90 Maxima idles/ runs very rough

Awesome forum folks! I'm curious if a few of you could chime in here.
My 90 Maxima started running rough intermittently and the temp gage would drop to zero, sometimes it would stall at idle. To make a long painful (& $$$$$) story short, I have replaced all sensors (Xcept crank angle) cleaned all connectors & grounds, checked all wires...and now it will hardly run at all! You name it, filters, plugs, cap& rotor...have been replaced & or double checked working. Code 12 keeps coming up for MAF sensor......It is new...and verified working correctly...I even took it back & got another one!

The engine runs so rough that thick black smoke comes out of the exhaust. Fuel pressures are fine, fuel is fine, ignition is fine.

As a last ditch effort I have ordered a new ECU from a salvage yard. I would love to hear any suggestions...I'm stumped!

P.S. great page "Walts Nissan Looks like stock"

-Jeff

...rough intermittently and the temp gage would drop to zero, sometimes it would stall at idle....

"Intermittent" is the worst word here... Some thoughts:

Possibly u have 2 or more problems simultaneous masking each other.

1. Idle: Have u cleaned IACV? If so, air leaks are possible.
2. Temp sensor wiring has a cut (=needle drops), engine drops to open loop. TPS & MAF will take care of injection input to ECU. (Cold engine, no O2 used)
3. Problem with TPS & its wiring; measure TPS resistance from ECU or TCU pins
4. Spark plugs? New NGK?
5. First maxima models will die if crank angle signal is bad. Also it will ruin idle... Distributor grounding pin is most probably bad: clean & add new gnd wire to engin -or- chassis (any gage wire works here). Check sensor for dirt bits .


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Thanks for the quick reply. Yes, I have cleaned and grounded the distr. I have not cleaned the IACV yet...but I will do so. The wiring from temp sensor has been replaced & verified good. The intermittent issue is no longer valid, It barely runs at all now....only if you keep working the throttle....its defineately not driveable.

I'm going to verify the wiring from the TSP agin....just to be safe.
As far as the crank angle sensor......if I have to buy another costly part my wife will strangle me! it looks clean and tests out fine...I can only hope.
The saga continues...........

I for got to add...Plugs=new NGK.

2 weeks ago I thought I had the problem (engine stumbling & temp gage going to zero) solved after replacing everything. The car ran very strong for a few days. Then suddenly at a stoplight the engine went chugga chugga->stall. It restarted but ran very rough...enough for me to limp it home. That brings us current to today.....the car is not driveable it runs so rough.

I agree with the temp sensor forcing it into open loop...this was most likely the cause for the rough running problem. I replaced the temp sensor wires last weekend after noticing high resistance in one of the two wires.

The MAF code is sending me into a tailspin. When I unplug the MAF, it seems to run a LITTLE better (not above 2000 RPM since it is clamped).

It is as if the more sensors I replace the worse it runs........

....Then suddenly at a stoplight the engine went chugga chugga->stall. ......

"When I unplug the MAF, it seems to run a LITTLE better"
- points to bad MAF, dunno. Very seldom there would be 3 dead MAF's ... still marginal possibility.
- How about its wiring? SMJ's, the 2 harness connectors at left foot corner.


- Smbdy told he bought 2 distr NEW caps in a row; both cracked broken. (My cap is now lacquered with engine lacquer.)

- how about big air leak? The rubber ting between the MAF plastic tube & engine,TB. Broken intake gasket? Some spray starter gas around to inspect leaks...
- gas pressure, tst

- temp sensor 2wires? Points you are in the EGRC circuit; that cannot affect too much on hihger rpm. AND the gauge & ECU are connected to the one wire temp sensor...

- test old NGK plugs which had no problem. I've had new, small engine NGK's fail.
- How about plug wires? They must contain Real wires, and it has to be verified that every end has been properly terminated: NGK's, Nissans own fail in this inspection. DIY... http://www.cardomain.com/ride/748507/12

Anyways, I think this is key: "Then suddenly at a stoplight..." ...only if one could figure out all the changes that happened prior to this...

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Well....here's the update. New PCM came in yesterday. I hooked it up......no change with the problem. I tested the TPS off of the car...its good. Reinstalled TPS...still....problem exists.

