Random P0172 And misfire below 700 rpm
 

I have been hunting this one down since I bought this truck. My truck is a 1995 Blazer LT 4x4. Every once in a while (twice a month or so and always when slowing down) my truck will throw a P0172 code. A couple of trips later, it will clear. I notice no difference in the way it drives. It always misfires on one cylinder erratically when under 700 rpm. It only does this when not in gear as well. It seems to misfire more often when it is warm. I get no other codes. At idle it also smells very rich. It does not make this smell to my knowledge under driving conditions. I tested this by following closely on a motorcycle. :icon_bike: My truck runs and drives fine other than these symptoms and I see about 18 mpg on the highway with my 2" lift and 31x10.5's which I figure is normal. Since I have owned it I have replaced: both O2 sensors, EGR Valve, plugs, cap, rotor, coil to dist wire, filters, and Idle air control valve. I have also seafomed it, and I run Lucas fuel system treatment in every other tank. My EGR has clogged about 4 times since I seafomed it. But it has been fine for a month or so. Any ideas? Thanks in advance.

Fuel leak?

Not that I can find.

Have you done a fuel pressure test, specifically a fuel pressure leak down test? If not, then you really do not know. A fuel leak does not always mean one that is visible.

Ok, will do. Any other ideas?

im glad you posted i almost bought an 02 sensor.i also have the same exact condition with my 1995 blazer 4x4 lt i replaced the spider and a nut kit and full tune up and all new vacuum lines and still i get the random po172.
good luck!!!
i let you know when i figure mine out.

Sweet. What falls under "full tune-up"? I swapped coils and ignition control modules with my wife's '95 blazer 4x4 LS which runs perfect. No change either way. So that's out. I'm about to change my wires. Because it needs to be done anyway. Have you changed your yet? I picked up a P0300 code this weekend. But it only happened once. Still confused. :icon_doh:

Check your distributor gear for wear

Changed my wires. No dice. I'm going to check my EGR again...just in case.

EGR was clean. I found out my distributor cap was cracked / slightly out of place. It seemingly fixed the problem. Time will tell. Keep you updated.