This problem is random, sometimes it runs well and after while it can start to misfire.
Sometimes it misfire after start up and before that it did run well.

From the start we had a P0303 misfire and I changed the fuel spider and that error code went away and have never been seen after that. A few weeks later it started the misfire on #4 instead. After this I changed that cap, cables and spark plugs. Just after that change it ran well for several miles, came home parked it. Started it up 30 minutes later and misfire P0304 again...

There is no noise from it, like valves or anything else that can sound mechanical..
It doesn't consume any quantities of oil and runs well (when it's not misfire)
What did notice at the time of cap and plug change is that the right bank exhaust pipe is leaking at the O2-sensor fitting. Could that screw up the fuel injection impulses?
The plug I pulled looked OK, not wet.

I saw in other posts that the vapor canister could have some thing to do with it. I sued to occasionally get error codes on that but that was awhile ago
There are no other codes except the P0304

I don't know what to look for.

It runs well and we have changed a lot of stuff on it over the years so it has been a keeper but my doubts starts to grow.

Thanks

 

First we need to establish if the misfire is real or not. If you ignore the SES light and your OBD2 scanner, can you actually feel the misfire happening?

Depending on your answer to this question, diagnostics for false misfire detection will be completely different from diagnostics for a real misfire. So please be certain about it.

 

Yes, there is no question about the misfiring, it runs unevenly and shake a bit. On idle you can see it not running as smooth as it do normally. You can feel it when driving to.

 

Les will take good care of you on your misfire problem so I won’t comment on that.

Regarding the evap system: the entire system is isolated from the engine by the purge solenoid which is normally closed and near the engine. This valve only opens for canister purging or brief testing so it can have no long term effect on the engine unless it is stuck open. I can help you with that problem if you like after you get your misfire problem resolved.

An exhaust leak can affect your fuel management and cause the truck to run poorly but probably no a legitimate misfire on one cylinder.



George

 

OK - thank you. It sounds like the misfire is real and not false misfire detection.

Next I need to establish the capabilities of the OBD2 scanner that you are using. What device do you have? Will it display the cam sensor retard value? If so please advise the cam sensor retard value (should be 0 +/- 2 degrees).

 

Sorry but my code reader can't read cam sensor data.

What I have noticed is that it seems to run OK when started from cold and then it runs OK until stopped. When starting again when it is warm it most often misfires. It feels like the misfire starts after a few seconds. It can also run OK for a short distance and then start to misfire.

We don't run it for longer distances now when it is in this condition, just a five minute drive to the stable where our horse is.

 

One of the common problems with intermittent misfires on Blazers is that the distributor gear gets worn and the rotor no longer points exactly where it should - crank sensor/PCM determines when the spark occurs, but rotor needs to be pointing to the right place. If not this can cause electrical misfires. A cam sensor retard value outside of the listed specification indicates a probable issue there. I would recommend you obtain Dash Command (for a 1997) from Google Play for your Android phone and a BAFX OBD2 Bluetooth adapter from Amazon. About $40 US. Then add the enhanced PIDs for your 1997 vehicle inside the app for another $10. If you have iPhone, there is also a version for it - but for iPhone you need BAFX OBD2 WiFi Adapter from Amazon (not bluetooth). This software will read the enhanced GM Powertrain PIDs on your Blazer and is really quite inexpensive. Tell me your cam sensor retard value.

Also a common problem is the fuel pump and fuel pressure. You should obtain a fuel pressure gauge to connect to the Schrader valve. When the misfire is occurring, is the fuel pressure above 52psi? Also, with key on/engine off what is the pressure right after the pulse?

Lets get past the two common things first, and if necessary we can go into further diagnosis.

 

Well I had one issue with it a few years ago when I changed a lot of parts on it, among others the fuel pump (and filter), after a lot of money spent on parts I found that it was the connector to the coil (a $2.00 part) that was bad, duh!

The distributor is one thing I have been thinking about. But before going there I will get that OBD2 adapter you suggest. I already have that app but with a cheaper connector.

I'll get back when I have the adapter and have read the values.

Thanks for now

 

Sounds like a plan

 

I solved this problem by buying a new car. Found a real nice 2002 S10 Blazer with only a bit over 100k on the mileage. My old one will become a donor car and all the new parts I have put on it the last years will be on the shelf for whenever they will be needed.
The new one is rust free and sold new here in Sweden, it is a true export model. It has been in the northern part were it is so cold that they can't use salt on the roads. Nice if you look for older cars without any rust. Even the user manual is printed in the Swedish language!

I will have some questions for the new one but that will be in other topics..

Thanks for the help!