The dreaded P0300 CAUTION LONG POST
#71
12-02-2008, 06:31 PM
RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
exact same thing mine is doing. i posted in another thread about this. ran a 3 step fuel system cleaner through mine. not sure if it has helped or not. seems to be still doing it but not as hard. i thought mine was the trans. but i see here that a manual will do it too. i hate my truck. where is my old ford when i need it? it broke down more but at least i could fix it. (sold it with 301,000 miles on it. had a 351 V8)
#72
12-02-2008, 10:31 PM
RE: The dreaded PO300 CAUTION LONG POST AND GETTIN LONGER
I'll be replacing the rest of the E3 plugs when I get some time available. I have used platinum plugs for years and especially on this Blazer because #3 behind the steering shaft is a bugger. I have had togrind down a socket that can be turned with an open end wrench to get that one out.
#73
03-21-2009, 11:49 AM
Suggestions to resolve P0305 code
This thread certainly has a lot of info, and we (my father-in-law, and me) have tried to take advantage of it, but we are near the end of our wits with a similar issue that we are hoping other eyes can see a solution we have overlooked.
The vehicle is a 1995 Chevy Blazer S10 4x4 with a 4.3L Central Port Fuel Injection system, and 269,000 miles. The problem is a misfire accompanied by a check engine light (CEL) that just appeared one day without provocation.
The repair history:
A scanner was connected to the vehicle (fortunately, it is OBD-II compliant), and the only code retrieved was P0305, a misfire on cylinder 5. The first approach to repair was to replace the distributor cap, rotor, spark plug wires, and spark plugs. The problem persisted. Indeed, after driving only a mile or two, the plug from cylinder 5 is coated with black soot (indicating the cylinder is burning rich).
Compression was tested on all cylinders multiple times, and readings for all cylinders were in the range of 162-170 psi. The number 5 plug wire was connected to a spark plug external to the engine to confirm the presence of spark. Spark was present, but we were not able to confirm consistency of spark. At this point we had spark, fuel, and compression so we did not understand why the engine was misfiring.
In frustration, it was decided to replace the timing chain since it was original equipment, and maybe enough slop had developed to account for the misfire. The two timing gears were also replaced, and after a difficult reassembly, the engine was started. The misfire persisted.
After a conversation with an experienced GM mechanic, he convinced us that a stuck poppet valve in the fuel injection system was suspect, and could explain all the symptoms. If the poppet valve were stuck open, excess fuel would be entering the cylinder causing the plug to foul, and resulting in the misfire. Replacement of the fuel spider that included the six poppet valves went smoothly, but upon reassembly, the engine still demonstrated a misfire on cylinder 5.
Consulting with another experienced mechanic, we connected a spark detector to cylinder 5. Again, spark was visible, but not consistent. And when the detector did not arc, arcing could be heard around the area of the coil. A visual inspection of the coil revealed scarring that indicated the coil was generating unreliable spark. Exuberant at identifying a potential cause of the misfire, we replaced the coil. At idle the engine seemed to be running much better, but as soon as we attempted to drive away, the misfire reappeared.
More consultation with a third experienced mechanic resulted in the replacement of the ignition control module, but the misfire continued.
In an attempt to confirm the compression readings, the valve cover was removed to examine the rocker assembly for cylinder 5. Nothing appears out of the ordinary. The valve action seems consistent with other cylinders, and no evidence of sticking is apparent.
At this point, we feel that the only components that could be at fault are the PCM, the crankshaft sensor, or the camshaft sensor, but we hate to spend too much more without some confirmation of which device is defective (if any). The only other information we have is from an OBD-II scanner recording real time data. The timing advance at idle (approx 750 rpm) jumps all over the range of -29 to 0 degrees. The reading does seem to even out when the rpm is increased to about 1500 rpm, but the scanner sample rate is only about 4 times/sec so errant readings may be getting overlooked.
Can anyone provide a suggestion on how to proceed. We hate to just throw money at new parts without some way of determining whether the existing part is defective. Is there something obvious that our addled minds are overlooking?
Snakebit
The vehicle is a 1995 Chevy Blazer S10 4x4 with a 4.3L Central Port Fuel Injection system, and 269,000 miles. The problem is a misfire accompanied by a check engine light (CEL) that just appeared one day without provocation.
The repair history:
A scanner was connected to the vehicle (fortunately, it is OBD-II compliant), and the only code retrieved was P0305, a misfire on cylinder 5. The first approach to repair was to replace the distributor cap, rotor, spark plug wires, and spark plugs. The problem persisted. Indeed, after driving only a mile or two, the plug from cylinder 5 is coated with black soot (indicating the cylinder is burning rich).
Compression was tested on all cylinders multiple times, and readings for all cylinders were in the range of 162-170 psi. The number 5 plug wire was connected to a spark plug external to the engine to confirm the presence of spark. Spark was present, but we were not able to confirm consistency of spark. At this point we had spark, fuel, and compression so we did not understand why the engine was misfiring.
