need help with engine codes, EGR/EVAP

[fireguy12117]

i did a quick search and didnt seen anything right off the bat, so my aologies if this has already been discussed.

got a 98 2wd with a 2.5. over the winter i started getting EGR codes 0401 and 0402. i put on a new vacuum solenoid as i though i properly troubleshot that part, but i still get codes. took the EGR off and cleaned it, verified it operated with a hand pump and threw it back on, still get the codes. verified none of the hoses leak, so i am down to the DFPE sensor that i am going to try to put a meter on and actuate the vavle while running and see what happens....any more input is welcome.

secondonly and most recently i have a 1450 EVAP unable to purge or something. i had this last summer and it would come and go. now its back and pissing me off. is there a quick way to troubleshoot this crap? i hate not being able to see all the lines, but is this typically something as silly as a gas cap gone bad?

anyhow, i just spent the last 3 hours getting nowhere, so any help is appreciated.

 

[fireguy12117]

so i put a vacuum pump on the EGR, meter on the DFPE sensor. didnt get a change in readings no matter what order i probed, but i can sure make the engine stumble and damn near die when i apply vacuum on the EGR vavle.

bad EGR valve?

 

[fireguy12117]

put a call into a friend who shed some light. he stated the hot exhaust gases being sucked into the intake at idle were causing the stumbling- that the EGR was working. i went another round measuring voltage on the DFPE sensors and didn’t get any changes. shut the truck off and pulled the sensor plug, probed the resistance of the sensor and had wide opens all around. i think that solves the insufficient EGR flow problem, now i need to try to figure out the EVAP.

i am just rambling on posting to myself for posterity sake, and maybe someone will get something from this.

 

[83blackbandit]

have you replaced the gas cap yet? i had similar problems on my 96 and a new cap fixed the problem.

 

[fireguy12117]

going to hit the parts early this week to get a new DFPE and if the cap is cheap enough, just throw a new one on and see what happens. my guess is that in the colder seasons there isn't enough much going on with the system, so perhaps the cap is bad but its never a problem until the solenoid fires and there is a vacuum lock or something...