Cutting out at about 3000 rpm

[dnudelman]

Hi guys,
My 94 q45 has awaken from its winter hibernation and the motor is cutting out around 2500 or so RPM. Changed the fuel filter, added injector cleaner. I used to have to Consult software for windows, but no more. Suggestions?
Thanks
David
94 q45 Base 160K miles.

[dnudelman]

No CEL, swapped MAF, no difference.

[VStar650CL]

After sitting all winter you might just have crappy gas. You might have a weak fuel pump that isn't spinning up as fast as it should, but you'll at least need a gauge to see if that's the issue. The MAF you can check with a voltmeter, the readings won't change with or without a load. Is it breaking up, or just dying and won't accelerate?

[dnudelman]

Thanks, its going to dealer friday for diagnosis.

[dnudelman]

Dealer says CMPS crankshaft position sensor failed. Replacements from Ngk, Standard, Spectra - taiwan. Anybody had experience with afternarket?

[VStar650CL]

That sounds like a likely diagnosis. The optos in those can fail, the wheels can crud up, or the seals can blow and drown them, all the same problems as the ones on ZX's. NGK is always a good choice for Nissan/Infiniti sensors and Spectra is generally reputable (I can't speak for that particular part, but my customers have done well with the brand). I'd steer clear of Dorman, their stuff is almost all China-cheap. SMP is a semi-crapshoot, some of their stuff is junk but you can usually tell by the way it's priced.

[dnudelman]

thanks, I have a spectra coming from Amazon. If it looks cheap, its going back and next choice will be the ngk.

[3Q Jay]

dnudelman contacted me earlier this week, and he and I have been discussing this off the board....but I want to add this here for future reference.
______________________
The tech may know this if he’s been there a long time, but unlike the more modern position sensors, this part actually affects the base timing of the engine.
So, that will need to be adjusted upon install of the new part. It’s very much like an old distributor.
#6 spark plug is much easier to get to than #1, for setting the base timing.
Also, you’ve been under the plenum…so if you are thinking DIY, this sensor job is not hard at all, just need to mind the keying where it inserts to the camshaft end, and either time it, or mark the V-notch in the housing it so it will be close enough until you can get it timed.

[dnudelman]

Update:
Japanese specialist shop did the install and timing with the new part. NO CHANGE.
So my questions to the wise ones here
1. The dealer consult error code was CAMSHAFT POSI SEN before the replacement.
2. The shop will check their work, but car starts up, idles normally but will not rev past 2500-3000 rpm. which describes the failed position sensor.
3. Is there a way to check the replacement part?
4. I have the old part, can I check it off the car?
5. Does the ECU need to be reset or clear the codes for proper operation after the replacement?

Thanks
David

[J30tChumpCar]

When you say cutting out, does it fade and not rev? Does it hard cut like a rev limiter?

No/bad signal from the airflow meter may not set a code but will do low rpm till 2500ish then cut, then repeat... even with the pedal to the floor.

[dnudelman]

hard cut, fail safe mode

[J30tChumpCar]

I know you already tried, but circling back with a known good airflow meter is what I would do.

[3Q Jay]

Update:
Japanese specialist shop did the install and timing with the new part. NO CHANGE.
So my questions to the wise ones here
1. The dealer consult error code was CAMSHAFT POSI SEN before the replacement.
2. The shop will check their work, but car starts up, idles normally but will not rev past 2500-3000 rpm. which describes the failed position sensor.
3. Is there a way to check the replacement part?
4. I have the old part, can I check it off the car?
5. Does the ECU need to be reset or clear the codes for proper operation after the replacement?

Thanks
David

David-
I would not be surprised if the aftermarket replacement has poor quality internals and is not working properly. Of course I hope that new parts are indeed quality new parts, but.....
I would definitely clear the ECU although I'm not aware of a 'latching' limp mode that would be a vestige from the original sensor failure scenario.
There are some diagnostic (bench) checks on page EF/EC 216. Did you try those?

[3Q Jay]

I know you already tried, but circling back with a known good airflow meter is what I would do.

I agree with subbing in a known good part as a diagnostic aid. But I'd focus on the CMPS, not the MAF at this point.

[dnudelman]

Jay, If I understand the timing instructions properly, there are 5 marks on the pulley. 15 btdc should be in about the middle??
With my timing light, I am measuring way more advance.

I am using the wire on the pass side of the valve cover as per Wes Stimpson write up on q45 timing. Let me know what you think about the timing. The motor is idling smooth. I'm going to disconnect the battery overnight to clear any stored codes.
Thanks
David

[3Q Jay]

David-
I recall 6 grooves in the pulley? 0-25 deg? so 15 would be the 4th hash. remember to be hot idle at about 650 rpm max in park, AC off.
Is your light a "dial back" light? if so, then what does the gun say when you have the 0 deg (yellow paint?) indexed?
Regardless, you are using the +12v wire, which feeds all the coils, which also means that your light is triggering not just from #6 (the desired one for setting timing), but from 2, 4 and 8 as well. probably no big deal, just something to keep in mind. More importantly, using the 12v wire is less definitive than using a stub of HT lead between the coil pak and plug #6. Yeah, it's a pain in the butt to do it the preferred way.
Practically speaking, my tests have shown anywhere from a 1 to a 4 deg offset between the two methods. It really all depends on how your light triggers. bear in mind that when you use the 12v feed to the coils, that line changes voltage (drops) when the ECU tells the coil to start charging the primary (think points dwell on your old alfa). the voltage on that 12v line will go back up at the instant the ECU opens the trigger pin on the coil to fire the HT (secondary) lead. So, is your light triggering on the rising voltage signal (likely) or the falling voltage? you might try flipping over the inductive pickup to see if that makes any difference?

[dnudelman]

1. I'll try flipping the pick up. the gun is not firing on the 4th hash.
I'll run through the hot idle proceedure.
If necessary, adjust the timing
There are no yellow marks on the pulley.
my light is a dial back light. at 0 btdc dialed in the first hash mark is CCW before of the timing mark a little.
test again
swap CPS
check timing.''

thanks
David

[dnudelman]

Since my last post
1 checked timing
2. Swap out CPS with a used one from from a junk yard
No change, cutting out - fail safe mode 3000 rpm
3. Took the car back to Infiniti of Bellevue that did the Consult Diagnosis. The service lead was not happy to see me. He is the only guy that can work on cars this old.
4. He checked the new aftermarket CPS as well as my original and the junk yard, all tested GOOD.
5. He checked the wiring harness, all GOOD.
6. I had left him my original ECU, I have been running a NICO ECU that Wes modified for about 12-15 years.
7. The tech at the dealer went to swap out the ecu, he noticed the wire from the NICO ECU that went to a switch in the glove compartment. The switch had been bumped and set to Valet setting. Problem solved, car runs as it should now.
They were generous and only charged me 1 hour of shop time.
I left him a good tip.
So now I have 2 good extra CPS plus the one in the car.

Big thanks to J3Q Jay who helped me along this journey.

[Q451990]

Wow - that would do it. I'm glad you got it figured out!