In frustration, it was decided to replace the timing chain since it was original equipment, and maybe enough slop had developed to account for the misfire. The two timing gears were also replaced, and after a difficult reassembly, the engine was started. The misfire persisted.
After a conversation with an experienced GM mechanic, he convinced us that a stuck poppet valve in the fuel injection system was suspect, and could explain all the symptoms. If the poppet valve were stuck open, excess fuel would be entering the cylinder causing the plug to foul, and resulting in the misfire. Replacement of the fuel spider that included the six poppet valves went smoothly, but upon reassembly, the engine still demonstrated a misfire on cylinder 5.
Consulting with another experienced mechanic, we connected a spark detector to cylinder 5. Again, spark was visible, but not consistent. And when the detector did not arc, arcing could be heard around the area of the coil. A visual inspection of the coil revealed scarring that indicated the coil was generating unreliable spark. Exuberant at identifying a potential cause of the misfire, we replaced the coil. At idle the engine seemed to be running much better, but as soon as we attempted to drive away, the misfire reappeared.
More consultation with a third experienced mechanic resulted in the replacement of the ignition control module, but the misfire continued.
In an attempt to confirm the compression readings, the valve cover was removed to examine the rocker assembly for cylinder 5. Nothing appears out of the ordinary. The valve action seems consistent with other cylinders, and no evidence of sticking is apparent.
At this point, we feel that the only components that could be at fault are the PCM, the crankshaft sensor, or the camshaft sensor, but we hate to spend too much more without some confirmation of which device is defective (if any). The only other information we have is from an OBD-II scanner recording real time data. The timing advance at idle (approx 750 rpm) jumps all over the range of -29 to 0 degrees. The reading does seem to even out when the rpm is increased to about 1500 rpm, but the scanner sample rate is only about 4 times/sec so errant readings may be getting overlooked.
Can anyone provide a suggestion on how to proceed. We hate to just throw money at new parts without some way of determining whether the existing part is defective. Is there something obvious that our addled minds are overlooking?
Snakebit
#74
03-21-2009, 03:07 PM
Are you certain that the fouled plug was caused by excessive fuel or is it possible that it is due to oil contamination? If the valve seals are bad, they could allow oil to be sucked into the combustion chamber and quickly foul a plug.
#75
03-21-2009, 03:48 PM
The valve seals are an interesting idea that we had not considered. I spoke with my father-in-law and he was of the opinion that the fouling is from excessive fuel. If it were from oil we would expect to have a smokey exhaust, and that is not the case. The only "smoke" we have seen from the tailpipe is water vapor when the engine is cold. We don't even get detectable black smoke to confirm the excess fuel in cylinder 5. And the misfire begins immediately even with new plugs. After driving the new plug as little as one mile, it will be covered in black soot. The other plugs will be clean. Everything we see now suggests to us that the problem is electrical, but if that is the case, our logic is telling us we should be seeing the misfire on more than one cylinder.
Is there any easy way to confirm the effectiveness of the valve seals without resorting to replacement?
Snakebit
Is there any easy way to confirm the effectiveness of the valve seals without resorting to replacement?
Snakebit
#76
03-21-2009, 06:38 PM
I am just tossing out ideas.
If it were electrical, you should be seeing the problem on more than one cylinder. That is unless there is a problem with how the distributor cap is mounted or possibly an issue within the distributor itself (worn gear at the bottom that chocks just at the proper position for #5...).
Even if it were fuel related, it should be seen on more than one cylinder.
If it were electrical, you should be seeing the problem on more than one cylinder. That is unless there is a problem with how the distributor cap is mounted or possibly an issue within the distributor itself (worn gear at the bottom that chocks just at the proper position for #5...).
Even if it were fuel related, it should be seen on more than one cylinder.
#78
03-29-2009, 07:30 PM
P0305 Update
Ok, I have some new info to present for evaluation. Our misfire problem continues on cylinder 5. We did break down an bought a replacement PCM. Unfortunately, this did not help. Not only did we continue to get the P0305 code, but we also ended up with an anti-lock brake warning light. We suspect this will require some sort of recalibration, but have not found the necessary procedure to follow. We will probably revert back to the original PCM to hopefully clear up the brake warning.
The new info we have is related to vaccuum readings. We obviously should have noted this before, but our vaccuum readings from both a vaccuum gauge and an OBD-II scanner indicate a value of about 14 in. We realize this is low, and are now suspicious of a leak in the intake manifold gasket. What we need is some sort of confirmation that all the other symptoms we see could be explained by such a vaccuum leak. We have checked all the external hoses and believe them to be solid. We are pretty sure the leak is not in the throttle body or with the plenum since the spider assembly has been replaced twice.
Does a low vaccuum reading equate to the PCM thinking the engine is under load, and cause more fuel to be provided? Would the presence of a leak near cylinder 5 screw up the air/fuel mixture in such a way to account for a rich burn?
