I got 154k on my 95 blazer (auto/4x4). I just changed the tranny fluid/filter 3 weeks ago. Since last night, I noticed that around 50-55 mph, the rpms would kinda jump in the 2000-2500 range as though it wasn't applying power properly. if I let off the gas and then reapply softly, it kinda smooths out and lets me keep cruising. The motor feels fine and sounds good and smooth so I thought this was a tranny issue.
I thought it might just be an overdrive issue, but the same thing happens in drive (3rd). Since this happens in more than one gear, I thought it might be the torque convertor, or perhaps I need to add more fluid...I checked the level on the dipstick and it seems ok.
Last year (Feb04) when I was handed the blazer, the tranny shifted roughly, so I changed the fluid/filter and it has been fine ever since. There was a difference in what I did in that fluid change and this recent change.
Last time I had a whole night to let the tranny drain (I ended up cutting the Y pipe so I could just remove the section of header to get the pan/filter out - then got that clamped up by an exhaust shop for 'easy' access next time). Because it drained so long I added at least 4.5 quarts. This time I did not have time to drain overnight and therefore I only added 4 quarts and it has been showing full. I wonder if perhaps I should just add an extra half quart and see how that goes....or perhaps the tq. converter is dying....not sure....
I talked to a couple guys in the shop here at work - they both immediately suggested fuel filter - I replaced it - same problem.
I changed the spark plugs. Still have the same problem.
If there was a vacuum leak, wouldn't I notice other symptoms like weak brakes and bad idle?
What else should I check?
I checked the u-joints and they looked ok.
Could this be a fuel pressure regulator issue? check this out, could this be the culprit:
fuel pressure regulator replacement
someone suggested to me that perhaps the throttle is sticking, and that I should remove the intake hose and drench the throttle body with carb cleaner and wipe it all up and continue to drench the intake manifold runners with the throttle open and then try to fire it up (expecting lots of black smoke via the exhaust) and then problem should go away...however that sounds a little sketchy to me....
Someone suggested looking into error code po1870 but that's not it. Finally took it to Chevy. the technician and i went for 2 drives. of course, i couldn't readily replicate the problem as much in front of him. I got it to jerk a little and so we went back and hooked up the diagnostic scanner and went for another drive. The tranny is code free. In fact the motor is code free too. He seems to think the tranny is fine but the motor might have a miss somewhere. I will change the spark plug wires and add a little tranny fluid and call it a day. (i checked with the motor running and the fluid did seem a little low)
I forgot to mention that after 2 rides with the chevy technician, and all things looking good, I drop him off, pay the $80 diagnostic fee and leave. As soon as I turn the corner, it starts acting up really bad.
I noticed this: It did not start happenening until the car had been driven (warmed up) and turn on/off several times within an hour. So it seems to be temperature related too. The technician says it is code free, but the behavior may be ignition related.
I'll change the plug wires tonight. What else in the ignition system can I troublshoot/replace?