My 90 Blazer 4.3 has 135,000 miles on it , it runs great going down the road or in park . Once you get the engine running for more than 30 minutes and come to a stop sign but mostly a stop light and sitting for 20 seconds it will die .. Right before this happens the engine will cough and surge then just die. I have no problems with it starting back up , it does have the check engine light on at times but doesnt stay on and I took it to autozone and they did the paperclip check. It would only flash the code 12 (entering system) and thats it... Going down the road id runs fine , it has a good idle the only otherthing I have noticed is while cruisng 55 or so and stomp the throttle it will leave a cloud of black smoke, for about 2 seconds. Please any help would be appreciated.

 

This sounds like you are having a problem with a stuck open EGR valve.

 

My '90 EGR is vacuum operated, so I assume yours is too.It can be tested this a couple different ways.

Do you also have this problem, say warmed upped sitting in the drive way in drive, or only when your driving and come to a stop in gear?

If you happen to have a hand vacuum pump or anything that can apply a vacuum, hook it up to the port on the EGR and use a small screw to plug up the vacuum line you pulled off the EGR. Start up the vehicle and apply vacuum to the EGR. If the EGR is working, the engine should stall. Appling the vacuum opens the valve allowing gasses to enter, with the engine being at idle, it will "overload" the intake and stall the engine.

If there is no change in the engine rpm when you apply vacuum, then its probably worth the time pullingthe EGRout and cleaning it out and checking or replacing it, although that my not be the real issue.

If the engine does stall out, its probably not the EGR.Check the vacuum lines for cracks, softness (collapses under vacuum) or disconnected running to and from theMAP filter and sensor (follow the vacuum line back from the EGR to find the MAP stuff, two black items on top of the valve cover, the filter is the round tube like object, the sensor is the rectangle box with electrical wires and hoses going to it).

If none of those things appear to be bad, It could be a bad MAP sensor. (sorry I've not had any bad ones of those, but I'm sure there are tests for it)

You can also drive test the EGR to see if the same thing happens. Just plug the EGR vacuum line likebefore and drive it. If you still get the same thing happening, then it is probably the EGR. If it runs worse (or better in some conditions), then the egr was probably working, and it should throw a code. Hook the vacuum line back up. Go back to check hoses and electrical connections.

If you've been doing any off road or dusty driving, you could also check the vacuum filter. On the end of that filter tube is a snap on cap. Careful not to break it, but it will come off with some finger effort and some twisting. Under that cap is a filter. It just pulls off, I have not had any bad ones, I just blow it out with some canned air and put it back, but I'm a city driver.

Removing the EGR is kinda a b#tch. Getting the bolts out, then getting it twisted out under the fuel lines, and around the distributor and oil pressure switch, but it can be done.

If you do take it out and clean it up or replace it, and you plan on keeping the truck for a while, spend the $5 extra and get the EGR gasket with the screen.

Good luck!

 

I thought of something else, if it is only doing it while in gear and stopped (ie foot on brake), check your vacuum lines to the brake booster, maybe even the check valve that goes into the booster. worst case it might even be the booster itself going south.