P0300 Codes Got Me

[Gabe25]

OK, I’m running into a little trouble. Here is the trouble. The almighty P0300 code (Multi-Miss Fire). Here’s what was done.”97” S-10 Blazer, 4.3 Vortec “W” motor. Lower In-take manifold gasket leaking anti-freeze. Radiator pressure test shows 16lbs. After 10 min. drops down to 9lbs. Motor running great. So, I decide to replace the lower in-take manifold gasket this weekend. Toke apart in the in-take and replaced gasket. Waited 24 hours for RTV to set. Mean time I decided to inspect the fuel injector and found that the fuel regulator is leaking, so I went ahead and replaced that as well. Now the 24 hours are up. I started her up and she is missing really bad. Sounds like I’m running a full race cam inside. Which I’m not. Anyway, I went and re-check the distributor to ensure the base line is properly set. No1 DTC full compression stroke. Everything is lined up. Harmonic balancer, timing mark and rotor. Try resetting the distributor one tooth advance and one tooth retard. Both ways no start. I was thinking maybe the harmonic balancer might of shifted. No such luck. So, I went ahead and replace Cap, Rotor, Plugs, and Wires. AC Delco of course. Still no luck. Oh ya, I forgot me mention that I tested the fuel pressure prior to replacing the tune up parts. It was 63 psi and dropped to 57 psi after 20 mins. Fuel pressure remained at 60 psi while the motor was running. Anyway, Still getting the P0300 code and missing bad. Checked EGR valve for carbon. Checked all vacuum lines for leaks. All OK. Checked fuel pulse with noid light. Test OK. Still nothing. Starts and runs rough, still pulling P0300 Codes.

What I’m thinking is the fuel injector housing is crack on the inside and needs to replace the whole assembly.

Any body have any ideas????

[MT-2500]

I would check the camshaft retard setting.
If over -3 or +3 degrees it can stir up a missfire.
You may need a good engine capable scanner to check and set it.
Also a good scannner will read out what cylinder/cylinders are missing or how many times.
If just one cylinder missing it helps narrow it down.

Fuel pressure does not point to a injector or housing leak.

Can you feel a miss on the road?
Good hot blue spark out of coil and to all plugs?

[Gabe25]

MT, Thanks. I Checked coil and end of plug wires, and got good blue spark. The scanner that I have is a Auto X-Ray 5000. I'll need to check and see if its able to test the camshaft retard settings. I'm in the office and I everything is at home. So I'll look at when I get home. As far as the miss. Its pretty bad. Like I said earlier. Motor sounds like I'm running a full race Cam on idel. Drove around the block and pretty much no power. Motor feels like starving for gas.

[MT-2500]

You are welcome and double check the plug wire firing order.
or remove one plug wire at a time to find missing cylinders.
Good luck and let us know how it goes.
MT

[Gabe25]

MT, I just was wondering about the cam shaft positioning sensor inside the distributor. Could this be causing my trouble? I just throwing ideas around in my head.

[MT-2500]

Originally Posted by Gabe25

MT, I just was wondering about the cam shaft positioning sensor inside the distributor. Could this be causing my trouble? I just throwing ideas around in my head.

It should set a code.
I had one go bad but it had a code and camshaft retard setting wws way off around 35-45 degrees.
Try running a cylinder balance test or remove one plug wire at a time and see if any cyylinders are dead /missing.
Good Luck
MT

[Gabe25]

Originally Posted by MT-2500

It should set a code.
I had one go bad but it had a code and camshaft retard setting wws way off around 35-45 degrees.
Try running a cylinder balance test or remove one plug wire at a time and see if any cyylinders are dead /missing.
Good Luck
MT

MT, OK I pulled one plug wire at a time and each time it ran worst. Re-checked firing order, and thought I had No. 1 & No.3 cross, but no chance. Working on getting a good scannner that will read out what cylinder/cylinders are missing. Although it seems like none of the cylinders are missing. Will update later.

[MT-2500]

Double check for vacuum leaks and you might try pluging the egr valve port at intake.
Good luck and let us know how it does.
MT

[Gabe25]

Originally Posted by MT-2500

Double check for vacuum leaks and you might try pluging the egr valve port at intake.
Good luck and let us know how it does.
MT

OK, I sprayed all the vacuum lines with carb cleaner and pulled the ERG and rechecked and cleaned. All looks good, no leaks and no carbon. Plunger move freely. I'll be bring home a Snap-No engine Diag tester tonight and run a complete diagnostic. I should be able to take over my on board computer and pull complete graphs of everything. We'll see what happens.

[Gabe25]

Still on going. Got home to late after after picking up the engine diag scanner. Then again I think it mite of been to many Crown Royals on the rock that made it to late. Anyway, I hope to finish this saga sometime today. Will keep you posted.

[MT-2500]

Good luck and let us know how it goes.

[Gabe25]

OK, Just finished the testing. The scanner is coming up with misfiring in cyliners 4 & 5 at about 30%. Now I'm total lost. I tried looking in my manuals on how to trouble shoot this type of trouble and found nothing. Are there any words of wisdom out there.

[16th hippy]

while you were spraying the vacuum lines and such, did you happen to spray the intake around those areas? might have a gasket leak there too. sounds fishy having misfires on both banks. just a thought.

[MT-2500]

A couple of things to check.
If you still have the scanner try the injector balance test.
Also check the injector plugin on top of intake and make sure it is pushed on and locked down good.

Cylinders 4 and 5 are right next to each other in the firing order.
Look the new dist cap over good and double check camshaft retard setting.

Also on 96-97 4.3 engines there is a tsb on o2 sensor wiring that can cause missfire or misfire codes and or 02 sensor codes.
Check the wiring and plug in for moisture or green stuff.
The moisture can get into the wiring at the starter area/plugin to the 02 sensor wiring.
TSB no. 77-65-12 april 97
Good luck
MT

[Gabe25]

Originally Posted by MT-2500

A couple of things to check.
If you still have the scanner try the injector balance test.
Also check the injector plugin on top of intake and make sure it is pushed on and locked down good.

Cylinders 4 and 5 are right next to each other in the firing order.
Look the new dist cap over good and double check camshaft retard setting.

Also on 96-97 4.3 engines there is a tsb on o2 sensor wiring that can cause missfire or misfire codes and or 02 sensor codes.
Check the wiring and plug in for moisture or green stuff.
The moisture can get into the wiring at the starter area/plugin to the 02 sensor wiring.
TSB no. 77-65-12 april 97
Good luck
MT

MT. When I scaned last night. I ensured that I do a complete total diag on everything. That included the injector balance test. I when as far as shuting down one injector at a time to see if there was any difference in the idle. Of course after each shut down I needed to restart the motor. I did a spark plug swap out to see if the misfiring cylinders would move. Plug 1 to 4 and Plug 2 to 5. No such luck. Still misfire in cylinders 4 & 5. Will continue again after work. Thanks for all your help. I'll keep you posted.