Thank your for your reply.

I have now completed the following tests and swaps:

Fuel Pressure Idle: 55psi. Drops 10 psi or so under WOT and steady 53psi to 55psi cruising at 70mph. (Pressure gauge taped to windshield.)

Full load test up to 4600 rpm on the road and no miss and full power..
Full Load test over 4600 rpm...heavy drop in power and flashing Check lamp.

Check for which cylinders drop out on scanner: Always P0300, P0302, P0303 P0301. This is the order in which the scanner lists the fault codes. Tried this 3 times and always same result. .

Run road test over 4600rpm to provoke miss-fire and when checked at the coils.....always cylinders #1 and #3 coil packs have been cut off by ECU. #2 is still firing when checked by pulling coil loom connector off and not cut by ECU although the code set includes P0302..

Swapped coil from #4 to #1 cylinder and this brand new coil is now found to be cut off by the ECU on return from road test....so still common to this #1 cylinder although original old coil works fine in #4 position. I never get 4, 5 or 6 cylinders dropping out.

I'm beginning to suspect high speed injector problem on maybe all injectors,(?) although the slump in power as miss-fire is detected is drastic. ...takes another 10 seconds of WOT to climb to 5300 rpm after miss-fire detected....during which time no change in fuel pressure.

I have watched the O2 on both banks under all sorts of driving conditions and they are reporting no lean condition. So, I have no 'Rich Stop Reached' codes or condition which lean injectors would trigger.

When ECU shuts off #1 and #3 on road test, the O2 nearly flat lines and will range maybe 250mV to 400mV while the Bank 2 is normal....and back at the shop, #1 and #3 are dead.

Don't see fuel pressure as a problem, although I am suspecting injector/s. power up to 4600 rpm is great and all scanner tests get a pass.


regards

dk



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Is this fuel pressure regulator referenced to manifold vacuum? If so, pressure should rise the higher the load / lower vacuum.



The ECU isn't going to cut out spark, it will shut off an injector to prevent raw fuel from overheating the cat.



The short and long term fuel trims likely won't react fast enough from the time the ECU sees a missfire and when it shuts off the offending cylinder.
Yes, since 1 and 3 are pumping air, O2 voltage will drop.

The fuel pressure drops about 8 psi when suddenly opening the throttle. It then climbs back to 55 psi under part throttle and remains at approx' 55 psi on road test.

I did not check the vacuum change to pressure you would normally expect as there is no hesitation . I will do that tomorrow.

I am sending all the injectors for sonic cleaning and checking to eliminate them as a contributing problem.

regards

dk

__________________
[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."