'95 Blazer with a P0300

[Blazer '95]

Hello.
I just purchased a '95 with a 4.3L vortec engine which needed some work. I put in a new exhaust system from the cat back, put in an 02 sensor (fwd of the cat), put in new AC/Delco spark plugs and did front brakes/calipers. The old plugs seemed to look like there was a rich mixture being burned.

The vehicle has a loping idle and I took it to the Zone and read the code...it is P0300 random/multiple cylinder misfire detected (I had the code socket under the dash...does this mean that I have the OBDII?). I bought some of the Techron fuel injector cleaner and put that in this morning.

I did a search and have found some good suggestions which are to:

put in new plugs, wires, cap, rotor, fuel filter, air filter, pcv valve.

-check fuel pressure

-check coil

So, in a nutshell...I should do all of these things prior to opening up the plenum and checking/replacing the fuel injector assembly?

Am I missing anything?

Thanks for any advice given.

[Gabe25]

That pretty much sums it up. Your fuel pressure will answer a lot of questions. I would check that first.

[Cailen]

I think the only thing you missed was check the MAF. Probably the second most useful check after fuel pressure if you're having idling problems.

[cobra1]

Originally Posted by Cailen

I think the only thing you missed was check the MAF. Probably the second most useful check after fuel pressure if you're having idling problems.

only one problem, a '95 Blazer doesnt have a MAF sensor.

[JA no Y]

Also wouldn't hurt to remove and check/clean your EGR and put a new gasket on.

[Blazer '95]

Well, I bit the bullit and pulled the plenum. There were puddles of gas on the passenger side of the engine (the pressure regulator side). The drivers' side has some also...but that side was black/oily...as opposed to the cleaner looking passenger side (due to the gas leaking, i suppose?).

I guess that the fuel injector unit needs replacing...is this a safe assumption?

[93LT]

Yeah, you need to change the injector unit and nut kit (fuel lines). Here is some picture of my project. She'll run like new then.

[Blazer '95]

Thanks for the pictures '93 LT...fantastic!!!

I just ordered the kit which contains the CPI, nut kit and gasket.

Is there any trick to breaking off the fuel lines from the nut kit? When I go to loosen them the whole assembly starts to rotate and I cannot see any place to use a second wrench on to keep it from rotating. I have not taken off the bracket that holds this assembly to the manifold yet. Is it better to remove the bracket and then slide out the nuts and then somehow grab ahold of them?

[Gabe25]

Remove the fuel lines first from the Nut Kit fittings. Once removed, then take off the retaining bracket that holds the Nut Kit in your lower plenum.

[BlazerLT]

Also remember to clean the EGR port which is the smaller hole in the fron section of the plenum, clean the port in the upper half you remove and make sure the lower is clean as well.

[93LT]

Originally Posted by Gabe25

Remove the fuel lines first from the Nut Kit fittings. Once removed, then take off the retaining bracket that holds the Nut Kit in your lower plenum.

Like Gabe25 says, there is a retaining bracket holding the nut kit in place, on the outside of the lower plenum, below the edge of the lower plenum. There is a T30 torx machine screw that hold the retaining bracket to the lower manifold (down low and in a awkward to get at). The retaining bracket is pictured in my photo of the Nut Kit. That torx screw is the hardest task of the entire job, to get to it and remove it without going insane, having the fuel line out of the way (pushed towards the distributor) really helps.

If you are turning the nut on the metal fuel line that connects to the metal collar of the nut kit, and the collar turns, someone may have removed the bracket, you would then need to slip the new bracket over the collars (there is a groove on the collars) of both fuel lines (should be able to do this by simply slipping it over them from the upper side, no need to actually fasten the bracket up from underneath for this task).

[Blazer '95]

Hello!

Well the new CPI unit arrived on Tuesday (along with a new nut kit) and I installed it yesterday (wed). This vehicle is now running like a champ...and I can hardly hear the engine at idle because it is soooooo smooth!!! WOW...what a difference!!!

Strangely, the results were not instantly good when I first started up the Blazer after replacement. The idle was a bit low and erratic...and the check engine light initially came on. I was a bit disappointed because I was expecting an instant result! After filling up the tank, I decided to take it for a run on the highway, but I was unable to open her up like I had hoped...(rush hour traffic and rain...#$&#) !!! Something happened while I was on the test run. The engine settled down and started to run alot better and was idling nice and smooth when I eventually stopped at a light!!!! I got this puppy home and put her to bed for the night.

This morning I cleared the code and fired her up...quiet and smooth. Another test run was completed with no codes occurring! The vehicle had been sitting for 6 months or so...so maybe there was a bit of bad gas still lingering - or maybe the computer was shocked to read that a new CPI was actually installed...in any event...the problem is now fixed...HORRAH!!!

I want to thank everybody for their information and help because without the information that you provided to me...this project may never have been accomplished.

[BlazerLT]

Got a couple extra things to ask you:

1.) Did you replace the nut kit and the upper plenum gasket?
2.) Did you clean the EGR passageway?
3.) Have you changed your oil yet.
4.) Have you done a tuneup lately?

[Blazer '95]

Originally Posted by BlazerLT

Got a couple extra things to ask you:

1.) Did you replace the nut kit and the upper plenum gasket?
2.) Did you clean the EGR passageway?
3.) Have you changed your oil yet.
4.) Have you done a tuneup lately?

The answer is yes to everything but the oil change. I will do that this weekend.

[BlazerLT]

Not to be insistant, but your oil will be completely impregnated with gas.

Every mile you drive with that oil you are doing damage to your bearings.