Maxima Forums - View Single Post - Power Surging During Acceleration (~3000-4500rpm)

rx7racr · 08-03-2008, 07:11 PM

UPDATE - 8/3... More Troubleshooting has been done:

Still no codes at any point (0505 only)

Borrowed an OBD-II scanner that worked with the max. I was able to observe the following while driving:

TPS
O2 voltages (x3)
MAF
Short/Long term Fuel Trims
IGN Advance
Vehicle Speed
RPM
Intake Air Temp
Coolant Temp
Open/Closed Loop Operation (x2)

OK - so I wanted to see if the TPS, MAF, IAT or 02's (or anything else) showed any erratic behavior during the surging episodes. After a number of passes through the 3000-4500 rpm range, with surging observed, it did not appear that ANY signals on the scanner were acting strangely (spikes etc...). From this, I think it's safe to say that the MAF, TPS, IAT, 02's, ECT, VSS and Crank Position sensors were all returning smooth (non-erratic) signals. I'm not exactly sure what the values should be on many of these sensors, but nothing seemed to do anything strange during the surging.

I also paid special attention to the IGN Advance, as I had suspected that the surging could be a retardation in timing - due, perhaps, to a faulty KS. Throughout the surging episodes, the IGN Advance stayed about where it would at other RPM ranges (at similar throttle positions), and it never spiked erratically.

So... The only thing that seemed to change (a little bit) during the surging episodes were the 02 voltages and the Fuel Trims (short-term more). The 02's (one of them in particular) seemed to read much closer to 1v immediately after the surging. Also, the short-term fuel trims (one of them in particular) seemed to go negative after the surging.

If I'm reading this correctly, both the high 02 reading and the negative Fuel Trim seem to indicate that the car could be running a bit rich during the surging episodes. What could cause this? Well - COILS certainly could! If one or more coils weren't firing properly, unburned fuel would be ejected into the exhaust, richening it, and sending 02 values high. Fuel trims should compensate for this by going negative (i.e. leaning out the mixture slightly.).

So I looked at each coil. None of the coils showed any visible signs of arcing or overheating, and I didn’t see any browning of the coil exteriors. With my ohmmeter set on 20k, each coil’s primary circuit (terminals 1+2, as in above diagram) measured between 1.52 and 1.71. It might be significant that 5 of the 6 coils were between 1.52 and 1.63, with the remaining coil measuring 1.71. It might also be significant that I measured these resistances with the engine/coils cold (remember, my problem only manifests when the engine is hot).

Any Ideas?

I might try buying a bunch of coils off e-bay, or maybe 2 new coils and just start swapping them around…

08-03-2008, 07:11 PM	#14
rx7racr Member Join Date: Jan 2004 iTrader: (0) Posts: 74	UPDATE - 8/3... More Troubleshooting has been done: Still no codes at any point (0505 only) Borrowed an OBD-II scanner that worked with the max. I was able to observe the following while driving: TPS O2 voltages (x3) MAF Short/Long term Fuel Trims IGN Advance Vehicle Speed RPM Intake Air Temp Coolant Temp Open/Closed Loop Operation (x2) OK - so I wanted to see if the TPS, MAF, IAT or 02's (or anything else) showed any erratic behavior during the surging episodes. After a number of passes through the 3000-4500 rpm range, with surging observed, it did not appear that ANY signals on the scanner were acting strangely (spikes etc...). From this, I think it's safe to say that the MAF, TPS, IAT, 02's, ECT, VSS and Crank Position sensors were all returning smooth (non-erratic) signals. I'm not exactly sure what the values should be on many of these sensors, but nothing seemed to do anything strange during the surging. I also paid special attention to the IGN Advance, as I had suspected that the surging could be a retardation in timing - due, perhaps, to a faulty KS. Throughout the surging episodes, the IGN Advance stayed about where it would at other RPM ranges (at similar throttle positions), and it never spiked erratically. So... The only thing that seemed to change (a little bit) during the surging episodes were the 02 voltages and the Fuel Trims (short-term more). The 02's (one of them in particular) seemed to read much closer to 1v immediately after the surging. Also, the short-term fuel trims (one of them in particular) seemed to go negative after the surging. If I'm reading this correctly, both the high 02 reading and the negative Fuel Trim seem to indicate that the car could be running a bit rich during the surging episodes. What could cause this? Well - COILS certainly could! If one or more coils weren't firing properly, unburned fuel would be ejected into the exhaust, richening it, and sending 02 values high. Fuel trims should compensate for this by going negative (i.e. leaning out the mixture slightly.). So I looked at each coil. None of the coils showed any visible signs of arcing or overheating, and I didn’t see any browning of the coil exteriors. With my ohmmeter set on 20k, each coil’s primary circuit (terminals 1+2, as in above diagram) measured between 1.52 and 1.71. It might be significant that 5 of the 6 coils were between 1.52 and 1.63, with the remaining coil measuring 1.71. It might also be significant that I measured these resistances with the engine/coils cold (remember, my problem only manifests when the engine is hot). Any Ideas? I might try buying a bunch of coils off e-bay, or maybe 2 new coils and just start swapping them around…