Claw50

Hello all,

I have searched for a thread for days and have seen symptoms close but not quite.....soooooo.....here it is;

Runs rough with stumble off idle. Has a rough idle witch appears to be about 100 rpm or so high. Driving it will stutter and buck. I can get it to smooth out a little at high rpms but if I shift up and lug at all it bucks. If I disconnect battery and let it set for 10 or so minutes, it will run smooth as glass for a few minutes and then it will rough up again. No issues starting. Will idle all day long roughly. I checked plugs 3 and 5 look like they are running maybe a little lean. As far as fuel pressure, I have 45psi at idle and a steady 55-60psi at higher rpm and under snap throttle it responds proportional in pressure as well. 125 psi compression in all cylinders. Disconnected vacuum at fuel regulator and it did not smooth out but idle raised a little and no fuel coming back up regulator. I have checked for vacuum leaks at all points and tested brake booster. I replaced a bad EGR valve I found during leak test. Fuel system is all new with new in-tank low pressure pumps and sending units in both tanks, new fuel selector switch and selector valve (stock high pressure pump)I may need a new fuel gauge as they let it bounce from bad sending units for years. It has trouble reading true after a few minutes. I have checked key on and running codes and have got no codes. I did a cap/rotor, plugs tune-up and a new battery. I removed the low idle circuit valve and cleaned but it did move freely. Cleaned the throttle body. Replaced MAF and was going to start looking at the distributor or crank position sensor (may be a knock sensor on this motor I forget) however, whatever is causing this rough running issue is not setting off a code but resets with the disconnect of the battery. I am stumped. I heard there is a sensor in the rear diff that has to do with speed input so I disconnected battery for 10 min, let the truck run at idle for a bit and it started to run rough without moving. I felt this may be a rough elimination of that sensor. The person I bought it from said he did not have the issue. It sat for a year or so due to a fried clutch he did not know how to fix. I got it for a deal with the new clutch in the box. previous owner said it ran perfect prior to parking it. I cleaned the rear fuel tank and there was almost no fuel in the front tank. it makes no difference when switch tanks. I did think injectors but felt it had good pressure but why would it run good for a few minutes after battery disconnect then start again. I can't help but think it is some sensor or system on a circuit not a mechanical issue.............HELP!!!!!!!

Soup Bean

Have you changed the fuel filter between the fuel tank selector valve and the high pressure pump? That's what I'd do. That would explain the symptoms. Bleed the pressure off the fuel system at the Schrader valve on the fuel rail first. Haynes recommends wrapping a rag around it. Be safe...

Claw50

Thank you Soup Bean…….yes I have. I looked in another thread on electrical issues and am going to try a fix with the distributor based off some possible corrosion. It’s a free try lol….