Infiniti Q45 1991 low engine power

[Leshiy]

Hello everyone from Belarus, Grodno. I have a small car repair shop, so I know a little bit about cars.

A year ago, I bought an Infiniti Q45, which was in poor condition but still running. Overall, the car moves well, and I've driven over 600 km without any issues.

However, I feel like it lacks power. When I floor it, the acceleration is almost the same as when I give it a gentle throttle. Even with the 1st gear forced on, the rear wheels only come off on wet asphalt. I think this car should just destroy the tires.

What was done:
1. Replaced the fuel pump, installed an additional pressure sensor, and the pressure does not drop below 3 bar.

2. Replaced the lambda sensors and knock sensors.

3. Adjusted the ignition using a stroboscope, 15 degrees before TDC.

4. Adjusted the throttle position sensor. The car has a kickdown feature.

5. Cleaned and adjusted the throttle valve and idle valve.

6. The spark plugs have been replaced.

Overall, the car is running better, but it still takes a long time to accelerate. After 4000, it seems to be running better. Can you provide any further guidance?

For errors - the second throttle position sensor (my car is 1991, and it does not have stabilization, but as I understand it, the ECU is installed from a car with stabilization control). And another error on the automatic transmission - the oil temperature sensor.

[VStar650CL]

You might have a transmission problem and not an engine problem. If the sprag clutch in the torque converter is shot and freewheels in both directions, it causes no torque multiplication. The unit will shift normally (but may shudder on accel) and will have no pulling power. The diagnosis is to do a stall test, the result will be much higher RPM than the book value if the sprag is bad.

[Leshiy]

Okay, I press the brake and floor the gas in first gear. The revs rise to 2000, then the rear axle breaks free and slowly increases, and the car starts to burnout.

[Leshiy]

When releasing the gas at speed, there's engine braking, just like with any torque converter automatic transmission. The transmission doesn't slip, and there's no vibration during acceleration or braking.

[VStar650CL]

Book for the stall shows 2100~2300, so that's healthy. Is your MAF reading right? Have you checked vacuum to see if maybe a cat is partially plugged?

[Leshiy]

I didn't quite understand about the vacuum. If we're talking about catalysts, they were removed by the previous owner, and the exhaust system is straight. If we're talking about air leaks, there might be some. The vacuum system on the VH45 is quite extensive.

The MAF is currently installed from the Audi 4.2, and it makes the car run better. Its readings are slightly higher than the stock one, but not by much.

As it turned out, the Defi fuel pressure sensor is lying by 1 bar, which means that the pressure in the rail drops to 2.5 under load. I understand that it should be at least 3 bar. I will try to install a more efficient pump tomorrow.

[VStar650CL]

If the cats were removed then it's unlikely to be a blockage. You can tell a blocked exhaust from a vacuum gauge, vacuum should recover to at or near the idle value after raising the RPM's to 2K or so. If it gradually drops to a lower value and steadies there, the breathing is obstructed.

[Leshiy]

Thank you, i understand.

So i wil try to make up some more fuel pressure. Than i will plug in the car my AEM O2 sensor for some AFR information.
Than may be i'll plug in the car some tuning fuel pressure controller.

Thank you for all advices!

[Q451990]

to NICO! You're in good hands with VStar.

I would add that the common failure points on this car are the fuel pump and it's control module. The module provides 3 speeds to the pump, so if one or two are out, it's possible that your pressure is ok at idle, but not at speed. Typically they just fail completely though.

Knock sensors are also a common issue, and can cause the timing/fuel map to default to a protection mode that just gives the car a "something isn't right" feeling without throwing a check engine light.

If you haven't found it already, the factory service manual is available at www.infinitiservicemanual.com

[Leshiy]

Hello. Sorry I haven't written for a long time. I installed 2 fuel pumps from the infiniti fx45, and now the fuel pressure is in order (up to 3.5 bar at full throttle). I managed to fix the engine errors (the second throttle position sensor). I rewired the ECU connector, added the signal wire from the second throttle sensor, and tricked it with the signal from the Audi air flow meter. However, when I connected the signal from the main throttle sensor to it in parallel, the ECU did not see full opening even with an additional 5-volt supply. There is still an error on the temperature of the automatic transmission, I will try to eliminate it using a sensor from Lexus. It differs in parameters, but an additional resistor on 1K should help.

At the moment, the car goes well when the engine (or automatic transmission) is cold. As soon as it warms up to operating temperature, the thrust immediately falls.

[Leshiy]

to NICO! You're in good hands with VStar.

