1990 q45 gradually over 2 months cannot exceed 2,100 RPM

[Q451990owner]

I first noticed that when I kick down I could not get past 4,500 RPM. I thought it was a transmission issue. But the problem was getting worse, it started bothering me when the RPM capped at 3,500 on all gears while driving. In idle no problem.
Then I noticed that it reduced to 3,100 .
When the car is morning cold , first turned on, I can drive for a couple minutes with no problem reaching high RPM (5000+) . After a minute or so when the car is warm, it choked with no power at about 3,000 rpm.
Now it's at 2,100 RPM.... It has become a major problem to climb hills....

I have e new fuel pump. New filter, new gas tank , new MAF sensor. I tested the fuel pump by jumping the connector to ground putting pump on high speed. Nothing.... I cleaned the CAS connectors, nothing. Changed fuel filters 3 times. They were dirty, however now not anymore. Put a new filter and immediately no difference.
Someone here suggested the temperature sensor for the coolant, but why would the car be losing it ability to go higher in rpm over time?
I'm suspecting a clog somewhere , that gets worse with temperature, perhaps a catalytic converter or exhaust .

Any ideas?

[qship96]

Time to take it to a professional.

[Q451990owner]

I agree. The only problem is that they want so much money .....
I found a decent Q45 mechanic that will accept the car on Monday. He will start with a pressure test on the fuel pump and go from there. This could very well be a bad pump, but if my memory is not wrong, I had the kick down problem already before I changed the pump.
What a weird car this is. Such a nice car to drive, but so many problems....

[BCC93QT]

Not the car. It is the fact it sat for 10 years and from the sounds of it you are not either wealthy or mechanically inclined enough to give it fair treatment.

[melvingoku]

^don't have to be wealthy to fix it. lol i"ve never herd of this problem on Q's......to save you the headache, I would take it to a professional or your local Infiniti dealer

[Q451990owner]

I called 3 dealers , they want $160 for 1st hour and an open check book ... They have no clue .
This car is not worth an open check book. It's easy to exceed its value with such repairs. I do like the car, it's not my main transportation , I am repairing this car to leave it in the states for when I come to visit so I don't need to rent a car. I will need it for a couple weeks every 3 months.
I plan to give it to my son when he is eligible to drive. I also plan to use it between selling my main car (2012 Toyota FJ cruiser ) until I leave which should happen by end of month .

[Infinitiguy19]

Is the car overheating?

Can you see smoke coming out of the exhaust?

[melvingoku]

welp my advice, if you plan to give it to your son(or keeping it for that matter) would be to fix it because youll make your money back on it. Q's run a longt time if you maintain them.

[Q451990owner]

I know. That's why I'm taking it to a mechanic on Monday . Let him figure it up.

[silverQ]

not the fuel pump. could be a problem with a faulty MAF or related wiring and connectors. car will run with the MAF unplugged try it and see if it acts the same or different. if not the MAF look to the distributor aka Crankshaft Angle Sensor aka Camshaft Position Sensor or related wiring and connectors. CAS has secondary mode when primary mode fails will limit engine rpms as well. would not put used parts on this car it will usually not work out well. wiring, connectors, hoses, injectors on this car are 5h1t and the temperatures under the hood are extreme due to high hp and no front grill on earlier models. personally had a 1991 q45 with 190,000 miles. best wishes

[Roy Evrard]

It might be worth checking for a plugged exhaust system. Have had this problem twice in my lifetime most recently with a BMW 740 (V8) this past summer. This time it was a plugged catalytic converter. Took quite awhile to convince my tech to check it but when he disconnected the pipe ahead of the cat the engine reved right up.

