I have been having issues with my '94 Silverado SWB 1500 5.0 TBI V8 for some time now. The truck has 103,000 miles on it and seemed to start having problems as soon as it rolled 100,000 miles (ironic huh?). I have thrown over $500 at it and haven't resolved a thing. Any help would be appreciated.
What it's doing/not doing...
The truck runs TERRIBLE when cold. It constantly loads up as if it's dropping to 4 cylinders. The truck is dumping fuel (smell) and appears to be running rich (smell). As it warms up it seems to run a bit better but still loads up on take-off and when maintaining a moderate speed. On start up the truck will idle high then drop off, load up and die.
Just to mention, I was having a problem with the truck idling high and shifting hard but it was resolved with replacing the Throttle Position Sensor.
What I have done so far...During the beginning of all of this I removed a clogged Catylic Converter and did not replace (yeah I know you shouldn't do this but I'm troubleshooting at this point). Being that the there is only 1 O2 sensor before the Catylic Converter I didn't think this would be an issue. Incidentally the truck ran great for about a week after doing this. BTW - I'm still running stock/original exhaust.
Over a period of a couple of months here is what I have replaced...Cap/rotor, plugs, both injectors, Injector wiring and clips, thoroughly clean Throttle body, checked/replaced as needed vacuum lines, Replaced complete Throttle Body with known good, replaced TPS, Map Sensor, ECU (twice with new), EGR Solenoid, EGR Actuates fine manually, Temp Sensor, Air/Idle Control Sensor, Spark Control Module, Fuel Filter, Pressure tested Fuel Pump (good), O2 Sensor and Intake gaskets.
Through all of this the truck has not thrown a single code other than the ones I forced when changing out various sensors.
I have bounced this around to all to my Old School Hotrod buddies but the problem is they are all old school as am I. ECUs and TBI are greek to me and I'm about to the point to throw my hands up and install a manifold and carb on it. Looking for a new brain to pick! Any suggestions?!

 

Looks like I can't get any love for my '94 Silverado here! Not a single reply.

 

You've defiantly tried. I ain't got a clue. Sorry I can't help.

 

If you're going to keep the truck, put a cat on it. I don't know that I would go buy a new one from the dealer, though. I might try one from a wrecker first. They are made better these days than the first ones that got such a bad reputation 25-30 years ago. Why did yours clog up? Usually these days they don't clog, but if they get hit hard (lowered car over a speed bump, for example) this breaks the innards which collapse and make a clog. A faulty O2 sensor will make it run rich. The O2 sensor is also sensitive to EGT and yours may be enough cooler now without the cat in front of it to make a difference.

Now, having said all that, I have read here MANY times that it is very common for the fuel pressure regulator to fail. I'd say that may well be your main issue, but I expect the missing cat is also contributing.

I'm old school like you, but have picked some knowledge up through experience and always trying to understand the systems requiring repair so I can figure out how to prevent the same repair in the future.

There are some real mechanics here who will hopefully comment.

 

Thanks for the replies. I keep going back to the cat but I have buddies with the same year model running around with dual exhaust with O2 sensor and no cat and they have no problems at all. I don't understand it.
I have found the Y-Pipe with Cat for about $190 w/shipping. I plan on replacing everything from the Exhaust Manifolds to the muffler.

The one thing I haven't done that I just realized is...Dropping the muffler altogether just for S**Ts and Giggles. There is a possibility that I may have a clogged muffler. Can you believe my 9 year old son brought this to my attention?! In my frustration I totally overlooked this. Will let you guys know. Thanks again!

 

Hey there. I am having a similar problem with my sons 1991. What did you finally figure out?

 

[B] i've got a 94 Chevy also And I am having the same problems .

 

I have the exact same problem, 1994 1500 5.7 running very rich when cold engine, when it warms up it it runs better, no codes, did you fix yours?? regards Steve

 

I have same problem on a 1994, did you get yours fixed??

 

I have the same problem, very rich when cold, black plugs, did you figure the problem out??