-to-cap gap, and failed plug wires are common causes of excess spark voltage, which makes rotor punch-through more likely.

God bless automotive (ignition) oscilloscopes that draw graphs of voltage vs. time for ignition secondary voltage.

Rotor "punch-through" was common in the early years of HEI.

The original HEI rotors were black plastic. The "updated, better" rotors were white plastic. Twenty minutes later, the aftermarket released thin plastic, white-colored rotors that probably weren't any better than the thick-plastic, black ones. Maybe not as good. But that's the aftermarket and cheap parts--it's always possible to cheat and make it cost less. And that's been going on longer than I've been associated with auto repair.

 

[HotWheelsBurban]

Glad you found it. Do you have a way to measure spark voltage? Excess plug gap, wide rotor-to-cap gap, and failed plug wires are common causes of excess spark voltage, which makes rotor punch-through more likely.

God bless automotive (ignition) oscilloscopes that draw graphs of voltage vs. time on ignition secondary voltage.

Rotor "punch-through" was common in the early years of HEI.

The original HEI rotors were black plastic. The "updated, better" rotors were white plastic. Twenty minutes later, the aftermarket released thin plastic, white-colored rotors that probably weren't any better than the thick-plastic, black ones. Maybe not as good. But that's the aftermarket and cheap parts--it's always possible to cheat and make it cost less. And that's been going on longer than I've been associated with auto repair.

Yup the early HEIs with the coil sitting on top of the carbon button, throwing 40KV at it, definitely ate up rotors. Back in the day we sold so many I didn't even have to look them up in the catalog. And if you ignored the rotor burn through long enough, it'd toast the module too. Once Standard/Blue Streak came out with the blue caps and rotors, that were heavier grade plastic and had brass contacts, they did last longer. Any GM vehicles we had got that upgrade, and we only had to replace one or two modules over probably 15 vehicles.

 

[Schurkey]

And if you ignored the rotor burn through long enough, it'd toast the module too.

Wild Guess: It wasn't the rotor burn-through that killed the modules.

The high firing voltage killed the rotors AND the ignition coils. The failed ignition coil then killed the module.

The failed coils could still provide (weaker) spark, but they'd draw excess current from the module to do so.

Repeat module failures of name-brand, properly-made modules (excluding Communist Chinese bottom-feeder crap) on HEI is nearly always due to a problem that begins when the insulation on the wires inside the coil fails, so the wires short to each other. When they short to each other, the resistance goes down and so the current draw goes up.

 

[GoToGuy]

How often cap and rotor? Installed at 170K and failed at 280K?

 

[Frank Enstein]

I got a better one this time. Should last a little longer.

Wires are 270 ohms per foot. NGK Platinum plugs. The spark was better than I gave it credit for, I was looking at it outside at noon.

 

[Frank Enstein]

Thanks for the help guys. Especially because it's not a GMT400.

The Astro/Safari forum people were silent about this.