'99 Yukon misfires and won't start

[ZippyCT]

Hello everyone,
I need some help here. I have a 1999 GMC Yukon SLT, 5.7 liter that is misfiring at speed causing the service engine soon light to come on. Also it occasionally will turn over and not start at all. It seems like it wants to, but either isn't getting fuel or timing is off. It shakes like an SOB while trying to start. I've had to tow it 6 times within the last year. Thanks AAA!!!
Between myself and my local mechanic the following things have been replaced:
Fuel Filter
Fuel Pump
Fuel Filter again
Distributor Cap/Rotor
Wires/Plugs
PCV valve
EGR valve
Crankcase Sensor
Coil Pack

It seems as though it runs well in very cold weather, but misfires in warmer or rainy weather. It usually will not start if sitting for 2-3 days.

My mechanic only has the OBDII tester. Should I bring it to the dealer? Will they have better diagnostic tools.

I'm thinking about replacing the TPS next. Any thoughts?
Please help!

[mustangmike351c]

I would check for a bad spider.

www.proautoelectricinc.com

[ZippyCT]

Thanks
What exactly is a spider?

[old_master]

A flashing SES light almost always sets a P0300 series DTC and is caused by secondary ignition problems: Ignition coil, plug wires, plugs, distributor cap and rotor. MOST of the time it's caused by a faulty distributor cap or spark plugs. Always use AC Delco when it comes to these parts.

[mustangmike351c]

Originally Posted by ZippyCT

Thanks
What exactly is a spider?

the spider is inside the upper intake. it supplies the fuel to each cylinder. they sometimes leak causing extra fuel to go through the intake to the engine causing poor fuel mileage, misfires, rough idle

[ZippyCT]

Thanks for the feedback everyone.

Well, I had the truck towed to the garage, again. The P1404 - EGR pintle position code came up, but apparently there is TSB for reflashing the VCM when a new EGR is installed. They reset the SES there, but I may need to go to the dealership for the reflash.
They diagnosed the "no start" problem as another bad distributor cap and rotor. Looked like severe arcing. They replaced it and it fired right up. Its been running great for a few days and no SES light yet.
BTW, I'm only getting 6 months < 5K miles on each distributor cap/rotor. The mechanic recommended that I replace the distributor itself with an aftermarket design that would eliminate this problem. Has anyone else had frequent replacement?

[old_master]

He may have suggested distributor replacement as a repair for a condensation problem in the distributor cap. If so, make sure the vents in the bottom of your distributor housing are clear. The vents allow air to circulate through the cap. If the vents get clogged, warm air from inside the engine rises past the distributor bushings and condenses on the underside of the cap causing the cap to fail prematurely.

[ZippyCT]

Thanks again. That's what they said the problem was also, but they didn't mention anything about the vent holes. I'll pull the cap off and see what I find out.

The SES light came back on today. I went to the mechanic and he said it was the EGR valve triggering the code. I'm going to pull off the one I bought and return it for a new one to see if that is the problem. The strange thing is that the light shut off while I was driving home from work. Seems to still be running OK though.

[old_master]

There's one vent hole about 1/4" in diameter, and it has a very fine mesh screen in it. There was a TSB several years ago that said the screen could clog causing a problem with condensation and to remove the screen completely. Please post your findings.

Ford had that same problem and their answer was to install a cap that has a vent in it. Seems to me that's a better idea being it's at the highest point in the distributor.

[jlaudio12w07]

keeping the distributor vented is crucial... condensation vapor will build up along the spine of the distributor up 2 the cap, and have nowhere 2exit... and ac delco parts r recomended

[ZippyCT]

Still had the problem occasionally. The vent holes were ok, but I did notice that the mounting holes/ears at the base of the distributor were cracked. It's a cheap plastic design. I'm ordering a new aluminum base distributor and hoping this is finally it.