Acquired a 2000 blazer that a squirrel had gotten under the hood. 4.3 Vortex. I replaced the injection wiring harness redid all the vacuum lines put new wires, plugs, cap and rotor. Cleaned the EGR and ran a bottle of both Seafoam and Lucas injector cleaner through it. Starts fine but has a miss below 1500, once it warms up it will start sputtering through the exhaust occasionally. Will drive but has no get up. I’m at a loss, only other thing I know to try is the catalytic converter. It ran fine when parked and yes I drained the fuel tank and put new fuel in. PLEASE HELP!

 

I'd suggest getting a readout of all of the pending and set OBD codes. A good reader will find the pending codes and those that don't always trigger a check-engine-light. This information will help with the diagnosis. A parts store should be able to help with this.

What brand cap and rotor did you use? Conventional wisdom on this forum is that only ACDelco brand will do.

 

If you haven't done this already, make sure you have your plug wires routed to the right spots on the cap. The drivers side is 5-1-3, so often times I wind up accidentally mis-routing them.

 

Only codes it’s throwing is 0300 which is the multiple misfire code.

 

*Moving to 2nd Gen Tech*

The random multiple misfire code can be a real pain to get to the bottom of. If all cylinders are actually experiencing random misfires, it indicates a systemic problem that is randomly occurring; fuel quality;pressure, spark intensity/timing, & inconsistent/low compression are some examples. Sometimes it pays to go into OBD2 generic data and watch the misfire counters on all cylinders at the same time to look for inconsistencies.

When you cleaned the EGR valve, were there any chunks of carbon hanging the EGR pintle valve open? A leaking EGR valve could cause some random misfire conditions and low power.

Have you run a fuel pressure test on it? The SCFI system requires >60psi for proper operation. The upgraded MFI system needs >55psi. See below on how to determine what you have and descriptions of them both.

Do you have access to the CMP RETARD value in your scantool? This is a number that represents how well timed the distributor is to the engine. As close to zero this value can be the better the ECM can control spark timing (as explained in the EDI Engine Timing thread).

Did the truck sit for a long time? I ask because the injection system in there from the factory (SCFI or CSFI) consists of an electronic injector that feeds a pressure actuated poppet nozzle. The pressure actuated poppet nozzle can become dirty and not seal off properly between injector pulses causing problems with combustion. If the system was upgraded over the last 24 years, it may have the newer MFI spider in it which came out in the mid-2002 4.3 engines and moved the fuel injector out to the end of the fuel lines inside the plenum, eliminating the pressure actuated poppet nozzles. This system was much more robust.

If you are interested in digging into it, it may be worth while to determine which setup you have to begin with and then go from there. An endoscope can be used through the throttle body to take a look at the injection runners. If it is just a smooth, rather small tube, then it is the original SCFI injection setup. If you see wires inside the plenum, then it is the upgraded MFI spider.

Further testing that requires some specialized equipment:

Cylinder compression & leak down tests will give insight into the health of the machanicals of the engine. All cylinders should be similar in the observed readings.

An injector pressure drop test can tell you if one or more of the injectors are misbehaving from a flow standpoint. These trucks are not the easiest to pulse the injectors on, but it can be done. You just have to be careful when hooking up the injector pulse tool to the terminals in the spider body on top of the intake manifold. Pulse the injector and observe the fuel pressure drop that occurs. All should be relatively close to each other.

Looking at the current draw on each of the injectors using an osciloscope with an amp clamp can be very telling as well. There will be a spike when the injector control is grounded, then a bump in the current drop off indicating that the pintle has moved before the current drops back to zero.

 

I think I’m going to replace the spider injector assembly next. Seems fairly easy to do and relatively inexpensive. The truck did sit for at least 3 years so I’m thinking a cracked or dry rotted injector line but what’s it gonna hurt to replace them. Fingers crossed.

 

Here is sonething to try before replacing the injector spider.

Examine the engine compartment at night with no lights to see if you can see any sparks jumping from the ignition wires to bits of metal.

If you see sparks, you need new wires.

This might be an unlikeky scenario, but it is quite easy to try.

 

swartlkk and Christine gave you excellent comprehensive advice. I will only add that I have had a number of vehicles sit for extended periods (years) and run like crap when first started up. Some had varnish for fuel that I had to pump out of the tank. In every case (for chevys) I put Chevron gas in the tank and ran the truck for 2-3 tank fulls and the engine smoothed right out and never needed new injectors. Be careful with the parts cannon, many replacements are inferior to present day after marker parts.

George

 

This has caused a no start, misfire codes and caused the failure of a new brand name fuel pump in just months in my personal experience. Also, I have seen squirrels chew through the air ducts quite a few times and even a plastic intake manifold once when I was a tech so a thorough check for vacuum leaks may be in order as well.