Mechanics

P0304, P0300

Chevrolet Astro

Hello, I have question. I hope you can answer. I have a 1999 chevy Astro 4.3L. 95,675 miles on it, auto trans, 2 wheel drive.
I scanned the vehicle and It is showing P0304 and P0300. Misfire at #4 cyl p0304, and Random misfire P0300.

So far I have changed the coil, distibutor, cap, rotor, wires, plugs (AC delco), Control Module and map sensor. I checked fuel pressure (61 PSI), checked oil pressure (71 psi @3000RPM) And it is still Mifiring same codes popping up.
I checked the # 4 plug dry after a run and wet after another run. Hmm.I don't get it. Oh I aslo checked main voltage wires at coil (near 14 volts) and near 14 volts at dist. Relucter. Please help.
Avatar
Troy96792
September 19, 2007.



Pull the distributer and look at the gear for wear. You may be able to just replace the gear.

Sounds like a bad injector, have to pull the top plenum off and bull the injector out. Hook the lines back up and crank it to see how it sprays if it does at all.

Tiny
Pulverisor
Sep 19, 2007.
You should check compression on that cylinder first before doing any other repairs. I just dealt with a astro that had a broken valve spring on #5 cylinder.

Tiny
Pulverisor
Sep 19, 2007.
I changed the distributor right after I made the post. Still no change. I will check compression and fuel today. I'll keep you updated if theres a change. Thank you for your response.

Tiny
Troy96792
Sep 20, 2007.
Checked fuel pressure again and its at 55 psi at idle. Then brought up idle to about 3000 rpm and it jumped to 60 then right back down to 55 while at 3000 rpm? What do you think. It's right at the boarderline right?

I replaced inline fuel filter already. Do you think fuel sender needs replacing?

I did not check compression yet.I can't find my tester. Haha

Tiny
Troy96792
Sep 20, 2007.
IT should be 60-66 at idle. I would call that out of spec.

Update.I put in a new fuel sender. Pressure test at 58 at idle. Hmm. Also, compression test 1, 3, 5 read 150
2 reads 149, 4 reads 130 and 6 reads 150. What do you think 130 is it still with in spec? I don't know. Just very frustrated. I did alsomost everything. Checked valve springs too. Checked ok.

Tiny
Troy96792
Sep 27, 2007.
Troy,

It can get really frustrating.I know. Especially when you have a situation that is tight to work in.

Anyways, the 130 sounds good enough for me, that's good new.

The fuel pump should be producing 60-66 psi-key on engine off. (If you leave the gauge on, how long does it hold pressure? I have seen misfires among other problems when it isn't in there. I can't say that it is definitly your problem, but it still sticks out to me. I see originally you did have 60 psi so the does give credence that it may not be. I know there is a recommended connector replacement on those as well.

The next are I would start looking at is the fuel inection system. The 4.3 CSI motors did have a problem with the units going bad, of sometimes the poppets are sticking. There are different products you can use, it comes down to running a few cans of pressurized fuel injection cleaner through the injectors.
Call the dealer with your VIN and find out if the recall was done on the fuel injector system, It was extended 10 years, 200,000 miles. Yours exhibits the symptoms.

Curiousity question: The 4.3s had a problem with a vent being plugged on the distributers. I know you replaced the cap with an AC delco. Was that in an effort to solve the misfire? Or was that previous to the misfire?

First off, I would like to thank you for all your input.
I found the problem. There was a pinch on the lower intake gasket. (I think) while off I changed the fuel regulator and injectors/poppets. It could have been the poppet or regulator. Either way It runs smooth now And I can go on living without the stress. Haha. Again I'd like to thank you for all your input. Aloha, Troy

Tiny
Troy96792
Oct 15, 2007.
Glad I could help, congrats!