Q45 stumbles @ exactly 3000 rpm

[RickyQ45AZ]

I'm new to this... so please excuse me. My 1990 Q45 failed emissions just after I purchased it and tried to get it registered. It was running fine, but smelled rich out of the exhaust, then failed emissions (like I said). I took it home and changed the oil, and installed a K&N air filter. Still on the jack stands, I tried to start it to circulate oil for a few minutes to check level on the dipstick (being new to the Q, I didn't know how much oil it would take). The car cranked but NEVER fired. Off the jack-stands, I changed the spark plugs & pcv valve. I fired the car (after several starting attempts), and drove around the block. In park and any gear while driving, the car stumbles @ exactly 3000 rpm. It idles very smooth but revs like it has a rev limitter at 3000. Just rat-tat-tat-tat-tat-tat, without fail! I was told to check all vacuum & fuel lines and electrical connections. I took the "coil covers" off and checked my work @ each coil pack to ensure bolt tightness and electrical connections. My thought was a computer issue, like it's in "fail safe" or limp mode or something, because I changed the plugs with the cables still connected to the battery (oops). ANY suggestions would be greatly appreciated. I'll be sure to add pics after I get it repaired as it is a really cool looking Q45 with a body kit! I'm really loving the car, just want to pass emissions and get it running as smooth as it looks!!!

[Q45tech]

Obviously you did not choose to have an EXPERT TECHNICAN analyse the 18 year old car and list the problems found to decide whether it needed $3,000 or $10,000 in repairs to bring it back to near new performance.

When we do prebuy inspections for clients on 90-93 Q we always find $3,000 at minimum in problems that may or maynot be obvious to the untrained.

What part of the emisssion test failed and what were all the various readings?

Probably easier to have the car towed to dealer for a paid list of defects, then we can help you decide what to do first.

AVOID UNTRAINED NON INFINITI TECHS LIKE THE PLAGUE, as they can often cause more damage just trying to diagnose.

Each dealership usually has at least one out of their 10 techs who is competent to work on early Q

WARNING the Q must be flatbedded, as rear wheels turning on the ground without engine running will very very quickly destroy the transmission like in a few miles depending on local temperature

The Q45 cost $38,000 in 1990 would be the equivalent of $65,275+ in 2008 dollars.

So that is the class of vehicle you are dealing with so expect that after you have repaired every defect that they will continue to need $3,000 each and every year to maintain to standard unless you acquire all the tools and skill and knowledge to maintain yourself but new parts will still average $1500 per year [including tires and brakes].

Restoring interiors or body work or paint is not included in any of above numbers!

Larger wheels adds serious stress to components so there will be an extra cost associated to that mod!

[Q45tech]

The 3,000 rpm stumble is a clue that one of the 2 connections to CAS or MAF maybe defective, corroded, or intermitent.

The FSM points [read fine print] out various safety limits preset in ecu like 2,000 or 3,000 rpm

[Q45tech]

I know CA requires a passing emission certificate for a sale to be valid doesn't AZ have a similar requirement?

[Infinitiguy19]

Could also be as simple as a fuel filter because I did'nt see that you replaced that and if that was the problem then you might need a fuel pump and control unit later on becuase of the extended stress on the pump from a clogged filter.

[maxnix]

1.) It was running fine, but smelled rich out of the exhaust, then failed emissions (like I said).

2.) I took it home and changed the oil, and installed a K&N air filter.

3.) Still on the jack stands, I tried to start it to circulate oil for a few minutes to check level on the dipstick (being new to the Q, I didn't know how much oil it would take).

4.) I changed the spark plugs & pcv valve.

5.) I'm really loving the car!

With no maintenance history, we can only guess.

1.) Bad O ring on an injector? Have you removed any of them?

2.) Lose the K&N. Known (to those who have read the previous posts) to be an MAF killer. OEM paper is best and least expensive.

3.) Why don't you download an OM and an FSM? They are free. TSB cost a one day subscription,

4.) Using OEM specified parts only, of course!

5.) Wait until you learn how to restore it to as new OEM condition.

[Kiven422]

You may want to check and see if your MAF sensor is plugged in. Hope its as easy as that.

[Haitian_King]

With no maintenance history, we can only guess.

1.) Bad O ring on an injector? Have you removed any of them?

2.) Lose the K&N. Known (to those who have read the previous posts) to be an MAF killer. OEM paper is best and least expensive.

3.) Why don't you download an OM and an FSM? They are free. TSB cost a one day subscription,

4.) Using OEM specified parts only, of course!

5.) Wait until you learn how to restore it to as new OEM condition.

I tried that website that offers the OM's and TSB's. I couldn't find the OM for my year. Or G50's in particular.

[maxnix]

I tried that website that offers the OM's and TSB's. I couldn't find the OM for my year. Or G50's in particular.

http://www.nissan-techinfo.com...id=54

[elwesso]

The 3,000 rpm stumble is a clue that one of the 2 connections to CAS or MAF maybe defective, corroded, or intermitent.

