dceng888

Hi Guys and Girls,

I am trying to help fix a friends Maxima, 2000 3.0L Australian version. I have searched through the entire internet trying to get a clear diagnostic path of how to fault find this problem. I do not want to drop new parts in unnecessarily until the problem goes away. I am bringing it to you guys for help before I relent and send it to the dealer.

The symptoms are when it is warned up it idles fine and has ok power under 10% throttle input, anything over that and it misfires or stutters badly. It can be driven ok if you are really careful on the throttle.

When cold it is worse and sometimes almost stalls, idles fine with an occasional mis.

There are no DTC's and I cannot read any sensor data, I was told the Australian version is not OBDII compliant.

I have tested fuel pressure and read 40psi at the pump going up to 45psi when at WOT. I clamped off the return line and it improved slightly.

I have replaced the spark plug with NGK platinum. I have replaced the coil packs as all the threads I read indicated this is a week point of the engine. Did not make any difference.

I have tested all crank and cam sensors, they ohm out ok and have a signal on them that changes with RPM.

I have tested the MAF sensor that has a DC voltage about 1.5v when at idle and goes up to 2.5v at about 3000rpm (linear with rpm increase)

What are the logical steps to diagnose this problem without dropping new parts in?

nestorlugo

iTrader: (11)

Spray it with this !!! Then clean the throttle body and repost...

The Wizard

iTrader: (43)

Have you done a power balance test to try to narrow down which cylinder(s) the problem is on? While the car is running, disconnect the connector at the coilpack and listen for a change in rpm. If no change in rpm, then you found a suspect cylinder.

Are you saying you don't have an OBDII port?

When you replaced the coilpacks, did you use OEM coilpacks or generic aftermarket coilpacks?

You're on the right track. The next logical thing to check are the injectors electrically. Start by listening to them with a long screwdriver to your ear or with a stethoscope to make sure they are clicking rhythmically and not sporadically. Then check the pulse width of each injector with a DVOM. If they pass those quick tests, you may need to pull them anyway for physical mechanical inspection (missing pintle caps, tired o-rings, clogged filter screens). Lastly, you may need to have them sent out for cleaning/pressure testing etc to see if they are mechanically sound internally.

dceng888

Thanks for responding guys,

I haven't got any MAF cleaner and its a public holiday tomorrow, I will get some this week and try it out.

I have tried the power balance test with no conclusive results. I tried disconnecting the coil pack plugs one by one and driving a little way. all plugs had a significant effect at idle and such take off was reduced, it was hard to tell if there was any difference at load.

I tried unplugging the front injector plugs one at a time and each had a significant effect on idle but I did not try driving to test at load. I cannot get to the rear injects as they are covered by the inlet plenum.

The car has an OBDII port and I can connect and read codes but no parameter data. There was a MAF code when I first plugged it in but that was after I pulled the plug on all the sensors including the MAF, the code has not come back since I cleared it.

What voltage range should I be reading at the MAF?

The coils I put in are ebay aftermarket jobs. I know, I know, you guys all say use only oem but all the reports seemed to be that they work but don't last long. They should for my purposes prove or disprove the function of the old set. There was absolutely no change from the old set to the new. Could I be getting screwed by a marginal performance design? I have tried regapping the old plugs to 0.9mm to see if a closer gap gives a better chance of spark under load with no effect.

I will report back after I clean the MAF and inlet.

D.Stillwell

^^ For MAF voltage = measure between ECM terminal 61 (white wire) and ground, should be 1.2-1.8v at idle during warm up.

dwapenyi

iTrader: (3)

Since your spark issue seems to affect all cylinders, you should check your condenser.

dceng888

I have tried another condenser. There is one under the back seat I think it is for the rear window demister radio noise. I swapped them over and no change.

dwapenyi

iTrader: (3)

How does the car act when it is cold, driving before it has warmed up properly? Describing the difference in behaviour may help narrow down the issue between open loop and closed loop operating modes.

I would also suggest to unplug and replug in the throttle position sensor. Perhaps a ground issue/bad connection....being down in Australia I would think there is no such thing a rust over there

dceng888

OK so I got some MAF cleaner today.