The car is getting worse. Now it cranks and sometimes catches...mostly won't run at all. When it does catch and run it is so rough it won't idle or rev at all. Any accelerator movement kills the engine.

New computer shows code 12 (MAF circuit problem)...just like the old computer. Hypothesizing that disconnecting the MAF will cause the engine to run in "limp home mode"...no revs above 2000 RPM....engine still reacts the same...no change. This along with the MAF testing out good leads me to believe there is another issue causing the code 12.

Since the engine barely runs at all...I suspect timing may be an issue. This weekend I will check the timing belt and timing of the engine....a timing belt that has slipped a notch would cause similiar symptoms.

If the timing cheks out (I replaced it 1.5 yrs ago ~ 10,000 miles).....I'll check the cat. converter for blockage.

This thing is going to fight me to the bitter end.............

Update.
maxima-850 Jeff-0

Completed all reccomendations by Nahkapohjola, removed timing belt covers to verify correct timing (timing is correct). Replaced coil and power transistor. Still wouldn't start. I decided to check the spark plugs.....they were fouled like you wouldn't believe! (brand new mind you) so I cleaned and reinstalled them. Now the engine starts and idles...still a little rough though because it's still in "limp home mode" with a code 12 for MAF circuit problem. I checked the MAF again, correct voltages are present (1.3V from pin B to ground, Batt voltage from pin E to gnd). What would cause a MAF code with a functioning MAF sensor and circuit?

Iwas going to check the CAT. converter but the threads on the bolts were completely rusted together....I'm not going to open that can of worms right now.

I decided to stop after 10hrs today...it's damn hot and muggy here in Kansas City right now. I'm really stumped now. I'm out of ideas.

..What would cause a MAF code with a functioning MAF sensor and circuit?...

The voltage level from MAF output has to change linearly with the rpm: the higher rpm, the higher voltage. I tried to detail sensor tst here, check Favorite Links also for manual: http://www.cardomain.com/ride/748507/9

Engine drops into safe mode =2000rpm limit, if: MAF, CamPos, TPS sensor disconnection. A/T tranny drops to neutral while driving, accel, breaking. Maybe temp & O2 disconnect, dunno.

Check that campos signal reaches ECU connector.
Check for air leaks after MAF.
Ign hivolt wiring, repLaced with rEal wires?
The ECU is a lottery machine; dont expect it to give any or right codes. (To replace ECU, somewhere there is a table which tells the ones will fit; the product codes have to be exact.)

CAT does not affect the process any way -except if- its totally blocked. Opening exhaust will help in such case. I dont beleive its issue in here.


hEre: +46F in the morning... summer is over.

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Well Gentlemen....It's fixed!!

Here's the scoop. There were no less than three issues at play here;

1st: I replaced a faulty wire from the temp sensor to the PCM. I actually replaced both of them. I thought they both went straight to the PCM......Well...one does. the other (black) Gnd I assume, goes to the trans control & most importantly, the TPS. I awoke this morning thinking of this (the schematic is engraved in my brain at this point). I wired them properly.

2nd: The spark plugs were destroyed (massive carbon fouling) from the engine running so rich. If your engine runs for about an hour in safe mode, your plugs are probably shot. I replaced them W/ new NGK's...again this week!!

3rd: I still got a code 12 (bad MAF ckt) and engine ran like crap with the MAF pluggen in & ran well (although <2000 rpm) and idled well with it unplugged. I checked the output signal and was astonished to see 8.5 volts!! Another bad MAF sensor from Napa!! I took it back & exchanged it for yet another remanufactured sensor and viola! it runs like a champ!

Lessons learned: Don't forget the simple stuff & Don't be afraid to question "new" remanufactured sensors.

Nahkapohjola...is it possible that my Max is "eating" MAF sensors or is it more likely that NAPA has poor quality control?

Nahkapohjola...Thanks for your help...your site rocks!!

Let's hope Its the poor quality control...I'm tired of troubleshooting this.

Well Gentlemen....It's fixed!!...is it possible that my Max is "eating" MAF sensors or is it more likely that NAPA has poor quality control?...

