Random Misfire 0300

[lyonsfam1]

Ok i have gotten this code once before, right after i put the wynjammer on.

the plugs were not gapped right so i changed them, still got a misfire. bought some new iridium plugs gapped at 40 still got it (always at high rpm right before i shift like 46-4800), decided the plugs sucked and went back to my old standbys NGK TR6's 1 stage colder gapped at 35, perfect. running that for about a month now and here we go again random misfire 0300 at 46-4800 rpm's

this is driving me crazy i cant figure out what is causing this to happen could the plugs be fouled, or is this something else i am missing. PLEASE HELP ME!

[03 Rado]

When was the last time you changed your fuel filter. SOunds like since it locked into a high rpm where this happens that its a fuel problem where its running low on fuel!

[ZR1 S10]

Well alot of the time 0300 can also be our crappy injectors starting to go.

I know when I had 0300 mine were getting clogged.

[biglouie_underpressure]

When was the last time you changed your fuel filter. SOunds like since it locked into a high rpm where this happens that its a fuel problem where its running low on fuel!
did you get my pm?

[xtreme canuck]

Ok i have gotten this code once before, right after i put the wynjammer on.

the plugs were not gapped right so i changed them, still got a misfire. bought some new iridium plugs gapped at 40 still got it (always at high rpm right before i shift like 46-4800), decided the plugs sucked and went back to my old standbys NGK TR6's 1 stage colder gapped at 35, perfect. running that for about a month now and here we go again random misfire 0300 at 46-4800 rpm's

this is driving me crazy i cant figure out what is causing this to happen could the plugs be fouled, or is this something else i am missing. PLEASE HELP ME!
My truck has thrown that code also- before and after the s/c but only at wot for more than 10 or 15 seconds in 4th around 5000 rpm. all my ignition is new and i just installed tr6s and re gapped at 35( hasn't done it since ). but the truck is running perfect so it is not something i am worried about . at wot there is no hiccup just smooth power. it is something you could spend 1000 $ on and never find.

[biglouie_underpressure]

Ok i have gotten this code once before, right after i put the wynjammer on.

the plugs were not gapped right so i changed them, still got a misfire. bought some new iridium plugs gapped at 40 still got it (always at high rpm right before i shift like 46-4800), decided the plugs sucked and went back to my old standbys NGK TR6's 1 stage colder gapped at 35, perfect. running that for about a month now and here we go again random misfire 0300 at 46-4800 rpm's

this is driving me crazy i cant figure out what is causing this to happen could the plugs be fouled, or is this something else i am missing. PLEASE HELP ME!
tell us about your ignition set-up.

[Hammer]

your ignition would help like big l asked. i am not thinking fuel, i think cap/rotor/wires/ignition or pre-ignition/spark on this one. sounds to me like you are loosing spark at high rpm, or spark quality atleast. i doubt it's the plugs, it could be your coil, cap, rotor, wires are shorting, many things like a spark jumping from one wire to another if they are touching, etc etc.

[lyonsfam1]

i upgraded all my ignition. accel wires,rotor,cap,and coil, and the ngk tr6 plugs i mentioned. i have checked them all for shorts and such but no luck. if its is a faulty injector who makes injectors for this engine?

[flatblack]

i have the same problem, and its done it ever since 23000 miles(when i bought it) on the truck....a while back when i had hypertech programming, and i got my cut out, it stopped doing it....before the s/c, and no programming about 4700-5k it would flash the ses light, now with the s/c and the cut out...its the same problem we are talkin about....i have a stock ignition...also, its like a hump the motor has to get over...about 4700 there is a misfire and then after that it keeps on truckin, but that hump is what is causing the problem. Wouldnt it make more sense if the misfire was at like 5200, instead of right before redline??

[Sparky2263]

Bulletin No.: 03-06-04-041

Date: August 26, 2003

TECHNICAL

Subject:
Poor Engine Performance - Misfire, Rough Idle, Service Engine Soon/Check Engine Light Illuminated, DTC P0300 Set (Inspect Distributor Ignition (DI) System Components and Replace As Necessary)

Models:
2001-2003 Chevrolet Astro, Blazer, Express, S-10, Silverado
2001-2003 GMC Jimmy, Safari, Savana, Sierra, Sonoma
2001 Oldsmobile Bravada
with 4.3L, 5.0L or 5.7L Gas Engine (VINs W, X, M, R - RPOs L35, LU3, L30, L31)

Condition

Some customers may comment on poor engine performance and the Service Engine Soon/Check Engine light being illuminated. Upon investigation, the technician may find DTC P0300 set.

