SB

iTrader: (1)

Just to reiterate what he's said, as I just looked at the wiring harness on the 502MPI:
page 26 - you can blow it up bigger: http://www.boatfix.com/merc/Techbk/96/96HGD4.PDF

Dk Blue wire from ECM goes to Cyl Injector #'s: 2,3,5,8 . These cylinders are all running at 14.5 A/F mixture. Note: their pink/black wires are also 'crimped' together.

Lt Green wire from ECM goes to Cyl Injector #'s: 1,4,6,7 . These cylinders are all running at 10.5 A/F mixture. Note: their pink/black wires are also 'crimped' together.


When he changes any injector connection with different color (dk blue to lt green, or vice versa) the A/F ratio changes exactly to it's corresponding value above.

DK Blue wires creating 14.5 A/F
LT Green wires creating 10.5 A/F

Waveform checked. All the same.

Pulse Width checked. All the same.

ECU was swapped to see if injector driver issue. Nothing changed

Wiring harness was swapped to see if wiring issue. Nothing changed.

articfriends

iTrader: (1)

Exactly, not to complicate things worse BUT as mentioned earlier thats at 3000, and as it revs higher , the afr numbers get closer, ie at 3500 they might be 11.5 and 13.0, 4000 maybe 12.0 and 12.8, around 4400/4500 they match somewhat then as it revs higher the rich side gets leaner and lean side goes richer. At 5600 at hp peak #8 is at 12.5 (where i tuned it) and #7 is at 14.5-15.0 (along with the other 3 in each batch). I tuned this on # 8 initially, i also had #8'batch at 13.8 to 13.5 or so and pulled some fuel that put it at the 14.5 we are seeing at 3000 because #7 was at 9.9 when i first switched o2 sensors before going to the 8 pack. At that point i quit doing anymore tuning as im focused on finding the problem as tune is going to change somewhere once we find the problem ( one of the 2 batches we are seeing is the actual tune, the other is being altered by something)

articfriends

iTrader: (1)

On a side note , i also got rid of the 5"slip over flex tubes and semi mufflers, went to 4x5 adapters, v bands and for ****s and giggles clamped my 5"gibsons off the Baja on last friday too, made 554 hp/580 ft lbs tq WITH this uneven afr. When its straightened out tq will be same since afrs are pretty even about where tq peak is but might see a little more peak hp once nbers match on top

Trash

This may have been alluded to but is there the possibility of some cross talk/interference on the guilty batch harness from ignition noise?

articfriends

iTrader: (1)

Plug wires are no where near harness, have rerouted stuff away and the afr difference VERY consistently is the same plus no changes at all from swapping out efi harness, i would think problem would be erratic?. Also has all stock ign (coil,module etc ) right now. Any suggestions?

articfriends

iTrader: (1)

As soon as i get back from this trip to fla Thurs im swapping both batches completely at injectors to see IF problem swaps with harness or stays w the injectors, anxious!

AllDodge

iTrader: (1)

My WAG at the issue, I'm thinking the MAP sensor. Between 3K and 4K the throttle body is not fully open and still drawing vacuum, but the vacuum is not much. ECM nor MAP is not that sensitive and the MAP is only a 1 bar.

sutphen 30

I'd almost be inclined to throw another distributor in it.its what the ecu uses as its trigger.the pick up coil or ignition module could be pooched alittle.

articfriends

iTrader: (1)

Ive actually swapped map sensor, had a 2 bar which has cruder resolution even with ecu set for two bar to a 1 bar along with a flag/scalar change to ecu, made no difference. And this is on my dyno so we are at 97 to 100 map even at 3000 because i can hold it there on the brake.

articfriends

iTrader: (1)

Thats something else to try when i get back in town thirs/fri although the single signal from distributer tells ecu the info and it uses it to trigger both injector drivers. I also have spare mefi4 ecu's and a harmess that i could swap on as a last ditch effort depending what i find from swapping batches completely from a to b and b to a thurs