Hey guys! I'm a long time reader, but first time poster. lol. Anyways, I'm having running problems with the '94 S10 Blazer seen in my sig pic. It has the 4.3, W code engine. Here's the beast:



Anyways, my problems started out of nowhere. This truck is my wife's daily driver, and one day she complained of it 'bucking' and losing power between 45 and 55mph. It had been running well, so I took it for a test drive and sure enough, it seemed to be down on power. It has also been getting terrible fuel mileage.

The other day, I changed the fuel filter, but the problem only got worse. I'm assuming that the fuel filter was partially-blocked, and now that the fresh one is in place, the problem has come out into the open.

About the Blazer:
-198K miles
-Mostly original
-New O2 sensor
-New fuel filter
-Gutted cat
-New header gaskets and donut gaskets

New parts (related to the engine) within the last 15K miles:
-Plugs, wires, cap, ignition coil, rotor button, igntion module (distributor pickup is NOT new. IDK how long its been on there)
-Engine and gauge temp sensors
-Fuel pump
-Air filter

After reading around here, I'm starting to suspect that the injector spider is going bad. The truck will still start and run, but it acts very cold-natured. It will stall out when cold. It also idles roughly. The whole engine shakes as if one or two cylinders aren't firing at all. When I get on the throttle, the engine bogs down and won't 'clean out', no matter how fast I try to go. (I smell raw gas coming from the exhaust). Its as if somebody has left a choke on.

I'm a mechanic and not a 'parts replacer' so I'd like to have a pretty good idea of what may be going on before I replace something that isn't supposed to fail or wear out with age and mileage. After taking care of the normal wear stuff, that didn't solve the problem, so I need help! Oh, and the 'check engine' and 'check gauges' lights do not come on while its running, except as they should when you first start the engine. Is there a sensor (besides the O2 sensor I just replaced) which could have failed and is causing the rough running? Or is it time to start checking fuel pressure and the injector spider for leaks? Or am I dealing with something else altogether here? (such as a bad ground somewhere?)

Sorry for such a long post. I'm just trying to be detailed. Thanks for any input!

 

Congratulations! You've discovered the joys of Central Multiport Fuel Injection. Most likely one of three things have failed inside your intake manifold: nut kit (the fuel lines that go to and from the spider injector), the fuel pressure regulator, or the injectors themselves. There are multiple posts about how to do proper diagnosis of your system and find exactly where the leak is. This is a very common problem on our beloved trucks.

If it were myself and I had a Vortec with almost 200k on the clock I would open up the intake manifold and replace everything. I would put on a new spider (including the fuel pressure regulator) and nut kit. With that many miles on it you'll want to replace everything because if everything is original it's only a matter of time before all of the components fail.

Others will no doubt have more input into your situation. There are a lot of brilliant mechanics around here.

 

Well good we dont have to explain the basics to you.

1. Check fuel pressure including leakdown rate

2. Pull codes

Only way I can see a new filter making it worse is drastic leak in spider or pressure regulator.
Open oil fill cap and sniff.
I'd read the plugs and see how bad things are. Are some showing lean, some rich, all rich.. etc

Your ECT resistance Should reflect temps..

Any other questions.. read up in the DIY section first. Gives you a head start

 

Thanks for the input, guys! I'll pull codes, check the plugs and fuel pressure/leakdown rate, and report back. Though it looks like its about time to take apart the intake and change out an injector spider. Awesome. Hopefully, if that is indeed the problem, fixing it will get another 200K out of this engine!