98 idling ruff

[in10mid8r]

I am having a problem with my 98 k1500 (5.7). It will start to idle ruff and smooth out ; ruff again, and so on. It seems to hesitate when I hit the gas while drive but if I put it to the floor, it will take off. I have replaced fuel pump, convertors, o2's, put a tune up on it last summer. I have pulled the plugs and they seem to be burning good. Put a scanner on it and I get random misfires on cly 6&8. Checked wires and they're good. My friend told me that the front o2's are reading a little low.

Can anyone help?

Jeff

[95Sierra2500]

If you're scanning w/something that can read actual data and not just misfires (like fuel pressure, etc.) you might get more information.

 

I'd recommend checking your dist. cap and rotor. That style tends to wear out and cause misfires.

 

Where did you buy the cats at to replace your old ones? Where the old ones bad?

 

You may also have a problem w/the poppet nozzles after your fuel injectors.

[in10mid8r]

The exhaust is a walker system. My friend is using a snap-on scanning tool. I changed the rotor and cap but there is no difference in the idling. Could you help me to tell him what really to look for. Gas pressure? O2's?

Thanks

[ChevyTech007]

Have you changed the fuel filter? Also, when you say the o2's are reading low, how low?

[in10mid8r]

I changed the fuel filter when I changed the fuel pump. My friend said they were dropping below 100 mv but I not real sure how far down they were going.

[ChevyTech007]

I would say you have injectors clogged. Have them cleaned by a dealer and go from there.

[in10mid8r]

Thanks for all the help. My mechanic spent an hour on the scanner and reading material and told me that he was pretty sure it was a bad o2. Guess what? New o2's go bad. Put new upstream o2's in and my problem was fixed.

[zthatzmanz28]

Thanks for all the help. My mechanic spent an hour on the scanner and reading material and told me that he was pretty sure it was a bad o2. Guess what? New o2's go bad. Put new upstream o2's in and my problem was fixed. 

 

<{POST_SNAPBACK}>

 

 

 

Seems to be a lot of this rough idle going around...We have a 1995 Silverado with 5.7 automatic that is doing the same thing...

 

We also did all the afore mentioned changes and replacements..

 

Our question is what is an upstream o2? is that a position for an o2?

 

Quite frankly we are some what stressed by this situation as it has spent much time and $$ in the dealership trying to identify the source.

 

We did flip the air cleaner cover over one day and it ran great for about 7 hours. It also seems to be worse when it is raining??