I would add that the common failure points on this car are the fuel pump and it's control module. The module provides 3 speeds to the pump, so if one or two are out, it's possible that your pressure is ok at idle, but not at speed. Typically they just fail completely though.

Knock sensors are also a common issue, and can cause the timing/fuel map to default to a protection mode that just gives the car a "something isn't right" feeling without throwing a check engine light.

If you haven't found it already, the factory service manual is available at www.infinitiservicemanual.com

Thank you, i have the manual for this cool car!

[Leshiy]

I have no any error codes about knock sensors, cheking by nissan consult diagnostic. But one of my new O2 sensors seems to bee broken, I am waiting for new one.

[VStar650CL]

You won't necessarily get codes from a bad knock. They're ceramic piezos which respond electrically to the distinctive knock frequency because of their resonant mechanical structure. The upshot of that is, they can simply drift "off frequency" as the ceramic and silicon ages. The ECM can really only check continuity through the element, so a sensor which has gone off-frequency will have normal diagnostics and won't cause codes, but it won't work right.

[Q451990]

they can simply drift "off frequency" as the ceramic and silicon ages.

Interesting! We've been told in the past that the ECU can recognize more than the resistance of the sensors based on folks trying to substitute a resistor in place of the KS, with the ECU still going in to the protective timing map. Have you found that to be the case? When they drift off of frequency, do you see the ECU responding oddly to the information it gets from the faulty sensors, or does it just switch to the more conservative timing map as if the sensor was open?

[VStar650CL]

The ECU's often do measure capacitance along with resistance, but nothing works if there's an open circuit. Dead ones (as opposed to off-frequency ones) usually have cracked ceramic and they'll fail continuity. The element itself requires mechanical stimulation to produce a knock detection signal, and since the ECU can't do that, it can't detect the condition. All it can tell is that the element is in one piece.

[Leshiy]

The ECU's often do measure capacitance along with resistance, but nothing works if there's an open circuit. Dead ones (as opposed to off-frequency ones) usually have cracked ceramic and they'll fail continuity. The element itself requires mechanical stimulation to produce a knock detection signal, and since the ECU can't do that, it can't detect the condition. All it can tell is that the element is in one piece.

Ok, i pluged in some new knox sensors (not original), and also try to connect used sensors from my lexus (they are working good on another car and have the same specs, cheked with multimeter). But I have no any positive results. Today i will plug my AEM O2 sensor and check what about AFR.

[Leshiy]

So with audi MAF we have AFR 11 - too much fuel. With stock MAF it is near 14-15 and this is good AFR. But when i drive it there is no any difference. This is so funny, i change any parametres like fuel pressure, air ratio and others, but it goes like a 1.6 engine)

Spark plugs changed today. But still i have no fun whith my vh45d)

Maybe the ecu dont let the engine to get more power, i dont know)

[cbird805]

I know this may sound silly, but it could be bad idler pulleys. Check your drive belts and idler pulleys. There's 3 of them: AC, Alternator, and PS. A seized pulley can cause a lack of power, but still idles and runs

[Leshiy]

I know this may sound silly, but it could be bad idler pulleys. Check your drive belts and idler pulleys. There's 3 of them: AC, Alternator, and PS. A seized pulley can cause a lack of power, but still idles and runs

Thank you for your assumption, but if the problem was with this, the belt would have torn or slipped off long ago. the car rarely drives, but if it does, it's in full throttle mode.

At the moment, the problem has not been solved, but apparently something is preventing it from full power. even without load, the engine spins thoughtfully from idle to maximum RPM. I will continue to look for the reason. the car leaves once every couple of weeks for a good mood :-).

[Leshiy]

Hello. I bought an ECU from a 1989 car without stabilization. It will arrive soon and I will check if the power is restored. Hope it will be a lot of fun :-)

[Leshiy]

I installed the correct ECU, a new air flow meter, and adjusted the ignition timing according to the manual. Practically nothing changed, but at RPMs above 5000, I started experiencing shooting sounds in the exhaust manifold. With the ignition set to early, these shooting sounds are gone. Could the problem be due to misaligned timing? I think it's worth checking. The engine diagnostics show no errors.

[BCC93QT]

It's not timing. Its fuel related injectors.... wont show a code if its the injectors...

[BCC93QT]

Injectors. All of them. Replace

[Leshiy]

Injectors. All of them. Replace

I think that it will be some problems on a high rpms if injectors goes low fuel. Now I take my engine off the car to instal BMW manual transmition, so all injectors will be cheked too) and not only injectors

[Leshiy]