1998 C5 Misfire P0300

[Grumpy]

Misfire p0300 and more

Hi All!
I new to this site and it's my first post.
I have a 1998 C5 convertible which has started to act up.
It started to misfire and the check engine light came on and P0300 showed up.
Judging from my feelings it some times runs smooth but not most of the time.
I started to troubleshoot and changed all of the sparkplugs with no change in performance.
Installed a brand new battery. no change

then found the CPV tubing completely rotten and replace it with new spareparts and no change in performance.
Disconnected the spark plugs cables one at the time while idling and noticed degradation in performance on all cylinders except when I disconnected the cable to cylinder 7.
Swapped the 5 and 7 spark plug cables. problem still remain at 7.
At some point arounf this time I stopped getting the Check Engine and P0300 dissapeared.

Swapped the 5 and 7 coils and problem still remains with 7
Checked all the supply voltages at fuel injectors, all 12 V.
Fuel injector cleaning fluid in the tank and no change.

Removed the fuel rail and the nr 7 injector. Tested it with a battery and it clicks. Tried blowing through it and when activating it with the battery it passed the remaining fuel and then air. I guess it's ok.
Swapped nr 5 and 7 injectors and the problem still remains with nr 7.


Any ideas are welcome.


Best
Garibaldi

https://www.summitracing.com/parts/a...yABEgI8WPD_BwE

Id do a compression test on all cylinders to check if you have a burn exhaust valve,
if cylinder #7 reads significantly lower that might be the issue.
but I have seen a defective cam position sensor ,
or a defective pigtail connector on one, cause similar issues
a good deal depends on how your loosing compression if thats the issue,
so theres no sense in getting into potential details,
until your compression test verify's or excludes,
the loss of compression issue in a single cylinder.
you need too deal in verified facts
at this point your simply eliminating or verifying potential reasons your pulling a trouble code,
once its verified we work on curing the issue/making repairs

Id also verify the cam lobe lift on both lifters on that #7 cylinder
as a worn cam lobe or defective lifter, or defective valve spring or rocker,
might contribute to the issue and not be making much noise.
u need to put a injector node light on cylinder 7 and check for it to flash
Id look for vacuum leaks ,
and loose electrical connections, defective oxygen sensors
and test as many sensors as I could,
while your searching for a cause.

Id pull trouble codes again and hopefully find more info

 

[Grumpy]

• Low Fuel Pressure– If there isn’t enough fuel getting to the engine, this will cause combustion to be less than optimal. Diagnosing low fuel pressure can be tricky. Typically, if you do have low fuel pressure, the vehicle will act fine when it doesn’t need a lot of fuel. But, it’ll sputter and act like it’s going to die at speed or under heavy acceleration. Here’s some information on how to tell if you have a bad fuel filter.
• Vacuum leak– If your Corvette has a vacuum leak, it can be very difficult for it to get the right air/fuel mixture. This will cause the cylinders to misfire and it’ll throw the P0300. Also, since a vacuum leak almost always affects each cylinder the same, you’ll typically get P0300 with it and not any cylinder specific misfire codes. Here’s a great article from Popular Mechanics on how to detect a vacuum leak. It’s easy (and kind of fun) to chase one down. Popular Mechanics: How to find a vacuum leak.
• EGR Problems– If the EGR system is not able to recycle the engine gasses right, it’ll throw P0300.
• Ignition Problems– Bad plug wires (if equipped), bad coil packs, and spark plugs can cause misfires to occur. This isn’t higher on the list because typically you’ll get a misfire in one cylinder specifically, and not a P0300 only. If you got a P302 or something similar with the P0300, it may be a good idea to check and see if there is any damage or failure from your ignition components. Here’s how to test a coil pack, how to tell if a spark plug is bad (video), and how to test plug wires (video).
• Cam or Crank Sensors– This one is very unlikely, but it does happen. If the ECU is not getting the right signal from these sensors, the vehicles timing is not going to sync up and it’ll misfire.
• Low Compression– If you have a leaking head gasket, bent valve, cracked head, etc.. that would cause compression to not be as high as it should, you’re going to get P0300. You should also feel the vehicle is down on power as well.

https://www.summitracing.com/parts/a...yABEgI8WPD_BwE

https://www.carparts.com/details/Che...E&gclsrc=aw.ds


I might be wrong, but Ive had similar issues that were resolved with a new cam position sensor replacement,
and since its not that expensive or hard to swap out.....
Id have tried replacing it.
frankly I talked to several of my more knowledgeable friends and
many suggested you swap out
BOTH THE CAM AND CRANK POSITION SENSORS
please let us know if you decide to replace those sensors and if the change results in eliminating the problem,
I know it might seem like a waste of your time and cash,
but Ive found that at times, you tend to find long shots pay off,
time, spent aggravation avoided and less effort, is involved,
if the parts don,t cost that much, or are hard to install,
to simply swap them out eliminating the potential.

