99 silverado - got my codes - what next?

99 4.8L silverado 180Kmi

Started late shifting into 2nd the other day. Not even a hard shift, just rpms go higher than usual and you almost have to wait on it or ease off the gas and it drops into 2nd. Drives fine otherwise. After reviewing this forum I decided to get my codes, expecting to see the infamous P1870 tanny slipping code. Got my codes from Autozone, they are as follows:

P0102 - MAF sensor circuit, low input P0171 - Feul Trim system lean @ upstream o2 sensor (left cylinder bank) P0174 - Feul Trim system lean @ upstream o2 sensor (right cylinder bank) P0420 - Oxygen storage ability of catalyst (left cyinder bank) below calibrated threshold (4.8L, 5.3L or 6.0L V8)

Okay, I somewhat understand what is going on here, but was hoping for more direct input from you guys.

it seams I should first check MAF for cleanlyness? (I do have the K&N FIPK) How can I go about checking it for functionality? Make sure it's clean and what about voltage thru it?

Are the "upstream" o2 sensors the pre-converters or post-converters?

What should I do first/ next? At roughly 50 bucks each on th o2 sensors, I'd kinda like to get it right the first time as to which to replace or if they need it at all.

Could this just be a vacume issue or faulty gasket?

Any help would me much appreciated.

Reply to
Dru
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Any ideas out there?

I'm thinking of a vacuum gage to check for leaks before replacing o2 sensors......?

Reply to
Dru

"Dru" wrote in news:1170173991.130133.98840 @s48g2000cws.googlegroups.com:

changing i wouldnt be throwing sensors in/could be a vac leak even tho that eng design isnt pron to it, i squirt water out of shampoo bottle aroung suspect areas to see and hear vac leaks/volts thru MAF is a tricky measurement, again make sure its constantly changing/ i assume you have done the first steps, fuel filter, check pres. at test port? reason to ask = fuel trim lean both banks............how does it drive?

Reply to
KjunRaven

Oil from the K&N filters will mess up the MAF sensor.

Whitelightning

Reply to
Whitelightning

Sorry for the late reply, we were snowed in the last day or so, but thank you for replying!

Ran a vacuum check the other night and seemed okay. Had a better OBD reader at that shop (father in law's friend runs a big rig mech. shop.). Same codes as above showed. We then ran up and down the road with this OBD tester going and it showed 1 2 silenoid (sp?) shutting off just before the shift into 2nd, even the 2 3 was shutting off at this time, but both were "on" until the point of shift change. Seems that this was causing the late shift? 1 2 shift time was reading from .

10 to .35 depending on how I ran the throttle. (I can let off the accel just as it hits 3000rpms and it drops into 2nd easier than if I keep a constant accel going. I picked up a new voltmeter yesterday and ran some checks as mentioned in my Chilton's book. MAF seemed fine, was tricky as you mentioned, but appeared okay. Read I should check resistance @ fuel injection electrical clips. Book says should be from 11.4 ohms to 12.6 ohms. All of mine read from 13.5 up to 14.5 or so. Averaging 14 ohms, but were all roughly the same ohms. How would a high ohm reading effect fuel injection, or would it? Didn't get a chance to test o2 sensors, will do that tonight.

Other than the late shift change, it still drives great. Even with the late shift change it is a smooth one, not jerky or clunky.

Fuel filter was replace just about 2 months ago, but need to check fuel pressure I guess. Gotta get that gauge from the shop. Is that a tough check?

Any other advice? Again, I appreciate your time with this. I gotta get this thing running a little better for the pregnant wife and 2 year old. We only have the one vehicle for now.....thanks

Andru

Reply to
Dru

No offense, but K&N claim the'y've done extensive testing to clear this myth.

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Like I said, I mean no offense. I actually would think the same. Reguardless, I've checked cleanlyness and all seems fine, I never over oil my filter and always follow instructions on this thing.

Reply to
Dru

BUT of course K$N would say that. It's not a myth. And their filters don't catch dirt either. No benefit to using them. In fact , they're a detriment.

Reply to
Steve Barker

Thanks for your help Steve.

Steve Barker wrote:

Reply to
Dru

I just hate to see people burn needless dollars AND ruin their engines at the same time.

So, you're welcome

Reply to
Steve Barker

Any advice on where to go with this now? I've had the FIPK on the truck for the last 85,000 miles or so. I'm not trying to be an arse, just wanted to focus on issue at hand.

Steve Barker wrote:

Reply to
Dru

Have you actually tried cleaning the MAF sensor and test driving after?

Reply to
aarcuda69062

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