fuel pump or transmission?

[Mayhem_J30]

It's been a bad month for the J..

OK, I think it's the transmission but if I describe it hopefully you other guys can verify.When cruising at a steady speed that puts me in the 2800-3000 rpm range like highway speeds the J starts to putter like it's running out of gas. It doesn't do it drastically and honestly the only reason I probably noticed it is because my louder exhaust exagerates engine noises...which is a good thing for diagnosis. Feels like it's running out of gas but not on such a severe level. I think either it's the TC engaging and disengaging rapidly at that speed or the fuel pump is randomly failing. I can hear my fuel pump in the morning on first start, but it's not as loud and dramatic as what failing fuel pump owners describe. More of a high pitched whine that most people might not even notice. Both are due to fail now at 120K+ miles. I only got it to duplicate the feeling once this morning on the way to work, so maybe it's just the beginning. I'm more likely to get the problem fixed before I"m on the side of the road, but need to know if I should be bracing for a 3-digit dollar fix or a 4-digit.

oh yeah, I only run chevron premium and had a transmission pan drop and fill at the beginning of this year.

[pitaq]

I had the exact same situation with my former '93 J30t (sold it a month ago). Between 2000-3000 RPM's, the engine would shudder and stumble a little bit. Manually shift into 3rd, thereby increasing the engine RPM's, and stumbling would immediately stop. Seemed to be worst while holding steady speed up a slight incline. Never had a problem when accelerating briskly right through the 2000-3000 range.

Dealership diagnosis was a faulty ignition coil, resulting in an occasional misfire. Sold the car with the miss, and don't know if new owner has found a cure or is just living with it as I did.

I also had the original transmission fail at 70k miles, and it felt NOTHING at all like what you are describing, so take that as an optimistic view.

[Mayhem_J30]

that does sound very similar to my problem. It sounds cheaper to. I'll check into.

[juiceman]

When checking the timing you use #1 or #6 cylinder (I think) and a light

Can you check each cylinder somehow to see if the engine is missing. Meaning the light frequency will skip or change. The marks on the pully will not show but maybe a greese pen mark every something degrees will allow you to see if the mark changes position intermittently indicating either a plug or coil problem.

Just a thought. Anyone add to this?

Is there a way to inspect the coil with a multi meter. Are resistance specs provided in the manual?

I know I did not answer questions only added some but maybe this will help direct your inquiry with others on the board

[Mayhem_J30]

Is there a way to inspect the coil with a multi meter. Are resistance specs provided in the manual?

Exactly what I was thinking. I went home to get the manual during lunch and to see if I could replicate the problem. Forgot to grab the manual though :rolleyes Could only get it to do it on the way back. Happened going up a acceleration ramp onto a freeway at the same RPM range. Definately feels more like a misfire then a transmission problem now.

[VimyJ]

You have probably already done this but trouble codes 11 and 21, crankshaft position sensor circuit and ignition signal circuit respectively, don't trigger the "check engine" light. EF & EC 50,51 in the manual.

"Bad month for the J"? Think of it more as your continuing education into Nissan mechanical engineering.:rolleyes Sounds like a three digit repair.

[Mayhem_J30]

had time to get the engine codes this weekend. 55, so it thinks it's fine when turned off... I checked all the sensor harnesses that might be related and none look corroded. I just might have to get the dealer to use the consultant when running to help diagnose the problem.

[Mayhem_J30]

sounds like a lot of Z guys have stumbling problems and it is related to the 02 sensor(s). they look like a pain in the rear to get to though. clogged EGR valves were also mentioned, which also looks like a pain to do. Oh well, gotta keep my baby happy.

[Mayhem_J30]

well, i checked and cleaned all of my sensor harnesses last night. none showed any corrosion but i figured it was worth a shot. Took it for a drive, No Success. As soon as it warmed up real good started stumbling again at 3000. Put it back in the garage. Gonna check sensor resistances tonight.Does any body know what the CAS resistance is supposed to be? Can't find it in the manual. I found MAF and TPS.If everything checks out OK, I'm gonna just have the dealer to a FI diagnostics. That would be the quickest way to figure it out.

NEVERMIND, i found the CAS Voltage needs to be 0-5V depending on crankshaft position.

