Misfire

[ZRXMAX]

Can't locate the source of a missfire. Under light throttle it runs ok, however, anytime you give it a little throttle it misses on what seems to be one cylinder. I have changed the coil packs back to my old stock ones because they still worked fine when I replaced them. They all show about 6 ohms resistance. Also checked the injectors with an ohm meter and they were all good.

The plug wires are pretty fresh and look to be in excellent condition.

A week ago it was running good and then the number 1 spark plug wire started coming off every minute. It turned out I had accidentally gotten some dielectric grease on the end of the plug. Once cleaned it stayed on.

When I changed the plugs I discovered that the insert in one of my spark plug sockets had stayed on the number 8 spark plug and came out with the boot when I reinstalled new plugs. Since it was the last new plug installed, and, you cant see in the plug hole without a mirror I didn't notice it until I changed all the plugs again to eliminate one possibility for a misfire.

Any suggestions on what to look at next will be appreciated. I have pulled the plenum twice and I am right back where I started. It did run real good briefly until the number 1 plug wire started coming off.

[Demps]

What are the plugs gapped at? I've found they don't always like 0.050". Symptom was stumble at throttle tip in. Easiest diagnosis I found was run it a gear high & ease into throttle. If it stumbles, I change gap to 0.035" & assess.
Ted

[ZRXMAX]

I will give that a try. I had changed to iridium's a while back without a hickup. Like I mentioned, I installed a new set because it was easy and cheap ! I have been watching you tube tutorials just to see what others say about testing basic parts.
Thanks... I hope this does it !

[ZRXMAX]

I re gapped my fresh set of NKGs to 35 and the misfire was minimized a tiny bit. This leads me to believe I might have a bad plug wire. Then again, it was running fine the other day until the number one plug wire started coming off.

Would that wire coming off hurt a coil pack from working normally?

[Pete]

If boot comes off change spark plug.
Leaking thru porcelain.
That will also fix misfire.

Pete



I re gapped my fresh set of NKGs to 35 and the misfire was minimized a tiny bit. This leads me to believe I might have a bad plug wire. Then again, it was running fine the other day until the number one plug wire started coming off.

Would that wire coming off hurt a coil pack from working normally?

[ZRXMAX]

Yes... I cleaned everything with Q tips and carb cleaner to remove any dielectric grease on all 8 a few days ago. Thanks

The other day even when it was running good something about it didn't seem like it normally does. Next time I pull the plenum I will check all the wires.

[Paul Workman]

Yes... I cleaned everything with Q tips and carb cleaner to remove any dielectric grease on all 8 a few days ago. Thanks

The other day even when it was running good something about it didn't seem like it normally does. Next time I pull the plenum I will check all the wires.

It's a pretty safe bet that whatever Pete suggests has considerable merit.

And, I can assure you from 40 years of using the stuff that dielectric grease is NOT going to cause the boots to come off of the plugs. Unless, the boot is flooded with so much to the point the boot can't be seated onto the spark plug, OR there is a leak due to a defective spark plug, as Pete suggested, the boot stays put.

Dielectric grease not only facilitates installation and removal of the boot, but acts as a seal against contaminants that might creep up the sides of the porcelain to the point where "spark tracking" from the electrode to ground along the outside surface of the porcelain insulator may occur.

Besides... There is ample friction between the boot and the walls of the sparkplug hole to secure the boot from slipping from normal vibration. Further, the boots have longitudinal ribs that would tend to vent gasses that escaped around the plug threads - all but eliminating anything but the most severe cases of leaking plugs.

Hydraulic pressure from within, e.g., due to a defective plug, is another matter. In that case, if there were no seal formed by the dielectric grease, the gas might escape undetected. The unintended consequence being to make it difficult to detect perhaps; another argument in favor of the dielectric grease?

By removing the dielectric grease, it seems possible that doing so may have created the chance for additional problems later, while doing nothing to solve the misfire issue.

Your mileage may vary...:cheers:

[ZRXMAX]

It's a pretty safe bet that whatever Pete suggests has considerable merit.

And, I can assure you from 40 years of using the stuff that dielectric grease is NOT going to cause the boots to come off of the plugs. Unless, the boot is flooded with so much to the point the boot can't be seated onto the spark plug, OR there is a leak due to a defective spark plug, as Pete suggested, the boot stays put.

Dielectric grease not only facilitates installation and removal of the boot, but acts as a seal against contaminants that might creep up the sides of the porcelain to the point where "spark tracking" from the electrode to ground along the outside surface of the porcelain insulator may occur.

