348 Cat sounds like 'Poof' 'poof' 'pop'

Oops. Sorry. No pics this time.

 

I cleaned and swapped the transistor power moduls from left to right and vice-versa.

Now I've got a spark on #8 (though not perfect), but no spark on #2 and no spark on #4.

So 1, 3, 5, 6, and 7 are perfect...#8 has a mostly good spark (some pauses in the spark indicator light flashing), but #2 and #4 are DOA.

Time to order parts. I've got a coil and a power transistor on the way. Those will go to the right side to see if they give me a good spark on cylinders #1, 2, 3, and 4.

 

"Interesting problem. Since cylinders fire on every stroke, the coil fires two cylinders at once, so each side (1/2) of the coil fires two wires at the same time. Is there any commonality there with the cyls that are a problem? If there is none, it's probably not the coil. It's really a baffling problem. Is the performance greatly affected? It must be if you're missing that much fire."

Yeah. Based upon which configuration that I've had her in with swapping spark plug wires, coils, and power transistors from side to side, as many as 4 cylinders (2, 4, 6, and 8) have had no spark...down to as few as two (#2 and #4 with the current configuration, #4 and #8 with an earlier configuration) without spark.

Would my spark indicator fail to light up if I had spark plugs that weren't firing (or does it light up only based on current flowing through the wires)?

Perhaps I need to go swap spark plugs, just in case I've got a problem plug (#4 hasn't had a spark in any configuration).

The data and power wires to the coils and power transistors look good, by the way.

There is commonality, though. The bad sparks are only on even numbered cylinders. If you'll look at the picture, the even #'s are at opposite corners, matching the dual diagonal firing map that's printed on the front of each coil.
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I swapped spark plugs between #4 and #1. No change. #4 is still not sparking, #1 still does.


(the odd #'s have always worked)


So it's not a problem with a spark plug.

 

Good ideas. Could be right.

I'm *thinking* (always dangerous) that the crank sensors are for left side and right side of engine, though (not odd or even cylinders). If I'm wrong about that then I need to swap crank sensors per your advice.

Likewise, it could be the pickup sensor on the back on the intake cam...but...my thinking on that matter is that if you have just 1 sensor for the entire engine that you'd see a common problem on the whole engine, not just on 2 right-hand-side cylinders.

Remember, right now I'm getting a spark everywhere except #2 and #4 on the right side (OK, #8 is only getting spark 80% of the time over on the left side).

I've swapped spark plug wires. I've swapped coils. I've swapped the power transistors to the coils. I've swapped spark plugs. In that order.

Over the series of swaps from left to right, there was one time that #6 didn't work and a couple of times that #8 didn't work.

#4 has never worked during this entire series of tests. With one combination of swaps one time, #2 worked.

I'm tempted to swap my main ECU's from side to side. I'll have 2 new coils and a power transistor by Friday, though. That should make an easy test for the weekend.

 

OK, just for a fellow Stooge I yanked the cover off of the rear phase sensor.

Clean.

Don't even think about trying to get me under the car to swap crank sensors tonight, either!
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Progress!

Fellow Stooge Plugzit's coil arrived today (thanks, Bruce!).

I installed it and now I've got 7 working cylinders with spark. Installing Bruce's coil got #2 firing again.

#4, however, nothing. I've swapped spark plug wires from side to side on that cylinder. I've swapped power transistors. I've swapped spark plugs.

#4 has no spark.

So I took my Fchat infrared temp sensor from Performance Devices and measured my exhaust (shooting the laser beam straight into the exhaust pipes from outside in the rear).

156 degrees F on the left side, 280 degrees F on the right side (i.e. #4's side).

I've got a new coil that was also supposed to be here today, as well as a power transistor that is back ordered.

Should I check or swap the front crank sensors, or would those have no bearing on just 1 cylinder not firing?

Do I just need to wait for the power transistor to arrive?

 

I have no idea.

I'm using a "spark indicator tool" to tell me that current is going down the spark plug wires. It lights up on all but the plug wire for Cylinder #4.

Would bad compression impact that electric current? Some sort of grounding issue of which I'm unaware, perhaps?

Do I need to do a compression test?

 

Thanks. I'll do it.

 

There are just 3 wires that go to the coil. The wasted spark thing may be mentally throwing me off, though.

When I first saw 3 input wires going to 4 spark plug outputs, I didn't give it much thought but just *assumed** that one wire was the power input and the other two wires were giving a binary signal to step through each of the four spark outputs (e.g. current on neither wire would give 00, current on one wire would give 01 or 10, and current on both wires would yield 11).

But it can't work that way with a wasted spark because two spark outputs are firing simultaneously every time. Maybe one wire is the power wire, and each of the other two wires signal to fire either of the 2 pairs of spark outputs.

Would it be safe to start the engine, then disconnect the cable with 3 input wires to the coil? If so, I could put a probe into each female jack to see what each of the wires is doing.

That could be a good test (if it's safe to try).

For another matter, is it safe (Timing wise) to swap my #2 and #4 wires to the coil? Does "wasted spark" mean that it doesn't matter if 2 and 4 are reversed on the coil? If for some reason #4 isn't making a good ground with the engine block, that test might help identify said problem.

Also, I'm not convinced that the ignition module (which I'm presuming we're both talking about the power transistor when we call it that) is good, by the way. The other side of the engine had a spark problem prior to swapping that module from side to side. That's the part that is back-ordered.

 

Still no spark on #4, weak spark on #2 and #8. The wires on the back of the phase sensor look bad, so I will back probe the connector to the phase sensor next.

Just back-probed the 3 wires going to the 1-4 right side coil. Red was a solid, unchanging 14.06 volts. Yellow middle wire was 14.22 volts, steady.

Red/Black was an unchanging 14.12 volts.

This has to be wrong, perhaps due to my simple Radio Shack voltmeter. I guess I need to put an Oscilloscope probe onto each wire.

Anyway, I don't see how #1 and #3 could be firing with an unchanging input signal to the coil. I should have seen a changing voltage on the Red input wire to the coil, as well as on the Red/Black input wire to the coil...and it may just be that my cheapo voltmeter is displaying the high voltage rather than switching back and forth.

 

I disconnected my phase sensor and started her up; no spark on any of my even numbered cylinders. Odds were just fine.

Hmmm...

 

Well, I'll know for certain when I get my new sensor.

Thanks for the tips and steps, everyone.



Stooges rule!