[Q45tech]

The CAS is an optical light source divided from a amplified photocell by a rotating disk with tiny slots evey degree and master [wider slots every 90 degrees [on a V8] 360 pulses per revolution . [[Some versions use a hall effect [magnet sensor] and a magnet whose field is affected by the slots]]The Q has 2 seperate system 1 pulse every 90 degrees [V6 every 120 degrees] and the other 1 pulse every 1 degree of exhaust cam rotation.

Thus the ecu knows when #1 cylinder is at Top dead center [via the wider start slot assuming the chain or belt and cams are assembled correctly.

Many sensors on a Q/J cannot be evaluated with simple resistance measurements! THE MAF and CAS are two examples

Since the chains or belts/sprockets are on increments of 10/20 degrees errors are at -20,-10, zero, +10, +20 degrees.

THE CAS is the MASTER CLOCK SYNCRONIZER for the ecu!

The ecu runs multiple timing signals [ ignition firing point, ignition duration, injector opening point and duration].

Since the OPTIMUM point varies with rpm and load even a 1 degrees change [misadjustment in CAS] changes all the timing points [not the duration just the start point].

If you start the spark too early you will get knock if you start too late all the fuel won't burn completely in time to extert the max force on the piston so power will be down...............fine line less than 10 degrees of CAS adjustment between the extremes.

[Mayhem_J30]

I only found Voltage in the manual not Ohms for the CAS. What should that be? On EF & EC - 234 a good number of sensors and equipment like FI's and coil packs are listed with appropriate Ohms, but CAS is not listed. I'm hoping it's something simpler like the CAS as it is to cold in the garage to spend all day pulling off the plenum to replace FI's."Since the OPTIMUM point varies with rpm and load even a 1 degrees change [misadjustment in CAS] changes all the timing points [not the duration just the start point].

If you start the spark too early you will get knock if you start too late all the fuel won't burn completely in time to extert the max force on the piston so power will be down...............fine line less than 10 degrees of CAS adjustment between the extremes."

Is this why(if it is the problem) the stumbling only occurs at load and at a certain engine speed? I'm sure the timing is absolutely correct but if the CAS is bad why just at that speed and load would it begin to perform poorly?

Sorry for so many questions. I feel like I'm so close to fully grasping the whole concept and how everything relates together; TPS, MAF, Coolant Sensor, CAS, KS.

At least if the plenum does have to come off I can replace things I've been wanting to get to like the pcv valves

[Q45tech]

You have to look at the CAS output with an oscilloscope to see the 360 tiny pulses.........or accept that the consult says its ok!Intermitents are tough because a drop out can occur [be short enough time] to confuse the ecu but not capture a code.

Same with MAF as a 20% wrong voltage can be created without a code especially at cruise or acceleration.

Intermitent knock sensors/harness can be a problem ok at cold crank but problems when hot. It is only checked at start and periodically not continuously.

[VimyJ]

Mayhem, how did your quest turn out? Did you get the stumbling fixed?

[Mayhem_J30]

Mayhem, how did your quest turn out? Did you get the stumbling fixed?

Honestly I haven't even had time to look at it recently. I've been in the mountains on vacation. I am making an appointment with our local dealer for a diagnosis of the problem.

[VimyJ]

Honestly I haven't even had time to look at it recently. I've been in the mountains on vacation. I am making an appointment with our local dealer for a diagnosis of the problem.

You went to those twisty mountain roads without your J? Well, I suppose snow might be a problem right now. Let us know how the diagnosis goes. Good luck.

[Mayhem_J30]

Bad news. The local Infiniti dealer diagnosed what I originally thought it was. The TC in the transmission is having engaging problems. I had the dealer do a full print out of all their results, so maybe I can go over it again. Man, I was really hoping that it would be a cheap sensor or something.So I guess I need to save up a bit more for a new transmission...unless of course you guys advise me otherwise. Looks like I can get one at aprox $2200 from infinitiparts.net...it's over $80 so I guess I get free shipping too. I'll have to call and find out what all it comes with.1) I plan on getting new transmission mounts while it's being done.What about sensors? Do these normally come with the new transmission or no...if no should I have them replaced?2) Should I use the place that normally does my transmission flushes or just go to the dealer for install?