Y33 Problem coil identification-need help!! (I'd like to solve this)

[bullittandy]

So, my salvage title 1999 Q45 has started smoking from leaking valve cover gaskets and I will be replacing them tomorrow. My car has the idle stumble issue but no check engine lights or OBD-II codes I cannot know which 1 of the 8 coils it is.

Since the coils will be off for valve cover R&R HOW CAN I TEST THE COILS OFF THE CAR TO FIND THE BAD ONE?!?

[maxnix]

This may not help, but my bad one was a little blacker in the little mostly opaque window. The new one was not. I can send pictures if you want.

But if there are no codes, maybe a coil is not the cause?

[Q45tech]

Remember warmed up idle is always on the absolute verge of dying.........producing ZERO extra HP/torque otherwise the rpms would progressively increase........just enough torque to rotate engine.

A dirty spark plug or intake valve/runner or injector..........one coil with slightly lower voltage.

Correlating the different sound [from exhaust pipe] with the sequential cylinder making it tells you the problem cylinder..............how many milliseconds from spark plug firing until the exhaust sound gets to rear.

All about quality expensive test equipment, just as it is with measuring frequency of vibrations in body

[NightRiderQ45]

Remember warmed up idle is always on the absolute verge of dying.........producing ZERO extra HP/torque otherwise the rpms would progressively increase........just enough torque to rotate engine.

A dirty spark plug or intake valve/runner or injector..........one coil with slightly lower voltage.

Correlating the different sound [from exhaust pipe] with the sequential cylinder making it tells you the problem cylinder..............how many milliseconds from spark plug firing until the exhaust sound gets to rear.

All about quality expensive test equipment, just as it is with measuring frequency of vibrations in body

I need layman's terms lol.

[Q45tech]

Please supply your Millers Analogy Score so I may develop a course that suits your Intelligence.

What is a layman, someone without a Masters degree in Physics or someone who made B's in a 4 year liberal arts college with poor standards.

The simple point is you must understand the timing of a V8 engine that each rev has 4 sparks which last a few milliseconds each and the time from spark to exhaust beginning and ending is known and absolute. The speed of sound from exhaust valve to rear tail pipe can be calculated.

As long as the rpm is perfectly unchanging the cylinder puffs are perfectly 90 degrees apart.

You must understand how to convert angular rotation [degrees] into milliseconds, then have a time base to accurately display time vs amplitude.

A common problem is most don't understand that a V8 engine has 4 cycles per revolution so it takes 2 revs for all 8 to fire.

600 rpm/60 = 10 rev per second and thus 40 cycles [of individual cylinders firing] so 1000/40 milisecs = 25 milliseconds between cylinder firings.

Not something you measure with a stopwatch.

A digital oscilloscopehttp://www.picoauto.com/wavefo...ndary

http://www.picoauto.com/engine....html

Without spending a few thousand on test equipment, you must swap parts with new know good items

[bullittandy]

Please supply your Millers Analogy Score so I may develop a course that suits your Intelligence.

What is a layman, someone without a Masters degree in Physics or someone who made B's in a 4 year liberal arts college with poor standards.

I can't believe that you're respected here.

Maxnix, I've pulled the passenger coils and no luck on a black spot-I was hoping to get lucky. Good info though so maybe it'll be on the driver's side.

[Infinitiguy19]

Its funny when your not the one be ripped apart or your no the one who cares for the other person. Plus Q45Tech is mean in a funny way sometimes.

But good luck with your problem Andy.

[Q45tech]

I was being serious and not mean since there are more exotic methods than the simple acoustic timing method but they require much more expensive test equipment than the ~~ $3,000 unit with software suggested.

Those with a laptop or a computer with a sound card can download free acoustic sprectrum analyser software or oscilloscope software and use that to record the exhaust soundtrack and view the misfire sound.

Sample an injector or coil voltage to identify cylinder number #1

http://freenet-homepage.de/dl4yhf/spectra1.html

http://www.bestfreewaredownloa....html

http://www.electronics-lab.com....html

[paranoidjack]

I was being serious and not mean since there are more exotic methods than the simple acoustic timing method but they require much more expensive test equipment than the ~~ $3,000 unit with software suggested.

Those with a laptop or a computer with a sound card can download free acoustic sprectrum analyser software or oscilloscope software and use that to record the exhaust soundtrack and view the misfire sound.

Sample an injector or coil voltage to identify cylinder number #1

http://freenet-homepage.de/dl4yhf/spectra1.html

http://www.bestfreewaredownloa....html

http://www.electronics-lab.com....html

Tech, how would an exhaust leak affect this test? I'm sure that many of the Q's that are experiencing this stumble, are higher mileage and likely to have exhaust leaks.

[bullittandy]

I have a possible clue!!! I'm also replacing spark plugs at this time and one plug has black sooty chunks on it-maybe the cylinder that was misfiring? I'm going to check the driver's side later and report back.

[Q45tech]

You will see 8 sine wave shaped sound pulses [per 2 revolutions], unlikely that any leak will be louder [higher in amplitude] than the primary. Anyway the 8 sounds will repeat...[40 times per second].............the misfiring cylinder will be quieter and have a different shape.............^ ^ ^ - ^ ^ ^ ^ ^ ^ ^ - ^ ^ ^

What you hear is the difference that lets you notice the misfire in the first place [if your ear is near exhaust].