I took some voltage readings from the MAF before and after cleaning. I didn't get accurate readings before as I was only looking for a response from the MAF.

Before cleaning and all warmed up. Idle 1.4v , at 4k rpm 2.05v.

After cleaning. Idle 1.4v, at 4k rpm 2.1v.

Performance was definatly improved after cleaning but still very poor, missing/stuttering under load.

My understanding of the FSM is that the MAF should read about 4v at 4k rpm.

Starting from cold the engine starts perfect but misses/stutters with any load input, it is pretty much undrivable until it warms up just a bit. It even backfires if you put the accelerator down to much.

From my readings I think the MAF is gone, I will price the replacement at the local dealer tomorrow, unless you guys think I'm on the wrong track.

D.Stillwell

^^ From what I remember in the FSM, it says to measure at idle and then at 2500rpm not 4000...

If you have a live data scanner you can easily do a few WOT pulls and log em, look at the MAF Gs/sec...it should be no less than 150 @ WOT with a healthy Maf on stock moror.

dceng888

[QUOTE=D.Stillwell;8997493]^^ From what I remember in the FSM, it says to measure at idle and then at 2500rpm not 4000...

This is the problem I am having finding good information on test voltages. Everywhere it states idle and 2.5k rpm voltages but nothing else. There is one spot only in the FMS - Step 8 Page EC-171 that states look for linear response from idle to 4k rpm (1.2-18v to aprox 4) I can't read live data it would be great if someone can confirm actual voltages.

dwapenyi

iTrader: (3)

Get an MAF from the junkyard......no need to go new from dealer.

D.Stillwell

The Wizard

iTrader: (43)

Don't be too quick to dismiss the injectors...

dceng888

Holy ST the dealer wants AU$951.30 for a new MAF.

He called me back 1 minute later and said they now do the insert only for AU$355.10

I might try the Ebay version for $90. Does anyone have any feed back on aftermarket MAFs.

Can anyone verify the correct voltage output at 4000 rpm for me?

nestorlugo

iTrader: (11)

CourtesyNissan has it for $76 oem

dceng888

Well for all of you who are dying to know, well at least for the next guy who has a MAF problem.

Yes I replaced the MAF and now good as new. I didn't get any dealership ecu upgrade.

I tried a $60 eBay MAF, I figured it was a good investment evan as a diagnostic tool.

The voltage measured at the MAF signal output is now:

1v @ idle
1.4v @ 2k rpm
2.1v @ 3k
2.4v @ 4k
2.6v @ 5k

topping out at about 3 volts when the engine is revved hard. I thought it was meant to go to about 4 volts, maybe the eBay aftermarket MAF is not that good, but it works!

Interestingly the engine seemed to run harder when cold, I guess it relies on the MAF and the ecu mapping when cold? Makes me think the normal operating mapping is optimised for fuel efficiency and reliability and can be tweaked for heaps more power?

D.Stillwell

^^ Voltage readings dont look right. Too low.

Aftermarket MAF is no good, it may work for some time, but its not good.

dwapenyi

iTrader: (3)

It's good you got it fixed, but those observations are backwards. When cold, the ECU is relying just a builtin pre-programmed cold run mode. Once the car reaches operating temperature, The ECU then "switches on" O2s etc. Your car runs best, and is the most powerful when warmed up.

As suggested, I would not trust an aftermarket MAF. Are there no junkyards in Australia? You should be able to get a used OEM MAF for cheap. If your concern is with used parts, remember that the MAF has no moving parts. It either works, or it doesn't. They usually fail because some electrical connection within the unit has broken due to constant heat/cold expansion cycles.

dceng888

Thats not entirely true. The old MAF was working but had a low output it would pass your basic testing of 1.4v at idle and 2v at 2000 rpm. I did not get a price from a wrecker (junkyard as you call it) as the prices are ususally not far from retail. And I would expect an old MAF to potentially have a low output like mine. The ebay one came with a 1 year warranty so I figured it was a safe bet.