Sick Chevy-Catalytic Converter??

My wife bought me a new, well, used, 1993 Chevy 1500 350 several months ago. Ran great, but I noticed decrease in power, especially going up a grade--down to only 40-45mph in a 65. Otherwise, on the flat, went pretty good, but seemed to be working a little hard. I saw where muffler was rusted out and thought maybe back compression was culprit. Installed new muffler, but no real change in symptoms. Wants to die when I come to stop and hesitates when initially accelerating and likes to gurgle. Yesterday, pulling hill in town at low rpm, sounded like someone with hammer under the hood. Changed the PCV, but on my road test I couldn't get enough speed to pull a moderate grade and ended up at about 10mph--thought I might have to get out and help push! Fuel economy poor and oil pressure fluctuates. I sure would appreciate any comments or suggestions.

I should add that it seems to idle fine, even though it will sometimes stall with slight acceleration after a stop. But I do notice a delay after turning the key prior to ignition--it doesn't fire right up. Kind of emits a diesel sound. Probably not related, I don't know for sure

A back pressure test taken at the o2 port will tell you if the cat is bad also check fuel pressure.

You said "notice a delay after turning the key prior to ignition--it doesn't fire right up" You might check your ignition switch, I have a 95 4.3 had the same issue. Is it the stock 350? Motor may be bad. Same symptons here at 184,610 miles. I pulled the heads and the entire right bank was burned up. Good news is a rebuilt long block with same serial number is only about 900.00 It is worth the new motor. I am loving my truck right now. I put a 4.3 back in it, but it runs great. I did not have time to install a 5.7 at the time, I only had the weekend to pull the old and put the new in. By the way the new motor will make that new muffler sound great.

plainsdrifter,
Here is the diagnostics for "Lack of Power, Sluggish, or Spongy" from my 90 Factory Manual.

- Check air filter
- Make sure both injectors are firing. If only one fires, swap electrical connectors to see if the other starts to fire (injector vs wiring to injector)
- Check Fuel Filter and Fuel Pressure.
- Check ECM Grounds.
- EGR Operation. Make sure it is not stuck partially open.
- Alt Output. Should be 12-16 volts.
- Engine Valve Timing. Perform compression test. (I would also add a worn timing chain would be the what will cause valve timing issues)
- Check Camshaft (look for worn lobes).
- Check secondary ignition voltage. (Coil Output and voltage reaching the plugs)
- Check Torque Converter operation. If it is locked up, it can seem like the engine has no power.
- Check exhaust for restriction.

You can check the exhaust using a vacuum gauge.
1. Hook it up to a vacuum port and warm up the engine.
2. Run engine at 1000 RPM and note the reading.
3. Increase RPM to 2500 slowly. Note the reading at a steady 2500.
4. If the difference in pressure drops more than 3 inches at 2500 than at 1000. The exhaust should be checked for restriction.
5. Disconnect exhaust pipe for engine and repeat steps 3 and 4. If the reading is still 3 inches or more that in Step 2, check valve timing.

My gut feeling is that this is fuel related. Replace the filter and check the pressure. Check the fuel injectors, you might be only running on 1. Your pump could also be on the way out.

How does it run cold? A clogged cat sometimes will be ok cold but the truck will run worse when the cat gets hot and starts to clog.

Unfortuately, you need a special tool to read the fuel pressure (along with a fuel pressure gauge). If you on this page you will one http://www.mytoolstore.com/toolaid/diagn01.html #37650.

Good luck and keep us posted.

//2000CAYukon

Update...Chevy Still Not Well. I followed the advice of 2000CAYUKON to eliminate the catalytic converter as the source of trouble. Last night I warmed up truck, parked in the dark but no red glow from converter (also no backfire). Today I inspected the injector streams, which look fine and no drops, changed fuel filter. Also swapped out the spark plugs. Road test, though, had same problem--hesitant acceleration, dies occasionally at stops, no incline with clattering under hood.
Since I had no experience with injectors, just to make sure I was on the right track, I started my other 350 Chevy (that runs well) and looked at the stream. Streams appear identical on both vehicles.

However, I did notice that the sick Chevy sucking a lot more air than the other when idling with the air cleaner off. Plus, when I shut the engine down, there is a sh-sh-sh-sh-sh-t sound-where it apparently is still pulling in air. The good Chevy, on the other hand, shuts right down with no lingering air gasp.

I was hoping that this might help pinpoint the problem. It appears that it might be getting too much air?????? Any ideas?

Does the lack of power happend both when the engine is warm and when the engine is cold?

Although, the spray pattern looks good, fuel pressure is still important for the engine to run properly. Specs call for 9-13 PSI.

A compression check should be done to eliminate mechanical issues as a problem.

Have the wires been replaced? Pull the coil wire off and make sure it has good clean connections on both ends. Check the resistance with a ohm meter? It should be under 5K ohms.

Has the timing been checked? Should be zero with black/tan EST wire disconnected.

Last question, did this problem happen suddenly or over time? Did it ever run the same as the good truck?

//2000CAYukon

2000CAYukon,

Symptoms occur whether cold or warm. I do not think that it has ever had the power of the other Chevy and would say that the performance has steadily worsened since I got it.

I appreciate your suggestions and I'll check those items, too.

Any idea what causes the clattering under the hood when moving from a stop on a slight incline to pull a hill?

2000CAYukon,

Symptoms occur whether cold or warm. I do not think that it has ever had the power of the other Chevy and would say that the performance has steadily worsened since I got it.

I appreciate your suggestions and I'll check those items, too.

Any idea what causes the clattering under the hood when moving from a stop on a slight incline to pull a hill?

Has the fuel filter been replaced since you got it? How did the injector spray pattern look? It would be nice to know the fuel pressure to eliminate fuel as the problem.

As for the noise, might make sense to jack up the rear and see if you can isolate where the noise is coming from. Front of engine, bottom, top?

Is the check engine light on? Does it come on if you turn on the ignition but don't start the engine (just want to make sure it is not burned out).

If it is on, see if any codes are stored.

//2000CAYukon

Not to long ago after just getting my 1988 sierra 1500 i put fuel injector cleaner it.. but i put the hole bottle in with only a quarter tank of gass. yes vary stupid of me so i went to work and after making the tuck sit for awial i started it and every time i would reverse or drive it would stall .... just die when driving sloww. i thought one of the hoses were fucked or somthing i cleaned the fuel injectors by spraying them inder the hood but noo diff... but i found the problem the fuel filter was fucked so i changed that and fixed the problem so somtimes i could just be something alittle as that ...