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-   -   1998 Z28 down on power (http://www.camaroz28.com/forums/ls1-based-engine-tech-19/1998-z28-down-power-880364/)

mrmint69 08-05-2014 01:40 PM

1998 Z28 down on power
 
Working on a 98 Z28 thats stock as far as I can tell. There are only 2 codes P137 and P157, that appear to be the rear O2 sensors. The car has 167,000 miles on the orignal engine and is starting to drop in power compared to a year or two ago. Even has a hick up once in a while while idling but not all the time. Can the codes cause the performane issues or are they only to monitor the cats? What would you do to check or test, replace of whatever?

mrmint69 08-10-2014 06:22 PM

Re: 1998 Z28 down on power
 
Did some searching and found almost everyone said the rear 02 sensors have no affect on the cars performance.

Injuneer 08-11-2014 02:05 PM

Re: 1998 Z28 down on power
 
The PCM does not take any actions that would affect engine power, when those codes set.

But, the 1998 factory manual indicates the codes could be the result of:
-lean injectors
-fuel contamination
-low fuel pressure
-vacuum or crankcase leaks

Those could affect engine power. I'm not sure why the lean condition wouldn't also show up in the pre-cat sensors, but this is what the manual shows.

Have you checked the fuel pressure? Are the long term fuel trims elevated?

mrmint69 08-17-2014 12:36 PM

Re: 1998 Z28 down on power
 
Quote:

Originally Posted by Injuneer (Post 6967002)
The PCM does not take any actions that would affect engine power, when those codes set.

But, the 1998 factory manual indicates the codes could be the result of:
-lean injectors
-fuel contamination
-low fuel pressure
-vacuum or crankcase leaks

Those could affect engine power. I'm not sure why the lean condition wouldn't also show up in the pre-cat sensors, but this is what the manual shows.

Have you checked the fuel pressure? Are the long term fuel trims elevated?

The car was parked for a year while he was in Afghanistan. So hoping fresh fuel and driving it will help. Will check fuel pressure also. Is it the same way as my LT1, with the schrader valve that can be hooked up to and ran up thru the cowl? so you can monitor while driving.

GaryDoug 08-17-2014 08:09 PM

Re: 1998 Z28 down on power
 
It's the same.

I think it's interesting to note that the manual also states that the pcm will set these codes when the car runs out of fuel.
Also, you might want to check to see if the O2 sensors have any extensions attached to fool the pcm into thinking the cats are ok. That might keep the outputs low.

akwa 08-27-2014 06:52 PM

Re: 1998 Z28 down on power
 
Ran fuel through it and it definitely helped a lot but still has a hic up while idling and at triple digits I smelt rotten eggs. I have a cutout so would that keep the cat codes from tripping? I'm going ahead and trying to replace the cats, I want to find some good high flow ones but don't need to pass emissions so I was also thinking just long tube headers and straight pipe with no cats?

I figured cats wouldn't give it a hic up at idle, only higher rpms? For new injectors what would you recommend? Its up there in mileage and I havn't been kind to her on the street. I did the basics (plugs, wires, intake, cleaned maf, etc) What would be some other maintenance needed at this point in the game? fuel filter, injectors, etc?

nikko 08-29-2014 12:23 PM

Re: 1998 Z28 down on power
 
How do you clean a MAF ::think::)

Injuneer 08-29-2014 02:45 PM

Re: 1998 Z28 down on power
 
Quote:

Originally Posted by nikko (Post 6967704)
How do you clean a MAF ::think::)

http://contentinfo.autozone.com/znet...05110/image/4/

.

Suprabuilder 09-08-2014 08:22 AM

Re: 1998 Z28 down on power
 
Down on power.....
Post 02 code.....
GM 100k mile cats......

When cats break down they plug and the car wont go anywhere plus set codes.


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