98 Q45 Transmission bucks and shudders/erratic shifting/no starting power

[QCumber]

Long time reader, first time poster. I have spent the past 5 days reading this board and a few other help sites to no avail.

My 98 Q45 has started to lose it's mind as far as the transmission is concerned.

Invariably, my transmission will shift erratically: sometimes downshift and rev the engine, sometime upshift and lose any kind of torque.

When I first crank it up and drive I get at least 5 minutes of normal operation, after that, 80% of the time I lose all starting power (feels like maybe starting in 3rd???).

While driving I get a weird bucking (almost like I am on a rocking chair...although not quite so soothing)...I usually slow down or accelerate and get rid of the problem.

Here is what I have done to date to diagnose/remedy the problem.

1. Went through the steps in the TSM for self diagnosis: nothing shows up.

2. Removed the transmission pan, replaced screen/filter, replaced gasket, cleaned up everything and replaced with Mobil 1 synthtic ATF.

Any thoughts on this before I surrender it to a transmission shop and be at their mercy?

Thank you so much in advance for any of your time spent on trying to help me!

QCumber

[qship96]

I doubt the problem is with the transmission,more likely to be a sensor-I would inspect the throttle position sensor first.Find a close Infiniti dealer and pay the 1 hour fee for a diagnostic check and post results here for further advice.

[goody90q45]

.......Here is what I have done to date to diagnose/remedy the problem.

1. Went through the steps in the TSM for self diagnosis: nothing shows up.

I'm curious if you pulled the codes from the ECU or did the transmission self-diagnosis? Or both? I'm not sure what on-board self-diagnosis is available for the 98Q. How's the fuel pump/pressure?

[QCumber]

I went through the steps on page 49 of the TSM for self diagnosis of the transmission and came up with nothing.

The only codes coming from the ECU are charge temp control.

Thanks again for the advice I will bring it to the dealer tomorrow to geta full diagnostics as suggested.

You guys rock!

[maxnix]

Here is what I have done to date to diagnose/remedy the problem.

2. Removed the transmission pan, replaced screen/filter, replaced gasket, cleaned up everything and replaced with Mobil 1 synthtic ATF.

Any thoughts on this before I surrender it to a transmission shop and be at their mercy?

2. did not result in in a complete ATF replacement.

First, you should not drive your car before it is at operating temperature!

Second, you post no maintenance history of the transmission (beyond your recent drain and fill - good for 4 qts.) nore the intake fuel system. More information please.

Since the transmission does not generate power, how do you know it is not your engine?

[QCumber]

"did not result in complete ATF replacement"Yes, I understand that I only replaced a portion of the ATF.

As far as records that is all I have. I rebuilt (body wise) this Q from the ground up over the summer, it had been an insurance total/sellout. I have inquired with Inifinity and it looks like all dealer maintenance stops about 50K miles ago. The car now has around 128K.

The engine seems to do fine without load. Not sure what else I can check though.

I have put a ton of time into this, just having a hard time seeing the light at the end of the tunnel.

[QCumber]

Ok, quick update.

Took it to the dealer this morning and spent most of the day there (mostly scratching my head).

They apparently decided that I was not getting enough compression and that (for $800) they would have me up and running in no time).

That almost got me laughing, I guess they see this old banker cat all dressed up nice and don't fathom that I was rebuilding motors in the back of my pop's shop before any of them were even born.

Took it home, all 8 of my cylinders have just the right compression (all getting ~150 after a few turns of the motor). All the plugs and coilpacks looked perfect, the piston heads all looked nice and clean.

I did a resitance test on the Throttle Position sensor and the readings match what the TSM say it should.

I am close to my 100th project car (mostly german) and I have never pulled so much of my (mostly gone) thinnning hair out!.

[metaverse3]

Go to your MAF... Mass air flow sensor.

Check out the harness going to it..especially the grounding wire (black). For that matter, check out all grounding points in the car..

A mass air flow sensor can cause the bucking you describe going in and out of failsafe limp mode confusing the ECU & TCU.. I had this happen on a maxima which had identical symptoms..made me think I was losing the transmission..

Remove MAF..clean the connector on the MAF..you can scrape it using a small flat blade lightly.. same for the engine side harness of the MAF.. use di-electric grease to seal the connection when done..

As for cleaning the MAF element itself, use electronic parts cleaner from your local electronics parts store.. (radio shack) Spray and let it air dry.. You will hear a lot of whodunit stories about not working with the MAF element. It is a man made part..so, unless it came from krypton, you can work it.. Make sure to use the electronic parts cleaner so it does not leave residue..

While you are at it..check the knock sensors as well..unless previously replaced, they are probably gone by now..

A check engine light or lack thereof is not the holy grail of a vehicle's performance.. There ar basic parameters that the car expects for it to perform. Old parts that are borderline can cause many issues.. Unfortunately, this is the gamble with an older vehicle or just plain age. Good luck with the troubleshooting.. Post back with results..

[QCumber]

Thanks again to all the people who are helping out.

Took the MAF out cleaned it as instructed, no change.

Put in a new MAF, no change.

Back to the drawing board.

Best I can tell this problem is only happening in the following situations:

1st thing in the morning, I let it warm up -> drives just fine (including a 3 hour trip) with no issues.

As soon as I park it for more than a few minutes and get back in and crank it for the second time that day it goes back to bucking and hesitating and erratic power.

The picture is a little clearer in my mind:

1 Could this be a vacuum leak? I am trying to follow up on that.

2 Head temp sensor maybe? Since the car is going to heat up some after I park?

Thanks again for any thoughts...

[Q45tech]

There is NO head temperature sensor just a coolant temperature sensor [feeding ecu which is worthless if low on coolant or exposed to steam].

[maxnix]

Vacuum leak would manifest itself on initial trip.

'how long does it sit before restart? Do you have another known good FPCU?
Modified by maxnix at 9:07 AM 12/1/2007

[ScottJackson]

If the fuel filter hasn't been changed as far as you know, change it. Other than that, it could be the MAF (mass airflow sensor).

[askaway]

This is late, sorry. Replacing with mobile one synthetic seems right, especially since the dealer recommends. You need to drain every drop of fluid you have in that transmission and replace it with the synthetic trans fluid nissan provides. I know, you think the fluid is right but no. I took the same trans out twice. I found out that it was replaced with the mobile synthetic before I got it. There was nothing wrong with the trans gears/components. Get the fluid online from nissan and shift away. Damn I hope some "gearheads" learned some from this 21 year old magician.

Thanks David