The FSM points [read fine print] out various safety limits preset in ecu like 2,000 or 3,000 rpm

I'll quote it again for emphasis.

The 3,000 rpm stumble is a clue that one of the 2 connections to CAS or MAF maybe defective, corroded, or intermitent.

The FSM points [read fine print] out various safety limits preset in ecu like 2,000 or 3,000 rpm

Did you check your ECU codes? 90-93 are known a little more to have funky connections especially at the CAS.

[Haitian_King]

http://www.nissan-techinfo.com...id=54

It looks like they stopped at 96. That wouldn't do me much good because it's OBDII right?

Thanks though.

[Kiven422]

a bad fuel pump is a common cause for failing emissions... even if it seems to run right

[Q45tech]

Never seen a bad Q fuel pump cause a failing of emissions, IF it can allow engine to reach 2,000 rpm. Emission testing is such a low load low hp application that most engine will run of very low psi and the O2 can adjust the 20% necessary to pass.

Fuel pumps are easily diagnosed with a fuel PSI gauge taped to windshield and driven under load. Or by a trained Q technican lying in the Q trunk/sitting in back seat on a drive.

[maxnix]

It looks like they stopped at 96. That wouldn't do me much good because it's OBDII right?

A few of the comfort and convenience features will not apply, but OBD II does not have a large impact on other operational functions.

[Q45tech]

Back in 1990 way before cable modems [1998] and dsl even before CD roms......................it was rare to spend the $20,000 necessary to scan in page by page or convert the LaTeX ... [book printing software] to *.pdf. {which didn't exist in 1990].

In 1994 I paid $1,500 for a 2 day school and software to burn new fangled data cds and $995 for a recorder + each blank cdr cost $12

Windows 95 made these easy and possible. As did Adobe 1995 Free Acrobat reader

Good reasons why there were no FSM *pdf prior to 1994. Can you imagine the the 50 floppies necessary to transport a 1990 FSM from one place to another.

1990 hard drives held only 40 MB not enough for the file.

[Kiven422]

Never seen a bad Q fuel pump cause a failing of emissions, IF it can allow engine to reach 2,000 rpm.

My Q wouldn't pass smog when the pump was bad so I had to pass it the other way. Most recent smog the fuel pump was replaced and it passed just fine perfectly legal.

The bad pump was good enough that we didn't have the need to replace it for a good 3+ years. It would pass 3000RPMs even to 4K as long as you used city level pedal pressure.

Hah - I still have Microsoft Word for MS-DOS on 6 floppy disks.

[Haitian_King]

Hah - I still have Microsoft Word for MS-DOS on 6 floppy disks.

You too?

I still have boxes of 5.25" floppies.

[RickyQ45AZ]

QTech.... I really appreciate your knowledge & advise, but I feel as though you condescend in many of your postings. I didn't have tens of thousands of dollars for the car, and in turn, I also did not have additional thousands for an expertly trained certified technician such as yourself. If I had that kind of money, I would've bought NEW! The car was a good deal, which I knew would require some $ and elbow grease to make it a nice ride. I'm new to this make & haven't had a chance to become fluent with repairs as of yet. I just needed some direction & assistance from anyone who may have encountered the same issue or KNEW what may be the cause. I wasn't expecting to be condescended to for asking a question. I found it quite common in many of your postings concerning other issues. Thank you very much for the information, it could've been a little friendlier is all I'm saying. Again, I do appreciate your expert opinion on this matter.

[RickyQ45AZ]

Thanks a lot! Yes, I replaced the fuel filter AFTER failing emissions, but forgot to include that in my posting. Post emissions failure I have done the following:oil change, replaced spark plugs, replaced pcv valve, replaced air filter with K&N (which I read in many postings was a mistake), and replaced the fuel filter. I don't know what a CAS is, but am considering replacing the costly egr valve before I go back to emissions testing center. Thanks again.

[RickyQ45AZ]

MAXNIX,Thanks a lot man!!! I checked the injector on the front of the fuel rail because it started making a "clicking" sound. After placing my finger on all of them, I could feel the clicking in the injector on the front of the fuel rail. After pulling it out of the rail, I noticed the screen was "funky" so I cleaned it and replaced the fuel injector, although the gasket was malformed around the outside of the injector. After starting the car, I realized that the gasket around the injector was leaking fuel, then I ordered the o-ring gasket set for the entire fuel injector system (guess what I'm doing this weekend). Thanks for the advise, any other input would be appreciated.

[96Qowner]

I don't know what a CAS is, but am considering replacing the costly egr valve before I go back to emissions testing center. Thanks again.

CAS is Crank Angle Sensor, but Nissan calls it CPS, Cam Position Sensor. The CAS connector, along with the MAF connector, is known to get corroded and cause trouble. Pull the connector and take a look - clean it up and apply some dielectric grease. It may be your problem - cheap n easy.