DTC P0300 misfire

[97ss497]

I'm getting a DTC code PO300 misfire condition. I just replaced the wires, plugs, added headers and a new y-pipe with o2 sims. A real slight change in rpm can be heard; the SES light actually flashes when revving at a constant 3k then stops flashing when the rpm's are back at idle. I made sure when I attached the wires to the plugs, opti and coil that I heard them "snap" on. Maybe I should have checked the resistance of each wire before installing them. Iheard that Taylor's were pretty good wires.
I turned off all the lights in the garage and didn't see any sparking anywhere under the hood, from above or below. Just for the heck of it I checlked the resistance across the #7 spark plug (NGK TR55) and it was around 5k; I checked 2 of the original AC's and they were 2k.

Any opinions on what I should look for or do next??

[fastTa]

That code is :Random/Multiple Cylinder Misfire Detected

Considering your ignition system is otherwise healthy, an unbalanced crank pulley or a faulty crank postion sensor could also be culprits.

[97ss497]

Any easy way to check a crank position sensor? BTW; I changed my knock module to a LT4 Knock module also.

[Flash 97 WS/6]

Since that is a Multiple Cylinder Misfire, I wouldn't worry about the plugs or wires...concentrate on the coil and wire, could be a weak/bad coil wire, try your old one if you have it.

[N20LT4Bird]

Originally posted by 97ss497
Any easy way to check a crank position sensor? BTW; I changed my knock module to a LT4 Knock module also.

If the vehicle is running smooth with no missing at all, it MIGHT be the crank position. You would need a scanner to check it. If you had an oscilloscope, you could check it that way for a good square wave too. Otherwise, if it runs poorly - coil, coil wire, opti, ignition module etc....

[Joe 1320]

One thing you might check for is the connections to the coil driver module. Occationally if the pins in the connectors aren't exactly straight, you get a intermittant contact that can cause a higher rpm random misfire.

[97ss497]

Joe,

Are you referring to the ICM? I didn't replace the coil or ICM during my additions to the car. What type of troubleshooting can I try on the ICM?
I'm going to take a look at the coil wire sometime today. I hope that's the problem. Will keep you posted. As always thanks for your opinions.

[Joe 1320]

The driver module is mounted right with the coil. But if you didn't mess with any coil connections or harness in that area, it's doubtful it would be the problem. If you dismounted the coil at any time, it just might be worth checking. In any case, it's a good idea to check the pin orientation in a harness connector, don't just take for granted that if it plugs together it works.

[97ss497]

I did a resistance check on the coil wire and it looked good. I checked the resistance of the windings on the coil and all three pins were around 6k.

I took the code out last night and ran the engine in the garage today for about 20 minutes; no code showed up but I still can hear a slight miss; it just doesn't sound right to me. I can't take the car for a ride because it's up on jack stands due to the installation of the BMR rear end components and the weather here being cold and crappy.

I was able to snag onto a Hypertech power scanner from a friend and this was the readout I got:

RPM- 0
Idleld- 3188 RPM
EGR d/c 0%
Bat 12.1
spark 0btdc
Retard 0 deg
IAPwb1 0.0 ms
IAPwb2 0.0 ms
stftb1 =1% 128
stftB2= 1% 128
LIFTB1 +1% 128
LIFTB2 +% 128
f1 TRIM C - 0
hO251B1 400 mv
hO252B1 varied from 396-624 mv
hO251B2 635 mv first check; 118 mv second check
hO251B2 varied from 388-620 mv
MAF 0.0 gls
Loop= open
TP (%) 0%
TP (v) 0.53 v
map 99 kPa
baro 100 kPa
IAC 101 counts
ECT 169 deg
IAT 81 deg F
EGR load 0%
AFR 12.0 1

I'm just learning some of this stuff so bear with me; what does this data tell me?

Thanks in advance.....

[97ss497]

ttt

[N20LT4Bird]

That tells me the car is off We really cant tell you much from that - you almost have to have the car in front of you with the scanner. If I had a particular symptom and a freeze frame on the scanner at the right instant, that would be a different story.

If you have a miss and the scanner isnt pointing to a particular cylinder (random misfire), then you most likely have a problem with one of the components mentioned above. If you do indeed feel a miss, you can eliminate the crank pos - becasue it sounds like its doing its job then. I would look at the opti and the ignition module. I would guess opti at this point. Anyone know if there is a procedure for checking the module w/o an ignition module checker?

[97ss497]

I didn't realize you could get readings with the car running; I did it with the key in "run" position. I should have asked my friend more questions about how to run his scanner (ok you can call me a moron now)

I'll post readings with the car at idle and at higher rpm's sometime today.

Thanks

[97ss497]

Problem solved!

Finally figured out the code problem. It was the cylinder 2 spark plug; when I installed it I must have forced it too hard trying to install it in the head and bent the electrode in so the gap was about .005. It's a pain installing that plug with the SLP shorties and air pump tube in the way. I was chasing my tail for the last 2-3 weeks; found a few exhaust leaks along the way and fixed them too. I'm happy as h that it wasn't the opti. Time to go have some fun.....