If a misfire was detected on #7 then the code should be P0307 not P0300.

Most Common P0300 Fixes
A lot of the time, P0300 is going to be fixed by something obvious, such as an EGR leak. When it’s not glaringly obvious what is wrong, a tune up is a great place to start.

Replacing the spark plugs, coil packs, and plug wires is not typically difficult or costly.

Is P0300 a Serious Concern?
P0300 is cause for concern and left unfixed can get worse. Fixing the problem causing the code to fire can save you time and money and keep your Chevy from breaking down.

off alldata for that code. I would check the o2 sensors first.Important Information - PIP 3056
Notes

Subject: 97-05 Vehicles with 4.8 5.3 5.7 and 6.0 Gen III V8 Engines and Misfires on One Bank - kw CEL diagnostics driveability DTC P0171 P0172 P0174 P0175 P0300 P0301 P0302 P0303 P0304 P0305 P0306 P0307 P0308 #PIP3056 - (07/12/2004)

Models: (00-05 Cadillac Escalade - C6 and K6) and (02-05 Chevrolet Avalanche - C1, C2 K1 and K2) and (99-05 Chevrolet Silverado - C1, C2 K1 and K2) and (00-05 Chevrolet Suburban - C1, C2, K1 and K2) and (00-05 Chevrolet Tahoe - C1 and K1) and (99-05 GMC Sierra C1, C2 K1 and K2) and (00-05 GMC Yukon - C1, C2, K1 and K2) and (03-05 Chevrolet Express G1, G2, G3, H1, H2 ) and (03-05 GMC Savana G1, G2, G3, H1, H2 ) and (04-05 Buick Rainier S1, T1 ) and (03-05 Chevrolet Trail Blazer EXT S1, T1 ) and (03-05 GMC Envoy XL XUV S1, T1 ) and (03-05 Hummer H2) and (04-05 Cadillac CTS-V DB) and (98-02 Chevrolet Camaro FB) and (97-04 Chevrolet Corvette YB) and (98-02 Pontiac Firebird FB) and (04-05 Pontiac GTO VB)

The following diagnosis might be helpful if the vehicle exhibits the described symptoms.

Condition/Concern:
Check Engine Light with a P0300 due to 2 - 4 cylinders misfiring on the same bank of the engine. DTCs P0171, P0172, P0174 or P0175 may also set for the misfiring bank.

Recommendation/Instructions:
If the published misfire diagnostic does not isolate the cause, perform the following suggestions as necessary:


Perform a fuel injector balance test for all 8 cylinders. If a fuel injector concern exists, it is possible to misfuel an entire bank of the engine, causing multiple cylinders on the same bank to misfire even though the root cause is a single fuel injector.
Inspect O2 sensor connections on the misfiring bank for corrosion or water intrusion. If water intrusion is found on the right bank, it may be due to the AC Evaporator Condensation dripping onto the O2 sensor harness. If this condition is found, reposition and shield the harness to prevent a repeat concern and repair the connections.
Check for excessive exhaust backpressure using the restricted exhaust diagnosis.
Swap the Position 1 O2 sensors side to side to see if the misfires move to the other bank of the engine. If so, replace the O2 sensor.
Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

NOTE: GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition.

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Chevy Corvette P0300 Diagnosis
P0300 is serious enough that you should take your vehicle in to have it looked at if you don’t know what you’re doing under the hood, but if you do, here are the recommended tools for getting the job done.

OBDII Scanner: ANCEL AD310 Classic Enhanced Universal OBD II Scanner Car Engine Fault Code Reader CAN Diagnostic Scan Tool-Black

Fuel Pressure Tester: Actron CP7838 Professional Fuel Pressure Tester

Leak Down Tester: OTC 5609 Cylinder Leakage Tester Kit

Combustion Leak Tester: Block Tester BT-500 Combustion Leak Test Kit – Made in USA

Good luck diagnosing P0300 in your Chevy Corvette!