Thanks for any insight you may be able to provide.
snakebit
The new info we have is related to vaccuum readings. We obviously should have noted this before, but our vaccuum readings from both a vaccuum gauge and an OBD-II scanner indicate a value of about 14 in. We realize this is low, and are now suspicious of a leak in the intake manifold gasket. What we need is some sort of confirmation that all the other symptoms we see could be explained by such a vaccuum leak. We have checked all the external hoses and believe them to be solid. We are pretty sure the leak is not in the throttle body or with the plenum since the spider assembly has been replaced twice.
Does a low vaccuum reading equate to the PCM thinking the engine is under load, and cause more fuel to be provided? Would the presence of a leak near cylinder 5 screw up the air/fuel mixture in such a way to account for a rich burn?
Thanks for any insight you may be able to provide.
snakebit
#79
03-29-2009, 07:59 PM
This does not make sense when you know how the PCM meters fuel. On a 95, there is only one injector... The PCM cannot independently modify fuel flow to only one cylinder. A vacuum leak would cause a lean condition unless it was somehow feeding air to the other 5 cylinders and not #5 resulting in more fuel to all 6 cylinders...
The other posibility is a restriction in the #5 intake runner...
The other posibility is a restriction in the #5 intake runner...
#80
04-02-2009, 10:22 AM
P0305 becomes P0300
Our saga with a misfire continues, and it is getting more and more frustrating. We don't know whether to shoot the car or ourselves. A couple of new data points have arisen, but we are not sure what they are telling us.
As indicated previously, the PCM was replaced, but the P0305 code remained. My father-in-law then decided that he would try replacing the intake manifold gasket to see if there was an improvement in manifold pressure. Prior to the replacement we were seeing PCM reported vacuum of about 14 in, and an external gauge was showing 13-14 in. After changing the intake manifold gasket the PCM reported vacuum came in at 16-17 in with the gauge showing about the same. We thought we were getting improvement because the error code given by the PCM changed from P0305 to P0300. This at least made us think that we had repaired a leak near cylinder 5, but something is still amiss.
If you recall, I mentioned that this replacement PCM gave us an additional problem in that it illuminated the anti-lock brake light, but our scanner did not report any related error code. We decided to see how the original PCM reacted with the replacement of the intake manifold gasket. Swapping back to the original PCM now gives us our P0305 code once again. On the good news side, the anti-lock brake warning light does not illuminate. On the confusing side, manifold pressure readings from the PCM dropped back to the 14-15 in level.
To review, we have replaced the following items:
Spark plugs
Spark plug wires (and swapped wires on cyl 5 multiple times)
Distributor cap (twice)
Rotor
Ignition control module
Timing chain and gears
Fuel injection spider (twice)
Coil
Engine temperature sensor
PCM
Additionally, we checked the Throttle Position Sensor, and it appears to respond in a uniform manner. We observed the O2 sensor behavior, and both seem to be performing in an acceptable manner. And to repeat, we have checked compression multiple times with all cylinders giving strong and consistent readings.
I believe the only components we have not changed in the ignition electrical system are the crank shaft sensor, and the cam shaft sensor. We would replace either or both of these if there were a convincing argument for how they could cause the symptoms we are seeing.
Does anyone have any insight on what to do, or where to look for a solution to this problem? TIA.
snakebit
As indicated previously, the PCM was replaced, but the P0305 code remained. My father-in-law then decided that he would try replacing the intake manifold gasket to see if there was an improvement in manifold pressure. Prior to the replacement we were seeing PCM reported vacuum of about 14 in, and an external gauge was showing 13-14 in. After changing the intake manifold gasket the PCM reported vacuum came in at 16-17 in with the gauge showing about the same. We thought we were getting improvement because the error code given by the PCM changed from P0305 to P0300. This at least made us think that we had repaired a leak near cylinder 5, but something is still amiss.
If you recall, I mentioned that this replacement PCM gave us an additional problem in that it illuminated the anti-lock brake light, but our scanner did not report any related error code. We decided to see how the original PCM reacted with the replacement of the intake manifold gasket. Swapping back to the original PCM now gives us our P0305 code once again. On the good news side, the anti-lock brake warning light does not illuminate. On the confusing side, manifold pressure readings from the PCM dropped back to the 14-15 in level.
To review, we have replaced the following items:
Spark plugs
Spark plug wires (and swapped wires on cyl 5 multiple times)
Distributor cap (twice)
Rotor
Ignition control module
Timing chain and gears
Fuel injection spider (twice)
Coil
Engine temperature sensor
PCM
Additionally, we checked the Throttle Position Sensor, and it appears to respond in a uniform manner. We observed the O2 sensor behavior, and both seem to be performing in an acceptable manner. And to repeat, we have checked compression multiple times with all cylinders giving strong and consistent readings.
I believe the only components we have not changed in the ignition electrical system are the crank shaft sensor, and the cam shaft sensor. We would replace either or both of these if there were a convincing argument for how they could cause the symptoms we are seeing.
Does anyone have any insight on what to do, or where to look for a solution to this problem? TIA.
snakebit