GM Vehicle Help

98 GMC 4wd K1500 with 5.7L

I've got a service engine light and a low end stumble. If I romp on the pedal and accelerate, no problems.

I borrowed a friend's code reader and got 3 store codes. The first I don't remember specifically what it was but the reader told me it was an EGR valve problem. The 2nd and 3rd stored codes were actually the same code - P1404. The reader told me that it was "manufacturer specific." Via a quick web search I found that it may also be EGR related. AFter clearing the codes, the only one that has come back at this point is P1404.

THough I do plan to get out within the next couple of days and pick up a new EGR valve - is there anything else that I should look at that could be causing these symptoms and error codes?

Where is the EGR valve anyway. On an exhaust manifold? Below the manifold on a pipe?

THanks for any help you can offer.

/Scott

Gottafish, the P1404 is an EGR position error code. A lot of times it is caused by the valve sticking open or closed. If it sticks open you will usually have a rough idle. Sounds more like yours is sticking closed if it has a stumble when taking off. The EGR valve is located at the front of the intake manifold under the throttle body right behind the water pump. It has a black plug going to it, and is mostly round on the top. Unbolt the EGR valve (2-10mm bolts hold it on), turn it over and look at it. There will be an open hole and a small pintle which has a torx screw head on it. Take a small screwdriver and push on the pintle. If it opens easily, it's not stuck. If it snaps open (you may here it pop) it was stuck. You can try to clean it with carb cleaner (spray through it and work it open and closed), if it continues to stick, you may have to replace it. If it is stuck open, you should see something in it (usually a small piece of carbon). Remove it and make sure it moves freely. If the carbon continues to get in it (carbon will build up in the intake and break loose sometimes) go to Lowe's over to the appliance repair parts, get one of those little screens that goes in the washing machine water hose. Cut the outer ring off of it and flatten the screen out. Then sandwich the screen between the gasket and the valve over the open hole, then bolt it back on. This will prevent future carbon boogers.

OK, you are right on track with the brake lights. The circuit runs throught the Multifunction (turn signal/hazard) switch and back to the lower brake lights. The high mount lamp runs straight from the brake switch. Yes, you do have to remove the airbag and steering wheel to change this part. You will also have to have a tool to compress the lock plate beneath the steering wheel. Wouldn't suggest trying this without the proper tools and never doing it before. Now, the rough idle could be a lot of things. If it feels like a missfire, check your plug wires, plugs, etc. If it just doesn't seem to idle as smooth as it once did, check for vacuum lines that may be off or cracked. Store bought fuel injector cleaner is a rip-off. There is nothing you can buy off the shelf that will do much good cleaning injectors. Most of it is designed to be used as preventative maintenance. It's not going to clean much out of the injectors if they already have a problem. Go to your local dealer and ask if they use BG products. This is a company that sells to dealers and independent garages. Their products are much better. Ask for 44K. It is a tank additive. It should run you about $18-$20 per can depending on how much the dealer marks it up. Their cost is about $13 per can. Add it to at least 10 gallons of gas or so. You can also try cleaning the throttle plate. If you remove the black rubber hose going to the trottle body and look inside it, you will see the plate. Use carb cleaner and a toothbrush or rag, open the plate by hand and clean both sides and the bore, especially the edges of the blade and where it closes in the bore. Another thing to keep an eye on with this engine is leaking intake manifold gaskets. Look on both ends of the engine at both cylinder heads. Look for lines along the head where coolant has been leaking and running down. If it's bad enough, you will see it puddled on top of the transmission bell housing. Don't put off having this fixed too long, the coolant will actually errode the alluminum heads and intake around the gasket sealing surface. Wait too long, and you buy expensiive parts. GM has redesigned the gaskets (make sure you use GM gaskets) and on the later ones, there are new bolts. Hope this helps you.