M-Z28

iTrader: (1)

Guys,

Need help on resolving power loss issues on a 1998 Z28. Currently 63000 miles on the car running slp lid, K&N air filter other than that all stock. It has had multiple codes from all 02 sensor lean, P0420 Catalyst System Efficiency Below Threshold bank 1.
This all comes and goes depending on how I drive the car. At 4500-5000rpm never fails sevice engine soon light pops up, but is now starting to come on more frequently and there is a hesitation throughout rpm. Also hard starts and GAS hog
Suggestions?? I would like to give detailed report back of my findings to help others...

99Bluz28

iTrader: (35)

1# Did this start suddenly, or has slowly gotten worse over time? If it started suddenly did you just start getting fuel from a different gas station?
2# Have you cleaned the MAFS yet with spray MAFS cleaner, if not start there.
3# Check the fuel pressure at the schrader valve outlet on the GM factory fuel rail, if your not getting right about 55psi or higher then replace the fuel filter. IF the fuel pressure is still low then it's very likely a bad fuel pump.
4# Check the condition of the spark plugs, and make note of their condition at all cylinders(for future reference), and if they're original sparkplugs, fouled,or damaged, replace them.
5# Now if you're still getting the same O2 sensor codes, replace the front O2 sensors.

IMO, these seem like the most possible cause/s for those issues, there could be others, just less common. The most likely to me seem like a dirty(k&n oil) or damaged MAFS, and/or fuel supply issue like a clogged fuel filter.

wssix99

iTrader: (5)

Here's a problem and, as mentioned above, the place to start. That oiled air filter will get you every time....

The oil will shed off the filter and coat the MAF in goo so it can't tell how much air is going in to the engine in certain situations. When this happens, it throws off your emissions and performance.

M-Z28

iTrader: (1)

Thanks for the responses:

I bought the car 2 months ago... Sluggish at first a little c-foam threatment and the car come to life, ran strong but still felt like there was power loss and back to the opening thread. So this what I have done so far before the thead was started.
New fuel filter
cleaned MAF with electiCal cleaner
recharged the K&N dried 100 miles later recleaned the MAF
added SLP lid
No performance changes to the car still getting worse as noted .....

Today I will check
Fuel Presure- if good will move on
Plugs &wires
reclean MAF with MAF cleaner

Thanks,

N20zuki

Do you have stock manifolds and cats? I had a 02 T/A years ago that I had to have the catalytic converter replaced on one side bc it was having these issues that you describe at only 57,000 miles

M-Z28

iTrader: (1)

Yes I have stock manifolds and cats....Looking to do full bolt on soon.. I'm sure a tune up is needed but I'm concerned of the power loss (running lean) at high rpm. I haven't ruled a bad cat out yet, but do fell like it's fuel or electrical at the moment

patSS/00

iTrader: (6)

There's a TSB from way back about the possibility of defective cats. This was not just fbodys, also other GM cars from the same period - it happened to my 01 Grand Prix. With the codes you're getting, and power loss, that seems most likely.

RPM WS6

iTrader: (3)

P0420/P0430 doesn't indicate a clogged cat specifically, just one that has a reduced oxygen storage capacity (not reduced flow), hence increased emissions. You would get this same code if you removed the cats entirely and never tuned for it. Generally what happens with these, and the reason for the GM TSB/warranty extension (FYI...this was only for 2000+ F-body, with the redesigned manifolds and cats), is that coatings wear off the substrate and the cats are no longer able to "scrub" the exhaust. At that point the cat(s) then become just a pass-thru that serve no purpose and the car would fail a sniffer test. One of mine had this code for years and it never caused a single driveability issue, I didn't worry about it because I didn't have to take a sniffer.

Having said that, there are things that can happen to cause a clogged cat though, such as overheated/melted substrate (due to misfires, too much fuel, excessive oil burning, etc.) or physical damage to the cat (such as impact) that can break up portions of the substrate and cause it to become lodged in such a way that blocks flow.

I would not first suspect a clogged cat though, based on what is known so far. I would re-clean the MAF but not with the spray cleaner. If it's gumed up with K&N oil, it will never get fully clean with just the spray. I prefer using Q-tips and rubbing alcohol, just be careful to not apply any real pressure to the wires, as you don't want to bend/break them. I simply allow the Q-tip to glide along the surface of the wires with almost zero pressure. This works great and will NOT cause damage if done properly.

If the above doesn't help I would next check fuel pressure and fuel trims (on each bank - requires an OBD scanner) before any other diagnostics are done.

wssix99

iTrader: (5)

It definitely sounds here like your oil shed of the filter, which would get on the MAF again. IMO - the marketing for these filters is all a bunch of hype. Obeying the laws of physics, the passages in these filters must be larger - which lets in more dust.

We would be happy to welcome you back in to the paper air filter club!


There's also the 'ol banana-in-the-tailpipe thing.

I also herd about another thing with a gerbil wrapped up in duct tape, but that was probably on a different website... But I digress;


^ I also had to use this procedure to clean mine after my first (and last) K&N experience. I second the caution regarding how fragile those elements are. It takes time and a steady hand. I found a magnifying lupe also helped a ton. Under magnification, you can see the black deposits on the silver element:

http://www.adorama.com/images/300x300/pk1964.jpg

M-Z28

iTrader: (1)

Okay,

#1)Fuel pressure checked out ok right at 58 lbs with very little change..
#2)Cleaned the MAF with q-tips and acohol.. and WoW!!!!!!! The power plant was back..Drove it around for a little while and man it was pulling good no issues. Stopped by Orieliys and they removed all codes. Hesitation was gone car was pulling good..... 15 miles later and bam there it was service engine light back on. Car went back went back to struggling in the 3500 rpm and up during acceleration

Man I thought I was in the clear..

What do you guys think???? Defective MAF

RPM WS6

iTrader: (3)

Is the K&N filter still in the air box? If it's over-oiled then it might simply be re-fouling the MAF shortly after every time you get it clean.

If a proper MAF cleaning made that much of a difference for 15 miles, then you can definitely rule out an exhaust blockage.

I'd get a paper filter and then clean the MAF again with the Q-tips, see how that goes. If you already swapped to a paper filter before the last MAF cleaning, then you might want to try unplugging the MAF and driving it like that (would default to SD mode), see if the 3500rpm+ issues are made better before actually buying a new MAF.

HUMBL57

Any chance you have a vacuum leak somewhere?

M-Z28

iTrader: (1)

Back to the paper air filter for me and recleaning of the MAF

I will let you know what happens.. I believe we are on the right track.....

M-Z28

iTrader: (1)

I have searched but have not found any thing. ....

M-Z28

iTrader: (1)

Failed to mention the hard starts got better after the MAF cleaning took place!!

M-Z28

iTrader: (1)

Need your opinion....leave the honeycomb on or off the MAF? ????

RPM WS6

iTrader: (3)

There is some debate about this; whether or not it helps, hurts or does nothing at all. Personally I always leave them on.

M-Z28

iTrader: (1)

OK cleaned MAF and went to paper filter---- No changes still running sluggish at high rpm. Had codes pulled and the rusults were
P0131
P0151
Both front o2's

Just for kicks un-plugged the MAF the took it down the road, it is definitely working..

???????
What's next
plugs & wires
new front o2's

blackbirdls1

iTrader: (5)

You prob might need new 02's

M-Z28

iTrader: (1)

Just purchased :
Acdelco plug wires and upstream o2's
Nkg tr55 plugs

I will try to install this afternoon. Remember stck manifolds any tips on install would be helpful