Great News! You won the triplebeast... happy for u!

MAF
- I suppose the MAF is suspect to die b/c of vibration. So if u do not have stock or better vibration dampeners, or for some other reason engine gets it jumping, possibly this kills the heater resistor or smtg...
- Bad packaging? The mailboys try to decimate all packets: jump on until cracking bingo sound
- Poor workmanship: typically these kind of simplex boxes are repaired by the guy from the street with 3min education, below min wage, longing for the beach

Nice to hear about the (amateur) web page. Anyways its from troubleshootin point of view where I happen to have 'some' edu&experience. It is not done like FSM (=teengirls interviewing R&D dpt). Amateur =no charge web domain, just a compilation what happened AND with those CDomain stupid limitations.

What u could do, pls:
I suppose u have now one junk MAF at least. Open it by heating the cover stuff out, draw/&take pic of wirings or whatever is inside. AND Deliver for us. I suppose all it contains are those two 5c resistors, but would like to know/see. (here we have more elephants than maximas in the junkyard. Btw. no elephants...)

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Unfortuneately, they keep the bad unit. It has a "core" charge associated with it. Check this link out :

http://www.autoshop101.com/forms/h34.pdf

Next time I'm at the junkyard (It'll bee soon, my drivers side window just fell into the door this morning as I rolled it up at work) I'll take a camera and get some pics. Here we have many Maximas in the junkyard.

BTW never wear shorts to a junk yard......even when It's 100 degrees @ 90% humidity out.....I was a mosquito dinner plate....30 bites=itchy welts.

I really hope it was the MAF going bad that caused the car to stall at the stop light a few weeks ago. It will take awhile for me to trust the Max again.

...It will take awhile for me to trust the Max again.

Good link. Toyota has some other good info pages of ECU etc. But where is Nissan???

I used to roam junkyards. But maybe some ten yrs ago gvmt gave em business education (!?). Nice way to use my money. As result, their prices rose above new parts... in principal that makes me nogo. But what one cannot escape is the 7.5$/gallon gasrobbery. The crooks who devide it among emselves, are screamin of joy of this Katrina -booty!

Hopefully u max starts, behaves, otherwise its future lies as mosquito breeding dish. Often with failed MAF u may limp home, so its not the worst failure.

Make sure you use 92 or 93 octain gasoline cause it will cause your sparkplugs to file out

Well, as I feared, my wife drove the car to work and it went into "safe Mode" again. I tried it later and it worked fine. It just seemed to do this intermittently. I checked all sensors that could cause the ECM to go into safe mode. They are all fine. Wiring to ECM from all sensors <.4 Ohms as well.

I remembered that Nak said the transmission going into neutral could cause the ECM to go into safe mode as well. It senses neutral by using the neutral switch which is part of the inhibitor switch. I have had one of these switches go bad in another car and it would cause no start intermittently. The key here is that there are 2 circuits or switches. One 12v switch inline with the starter solenoid and the other, a low voltage < 3v I assume, from the ECM pin 45 to pin 46. I checked the resistance between the wires that go to pins 45, 46 and found 82 Ohms !! this would probably appear as an open for a 3v ECM. I removed the inhibitor switch (pain in the A$$) from the drivers side of the trans. After dismantling the switch, I found it was filthy with dirt, grease, and corroded contacts. I cleaned it thouroughly and polished the contacts, reinstalled it and as of yet it hasn't gone into safe mode. I'll report back after I drive it for awhile.

Nak, what do you think of my theory here?

-Jeff

...the ECM pin 45 to pin 46. ...

Wassup. Pin 46 is A/C input to ECU.

If problem renews, to tst, make a jumper wire to bypass suspect sw.

click http://www.cardomain.com/ride/748507/1 ---p.7 & p.15

http://memimage.cardomain.net/member_images/4/web/748000-748999/748507_333_full.jpg

http://memimage.cardomain.net/member_images/4/web/748000-748999/748507_221_full.jpg

Whoops!, my bad. I meant 44 & 45. I typed the last post from memory while at work. So far so good. It ran really well today. It seems stronger now.

I'll hold my breath.......It's off to Boston for the week! It looks like I'll need an ark for the trip when I get there.