Misfire

[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

[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]

Originally Posted by 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."

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.

Pete

[SAM/CH ZR-1]

Originally Posted by Pete

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.

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.



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.




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

[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???