Exhast leaks are rare unless the piping has been damaged by owner abuse.

Random misfires are usually a combination problem: Dirty spark plugs and intake valves; a weak output coil or oily dirt on connector between coil and plug- shunting some of voltage to ground before plug fires; or a dirty injector making a cylinder so lean that the previous 2 add up to a misfire.

We see many coils replaced where the problem is not the coil but the connector from coil to plug..............but the 2 are integrated and you cannot by just the connector jumper [called the boot].

This might work if the problem is actually the coil:http://www.tooldiscounter.com/...76560

Here is a testing video:http://www.youtube.com/watch?v=n5W2DXboy7M

http://www.asashop.org/autoinc/feb2003/mech.htm

SUCCESSFULLY SOLVING MISFIRES without replacing all the coils separates the ENGINEER, from technican, from mechanic.

[NightRiderQ45]

Please supply your Millers Analogy Score so I may develop a course that suits your Intelligence.

What is a layman, someone without a Masters degree in Physics or someone who made B's in a 4 year liberal arts college with poor standards.

Wooh, someone is acting their shoe size again. Did someone forget to take their metamucil? I was being sarcastic. Remember, I didn't ask the original question. I'm a electrical engineer who graduated from a great school so please route your asinine remarks to some of your fellow co-workers who probably will faint at the tought of solving an engineering equation! Keep coaching and giving them valuable information so I can pay them to work on my car!

[maxnix]

I have a possible clue!!! I'm also replacing spark plugs at this time and one plug has black sooty chunks on it-maybe the cylinder that was misfiring? I'm going to check the driver's side later and report back.

Well, for that plug, you may have found a problem, but what is the cause?

When I have had the VH41DE log plenum off, the first thing I noticed was the unequal distribution of the soot, in part I believe from the way the EGR tube is configured.

[bullittandy]

Okay, I've got the valve cover gaskets changed and along with them, the spark plugs. My previous post spoke of one plug that had black sooty deposits, it was the plug on the passenger side closest to the firewall. I replaced that coil with a new one and in addition to the new plugs, cleaned the TB and MAF wire and some amount of the plenum (on car).

The car runs much smoother (previous vibe in shifter is reduced) and the power is better. Previous the car ocasionally stumbled at idle and also felt hesitant sometimes on hard acceleration. I'm wondering if that bad plug was misfiring more than I thought.

enjoy the pics: (bad plug bottom lower right)http://s469.photobucket.com/al...tandy/

[qship96]

Andy, the plugs actually dont look bad- how many miles were on them? I wonder if the one plug with the buildup of crud on it was actually excess anti-seeze compound from someone using a little too much of it during installation?
Modified by qship96 at 8:17 PM 11/8/2008

[bullittandy]

No record of last plug change so.....

Drove about 15 miles and still good-will continue updates to see if problem is solved.

[bullittandy]

Idle stumble is back, new plugs, one new coil (guessed on which one to replace) and TB and MAF cleaning.

I'm going to try swapping out the FPCU from my parts car in response to a mysterious post that Q45Tech posted a while back.

[maxnix]

The FGY33 FPCU is a different design than the G50 and is not known to fail in that manner. However, there have been few if any posts about replacing FGY33 fuel pumps.

[Q45tech]

The 97 and later FPCU use a fixed resistor in parallel with FPCU to supply voltage in the idle and cruise mode.

[maxnix]

So if the output and plug configuration are the same, should we start hoarding FGY33 FPCU?

[bullittandy]

zerothread?id=371780

Here's the mysterious thread I was referring to. Since I'm not a technician i'm going to simply swap parts and see what happens-especially since this problem still does not have a solution.

[maxnix]

....since this problem still does not have a solution.

Similar symptoms may have different causes.

In my case, it was only 99.5% resolved until I returned intake manifold, lower runners and EGR tube to clean as new then never a hint of a stumble for the last 6K miles.

[bullittandy]

Yeah!!!!!!!!!!!!!!!!!!!!!!!!!!! It's gotten worse!!!!!!!!!!!!!!!!!!!

I'm serious, the CEL/MIL is on!!!! I'm going to be able to get a code!!!!!!!! I'll report back, I did buy 7 new coils and am waiting for them so the CEL may be supurfurlous.

[bullittandy]

I just replaced the other 7 coils and now have 8 brand new coils and 20 miles with no stumble. This after the car started stumbling constantly.

I feel pretty confident that the idle stumble on the 97+ cars is a coil problem and once we find an easy way to discover the bad coil then life will be great again!!

[maxnix]

I feel pretty confident that the idle stumble on the 97+ cars is a coil problem and once we find an easy way to discover the bad coil then life will be great again!!

Read the code, switch the coil, follow the code.

Could hardly be easier or more efficient in that good coils aren't being replaced.

[bullittandy]

It was quirky timing, I ordered the coils when there was no code and while they were in route the CEL illuminated. Instead of swapping the one coil I figured I'd replace all of them.

Don't want to repeat any labor-right Maxnix??????