Besides... There is ample friction between the boot and the walls of the sparkplug hole to secure the boot from slipping from normal vibration. Further, the boots have longitudinal ribs that would tend to vent gasses that escaped around the plug threads - all but eliminating anything but the most severe cases of leaking plugs.

Hydraulic pressure from within, e.g., due to a defective plug, is another matter. In that case, if there were no seal formed by the dielectric grease, the gas might escape undetected. The unintended consequence being to make it difficult to detect perhaps; another argument in favor of the dielectric grease?

By removing the dielectric grease, it seems possible that doing so may have created the chance for additional problems later, while doing nothing to solve the misfire issue.

Your mileage may vary...:cheers:

Thank you for that detailed explanation on spark plugs. In my life I have never had a spark plug that leaks and blows the boot off.

I will pick up another plug and re grease the boots and see what happens.

I always use dielectric when putting plugs in. I was talking to a mechanic friend of mine and he mentioned I might have gotten some grease on the connector and that might be the problem.

Also... number 7 was misfiring so I put another stock coil pack on it from a low mile Z and it seems to be working just fine now.

Yes... I think my mileage will vary!

Thanks Pete... Thanks Paul... I will update you when I get it done.

[Bearly Flying]

I think you want to use Anti seize on the threads and dielectric grease on the ELECTRICAL connection

[ZRXMAX]

Thanks... that is what I have always done.

Update. I was able to locate another NKG plug to replace the plug that leaked air past the electrode. It wasn't a U Groove plug like the rest ( they didn't have one in stock and I am commuting daily )

It is running about 50% better but still misses alot at idle and anytime below 2500 rpm. Once above 2500 it runs smooth up to about 4000 and then starts to miss again.

Will find a U Groove NKG plug tomorrow and see if that fixes it.

Also have code 24 and 61... will fix 24 first and see what happens after that.

This whole situation is just weird... It appears #7 is the plug that misfires... I ohm checked the wire and changed to coil pack... will keep searching.

Thanks to all. :handshak:

[Pete]

Paul is correct about the grease,if all is good should not have any issues.
Not too many have heard this myself included till it happened to me.
Been racing for so long you see a lot of crazy $hit and still learning.
Another thing i have learned is our LT5's don't like those fancy/pricey spark plugs.
Buy a set of regular resistor A/C Delco spark plugs $1.50 each gap .035 try it only $12 if they don't fix it i'll buy the plugs from you.
Never understood why people would spend $10-$20 on one spark plug most of us put 2-3k miles a year no need for 100k mile spark plugs.
The fastest ZR-1's run resistor AC Delco's.

Pete
http://www.agcoauto.com/content/images/engine/spark_plug_leaking_around_ceramic.jpg

[SAM/CH ZR-1]

It's correct the LT5 does not need extrem expensive spark plugs, but good ones.

I use in my own and my customer cars the Bosch PLATINUM +4 or those from Brisk LGS serie. They work great, don't cost to much and the trottle response increase noticeable. No misfire.

[XfireZ51]

Sam I found this interesting item re:Bosch platinum plugs. Apparently this also affects Ford EDIS which is "waste spark" as well.

"The problem that Bosch has acknowledged when using their Platinum plugs
in engines with waste spark ignition systems stems from the tendency of
electrode metal to get transferred depending upon the polarity (direction
of current flow) of the spark. In waste spark ignition systems, 1/2 of the
plugs always see reverse polarity sparks. Given the very narrow platinum
center electrode of the Bosch Platinums, performance will be degraded more
significantly when reverse polarity sparks will cause material to be
transferred from the large ground/outer electrode onto the narrow platinum
center electrode's exposed end surface.
In cars with conventional (1 coil) ignition systems, every spark is of
the same polarity, for which the Bosch Platinums are optimized, leaving
them to deliver their designed-in advantages, which include:
o reaching self-cleaning temperature faster ("than any other plug")
o maintaining the spark gap and low firing voltage requirement throughout
their service life. (even in my high-stress turbocharged application)
While there remain some cars with conventional ignition systems which
do not seem to get along very well with Bosch Platinums, which seemingly
no one can explain (maybe all their sparks are of the 'wrong' polarity
in some cases), they did and do good work in my '95 854 Turbo."

[SAM/CH ZR-1]

A interesting article. I can only say from my made experiences the LT5 work and perform well with these spark plugs. The focus is more on the Brisk LGS. In general I replace the spark plugs after 30'000 Kilometers.

[Pete]

Sam I found this interesting item re:Bosch platinum plugs. Apparently this also affects Ford EDIS which is "waste spark" as well.