[Q451990owner]

It was the first thing AAMCO checked. They took it all apart to check for free....
I put anew fuel pump (airtex) and waiting to finish the plenum job. Ordered the 8 broken hoses for $210 and they should one on Wednesday . Can't wait

[Q451990owner]

Problem FIXED.
AAAMCO Northridge , los angeles fixed it like champs.
I love the car now. It has so much power. It runs smooth like silk.
here is how this went down.
1) I took the car for a diagnostic to an infinity specialist Donald at car zone auto repair. He had the car for 3 days. He tested tthe fuel pressure in the engine, it was fine . He tested the mass airflow meter , it was fine. He tested the car on a dynometer was fine he tested computer codes and much more. Found nothing , charged $75 and could not find the problem.
I took it to AAMCO at northridge on Reseda blvd , the diagnosed the car while I was waiting for 4 hours, took apart the 4 stages of the mufflers, tested pressure, then drove it with the newer attached , and bam. Pressure dropped as soon as RPM reached 3000. While driving.
They charged ZERO for the diagnostic, and quoted me one hour to change the fuel pump.
Then I decided to let them do the plenum job, they quoted me $325 for both jobs.
I bought BJ re manufacturing injectors for $26 each from rock auto. Got a gasket kit for $15 and new fuel filter.
They took the plenum out and replaced the pump in a few hours, then gave me a list of 8 hoses that needed to be changed, I ordered them For $215 From the Arizona infinity parts we use on this site.
They got the parts yesterday and put it all together, and my car is running smooth as silk. Fixed all the problems at AAMCO.

Prior to going to Donald I tried operation Z and another specialized place, and they are out of their mind price wise...

I strongly recommend AAMCO . They are not all the same, as it's a franchise, just call around and check their attitude. The place in Northridge is amazing. Ask for James . I saw how he treats BJ is customers and it's a pleasure to be one of his customers.

Thanks everybody for your help. This site is invaluable. I printed the step by step plenum removal manual and gave it to them prior to doing the job. God bless all the good people who helped me. Have a wonderful holiday season. I know I will.

[Infinitiguy19]

What is a "BJ Customer"?

The Car Zone folks didn't do a fuel pressure test while driving?

What did you do with the exhaust again?

[qship96]

What is a "BJ Customer"?

Ask any streetwalker.......

[Q451990owner]

It is a typo , BG recondition fuel injectors is what I wrote and edited , and it got all messed up as I wrote it on my phone ...

I'm just happy to finally enjoy this car after investing $2,500.

[paranoidjack]

Man, why did everyone beat this guy up so bad?

What is this forum for? It is for people who are enthusiasts to come together and form a community. One in which knowledge and information is shared to help everyone.

His first post was concise, to the point, and showed his competetence. He demonstrated he had replaced some parts, showing inclination and ability, and was merely looking for guidance.

To tell him to take it to a professional was not a contribution to the community, or to him. Some cannot change an air filter by themselves and need a professional, and some stop at inner transmission workings.

The point is that we all know the endgame is to pay a pro. If no one answered his post, ever, he would take it to a pro. The way I see it, if you don't have something to add to the conversation, it's best not entered into the infinite stores of the internet.

I'm glad you got it fixed. Let us know next time you have an issue. I was with the guy that talked of CAS, and I was going to suggest TPS, but I surely would not have bother posted "Just give up."

[Q451990owner]

I finally , just started enjoying this car. Engine runs so smooth, transmission is like silk smooth, it only has 4,000 miles...
The car just wants to go faster, it has so much power. I saved a ton of money with the injectors. Got them for $26 each... New plugs new tires new fuel pump new Mass Airflow Meter, new window regulators (2) new gas tank , new sending unit , new fuel door solenoid, mobile 1 oil, synthetic transmission oil, new transmission cooler , fixed speaker amps and new wipers and fuel filter and air filter. $3000 later I had a great car.... Could have I done better by just buying one ? Mine has 89,000 miles

[paranoidjack]

Sounds like you did well man! Happy to hear it worked out. Mine has 244k and still feels great. These cars are pretty bulletproof. Never ignore check engine lights though.