Hey all, been lurking here for a while and finally decided to post as I have a few problems.

I have a 1999 silverado LT 5.3L V8 292,000kms

The engine light came on the other day and I had a friend check it out with his scanner. There were multiple codes and I'm not quite sure what to do.

I got P0300 Random cylinder misfire (I'm thinking new plugs and wires)
P0404 EGR flow CKT range/perf
P0405 EGR flow sensor A circuit low input ( I don't know what to do about this one...............)

and then I got P0420 catalyst efficiency below threshold ( I"m thinking that this might be from the new magna flow exhaust I just put on 2 days ago)

I have no problems with my truck at all, it may be a little slugish some times but that's about it.

If anyone has any info on how to go about remedying these problems please let me know what to do.

Thanks, Derek!

 

On the random misfire. When was the last time you did a tune up. If you're going to replace the sparks and plug wires you might as well get a new cap and rotor as well. I did all that of mine with Nascar brand plug wires and cap and rotor with AC Delco sparks for 85. I'm sure you knew. Just thought I'd put in the input I can.

 

I use all acdelco on my tuneups i tried other stuff and it was junk. About the egr put a vaccum pump on the egr while it is running, aply vaccum if it bbogs down the egr valve is good if it doesent the egr is bad. I just replaced my egr valve solenoid since its like 10 bucks. Also check vaccum lines going to EGR valve

 

sounds like all the problems are stemming from the EGR. Take it to your local shop to have it properly diagnosed. You neem a scan tool in order to pin-point the problem. Most likely it will be the EGR itself, but could be wiring or the ECM

 

Could anyone show/tell me where the EGR is on the truck? I don't have a hanes manual yet.

 

hey shawnvw look at my post if you would thanks

 

If the EGR valve is stuck open at all it will cause a PO300 random misfire. Your truck probably does not have any vacuum lines to the valve, it should be all electronic. It should be a cylinder looking thing about 3-4" tall. The body of it should be black and the base silver. On the top it will have a flat connector with I believe 4 wires. It is held on by 2 13mm bolts.Remove the valve the smaller hole should have what is called a pintle in it that moves up and down if the pintle is jammed up buy a piece of carbon this will cause your PO300 and Egr codes. If you buddies scan tool has the ablitly to command the valve open, use it to slowly open the valve mine commands 10% at a time. The pintle should move up smoothly and stay in the commanded position if it does not the valve is bad. If it flutters while moving it is bad. As far as the PO420 is the converter still on the truck or did you remove it when installing the magna flow system?

 

Thanks for all the info MDTAHOE!! I still have the converter on my truck all I did was replace the muffler nothing else.

About the pintle, I'm assuming I can replace that as well? Does it just pop out?

 

The pintle is part of the valve. If it does not move properly then you have to replace the EGR valve.

 

Just called part source for the EGR valve and it's over $200!!!!!