Cause

This condition may be due to high levels of internal corrosion in the distributor, causing spark to go to the wrong cylinder. This corrosion is attributed to a lack of air flow internal to the cap caused by the EIP screens being clogged with debris.

Correction

Inspect the internal components of the Distributor Ignition System using the procedure listed below. A new distributor base has been released for service with improved airflow screens.

1. Inspect the distributor cap. You may notice a white residue on the cap walls. For higher mileage occurrences, the interior of the cap may have changed to medium brown in color.

2. Inspect the distributor rotor. You may notice the presence of black streaks on the plastic surface. More typical evidence would be visible green spots on the copper surface of the rotor segment.

3. Inspect the distributor base. You may notice high levels of surface rust on the distributor shaft or surface contamination on the sensor hold down screws.

4. Inspect the distributor EIP screen. The screens should be free of any debris and the mesh should be visibly porous. All of these inspection can be done on-vehicle. If there is evidence of this internal corrosion, replace the affected component. Refer to the appropriate procedure in the Engine Controls sub-section of the applicable Service Manual. In addition, it has been determined on the Sierra and Silverado applications with the 4.3L engine that the A/C accumulator line is routed directly above the distributor area and condensation from that line can aggravate the corrosion condition. For these vehicles, install the foam sleeve, P/N 15190971, to the A/C line. Cut a slit in the sleeve and secure to the line using tie-straps.

[lyonsfam1]

sounds interesting. so where is this EIP screen located to check it?

[Sparky2263]

I am assuming it to be a vent screen located in the distributor base.

I'm curious about the lean possibility. Easy to ck. Either tap into the O2 sensor with a voltmeter or use a scanner. If it is getting lean at the top the O2 sensor will show it. Full throttle is always over .9 VDC. If it was going lean you'd see a steady downward drop in voltage before it started misfiring.

[lyonsfam1]

i have a a/f ratio gauge connected to the o2 sensor and it says at wot i am rich.

[Sparky2263]

That would pretty much eliminate a lean condition. On the side the a/f is hooked up to.

See if you can find someone with an ignition scope. Mine is practically indispensible in diagnosing weird ignition problems.

[lyonsfam1]

if i take off my dis cap can i see these screens that might be clogged? im just trying to figure out what i will be looking for.

[Sparky2263]

I just ran across the bulletin. But I seem to remember a screen in the base.

Mostly what I've found is crossfire in the cap. If the distributor isn't phased properly it will add to a crossfire problem. Cam sensor sync. can be viewed with most scanners and can be used to properly "time" the distributor as far as cam "sync." is concerned. I'll find you some details. Gimme a minute.

[Sparky2263]

NOTE: There are two procedures available to install the distributor.
Use Installation Procedure 1 when the crankshaft has NOT been rotated from the original position.
Use Installation Procedure 2 when any of the following components are removed:


The intake manifold
The cylinder head
The camshaft
The timing chain or sprockets
The complete engine If the malfunction indicator lamp (MIL) turns on and DTC P1345 sets after installing the distributor, this indicates an incorrectly installed distributor.
Engine damage or distributor damage may occur. Use Procedure 2 in order to install the distributor.



Turn OFF the ignition.
Remove air cleaner assembly.
Remove the spark plug wires from the distributor cap.
Twist each spark plug boot 1/2 turn.
Pull only on the wire boot in order to remove the wire from the distributor cap.
Remove the electrical connector from the base of the distributor.



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Remove the two screws that hold the distributor cap to the housing.
Discard the screws.
Remove the distributor cap from the housing.

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Use a grease pencil in order to note the position of the rotor in relation to the distributor housing (1).
Mark the distributor housing and the intake manifold with a grease pencil.

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Remove the mounting clamp hold down bolt.
Remove the distributor.

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As the distributor is being removed from the engine, watch the rotor move in a counter-clockwise direction about 42 degrees . This will appear as slightly more than 1 clock position.
Note the position of the rotor segment.
Place a second mark on the base of the distributor (2). This will aid in achieving proper rotor alignment during the distributor installation.
INSTALLATION PROCEDURE 1

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If installing a new distributor assembly, place 2 marks on the new distributor housing in the same location as the 2 marks on the original housing.
Remove the new distributor cap, if necessary.
Align the rotor with the second mark (2).


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Guide the distributor into the engine.
Align the hole in the distributor hold-down base over the mounting hole in the intake manifold.

