1993 Chevy Truck

smjoe · Posted at Sat Nov 07, 2009 1:53 pm

Engine Performance problem
1993 Chevy Truck 6 cyl Two Wheel Drive Automatic

Ok so I really need some help figuring out why my truck runs the way it does. First of all when I start it up when its cold and let it idle for a few seconds without revving it, it will sound like the rpms will drop lower than the idling speed and shake violently and die out, other times it will drop to a really low rpm and shake and sputter and it will go back to the idling rpm.

When I take off from a stopped position with the rpms a little above idle it will seem to go good, but then down the road (without changing the rpms) it will completely lose power and will start to hesitate and skip. It seems like the further I press my pedal down, the longer it will skip. Sometimes it sounds like the engine was shut off for a few seconds and then started back up again. The pedal does have some hesitation, I will press it and a second or two later I hear the engine rev. This happens when I'm in gear driving, but doesnt happen while i'm idling in park. Theres a complete loss of power when I go up hills, I have to put the pedal down to the floor, full throttle, wait about 4 seconds of skipping and then I will start to gain some speed when going up hills.

I've replaced the distributor cap, spark plugs, spark plug wires, new converter, manifold, y-pipe (huge rusted holes in this, I thought it was interfering with the o2 sensor), and the whole exhaust system behind the converter. I checked my vacuums visually and there seems to be no leaks.
I wonder if a bad o2 sensor could cause this?

If you need any more information just ask me, I'm very confused and I really want to figure this out. I've also heard that chevy's timing chain goes at about 100k miles. My mileage is 82k
Any help I would greatly appreciate it.

mathiaso · Posted at Sun Nov 08, 2009 2:10 pm

hello smjoe

Do you have engine light on? that would be helpfull.
if there is, what is the code?
need code to diagnose the system at fault.
thanks

smjoe · Posted at Sun Nov 08, 2009 2:46 pm

hey mathiaso,

yes the engine light is on, and I forgot to mention that the scanner fails to retrieve the codes every time I try to use a scan tool on it. I've recently figured out that a stuck thermostat can send the ecm into an open loop preventing diagnostic scans to be completed. Also a shorted O2 sensor can prevent a scan to be completed, correct me if I'm wrong. I did try the trick with the paper clip and I got a code 14, I don't know what this means but code 12 flashed 3 times which is normal? Then a code 14 flashed 3 times and it repeats the process.

I've been doing some research and I figured out a clogged fuel filter could be contributing to much of the problem. Today I removed it and tried to blow through it and I couldn't. It was completely blocked. It is sunday and the auto shops are closed so I'm waiting until tomorrow to pick up a new filter. I tried to clean my current one just until I can pick up my new filter. I tried it out and the truck idles much more longer and smoother and when I rev it it seems to cycle through the rpms much smoother. Again correct me if I'm wrong about these things, I need all the help I can get. After I replace my o2 sensor and fuel filter tomorrow I'll test it out and tell you if the problem still exists.

mathiaso · Posted at Sun Nov 08, 2009 3:52 pm

To be precise with definition for flashing codes
I'm really going to need more informations:

write your engine informations in this format:
1993
3.1 L
TBI (VIN Z) engine.
does this correspond to your truck?

smjoe · Posted at Sun Nov 08, 2009 5:14 pm

1993
4.3l
TBI (Vin Z) Engine

its a V6 if that helps any.

mathiaso · Posted at Sun Nov 08, 2009 10:00 pm

yes ,code 12 flashed 3 times which is normal.
it is just diagnostic mode.
code 14 is the coolant sensor or circuit /high temperature indicated.

Causes:
A bad connection at the sensor
An open in the ground circuit between the sensor and the PCM
A short in the voltage feed between the sensor and the PCM
A bad temperature sensor (shorted internally)