Power Loss Question

I have a 1998 Chevrolet K-1500 truck with 125,000 miles. I have been experiencing power loss for the past year or so. Most days my truck drives like it is somewhat bogged down and has trouble gaining speed on the highway. Yet on probably two to five days out of the week my truck runs like it was brand new with the power and accelertion it should have. What is causing this very noticable difference in performance?

Could it be the ECM Computer? If not, what experiences have you had?
Please help, I am tired of throwing money into this truck for no results...

Do you keep up with routine maintenance? Do you allow the vehicle to warm up for a good 3 to 5 minutes before driving it?

Most power loss problems are caused by
1. clogged fuel filter or weak fuel pump= LOW FUEL pressure.
2. With your mileage you also might look at the cat starting to clogg and causing a ehaust flow problem and that would cause a lack of power.

Hey Fireplug, how do you check yout cat other than wait for rotten egg smell???

I do keep up with routine maintenance. I have replaced: the fuel filter, fuel pump, spark plugs, wires, distributer cap, dist. rotor, ignition coil, ext. And yes, I also do let my truck warm up before I drive it for a couple of minutes.

How do I know if my cats are getting clogged? Should I unbolt the assembly and look at them? And could this be the case in that some days my truck is boggy feeling and other days it runs like new?

Well the very first thing I would do if I was you is to check and see if anything is loose inside the cat.
To do this just smack it (not to hard) with a rubber hammer or something like that and see if there is a rattle sound from inside the cat. If there is then the insides are coming apart and could cause a clogg 1 day and be open and free flowing the next.
I have seen a lot of cats come apart and not only destroy its self but also fill the muffler with crap also.
The other way would to loosen the cat from the front pipe and drive it and see if you still have a power loss BUT it will be very loud and the exhaust fumes getting into the cab is not good. Also the Cops dont like that to much also.
I would say unless you have a GOOD vacuum gauge and know a lot about engine vacuum and how to read it the correct way. I would say take it to a GOOD muffler shop and tell them about your power loss and do they and could they do a cat check.

Do you think that I can rule out the ECM Computer?

Thanks, Fireplug, for your advice. I appreciate it and I will keep you posted on how the cat. conv. check checks out. Thanks again.

For that year i am surethat there are prom updates that can be downloaded into the pcm. That has to be done at the Dealer. As far as the pcm being junk i would not thing so. Most pcm problem dont act the way your truck is.
You are welcome

Ever changed the oxygen sensor?

An oxygen sensor can be worn enough to make an engine run poorly, but may not always throw codes and make the 'service engine' light come on.

The o2 would not cause a lack of power 1 day and then run good the next day.
This forum puts way to much on the 02 sensor.
Sure over time they go bad but most times they go bad because some other part went bad first and took out the o2s with it, say like a bad map or bad injector causing a rich running system so the o2 code is set and everyone runs out and buys a new o2 Why , fix the upstream problem first before we fix the down stream problems

Fireplug is right. My truck is throwing a code and I took it to the dealership to test the O2 sensors, because my first instinct was that they were bad. However, after the diagnostics test, the mechanic said that I do have a faulty catalytic converter on bank two of my engine. I'm glad I did the diagnostics, because now I know what is causing this noticable and dramatic power loss to my truck.
I will keep ya'll posted on how the repair goes and to see if the power is restored.

Another question for ya'll. The mechanic said that the reason my cats are clogged is due to two reasons. 1.) Using fuel injector and system cleaners push all engine residue into the cats causing them to clog, and 2.) Because of collant leaking into my system is causing the insides of my cats to deteriorate, (I got this problem fixed.) This was from a torn intake gasket. Can years of using fuel and engine cleaners cause your cats to clog???

That is a very good question.
The coolant leak I would say yes but as per the injection cleaner I really dont know about that 1.
When antifreeze burns it leaves an oil film on what ever it comes in contact with and that would cause a cat to over heat in spots but the cleaner i am not to sure about.
Very good question!!

With a cloged cat keep a eye on you coolant levels. Why ? Because exhaust backpressure can and will cause a headgasket to blow( the pressure has to go someware) and burn exhaust valve(heat cant get out of the cylinder)

Thanks again Fireplug. I really appreciate it.

Another testimony regarding "the bad O2 sensor theory":

Just before the new year my sisters Blazer had a SES code pointing to one of the O2 sensors. Like many peop;e that visit this site, I automatically thought "replace it!" Well, got it inspected and shortly after 2 more codes pop up leading to 2 different O2 sensors. This vehicle has a total of 4 and since 1 has already been replaced and 2 others come up, I figured get 3 and be done with it since it wouldn't be long until that code popped up.
After putting a little thought into what exactly an O2 sensor is and what it actually does, I started to wonder if replacing these O2 sensors would actually fix everything or is there another cause.
I started a thread in the Blazer setion on this site asking ?'s before installing these O2 sensors. Why pay $180 on something that won't fix the real problem.? While some replys helped confirme my theory and others offered me real good advise, I decided it was worth looking at my sisters Blazer a little closer. I spent $6 to $8 on Berrymans B-12 to clean the air intake, MAS, EGR, PCV, throttle body lookin thing on fuel inection, etc. Also rexharged her K&N while I was at it, and reset the computer, 2wks later, I returned the 3 O2 sensors seeing as how SES light has not come on. No codes.

Moral of story, "If it ain't broke, don't fix it"

Rather find out why your O2 sensor will not communicate w/ECM.

Think about this, why would auto manufacturers keep using O2 sensors that are known to go bad, and use more of them at that? Throughout the years certainly there has been some R & D on these things. With how competitive the auto industry is, I imagine one of these manufacturers would have came up with an O2 sensor that will last or even an altenative to the so-called problem. What makes me think that? If a company can build a reputation on not having some common problems regarding regular maintenance, they would most likely gain more buyers, right?

Anyways, don't replace your O2 sensor, figure out what the real problem is first. I saved $189 by doing so. Would of been $225 had I done this prior to the first O2 sensor