1990 Q with 1995 Q engine has issue with tach and also stumbles at accel.

[mattd1979]

I have a problem with a Q that my Mom owns that use to be my nephews. What happens to start with is when you first start the car, the needle on the tach will jump to 5,000 and bounce as it comes back down to 800 rpm. This all happens as the engine starts and the engine seems to bounce along with the tach although it isn't turning 5,000 rpm when it first starts. It will also start to hunt as the needle on the tach bounces while accelerating from a stop until you get to your cruise speed. If you put it to the floor, it will surge until it passes 2700 rpm then it smooths out. I replaced the instrument cluster with another known working unit, but it still does the same thing with the replacement tach. It doesn't always do this. It only seems to do it about 70% of the time. The other 30%, it starts up and drives just fine. This all started to happen about 6 months after I did the engine swap. Does the Tach get it's signal from the CAS?

[Q45tech]

The ecu gets the signal from CAS then converts rpm into a 0>5 volt signal which feeds the tach voltmeter.Similar to speedometer except the speed sensor signal is converted outside of ecu and then sends the 0>5 volts to ecu. speedo voltmeter, ps steering computer, cruise and transmission via tcu.

Not unusal for these cluster voltmeters to fail after 10 years giving weird, sticky, jumpy displays.

Usual fix is to buy a junker entire cluster [so you have more parts for future] and swap..............years and options must match.

[Q45tech]

Remember the CAS sends 2 different signals: 1 degree resolution and 90 degree resolution the 90 ecu is very demanding of both. Which may create problems in trying to use a 94-95 CAS with a 90-93 ecu.

[mattd1979]

So would you say that it would be better to run the ecu that came out of the 95 in th 90 to be paired with the 95 engine?I was thinking that if the problem is with the older ecu, then I would have been having the symptoms above happen right after the engine swap as I was using the 90 ECU right after the swap.I did swap in the 95 ECU at one time for some other reason but the check engine light would stay on because of a sensor on the engine that wasn't connected because the 1990 engine harness doesn't have a provision for it. The sensor in question is the one that is right behind the EGR valve. I have swapped the speed cluster already with a known good unit with the same results. I suppose what I will do is just recheck the connection at the CAS sensor where it is spliced to make sure nothing is coming loose now that I know that the CAS is where the tach signal originates from. Is the CAS known to go bad? If the bushing that the CAS shaft rides in becomes worn causing play in the shaft, will that cause it to stumble up to a certain RPM? Thanks

[Q45tech]

YES

[mattd1979]

Are you saying yes to all of the below questions?

1. Would it be better to run the ecu that came out of the 95 in to the 90 to be paired with the 95 engine? If yes then what do I do about the check engine light staying on all of the time?

2. Is the CAS known to go bad?

3. If the bushing that the CAS shaft rides in becomes worn causing play in the shaft, will that cause it to stumble up to a certain RPM?

4. Is it even common for the bushing to wear out? The engine has about 85,000 miles on it now.
Modified by mattd1979 at 11:21 AM 8/19/2009

[mattd1979]

Update......

The car was finally available for me to take a look at. I checked all of the splices that I made when I did the engine swap in which all turned out good. I cleaned the connector to the CAS and I also cleaned the ground connecting points. I started the car and it continued to do the stumbling with the idle and it would surge as I would increase the throttle until it passed 2000 rpm in which it would clear up. I connected the laptop to the car and found that it had a code 43 I think for knock sensor and codes 33 and 53 for both o2 sensors. I decided to unplug the sensors to see if the problem cleared up. It cleared up and stayed that way as long as the connectors were unplugged. I plugged each one back in seperately so that I could monitor each by itself and noticed that when you first plug them back in, the gauge would sweep from left to right equally at 2000 rpm and then each would gradually begin to peg the gauge and at the same time, the engine would begin surging. So, I'm looking at a new set of o2 sensors. So I didn't have to swap in the 1995 ECU. The number to the ECU that is in the car now is 23710-64u05 according to obdscantech.

[goody90q45]

From the 14 page Nissan/Infiniti ECU list, that part number ECU is for a 91Q base (no TCS or active) with federal emissions. The number on the faceplate of the ECU should be A18-A21 P66.

Your surging problem sounds like a MAF issue. Have you cleaned the connector and MAF pins of all corrosion, coated it all with dielectric grease and tightened the pins on the connector?

[mattd1979]

I mentioned the problem in the last post. The o2 sensors are bad. I had already did a MAF swap with no change using my car as the test mule about 3 months ago. The MAF worked fine on my Q and the MAF that I swapped to the other car had no effect. This was before I ever had the consult interface to monitor the o2 sensors. The o2 sensors both peg to the rich side. The test was done with the engine revved at 2,000rpm. I compared it to mine in which the o2 sensors alternate between lean and rich like a pendulum on a clock. When I unplugged both o2 connectors the engine smoothed out and idled steady with no hesitation when accelerating from a stop. Thanks for the info on the ECU number. I have another ECU number for you. It's out of my Mom's 1991. 23710-64u09.
Modified by mattd1979 at 10:00 PM 8/30/2009

[goody90q45]

.....I have another ECU number for you. It's out of my Mom's 1991. 23710-64u09.

That ECU is for a 91Q, fed emissions, with traction control

[mattd1979]

Thanks goody94q45. You've been a big help.