Happy Good Friday to all!

I've been having a P0304 for several months now, and occasional P0300 Steady light.

I've changed plugs, wires, cap, rotor and lower intake manifold gaskets.

I've checked spark several times, mainly on 4. All good.

Last time I checked fuel pressure (a couple months ago) good at 60+ psi. Could not do leak down test because cheap HF tester leaks!
However, two days ago after the truck cooled off a couple of hours I used my finger nail to relieve the pressure and 'a lot' was there.

Anyway, two days ago I decided to go into the plenum. I performed the 'poor man's injection cleaning' on number 4 and 2 only. Air at 60 psi after a shot of carb cleaner several times. Poppets did open. 2 opened first time. 4 required 2-3 attempts but did open and whistle. I did not change any gaskets, but cleaned well and old gasket looked good.

I put all back together and Blazer runs rougher than ever. My code reader is in Atlanta, along with my fuel pressure gauge and plenum gaskets {why I did not YET change} (Left over from the LIM change). I'll be going there this weekend and hope to have a fix on this problem.

I drove about 8 miles with a flashing SES upon any acceleration and steady at idle. Stopped at Advance and they read P0300 only. Drove another 30 miles and stopped at Autozone and they get P0300 and P0304. Back to where I started, but worse!

Question: Does the FPR have a hose that hooks into it? It has the nippled connector, but I could not find a hose. I assume being inside the air flow, it does not need one.

I ask because I am trying to figure out what I have done. I understand that I also may have fried one or both of the injectors I attempted to repair.

I guess I need to invest in a compression gauge as this has not been tested. And get a better fuel pressure gauge.

Your thoughts?

 

Here is an update:

I think I found elsewhere that the FPR has no vacuum hose. Correct me if this is not true.

I drove it about 10 miles from work to fuel up (MPG has sucked as well!). Same flashing SES light whilst accelerating. I read somewhere to disconnect the MAF if having this problem. I did so and only a constant SES light the next 10 miles or so to the parts store for MAF cleaner. Blazer idled noticably smoother, albeit still skipping. I connected the MAF back up at the store and the rougher idle returned and the flashing SES upon acceleration. About a mile from my house I disconnected it again and the SES was steady.

I am about to clean the MAF and will report back.

 

OK....cleaned MAF sensor.

No change. SES steady on unplugged. Flashes when plugged.

 

I don't know if we got a holy Saturday, but HOLY SATURDAY! My guess would be secondary ignition.


Hope you find the correct egg.

 

I think I have finally fixed it. Hope this does not jinxed it.

I replaced the 4th injector. I wish I had the funds to have done the MFI conversion, but my budget only allowed to replace the single injector.

So far 3 trips and over 100 miles, no SES light and much smoother running!

 

I jinxed it. Right after posting this, I started up the Blazer and before I left the parking lot SES is back on. And it is P0304!

I'm starting a new post.

 

Are you dead on sure #4 is getting juice from distributor

 

$5 Harbor Freight inline spark tester says so.

How else can I confirm?

Thanks!

 

Well I can say this if you got spark and fuel in the cylinder in my mind has to be timing of # 4. So let's track it. I like simple, let's just say no lifter or valve problems.


Check to make sure distributor has no cracks on the plastic hold down screw seats.

 

I agree ^^^^^^ If you know you have spark, and you know you have fuel, that just leaves air and compression...

Assuming that the intake passage for #4 is not completely clogged, then you have a compression issue... Valve seals, piston rings, timing and timing related parts...

I realize that this is an old thread, but for those of you in a similar situation, this is the point where you test the cylinders compression... If the cylinder isn't holding proper compression, you've got a seal problem or a valve spring that isn't shutting your valves completely...