Loosing spark 89 4.9
#1
02-19-2009, 09:07 AM
Loosing spark 89 4.9
Hi gang, just a quick poll of the collective brain. Have done some searching and think I have a plan.
89 F250 4.9 with 460k miles, Nothing but wires/cap/rotor have been replaced before. Earlier symptoms, usually under way, sometimes at idle, a stall condition where the tach hammers right to zero from running rpm then leaps right back up, not following engine revs (Manual tranny)
Last night pushing snow, not going fast and getting stuff soaked under the hood but it croaks, good voltage, fast cranking, key on has the fuel pump run for its normal 2-3 second cycle. Cranking yeilds no fuel pump cycle afterwards.
Open hood, key on, in neutral, remove start wire from solenoid, jump to hot, cranking but no pump run on after. Remove coil wire from distributor cap and place near ps bracket bolt to give a 1/2 inch gap to check spark, crank, no spark but hmm, fuel pump does a 2 second run. Connector check, toy around with it. Put coil wire back on cap, acts like early spark that stops the engine from cranking but only once, then nothing, and no fuel pump run. Remove wire from cap and presto, fuel pump runs again.
Very careful in removing coil wire not to disturb any of the other harnesses, the twice that spark returned, it started off erratic and became constant, enough to start and run for a little bit.
Died three times - Ran idle for a half hour to warm up and defrost, plowed for 30 minutes, died for 10 minutes, ran for 15-20 minutes, died for 20 minutes, ran for 5 minutes, no restart.
The baffling part and may not be related is that removing the coil wire from the distributor cap makes enough signal for the fuel pump to catch a spark signal and run its little cycle? I can't see where changing out a 20 year old coil and TFI module could be bad. Could be a flaky hall effect sensor too.
Of course I'll go over the harnesses with a fine tooth comb so to speak, look for any chafed wires first before hamhanded replacing parts ***** nilly but someone has to keep the parts guys busy! maybe get a whole boneyard or reman distributor to tinker with.
Been an avid reader for a while and have found a lot of good useful stuff! Any tips, advice, flames welcome!
89 F250 4.9 with 460k miles, Nothing but wires/cap/rotor have been replaced before. Earlier symptoms, usually under way, sometimes at idle, a stall condition where the tach hammers right to zero from running rpm then leaps right back up, not following engine revs (Manual tranny)
Last night pushing snow, not going fast and getting stuff soaked under the hood but it croaks, good voltage, fast cranking, key on has the fuel pump run for its normal 2-3 second cycle. Cranking yeilds no fuel pump cycle afterwards.
Open hood, key on, in neutral, remove start wire from solenoid, jump to hot, cranking but no pump run on after. Remove coil wire from distributor cap and place near ps bracket bolt to give a 1/2 inch gap to check spark, crank, no spark but hmm, fuel pump does a 2 second run. Connector check, toy around with it. Put coil wire back on cap, acts like early spark that stops the engine from cranking but only once, then nothing, and no fuel pump run. Remove wire from cap and presto, fuel pump runs again.
Very careful in removing coil wire not to disturb any of the other harnesses, the twice that spark returned, it started off erratic and became constant, enough to start and run for a little bit.
Died three times - Ran idle for a half hour to warm up and defrost, plowed for 30 minutes, died for 10 minutes, ran for 15-20 minutes, died for 20 minutes, ran for 5 minutes, no restart.
The baffling part and may not be related is that removing the coil wire from the distributor cap makes enough signal for the fuel pump to catch a spark signal and run its little cycle? I can't see where changing out a 20 year old coil and TFI module could be bad. Could be a flaky hall effect sensor too.
Of course I'll go over the harnesses with a fine tooth comb so to speak, look for any chafed wires first before hamhanded replacing parts ***** nilly but someone has to keep the parts guys busy! maybe get a whole boneyard or reman distributor to tinker with.
Been an avid reader for a while and have found a lot of good useful stuff! Any tips, advice, flames welcome!
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