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-   -   Stumble troubleshooting advice (

KivPanther 02-20-2021 05:13 AM

With the loose gas cap on the way home I noticed a few things. The stumble didn't go away, but it definitely seemed less intense. It also didn't start doing it until the engine had fully warmed up to operating temperature and only gradually came on once it did. Seems like I might consider replacing the gas cap and cleaning out the filler neck at the very least while hunting for the rest of it.

LugNut1990 02-20-2021 09:18 PM

Interesting! If not a venting problem, next _guess_ is the fuel pump or sock. Before that (PITA job) I'd check out the wiring, grounds, etc. Be careful!

KivPanther 02-21-2021 08:02 PM

Shall do. I'm also going to run another can of seafoam in the crankcase since I noticed that the rockers and inside of the covers were covered in crud when I replaced the valve cover gaskets. Gotta love farm trucks driven by 90-something year olds!

KivPanther 02-22-2021 07:13 PM

I did a quick test on the gas cap valves per the FSM and found out that while the intake is working, the relief is not. So new gas cap anyway.

kenmack 02-23-2021 08:48 PM

You might consult the factory service manual (FSM) in the EF&EC section which has some good flow charts for servicing. You should start on page EF&EC-45 which will direct you to the flow chart specific to your issue.

KivPanther 02-23-2021 10:08 PM

I have practically memorized that section of the service manual. I'm still at a loss, hence my request for out-of-box thoughts.

Deerhurst 02-24-2021 01:00 AM

I got 2lbs of tannerite when you are fully fustrated!

Got a quick recap of what has been done to job our memories?

KivPanther 02-24-2021 07:07 PM

Sure thing. To date:

  • New distributor
  • New NGK Iridium plugs
  • New NGK plug wires
  • All new injectors and seals
  • Replaced a bunch of vacuum hose and can't find a leak with my current test methods (smoke)
  • New fuel pressure regulator
  • New fuel filter
  • Throttle body cleaned
  • MAF cleaned
  • Throttle Position Sensor tested working
  • Throttle wires adjusted correctly
  • Timing double-checked and steady at 15 BTDC
  • New gas cap
  • New air filter
To re-iterate, the stumble does not happen at idle or under full throttle acceleration. It only seems to do it when my foot is barely to lightly on the gas and only between about 2500-3200 RPM.

Deerhurst 02-24-2021 08:58 PM

Does the TPS have a dead spot? Easiest to see with an analog meter.

KivPanther 02-25-2021 04:30 AM

It seemed steady with my digital meter but I'll double-check. I don't have an analog meter anymore so I'll just go extra slow.

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