"The problem that Bosch has acknowledged when using their Platinum plugs
in engines with waste spark ignition systems stems from the tendency of
electrode metal to get transferred depending upon the polarity (direction
of current flow) of the spark. In waste spark ignition systems, 1/2 of the
plugs always see reverse polarity sparks. Given the very narrow platinum
center electrode of the Bosch Platinums, performance will be degraded more
significantly when reverse polarity sparks will cause material to be
transferred from the large ground/outer electrode onto the narrow platinum
center electrode's exposed end surface.
In cars with conventional (1 coil) ignition systems, every spark is of
the same polarity, for which the Bosch Platinums are optimized, leaving
them to deliver their designed-in advantages, which include:
o reaching self-cleaning temperature faster ("than any other plug")
o maintaining the spark gap and low firing voltage requirement throughout
their service life. (even in my high-stress turbocharged application)
While there remain some cars with conventional ignition systems which
do not seem to get along very well with Bosch Platinums, which seemingly
no one can explain (maybe all their sparks are of the 'wrong' polarity
in some cases), they did and do good work in my '95 854 Turbo."



Ding Ding Ding, we have a winner give that man a cigar.

Buy any good resistor plugs change every 5k miles 5-10 minutes to change out,still cost less. and headache free.:dancing

Pete

[SAM/CH ZR-1]

Ding Ding Ding, we have a winner give that man a cigar.

Buy any good resistor plugs change every 5k miles 5-10 minutes to change out,still cost less. and headache free.:dancing

Pete

Wait with the cigar.
I try and test your prefered spark plugs and let you know the results.

[Hog]

Here is a good comparison of plug materials.
http://i1202.photobucket.com/albums/bb373/Paul_Schermerhorn/Ignition/sparkPlugChart_zps57wnxgad.jpg (http://s1202.photobucket.com/user/Paul_Schermerhorn/media/Ignition/sparkPlugChart_zps57wnxgad.jpg.html)


There is a lot of hype about plugs, there really isn't power to be gained so long as there is a good spark to begin with. There are advantages to spark plug indexing and/or unshrouding the spark kernel by cutting the ground electrode back.

Here is a pic of some NGK race plugs, some of these types of plugs are $200 a piece.
http://i1202.photobucket.com/albums/bb373/Paul_Schermerhorn/Ignition/ngkraceplugs_zpsstz2jmh2.jpg (http://s1202.photobucket.com/user/Paul_Schermerhorn/media/Ignition/ngkraceplugs_zpsstz2jmh2.jpg.html)



Delco plugs still have a mail in rebate again this year.

http://i1202.photobucket.com/albums/bb373/Paul_Schermerhorn/Ignition/DelcoPlug16_zpsl4kyfbnv.png (http://s1202.photobucket.com/user/Paul_Schermerhorn/media/Ignition/DelcoPlug16_zpsl4kyfbnv.png.html)

[ZRXMAX]

Back to square one with the misfire problem. Yesterday I put the stock chip / memcal / prom back in or whatever you guys call the blue electrical component that clips inside the ECM.

I thought my problem was solved as I got it out on the road and warmed it up to normal operating temperature. When I applied full throttle the LT5 ran without missing.

I went through 3 gears three times and all was good.

This morning as I drove to work ( 64 miles one way ) it started immiediatly doing exactly the same misfire characteristics again. Any time you use more than a little pedal it misfires. When it idles it misfires.

When you increase rpm slowly under a light load it will miss and then smooth out and cruise without missing. Seems to run good around 3000 rpm to 4000 rpm under light throttle.

I am convinced its not the ...plugs, wires, coil packs, or injectors.

The fuel pressure seems a little bit low so I am going to change out the fuel filter and install new pumps that I have here waiting for the day they will be needed just to see what happens.

It appears I am running out of part replacement options. I am thinking its the ECM or the ignition module under the plenum. Or, possibly an intermittent ground fault. I really don't know... just guessing now.

[XfireZ51]

I really think you should find someone who can do a scan of the motor while exhibiting the symptoms you are describing. Hunt and peck doesn't help anything.

[A26B]

I agree with Dom about data logging. I am also assuming you have pulled DTC's and found nothing.

Your last post indicates the misfire/rough running is in closed loop (<3000rpm) but smooths out above 3000 rpm which is in open loop. This can be a failing/shorting O2 Sensor. A shorting O2 sensor will trim the fuel on one bank only & cause a very rough running engine in closed loop but not in open loop.