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As the distributor is being installed, observe the rotor moving in a clockwise direction about 42 degrees .
Once the distributor is completely seated, the rotor segment should be aligned with the mark on the distributor base (1).
If the rotor segment is not aligned with the number 1 mark, the driven gear teeth and the camshaft have meshed one or more teeth out of alignment.
In order to correct this condition, remove the distributor and reinstall the distributor.

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Install the distributor mounting clamp bolt. NOTE: Refer to Fastener Notice in Service Precautions. Tighten Tighten the distributor clamp bolt to 25 N.m (18 lb ft) .


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Install the distributor cap.
Install two new distributor cap screws. Tighten Tighten the screws to 2.4 N.m (21 lb in) .
Install the electrical connector to the distributor.
Install the spark plug wires to the distributor cap.

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Install the ignition coil wire. Note the correct orientation of the wire boot.
Refer to installation procedure 2 if malfunction indicator lamp is turned ON after installing the distributor. IMPORTANT: If the malfunction indicator lamp (MIL) is turned ON after installing the distributor, and a DTC P1345 is found, the distributor has been installed incorrectly.

[Sparky2263]

INSTALLATION PROCEDURE 2
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Rotate the crankshaft balancer clockwise until the alignment marks on the crankshaft balancer are aligned with the tabs on the engine front cover and the number 1 piston is at top dead center of the compression stroke. IMPORTANT: Rotate the number 1 cylinder to top dead center (TDC) of the compression stroke. The engine front cover has 2 alignment tabs and the crankshaft balancer has 2 alignment marks (spaced 90 degrees apart) which are used for positioning number 1 piston at top dead center (TDC). With the piston on the compression stroke and at top dead center, the crankshaft balancer alignment mark (1) must align with the engine front cover tab (2) and the crankshaft balancer alignment mark (4) must align with the engine front cover tab (3).


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Align white paint mark on the bottom stem of the distributor, and the pre-drilled indent hole in the bottom of the gear (3).
With the gear in this position, the rotor segment should be positioned as shown for a V6 engine (1) or V8 engine (2).
The alignment will not be exact.
If the driven gear is installed incorrectly, the dimple will be approximately 180 degrees opposite of the rotor segment when the gear is installed in the distributor.
NOTE: Refer to Distributor Driven Gear Can Be Installed in Multiple Positions Notice in Service Precautions.

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Using a long screw driver, align the oil pump drive shaft to the drive tab of the distributor.
Guide the distributor into the engine. Ensure that the spark plug towers are perpendicular to the centerline of the engine.



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Once the distributor is fully seated, the rotor segment should be aligned with the pointer cast into the distributor base.
There may be a 6 cast into this pointer, indicating that the distributor is to be used on a 6 cylinder engine or an 8, indicating that the distributor is to be used on a 8 cylinder engine.
If the rotor segment does not come within a few degrees of the pointer, the gear mesh between the distributor and the camshaft may be off a tooth or more.
If this is the case, repeat the procedure again in order to achieve proper alignment.



http://www.sicgmtrucks.com/forum/attachment.php?attachmentid=1299&stc=1



Install the distributor mounting clamp bolt. NOTE: Refer to Fastener Notice in Service Precautions. Tighten Tighten the distributor clamp bolt to 25 N.m (18 lb ft) .


http://www.sicgmtrucks.com/forum/attachment.php?attachmentid=1296&stc=1




Install the distributor cap.
Install two new distributor cap screws. Tighten Tighten the screws to 2.4 N.m (21 lb in) .
Install the electrical connector to the distributor.
Install the spark plug wires to the distributor cap.


http://www.sicgmtrucks.com/forum/attachment.php?attachmentid=1302&stc=1




Install the ignition coil wire. Note the correct orientation of the wire boot.
Repeat installation procedure 2 if the malfunction indicator lamp is turned ON after installing the distributor. IMPORTANT: If the MIL is turned ON after installing the distributor, and a DTC P1345 is found, the distributor has been installed incorrectly.

(Courtesy Alldata)

[lyonsfam1]

well i took off the cap and rotor and found the screen. there was some white powder in and around it so i blew it all out and went for a drive.

seemed to do well but by the 4th wot shift in 3rd the 0300 came back :mad:

[Sparky2263]

Sure is sounding like a fuel starvation issue.

[<-~Jo~->]

sparky are you doing these drawing by your own or your getting them from the internet either way great work on giving all that info . !

[Sparky2263]

(Courtesy Alldata)

[bvr775]

when you clean the screen spray some red battery stuff (anti corosion ) to keep it from doing it agian.