EGR Question

[TC70C10]

On my 85 K5 with 350 and California emissions I experience a hesitation/studder from a dead stop. I generally just pump on the accelerator and after that I'm fine. My buddy has a 84 K10 Pickup and he told me he thinks its the EGR. Anyone know a good test? Someone else thought it might be in the carb. Truck only has 77k original miles.

Thanks,
Tim

[Brad_Olson]

It's possible the valve is fouled, especially if it's the original. Remove it from the intake and apply vacuum to see if the pintle moves. If it works OK it's possible that the TVS that supplies the vacuum isn't working, so that's another thing to check.

I've heard differing opinions on whether or not to clean an EGR valve; I used to clean them with some light media blasting.

Brad

[PHOENIX]

I have expierenced similar problems.

Take the vacuum line off the egr valve and plug the line.
Take it for a drive. If the problem stops, its egr related (egr, tvs, vacuum supply, carb tuning).

The vacuum line going to the EGR runs through a TVS (thermal vacuum switch). The TVS only allows vacuum to pass though onto the EGR if the truck is heated up. If you have the problem when cold, it could be the TVS. Try the test above when cold and hot and see if you find a difference. There is a vacuum delay valve you can install between the TVS and the EGR. The delay valve stops some of the vacuum from passing through, which results in the EGR "kicking in" a little later in rpms.

I replaced the tvs, no change.
Replaced the EGR, no change.
Installed a vacuum delay valve (help section @ checker), helped a bit.
Did some more carb tuning with all the new components and everything is working fine now.

Also what carb do you have and what port do you have supplying the vacuum for your tvs and egr?

Do you have a tool for reading vacuum?

[TC70C10]

I drive about 12 miles to work one way (1 gallon of gas if you know what I mean). Hesitation is noticeable when I start out of the driveway in the morning and at the last red light before I get to work. I replaced all of the vacuum lines when I bought the truck because they were pretty dry rotted. All the vacuum lines should be in their original location.

The previous owner didn't believe in spending any more money on the vehicle. He's in pre-retirement mode. I've been trying to buy this truck for a couple of years. I ended up buying my 81 a couple of years ago while I was waiting for him to call it quits. He gave a great deal $250 bucks. He was the original owner and I have all the paperwork on the truck. I worked on it the whole month of January to get it where I wanted it. Basically alot of cleaning, swapping out shocks, plugs, wires, window motors etc.

I'll try a couple of these tests this weekend and see if I notice a difference. I know on my boys 95 Blazer I took of the EGR and it was completely gunked over with carbon.

Thanks,
Tim

[swervin ervin]

It could be carb related also. It's very possible the accelerator pump could be going south. Although, it wouldn't be a bad idea to replace the EGR either especially if it's the original.

Reason I say acc. pump is because of the way you say it does. A little when cold and more when warmed up. It takes a lot less gas to run right when cold because the choke is closed. But when warmed up it gets worse. Take off the air cleaner and with the engine off, give it some gas and look down the carb throat to see if there are two steady streams of gas going in. If it looks jerky (for lack of a better term) or skips instead of being steady, I say the pump is gone and it would be time for a carb rebuild.