Random Engine Misfire

[toomuchbeer]

Someone help. I have a 1998 Chevrolet 1500 4X4 with a 4.3 Vortec V6. Sometimes if i hit a good steady long incline i get a code that comes up that is "Random Engine Misfire" in #3 and #5 i believe it said, now wether that changes every time the code came up i cannot tell, i only heard that one time when i have it connected to a code reader. I have been to other forms and got suggestions as to what it could be but am not sure anymore. One i know of that seems to be quite known is that it is the Central Port Injection not working. But when i read the symptons that other people have when they say it is this they are nothing like mine. They say that it has touble starting and rought idle. I don't have that. They say it smells of gas. Mine does not. And they say there is a rapid loss of fuel. And i don't think i have that. Every tank seems to be about the same. I live in Canada, so i am measuring in Kilm. not miles and i get on average about 700K's or so out of 120Litres of gas, now i am not totaly sure as to what it is suppose to get but that's what i get about every time. And now there is a new code. It is "Catalist efficency low Bank One. What's that? Does it have anything to do with the misfire? A shop said that it could be the O2 sensors gone. Now i was told that i have two of them and i had both replaced a couple days ago and now the engine light comes on again today. I don't actually know if it is the same code again but i am guessing with my luck it is. Now i was told buy a friend that maybe it might be the Cat.Conv. is done. Could it be that? And if these two problems are not related to each other then what is the reason for the misfire and what is the reason for the other. This is driving me crazy. Those o2 sensors cost $300.00 plus for both. If anyone could help, please email me at: [email protected]


Thanks

Ryan

[Macgyver007]

hi Beer

I have a 97 Blazer and I am going through similar problems. Just wanted to correct you or update you depends on how you might look at it. There are actually 3 O2 sensors on that vehicle.

1 in the Left Exhaust pipe, just below the brake master cylinder, 1 in the right pipe just before the Y connections, and the 3rd is just after the Cat. I have gone 2 for 3 right now and I am expecting the 3rd is not going to be far behind.... $$$$$$

[bottomtech]

Random misfires are usually associated with fuel problems, whether quality or quantity. I've cleaned alot of injectors on these, some for slight clogging, others for just plain sticking closed.
The engine itself should be okay, because the misfire moves around. Everything from the plugs to the cap the same way. Check the coil terminal for any rust on the metal and the cap for carbon tracking.
When I get a 4.3 for a P0300, one of the first things I check is injector pressure drop. This pulses each injector individually while you watch the amount of fuel pressure drop. This tells you if any injectors are flowing less, which would tell if you need to clean 'em.
Yes it could also be another sensor causing the wrong amount of fuel to be sent into the motor

[GMMerlin]

Originally Posted by toomuchbeer

Someone help. I have a 1998 Chevrolet 1500 4X4 with a 4.3 Vortec V6. Sometimes if i hit a good steady long incline i get a code that comes up that is "Random Engine Misfire" in #3 and #5 i believe it said, now wether that changes every time the code came up i cannot tell, i only heard that one time when i have it connected to a code reader. I have been to other forms and got suggestions as to what it could be but am not sure anymore. One i know of that seems to be quite known is that it is the Central Port Injection not working. But when i read the symptons that other people have when they say it is this they are nothing like mine. They say that it has touble starting and rought idle. I don't have that. They say it smells of gas. Mine does not. And they say there is a rapid loss of fuel. And i don't think i have that. Every tank seems to be about the same. I live in Canada, so i am measuring in Kilm. not miles and i get on average about 700K's or so out of 120Litres of gas, now i am not totaly sure as to what it is suppose to get but that's what i get about every time. And now there is a new code. It is "Catalist efficency low Bank One. What's that? Does it have anything to do with the misfire? A shop said that it could be the O2 sensors gone. Now i was told that i have two of them and i had both replaced a couple days ago and now the engine light comes on again today. I don't actually know if it is the same code again but i am guessing with my luck it is. Now i was told buy a friend that maybe it might be the Cat.Conv. is done. Could it be that? And if these two problems are not related to each other then what is the reason for the misfire and what is the reason for the other. This is driving me crazy. Those o2 sensors cost $300.00 plus for both. If anyone could help, please email me at: [email protected]


Thanks

Ryan

The catalyst code is most likely a result of the misfires...an engine misfire over time will destroy a converter.
On the 98 V6, it is equipped with poppets on the end of the injectors..sometimes they will stick closed. Most of the time the symtoms are a cold misfire or hard start, but I have found that sticking poppets will also cause a loss of power, low fuel mileage and some misfire complaints.
Conventional cleaning methods DO NOT work with these..you will need some specialized equipment that injects high pressure nitrogen into the poppet to unseat it, then follow with a 5-10% mixture of gas and TOC.
Last but not least, these engines will also have a valve stem that sticks in the guide that will cause the misfire counter to go nuts, while the driver doesnt notice the misfire.
The repair for that one is to remove the heads and service the guides...although, some people have tried "snake oils" such as Sea Foam with some good results.. ( I have tried Sea Foam with mixed results, but it is an inexpensive alternative)

[Paraquat.]

I have the same problem. Other forums said to tighten the gas cap, someone else said distributor bearings are spinning out of alignment at certain rpms but I shook it and didnt notice a problem.
Ive run cleaner, Ive run additives, Ive run out of options.
http://www.mastrianni.net/stevespict...ges/repair.htm


--Steve