Many moons ago, I had headers & custom exhaust installed in Houston. Turned on the AC & headed home to OK. Stopped in Gainsville, TX for fuel, restsarted and ran so rough I thought the engine was toast. Nothing visibly wrong and would smooth out above 3000 rpm. I drove it home OK by keeping rpm above 3000. Next morning, put it on the lift. We had installed a O2 sensor "lead-extender" on the right bank to clear the headers. As it turned out, the connector was under the heater core drain and AC condensation was dripping on the O2 Sensor connector. Pulled it apart & water ran out. Dried it out & it ran fine. I did replace the O2 sensors anyway and the longer leads on the Bosch replacements eliminated the need for the lead-extender.

A couple of years later @ BG, a good friend had a rough running Zee, below 3000 rpm. I suggested O2 sensor. He changed them out & resolved the problem.

Data log if you can, but pay close attention to fuel trim on just one bank. Maybe???

[XfireZ51]

It's possible the O2s "drop out", meaning the signal goes to 0, but that would suggest a lean condition to the ECM. I saw that happening on a number of my logs until I finally changed out the Bosch 02s for AC Delco. Then the signal was solid as a rock.
The symptoms that this is happening at idle and below 3000rpm suggests it's happening at higher vacuum/lower MAP. So question is whether there's a vacuum leak causing a lean condition and so a stumble?

If u have Bosch 02s, I'd swap them out for the hell of it.

[ZRXMAX]

Solid recommendations ! Don't know why I didn't think about these a while ago. Bad 02 sensors can really cause weird things to happen. Will try it tomorrow. Thanks

[ZRXMAX]

I found the problem... cam cover bolts adjacent to the #1 spark plug were getting loose. Lesson learned! :cheers:

[Dynomite]

I found the problem... cam cover bolts adjacent to the #1 spark plug were getting loose. Lesson learned! :cheers:

Which Cam Cover Bolts?
How Loose?

Exactly how does a loose or a couple loose cam cover bolts cause a misfire?

Was Number 1 Spark Plug Port full of oil (were the Cam Cover Bolts THAT LOOSE)?
That Loose as to cause the Cam Cover "O" Ring to fail on Number 1?

[A26B]

I found the problem... cam cover bolts adjacent to the #1 spark plug were getting loose. Lesson learned! :cheers:

You're about 3 weeks early. April Fools day isn't for another 3 weeks yet, but you sure got me on that one. :cheers:

[Dynomite]

You're about 3 weeks early. April Fools day isn't for another 3 weeks yet, but you sure got me on that one. :cheers:

I am confused :p

Two issues reported recently (This Misfire issue and a Pilot Bearing or Throwout Bearing failure at 20K miles) and my issue with a cracked impeller on a NEW Water Pump ....I am thinking ANYTHING IS POSSIBLE ;)

The Cracked Water Pump Impeller (NEW WATER PUMP) issue I caught right away but did take a bit of diagnosis to eliminate an Air Locked Water Pump as I had just drained Coolant.

Damn.....I am not even looking at this Forum on April Fools Day or for a week after :D

[ZRXMAX]

Which Cam Cover Bolts?
How Loose?

Exactly how does a loose or a couple loose cam cover bolts cause a misfire?

Was Number 1 Spark Plug Port full of oil (were the Cam Cover Bolts THAT LOOSE)?
That Loose as to cause the Cam Cover "O" Ring to fail on Number 1?

When I was putting the plenum back on for the third time and holding a 40 torx in my hand I looked at those bolts and thought... I wonder if they are loose?

Indeed they were ! I estimate they might have had 10 lbs of torque on them as they sat. Keep in mind their was no oil or any leakage of anything to be seen inside plug hole # 1.

So, I looked up the torque number and applied it.

Keep in mind I had reported early on that the #1 boot kept coming out. When I would re install it the connector would emit that little click that indicated it had slipped into place at the top of the plug.

To get it off required the same amount of effort as any other plug. So, I have to assume air pressure was building up and blowing it off.

I will see what I can come up with for April Fools ! :)

[Z51JEFF]

You have more patients than I do. After the first plenum pull,if the problem is still there I'm throwing new parts at it.🤑

[ZRXMAX]

You have more patients than I do. After the first plenum pull,if the problem is still there I'm throwing new parts at it.��

I did throw new parts at it... actually, I was recycling parts that were stilll good but were removed as preventative maintenance. Coil packs, ECM, chip

inside ECM, map sensor, plug wires, spark plugs... also checking fuel pressure several times, and, new O2 sensors were installed. We were down to 3 items. The module under the plenum, crank sensor, or cam sensor.

We also did a data log on a short 4 minute run and everything appeared to run in the normal range... so... the head knocking was getting painful! :-x

[Z51JEFF]

The cam position sensor will give a code,can't remember what it is. The full power will be cut,check engine light will come one and the car will run like its starved for fuel,at least that's what mine did but it didn't have a miss.