P0300

[murr2424]

ok. i've spent a mint trying to get my car back in order and i still can't solve this last little riddle. car is throwing a P0300 and idles bad. under accel. car still runs rough. i replaced the head gasket and all other gaskets for upper engine rebuild including intake manif., replaced the coil housing, plug wires, & spark plugs. i've checked the throttle body, vac lines, fuel rail, FPR, FP, FI's, map sensor, knock sensor and they all check out. i know the timing chain is on properly (help of a mechanic) and the car ran good for the first crank after i replaced the plug wires and coil housing. then it started to slowly going back to running poorly. oh yeah, i had the ICM checked at auto zone and it checked out. should have gotten the coils tested but ran out of time. i'm tire and out of money. should i give up and take her to the shop or risk spending more and not solving problem? is it the coils? any ideas?

d

[HornetGT141]

I'm going to wait for Rick (rixGAphx) or someone else to get you a more indepth questioning because they are a lot better mechanically than me but I can tell you that code is for "Random/Multiple Cylinder Misfire Detected", does it have any other codes, such as P0301, P0302, etc...? That would tell us which cylinder is misfiring.

[murr2424]

nah, it's been throwing the po300 code consistently with no other codes...

[rixGAphx]

'96 4-cyl, 11-yrs old, so about 130k miles?
Engine 'rebuilt' to some extent (top-end only?)

When the engine is warmed-up and running (crappy though it may be), does the tailpipe smell strongly of exhaust, or even unburned raw gasoline?

You have plug wires??
I thought the 4-cyls had 'boots' or such, not actual plug wires. :confused:

Anyhow, at this point I would pull the plugs and keep them in order, left to right.
Shine light on them nicely, and photograph.
Post the pics here.

The condition of the plugs will indicate a lot about richness, leanness, sparking or not, etc.

Please tell me these are Platinum plugs of a 'conventional' single-electrode type.
The GA engines will soon destroy non-platinum plugs, and they aren't happy with exotic electrodes like split-fires or multi-prongs.
The best plugs seem to be ACDelco Platinum; either RapidFire ($$) or Professional ($$$).

I think the 'Champion Plugs' website has a good photo-reference of how plugs should look, and how to troubleshoot problems based on how they actually look.
But I can't find a link.

I would do a compression test while the plugs are out.
* * *

How old are your O2 sensors, catalytic converter, and air filter?

Hope this helps,
-Rick

[murr2424]

thanks for the reply rix. yeah, all indications suggest it's running rich. i pulled the plugs, which are not platinum btw, and they reek of gasoline. you're right, i meant to say boots instead of wires. i guess i'll start by replacing the plugs with platinum ones and i'll try to get some pics up tomorrow. i've already done a comp. test and came up with 210 on each. 02 sensor and cat are probably the same age as the car, but the air filter is about a month old...

[HeyDace]

Youve replaced everthing in the secondary ignition EXCEPT coils. I would test spark output. You may have weak coils.

[murr2424]

how does the car eat up non-platinum plugs?

[carlover626]

how does the car eat up non-platinum plugs?

Your engine fires on both the intake and exhaust strokes and not all plugs are intended for this type of cycle.
I would make sure you have the recommended plugs (AC Delco Platinum Tip, $7 a peice i think) before you go too far into this. I have heard many stories here of misfiring due to the incorrect plugs on the 2.4.

[rixGAphx]

Originally posted by murr2424
how does the car eat up non-platinum plugs? Regular, non-platinum plugs have center electrodes and ground electrodes made of nickel-steel alloy.
Pretty tough stuff, actually, and they work fine for lower-powered ignition like a lawn mower or a '69 Dodge with points/condenser and a 12,000 volt coil.
But the power of the spark is so low, that it can only jump a small gap, about 1/32" (0.032).
And every spark actually burns a few iron molecules, creating ferrous oxide (rust).
So every 5,000 miles or so, back in the 'good old days', we would remove the plugs from the Dodge, clean them, file the center electrode, and gap them back to 0.032 or whatever.
Good-to-go.

Modern ignitions use MUCH higher voltages, and they can create a hot spark that will jump nearly twice the distance.
1/16", 0.060. And that spark is as hot as lightning.
We would have KILLED for this kind of spark in '69, since it ignites the fuel-air mixture much better, therefore more power from each cylinder, every firing. Woo-Hoo!!

But, this spark is SO hot that it just eats the hell out of the nickel-steel electrodes.
They just erode away, like they were made of sandstaone and water was just washing over them.
If you want to remove/clean/file/gap/reinstall cheap conventional plugs frequently, say every 3-5000 miles, be my guest.

To make a plug last longer, weld a TINY spot of expensive platinum (or iridium) to the tip of the center electrode.
Platinum is one of the hardest, high-temperature-resistant metals in existence, and it carries electricity well. Iridium is even better (and more expensive).
So this tiny expensive amount of platinum protects the electrode so it lasts a lonnnnnnng time.
When it wears out, you can't file/regap, 'cuz the platinum is finally gone.
Because of EPA clean air regulations (and longevity of the emissions systems), car manufacturers MUST use platinums to get the required life from plugs.

With 'double-spark' ignitions like those on the GA, BOTH electrodes are being eroded by the high heat (the 'lightning bolt' only burns the electrode it is jumping TO; on a 'double-spark' ignition, the waste spark (on the exhaust stroke) jumps the opposite direction).
So the best plugs are 'Double Platinums' with a tiny spot of platinum on the ground electrode (as well as the center electrode).
ACDelco 'RapidFire' plugs are single-platinum.
ACDelco 'Professional' plugs are double-platinums, and they cost more.

'Platinum Plugs' are NOT just 'snake oil', they really work; and they're cheaper in the long-run.

Hope this helps.
-Rick

[Jchiasson]

That is some write up!:bow:

[murr2424]

well, i've been enlightened. i have to say i was skeptical of platinum plugs before rick's disertation and my latest experiment with plugs, but now i'm a believer. i stopped by the parts store yesterday and picked up some ac delco professionals, slapped em on my car and presto! she runs like new! it's absolutely amazing the difference it made, especially since the plugs i changed out were brand new. guess i underestimated the power of platinum! thanks for all the help guys, especially you, rick! you saved me a lot of $. hopefully i can return the favor...

doug

[rixGAphx]

Originally posted by murr2424
well, i've been enlightened. i have to say i was skeptical of platinum plugs before rick's disertation and my latest experiment with plugs, but now i'm a believer. i stopped by the parts store yesterday and picked up some ac delco professionals, slapped em on my car and presto! she runs like new! it's absolutely amazing the difference it made, especially since the plugs i changed out were brand new. guess i underestimated the power of platinum! thanks for all the help guys, especially you, rick! you saved me a lot of $. hopefully i can return the favor...

doug Glad you're on the road again, with a smooth and powerful GA!! :thumbsup:

And glad I could help; it's one of my few 'pluses' this week :D :D

Take care, and pass the favor on.
-Rick