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Hey All. Im working on a friends 1997 Mazda B4000 4.0 liter V6 automatic. Since summer 2024 it hesitates for split seconds intermittently at high speed in overdrive and 4th gear and progressively getting worse. 283700 kms
All this I checked recently:
New fuel filter, spark plugs, wires, coil pack didn’t make a difference in the Fall
Seafoam, gasline antifreeze hasn’t made difference.
Air cleaner good
Idles normall. 854 rpm
Tested with fuel cap loose no difference
Cleaned battery connections. Battery voltage is good and doesn’t change when running on highway.
Automatic transmission overfull since budfy bought it 10+ years ago.
Steady bearing new
Rear differential oil full. Diff temp 110 F.
Rear pinion not loose up and down. Not sure about backlash
Transfer case output shaft not loose upmand down
All u joints good
Cleaned MAF sensor
No apparent vacuum leaks with propane torch opened.
3 Injectors right side seem to sound ok. Was able to reach front left injector it sounded fine
Fuel pressure at 30 psi when at idle and reving in park. Turning key off & on 3 times fuel
pressure went up to 36 psi
Clutch fan seems good
Replaced leaky water pump.
Today I am going to check fuel pressure regulator for black soot/sludge, wet throttle body past throttle plate. Also test fuel pressure on highway today to see if it’s dropping when hesitations occur. Fuel pump never changed he says. Also check ground from fuel pump. Im thinking fuel pump. Just read earlier post to disconnect IAC to check again for vacuum leak. I’ll try that. A month ago engine light was on P0171 and a vacuum lines on left side of engine to a metal tube was disconnected so put new rubber line on. Line went to a switch on left side of engine intake. I erased code. It hasn’t come back. I read on here another problem could be O2 sensor 1 bank 1 yet no codes. Looks like passenger front inner fender well needs to be removed to unplug it or buy those new style plyers to reach in there to unplug it. Sensor is about $100 CAD. Buddy said try it but I don’t want to throw money at it.
All this I checked recently:
New fuel filter, spark plugs, wires, coil pack didn’t make a difference in the Fall
Seafoam, gasline antifreeze hasn’t made difference.
Air cleaner good
Idles normall. 854 rpm
Tested with fuel cap loose no difference
Cleaned battery connections. Battery voltage is good and doesn’t change when running on highway.
Automatic transmission overfull since budfy bought it 10+ years ago.
Steady bearing new
Rear differential oil full. Diff temp 110 F.
Rear pinion not loose up and down. Not sure about backlash
Transfer case output shaft not loose upmand down
All u joints good
Cleaned MAF sensor
No apparent vacuum leaks with propane torch opened.
3 Injectors right side seem to sound ok. Was able to reach front left injector it sounded fine
Fuel pressure at 30 psi when at idle and reving in park. Turning key off & on 3 times fuel
pressure went up to 36 psi
Clutch fan seems good
Replaced leaky water pump.
Today I am going to check fuel pressure regulator for black soot/sludge, wet throttle body past throttle plate. Also test fuel pressure on highway today to see if it’s dropping when hesitations occur. Fuel pump never changed he says. Also check ground from fuel pump. Im thinking fuel pump. Just read earlier post to disconnect IAC to check again for vacuum leak. I’ll try that. A month ago engine light was on P0171 and a vacuum lines on left side of engine to a metal tube was disconnected so put new rubber line on. Line went to a switch on left side of engine intake. I erased code. It hasn’t come back. I read on here another problem could be O2 sensor 1 bank 1 yet no codes. Looks like passenger front inner fender well needs to be removed to unplug it or buy those new style plyers to reach in there to unplug it. Sensor is about $100 CAD. Buddy said try it but I don’t want to throw money at it.
