Hi,
I've seen this mentioned a few times in different threads but to my knowledge no one has detailed the exact solution. So here goes.
As soon as temperatures would drop below 0°C (32 F) my 1991 PZJ-77 would have a hard time starting. The colder it would get the worse the symptoms. Chuffing, white smoke, couldn't hold idle even with the throttle knob turned >1500RPM. It would feel like the injection pump was being fuel starved. Priming at the fuel filter would fix things temporarily but 30 seconds later it would start running rough again. I noticed that fuel would seep out from around the cap of the fuel pre-heater after priming multiple times (see picture below).
I assume that if fuel can come out when the fuel pressure is high, air must be able to get in as well when pressure is low and especially when temperatures are very low. So I removed and disassembled the fuel heater finding that 2 out of the 4 O-rings inside were hard and brittle (the ones around the intermediate white plastic part). When removing the heater element be careful not to break the two small plastic tabs that hold it inside the metal cap as they too can become brittle with time. This particular heater and filter-cap is no longer available so be extra gentle.
I had to order a bunch of O-ring sizes as I couldn't get reliable measurements of the old ones' section, ID and OD. Here are the ones that ended up being just the right sizes for my heater (see picture below). After changing the O-rings and reinstalling the fuel heater I primed the fuel line once again and the truck started immediately without hesitations or chuffing and it ran steady at normal idle RPMs.
While you're at it you might want to check if the pressure switch and element still work. For the switch to engage, you must pull a vacuum through the small end of the brass heater element. I used a length of 3/8" ID fuel hose and a large syringe to achieve this. You will hear a small click inside the heater element once you've reached a low enough pressure. Using a multimeter, check resistance between the brass body and the exposed terminal at the back. You should read an open circuit at rest and a near short when you pull the syringe (<1Ω in my case) . See the official procedure below.
Hope this helps!
I've seen this mentioned a few times in different threads but to my knowledge no one has detailed the exact solution. So here goes.
As soon as temperatures would drop below 0°C (32 F) my 1991 PZJ-77 would have a hard time starting. The colder it would get the worse the symptoms. Chuffing, white smoke, couldn't hold idle even with the throttle knob turned >1500RPM. It would feel like the injection pump was being fuel starved. Priming at the fuel filter would fix things temporarily but 30 seconds later it would start running rough again. I noticed that fuel would seep out from around the cap of the fuel pre-heater after priming multiple times (see picture below).
I assume that if fuel can come out when the fuel pressure is high, air must be able to get in as well when pressure is low and especially when temperatures are very low. So I removed and disassembled the fuel heater finding that 2 out of the 4 O-rings inside were hard and brittle (the ones around the intermediate white plastic part). When removing the heater element be careful not to break the two small plastic tabs that hold it inside the metal cap as they too can become brittle with time. This particular heater and filter-cap is no longer available so be extra gentle.
I had to order a bunch of O-ring sizes as I couldn't get reliable measurements of the old ones' section, ID and OD. Here are the ones that ended up being just the right sizes for my heater (see picture below). After changing the O-rings and reinstalling the fuel heater I primed the fuel line once again and the truck started immediately without hesitations or chuffing and it ran steady at normal idle RPMs.
While you're at it you might want to check if the pressure switch and element still work. For the switch to engage, you must pull a vacuum through the small end of the brass heater element. I used a length of 3/8" ID fuel hose and a large syringe to achieve this. You will hear a small click inside the heater element once you've reached a low enough pressure. Using a multimeter, check resistance between the brass body and the exposed terminal at the back. You should read an open circuit at rest and a near short when you pull the syringe (<1Ω in my case) . See the official procedure below.
Hope this helps!
