'90 EFI 351W

Im getting code 31 KEYON ENGINE OFF, and in continous memory and sometimes code 32. I know this is related to EGR. Code 31 is setting my check engine light. On the highway this light goes off. As soon as I slow down after a minute or 2 it comes on. On a cold start in the morning its takes about 10-15 minutes of city driving then the light will come on.
Is this related to some temperature setting?


Now, i have a breakout bothanks ebay) and as soon as the code 31(check engine light) comes on i notice the egr solenoid voltage doesnt change anymore at any speed. In addition the voltage is at 19.7V !! This is way too high Previously ive noticed the EGR solenoid gets about 10.5(open) to about 15 V(closed) in its range.

Is this an electrical problem. I think it started when my passenger power door lock stopped working a month ago. Probably not related.


In addtiion i see what appears to be leaking on the top of my battery. Its not wet just looks wet. I dont remember this before. Is this related?

 

In a sense yes, the light triggers because the EGR system failure is affecting the computer's ability to control engine performance parameters. As the engine heats up the lack of proper EGR sytem function triggers the light. EGR is not introduced into the combustion cycle until the engine has reached normal operating temperature. The fact that the light goes out again means nothing... other than the fact that the condition doesn't cause enough of a problem to trigger a hard fault code which would leave the light on all the time even after shutting the engine off and restarting the truck. Basically, the problem is there and should be dealt with, but you aren't hurting anything if you need to continue to drive it for a few miles home.

Ok, the fact that you have ANY component with MORE than battery voltage other than the ignition coil (which pumps out a helluva lot more) is concerning. The truck's electrical system functions at or about 12VDC with a range of 11.5 - 13.8VDC (min. - max.) What kind of voltage do you have at the battery when the truck is running? The alternator is still voltage regulated its just internal to the unit rather than a separate component as they were in the early days. The seepage at the battery top is also indicative of an overcharge to the electrolyte assuming the caps have never been removed from the battery in question.

 

Sounds like your alternator reg is on the way out and over-charging the battery and causing the high voltage at the EGR.

 

'90 EFI 351W

Thankf for the information.
The +5 V higher than normal voltage was actually a misreading caused by my Multimeter battery dying. I tried another meter and get normal readings. Thanks for the info about that anyway.
I still might change the alternator one day


Im still unsure about what to do with the code 31 on my egr and engine light coming on and off. It comes on at the same time when the computer doesnt lower the voltage to the EGR solenoid to open the egr valve(my breakout box tells me this). Is the check light related to another condition. This all only happens at driving speeds below about 35mph, driving above this speed for about a minute will make the light go off. When i slow down again or stop its there. If i shut the engine off then turn in on again its still there.
So im not sure thers a problem with egr system but rather the computer is not turning it on due to some other condition which the causes the engine check light and code 31?

I changed the egr valve and evr sensor about 2 years ago with no problems since except now. I dont want to change parts for nothing.

 

Ive determined whats happengin with code 31(low EVP voltage)

On cold start the EVP voltage stayed above 0.24V. After about 15 minutes it slowly drops with no throttle(no vacuum from EGR solenoid ) till it reaches below 0.23V . Once that happens for a period of about 30 seconds(like at a stop light), the check engine light comes on. This stops the computer from sending signal to EGR solenoid once i start moving again. Its a catch-22.
IF i go on the highway the evp voltage slowly sometimes climbs and if it goes above this .24 volts for more than 30 seconds the check engine light goes off and normal egr starts again.

Anyway i measured the resistance across the vRref and EVP signal like it says in the haynes manual and its maximum 4200 ohms with no vacuum. The book says it should be 5000 with no vacuum. Could this be causing a the EVP voltage to drop below the 0.24V threshold and causing it to shut off?