7.3 IDI idling issue

[Cariboo4x4]

Hi All

I have a 1989 F250 7.3 IDI. Lately we had a spell of -15 celcius or 5 degrees F. I have been keeping block heater plugged in. It has like 300,000 kms on it or 187,500 miles. On start up instead of going to fast idle right away it goes to a rough idle right away and puking out excess exhaust. Lately its been doing that more often. Id say last 4 days over past 10 days it did it twice so I just shut it off. I don’t know the system very well. It does burn a bit more oil than normal but its been like that for last year. I understand there is a CDR valve on back of intake yet took it off and diaphragm seems sealed. Not sure how the cold start solenoid works. I researched to press throttle once to set it on high speed idle yet haven’t tried that yet. Normally dont even press throttle on start up. It was running awesome till this freezing cold weather started and this weekend its warming up to -3 C or 27 F yet want to be ready for next big dip in the freezing weather. Any ideas? Thank you

 

[Tom in Mo.]

Did you check for water in the diesel fuel? Once I started using Howes in the winter I didn't have any more water issues. It started and ran good in a -26 F Montana February.

 

[Cariboo4x4]

I drained the water seperator underneath fuel filter a couple times because “water in fuel” light was coming on. Did your truck have rough idle like that too? Adding the Howes product corrected the rough idle?

 

[Cariboo4x4]

Been researching air intrusion into fuel return lines can cause the rough idle. I’m trying to get my head around how air into fuel return lines eould cause engine to run rough.

 

[Tom in Mo.]

With cold and moisture in the fuel the gelling will start early. Gelling fuel acts like the rough idle and generally rough running. I'm only suggesting the fuel issue because I like to check the simple stuff before taking parts off.
Once bought a tank of fuel that was loaded with water. Had to stop every ten miles to drain until it worked it's way out. Ran like crap for a week.

 

[Tom in Mo.]

Yeah that doesn't make sense.

 

[Cariboo4x4]

Thank you Tom. Once I figure it out I will post it.

 

[Cariboo4x4]

Another late reply. I learned rubber line from fuel return line to top of fuel filter housing head can be a culprit of air intrusion. I disconnected it at filter head and plugged line and put sealer with pipe plug in housing. I also found fuel leak in hose going from metal line at passenger side front frame rail to mechanical lift pump. I’m pretty certain that fuel leak was the culprit that was causing all the air intrusion problem. Truck has been running great since new rubber line installed.