RE AND CHERYL

iTrader: (31)

I'm working on a friends 02 silverado we recently put a new motor in. First it was running fine but experienced extreme spark knock under WOT(the old motor did this too), tried switching to super but it made no difference, no SES except for 0300 for a random misfire.

Now it is running like crap and barely makes 30mph, it misses continously and has the above codes. Fuel pressure is fine and I do not think it is the MAF because there is no change when the MAF is unplugged.

Please Help

Re'

RE AND CHERYL

iTrader: (31)

p0101 is a MAF signal out of range and p0300 is a multiple cylinder misfire for those who do not recognize them

Re'

flame

iTrader: (13)

Plugged cat would be my first guess. See if your scanner can bring up miss history. If all the misfires are on one bank i.e. cyls 1,3,5,7 then your left cat is plugged 2,4,6,8 right cat

jimmyblue

iTrader: (11)

If the MAF unplugged changes nothing, that's not a good
MAF situation.

Check the ENG SEN fuse? If you have a scan tool, see if
the MAF is showing any frequency at all?

RE AND CHERYL

iTrader: (31)

I only let it run for a few seconds with the MAF unpluged to see if it changed anything, a GM tech on another site said it would point more to the clogged cat if it didn't change with it unpluged.

My scanner has a live scan feature but does not display cylinder misfire. What I did notice though was that bank one showed a long term fuel correction of -1.6% and bank two was 20.3%, would that point to a clogged cat too?

Re'

pdsq98gt

Sounds just like a clogged cat or 2

flame

iTrader: (13)

What happened to the original motor that the motor was changed? That may help too.

RE AND CHERYL

iTrader: (31)

Well I dropped the y pipe and started the engine, It ran perfect. I installed another catted y pipe I had sitting around from another silverado I worked on. It runs perfect and the spark knock is even gone. I have seen cats go bad but never with these symptoms. Well...gotta get a new catted y pipe now (the one I installed has bad cats because a blown head gasket dumped a LOT of water through them).

Thanx for the help guys.

The extreme spark knock trashed the bottom end.

Re'