My 85 240 wagon suddenly developed a high speed stumble. Seems that as I accelerate and reach 55mph I feel slight intermittent engine stumble that continues as I accelerate. Doesn't happen at slower speeds.

Any ideas?

 

What happens during heavy acceleration? High speed stumble could be due to a fuel starvation, fuel filter, pump, etc. Do a basic tune up check too.

 

Will be checking hoses, replacing amm, replacing fuel pump relay, checking in tank pump, cleaning fuses, etc.

 

replace your fuel pump -I had the exact problem on my '91.

 

my 92 turbo 740 had a high throttle, high RPM stumble due to the TANK fuel pump failing. if the main pump is failing, the engine stops cold. with the bad tank pump, my main fuel pump was struggling, and noisy even at idle. new tank pump and I couldn't even hear the main pump anymore, quiet soft happy humm.

but, yeah, first bring it to stage 0. fresh plugs, wires, cap, rotor, check everything under the hood, especially the vacuum and intake plumbing. also check that vacuum line that runs to the mopar ICU on the right fender of those 85-88 240's, if thats split and leaking, your spark doesn't advance properly.