drivability question on 1998 Nissan Altima

i have an intermitent short /mis that seams to happen more often if most acessories are on . its happenedat all speeds but mostly on hiway.ive replaced the altinator an fuel pump.ive checked the mass air flow sensor by tap test and by unplugging it. the egr valve by unpluging it when conditions came up . no codes show

by in Arlington, WA on September 17, 2010
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1 answer
ANSWER by , September 18, 2010
Some intermittent problems are very hard to find. I have ended up "teeing" in a fuel pressure gauge and taping it to the windscreen of the car and then driving the car with an hand held oscilloscope on the seat of the car to look at injector pattern, coil patterns, mass air flow and O2 sensor patterns when the problem occurs. Start with the engine running wiggling all the wires in the engine compartment and see if moving any particular harness makes the engine run poorly. I can't remember if it was your year range but some Sentra's used to have a bad ground wire that would frey at the air flow meter harness putting an auxiliary ground made the car run like a champ.