96 blaz- error code 0300, 0306, 0303 - TBI

Hey all.
Been reading for a few weeks and not sure if I have seen this question or not.
96 Blazer 4.3 TBI . It stored error codes 0300, 0303 and 0306 (random misfire on 3, then 6). I changed plugs (first Bosch platinum then, after reading this forum chucked them and put in the AC). Then changed wires, distributor cap (HEI) and rotor. Cleared the codes and guess what - same thing.
I pulled all plugs again and checked them - all look fine - no fouling or oil. Checked wire routing and made sure they were all clear of contact with each other.
Checked fuel pump - pressure is excellent and steady at all RPM's.
Still no change.

What was the pressure?

Could also be clogged poppits, have you tried running a bottle of techron through?

BTW It's not TBI (Throttle Body Injection). That is just a throttle body. There are six injectors inside the plenum.

What was the pressure?

Could also be clogged poppits, have you tried running a bottle of techron through?

BTW It's not TBI (Throttle Body Injection). That is just a throttle body. There are six injectors inside the plenum.

Thanks BLAZEE
Sorry about the TBI goof
Not sure what techtron is?? Do you think a clogged poppet could also cause the engine to sound like it has a valve tap - aroung #6 cylinder??
Pressure was 56psi

have you ever replaced your fuel filter?

Also, it looks like the #3 and the #6 injector will need replacing.

http://cgi.ebay.com/ebaymotors/NEW-MULTIPORT-FUEL-INJECTOR-GM-CHEVROLET-GMC-TRUCKS_W0QQcmdZViewItemQQcategoryZ33557QQitemZ7992 914199QQrdZ1

Techron is the best fuel injector cleaner that you can use, it is made by Chevron. They also make the stuff that GM uses. Techron is extremely similar to the formula that GM sells, but it is half the price.

I doubt that it will sound like a valve tapping.

Your pressure looks low, was it taken with the engine running? When you turn the key to the on position (engine off), the pump runs for 2 seconds...the pressure should be 60 - 66 psi. If it is low, you can try changing the fuel filter.

If they poppits are clogged badly, you may need to replace the injectors. I recommend switching to the updated MFI injection. It does away with the troublesome poppits.

Also you can run a strong dose of Marvel Mystery oil in the fuel tank to clean the injectors and the varnish in them.

I recommend a shock dose of 16oz / full tank.

Also you can run a strong dose of Marvel Mystery oil in the fuel tank to clean the injectors and the varnish in them.

I recommend a shock dose of 16oz / full tank.

OK then - Techtron and Marvel - probably a couple tanks of gas and hopefully it'll be fixed - if not I'll go for the upgrade Blazee suggests. These have been a problem for a while.
Thanks gang

Don't put them both in the tank at the same time. I hope that it works for you, but it may not because they can only clean where they can flow and if it is completely cogged, the cleaner won't be able to work.

I have a TSB that I can send you that tells about the MFI. It has part numers and has the procedure to upgrade.

Replacing your two injectors will cost you a little over $100.00 if you do the work yourself. But you can upgrade the whole system with the MFI (with six new injectors) for a little less than $200. If you want the TSB just PM me your email address.

The parts are available from www.GMPartsDirect.com (http://www.GMPartsDirect.com)

Sent. I just wanted to add that it is only a possibilty that the injectors are the problem. Unfortunatly there isn't a good way to test them yourself. So you should make sure other things have been ruled out first. I would start by verifying that the fuel pressure is within spec.