1999 Blazer p0300 code

I have a 1999 Blazer 4.3L that just recently started shifting hard going into first gear. We got an error code of p0300 (random cylindar misfire). So my husband checked all the plugs and then we restarted it and when it was idling it started to, what sounded like "backfire". Anyone ever have this problem before? Also any ideas?
Other info my husband thought would be helpful...The plugs we have are bosch platinum 2's. Was thinking we should go with AC Delco, or another OEM type plug. Cap & rotor, and wires are only about 8000 miles old.

Please help.

Don't use Bosch plats, they are known to cause a misfire in our engines. Swap them out for stock AC Delco Platinum plugs that are made for your truck.

Also, make sure the new AC plugs are gapped properly before you install them.

We are planning on doing what you suggested this weekend. Will keep you posted. Thanks for your reply.

good luck

Also, any check engine lights on the dash?

Yes we did get a check engine light. Also we replaced the spark plugs with AC Delco ones, however it is still idling rough and the smell out of the exhaust is very rich. Anymore ideas? Think she is headed to the shop otherwise.

Was the P0300 the only code?

Also, I would check the code.

A random misfire is caused by a defective coil not supplying good spark or a fuel pump or fuel pressure regulator not supplying enough fuel pressure.

P0300 was the only code, and it throws it twice every time the SES light comes on. The scanner always shows 1 of 2, and 2 of 2, with the same code.

Is the fuel pressure regulator a comlpetely seperate part than the pump, as in not in the fuel tank?
How do i go about checking fuel pressure? What tool is available for this? Can i do it from the fuel rail?

Is it a better idea just to replace the coil first? Staying with the idea of change the cheapest/easiest part first and work your way back.

Thanks for all the help guys.
Karen

The fuel pressure regulator is located with the injectors, which the injectors are somewhat hidden below the black upper manifold. If you look at the intake induction system where it turns down onto the throttle body, right behind that you will see the fuel supply and return lines going down into this hidden area.

The fuel pressure can be tested by using a Fuel pressure gauge tester, available at most automotive stores.

There is a valve built in the fuel line that the above tester would simply screw on to. The valve is right near the distributor cap, towards the back of the engine.

The fuel pressure regulator is located with the injectors, which the injectors are somewhat hidden below the black upper manifold. If you look at the intake induction system where it turns down onto the throttle body, right behind that you will see the fuel supply and return lines going down into this hidden area.

The fuel pressure can be tested by using a Fuel pressure gauge tester, available at most automotive stores.

There is a valve built in the fuel line that the above tester would simply screw on to. The valve is right near the distributor cap, towards the back of the engine.

Yes it is on top the motor towards the back, right in front of the distributor cap, it looks kind of like a tire valve with a little black cap on it.

I read on here somewhere that AutoZone will rent you a gauge.

Yip, that is where it is.

Other info my husband thought would be helpful...The plugs we have are bosch platinum 2's. Was thinking we should go with AC Delco, or another OEM type plug. Cap & rotor, and wires are only about 8000 miles old.

Please help.
I used Bosch Platinum 2's in my Impala one time....they were junk I had to change them out in no time. just a little tip for anyone reading this. Don't use them.

Yea, and the +4's are a NIGHTMARE.

Known to fail, break and have lots of nice metal bits bouncing around your cylinder.

Ok, he replaced the coil and fuel filter last night. No change. It idles at around 850 and rough. He thinks it is spark related and not fuel b/c there is such a rich smell from the exhaust; but then again he's been wrong before.
And it backfires about once every 10 seconds or so. Is this b/c the computer is retarding the timing so much?

Still brings the P0800 code twice every time, and comes on about 30 seconds after car is running.

On another note, the Platinums being replaced with the AC Delco didn't make much of a change. They were 2's, and all parts were intact.
I think he is at his wit's end. I think we are taking it into the shop tonite.
Thanks for all the help guys,
Karen

Check everything from the cap and rotor to the vacuum lines.

Anything else acting weird?

Still brings the P0800 code twice every time, and comes on about 30 seconds after car is running.


Was this a typo? Did you mean P0300 instead?

Yes, typo

P0800 is an typo. STILL P0300

Yes, sorry, P0300. Nothing else seems weird. But then again, it's hard to tell what else is wrong when the idle is so rough, it's backfiring, and it smells so rich. I did notice after i changed the coil and erased all codes, the SES originally turned off. After about 1 minute of run time, it came back on with two P0300 codes, and an additional o2 sensor code. That was the first time the O2 has ever thrown a code. I erased all three, changed out the fuel filter, and tried again. The two P0300 returned, haven't seen the o2 again. Probably a fluke?

I think she is going into the shop tonite. I will update you on what they find out.

Recap:
What's wrong:
P0300 -- rough idle, backfire sound

What's been replaced:
plugs -- ACDelco, replaced this week
wires are less than 8000 miles old, so are the cap and rotor.
coil has been replaced this week
fuel filter replaced this week

Karen's husband, Eric

Ok we took it to the shop. Found out what it was also.. Much to my husbands dismay it was two iginition wires switched on the drivers side. So it was an easy fix. Thank you all for your replys.... Hope this post can help someone in the near future.

Numbers 1 and 3? They don't go in the same order that the rest of them do, so I can see it being mistaken.

Good to hear that you got it fixed.

Excellent to hear.