Stumble/hesitation problem

[fendesj]

I am having a problem with my 02 Maxima SE auto with 44K miles. It sometimes stumbles/hesitates on the highway around 70MPH and 2500RPM. It happens when applying light to moderate throttle. The usual scenerio is when going up a hill on the highway around 70MPH and I have to increase the throttle slighty to maintain speed or pass someone. It doesn't allways do this but its often enough to bother me. It never does this going down hill or on level road. I allways use 91 or 93 octane fuel. I am guessing maybe its the knock sensor. What do you think and how would you go about diagnosing this? Also I had the MAF replaced at 39,000 miles so its new.

[fendesj]

Also my gas mileage has dropped to around 21MPG. I do mostly highway driving 25 miles to work each day. I was getting around 25 or 26. Any ideas?

[fendesj]

OK, no replies yet. I have more info that might make it more interesting. I hooked up an OBDII logger (carchip) and got some data. There were no stored DTC's so I guess knock sensor is ok. Cruising on the highway at steady throttle around 70mph. TPS reads 9 to 10%, RPM is around 2700, and spark advance is 25 degrees. I step into the throttle a bit to hold speed on a hill. Throttle goes to 17% and spark advance goes to 2 degrees. Does this seem like excessive spark retard? Would this cause the stumbling? I also notice the spark advance sometimes going negative which I guess means ATDC. Is this normal. Does the ECU retard like this when the auto transmission shifts to make shifts smooth?

Now today my check engine light comes on. I pull the code and its P0138 - O2 Sensor Circuit High Voltage (Bank 1, Sensor 2).

Isn't this the rear sensor that is only used to check CAT operation. If so this can't be the cause of my problems right?

[s13sr20chris]

that all sounds normal

rear o2 has no effect on fuel trim

[s13sr20chris]

check out the things mentioned in this thread and let us know the results.

http://www.nicoclub.com/zerothread?id=81587

the only common things on the a32 max were maf, coils, o2 sensors, and cats. those are all possible causes of drivability issues.

[fendesj]

Thanks for the reply. The 02 Maxima is an A33. I found a Nissan TSB for the P0138 code. The TSB says to replace the rear O2 sensor and re-flash the ECU. Because I had the hesitation/stumbling/milage problem before the code was thrown I don't really think this is the problem. Plus as you say the rear O2 sensor doesn't impact fuel trim.

So its normal to see the spark advance go to just 2 degrees BTDC when increasing the throttle on a hill?

My poor gas milage started after the dealer replaced the MAF. This was done according to a TSB that also included instructions for re-flashing the ECU. The new MAF was a different part number then the old one and the TSB has specific instructions about re-flashing depending on the p/n of the ECU and MAF. I suppose its possible this was not done correctly. Its going to the dealer on Monday so we will see what they find. If they just replace the rear O2 sensor I wouldn't expect it to fix my problem. I will update you with the results.

[s13sr20chris]

02 max?

oh duh. i refered to it as an a32 because i thought you said 99 max. ok, i would have mentioned the countermeasure maf and reprogram bulletin. if you can get your hands on a consult printout i will look up the ecm p/n and see if you have the latest. that spark advance is typical. it will go even farther than that under the right circumstances.

the a33 doesnt have too many common probs. they had some issues with cats, the y-pipe, and o2 sensors. the big thing on the a33 is the maf but you have one already.

[fendesj]

Chris, thanks for the reply. It went to the dealer today for the P0138 code. The dealer performed TSB #NTB02-051A. This consisted of replacing both rear O2 sensors and re-flashing the ECU. I asked the service writer for a copy of the Consult printout. He was very nice and did this for me. It showed my starting ECU P/# as 23710-5Y711 and after the reprogramming it was 23710-5Y714. Can you tell if this is the latest level? Back in November I had TSB #NTB03-023 done which was to install the newer MAF p/n and re-flash ECU. So they installed MAF p/n 22680-AM600. I don't think they re-flashed the ECU however because this TSB shows ECU p/# 23710-5Y711 as the starting level for early production 02's with auto transmission. Can you verify this? My invoice for when the MAF was replaced says nothing about the ECM reprogramming but today my invoice specifically states it was done. So I think this may have been the cause of my problem. I won't know if its fixed until I drive home from work tonight.

[s13sr20chris]

i will check tommorow at work.

[fendesj]

I will be interested to hear what you find out. I can say that the re-flash seems to have fixed my problem. I have not been able to make it hesitate or stumble climbing hills on the highway. It just pulls nice and accelerates smoothly when tipping into the throttle. I hooked up my data logger and it looks like much less spark advance is being pulled out when tipping into the throttle. Before I was seeing the advance go from 30 - 40 degrees at steady cruise down to 2 - 10 degrees. Now it drops the advance to around 20 degrees. Its to early to tell how my gas mileage will be impacted but I am expecting an increase of 10% or so. Chris, does Nissan make available a list of changes incorporated into each new ECU software release? Thanks.

[Q45tech]

Tip in throttle [light > medium load] retard is always a place to look as oem are very conservative to avoid knock in summer with iffy gasoline [even 93 octane].

One of the old JWT ecu tricks was much less tip in retard to make the engine feel more frisky.........gain those 0.1 seconds and they add up

[s13sr20chris]

shoot, brought home the wrong list of ecms. i have not forgotten!

[s13sr20chris]

ah hah, no wonder it was not on the list.you have the latest ecm for 02 a33 a/t STANDARD maf(p/n 22680-6n201)the countermeasure maf is p/n 22680-am600

[fendesj]

Well now I am concerned because I have the MAF with P/N 22680-am600 (why is this called the countermeasure MAF?). This was installed a few months ago per TSB 03-023. Are you saying I should have a different ECM P/N which means different ECM software? Can you tell me what ECM P/N I should have? Thanks.

[s13sr20chris]

the countermeasure part is an updated part released to solve a problem that a brand new "regular" part would not fix. in your case the ecm p/n you should have is 23710-6y314.

[fendesj]

Is it possible the 23710-5Y714 code could also support the newer MAF? Or is it a definite I should have 23710-6y314? I called the dealer and their first response was that it was impossible to reprogram the ECU incorrectly. I think they misunderstood me however and they do seem willing to work with me. I read the TSB's and it looks like an ECM ID Code is supposed to be entered during the procedure if you have the updated MAF. Would this change the ECM code from the 23710-5Y71x train to the 23710-6Y31x train? Thanks.

[fendesj]

Chris, the dealer called me back and after talking it over (and probably researching it) they reached the conclusion that I needed to have the ECU reprogrammed. So I went over there this afternoon and they did the reprogramming. They were very nice and apologized for the mistake. They gave me the printout from the Consult reprogramming and it now shows I have 23710-6Y314 as you said I should. Thanks for your help.

[s13sr20chris]

no prob, hope that solves everything for you.