1990 Q45 cannot get past 3,000 RPM please help....

[Q451990owner]

I have recently had rust in my tank, replaced the tank, replaced the fuel pump to a bosche 69648 (recommended by amazon as correct part , is it?) , changed sending unit, replaced filter like 3 times to get rid of rust , and there is still a lot of rust in the system, replaced MAF sensor, changed all 8 spark plugs, and the car simply cannot go past 3,000 rpm.... It feels like it starves for fuel at 3,000 rpm when driving.
My question is could it be the wrong pump? Do these pumps have different speeds? Could it be the fuel pump control module? When I had an airtex fuel pump this never happened. This is driving me crazy. Could it be that my filter got clogged again? It got real dirty after only 30 miles... I'm already on my third filter , and now I have 300 miles on this Bosch filter. I put more redline (2nd time) and car runs much smoother now, I had to replace 3 injectors (1,2,8) and had an intermittent injector that got fixed by redline.

Help............

[SanCarlosQ45]

I think I recommended you check the fuel pump control unit, maybe not. Yes these pumps have three speeds, so there needs to be a speed controller. There is a box above the fuel tank that may have a bad solder trace because of the excess current being drawn by the pump. You may see a burnt connector, but the damage most likely is internal. So what could be happening is that there is not enough fuel pressure because the pump is not going into the 2nd and third speed. There is post in this link that explains how to bypass the FPCU:

post6502162.html?hilit=FPCU%20alligator#p6502162

Did you not remove the tank and clean it, or if it was that bad replace it?

[Q451990owner]

Do I have the right fuel pump? Bosch 69648, is there such a thing as a wrong pump?
Is the speed of the pump determined by the control module? It was working just fine before I changed the airtex pump to a Bosch .
And could it be that the guy who put it back together did not connect a
Something ? Or that it is connected wrong?

[Q451990]

If you're using an aftermarket fuel pump all bets are off in terms of most of us knowing how to advise you... I have no idea how compatible it is to the rest of the control system. Maybe a few members have gone aftermarket on the fuel pump, but I'm not aware of any off of the top of my head. You might try bypassing the controller completely (run the pump in high mode all the time) as a diagnostic.

There's a picture around here somewhere to show what pin to ground, but I can't seem to find it at the moment.

Heath

[Q451990owner]

I just called Bosch and they verifies this pump is for all 1990-1996 models , and I tried the jumper , the pump worked faster, but the car runs the same , around 3,500 -4,000 now it stops accelerating . I also cleaned the oxidized connector to the throttle position sensor...
What can it be?

[Skibane]

Can you rev it above 3000 RPM with the car in Neutral or Park (i.e., with no load on the engine)?

[Q451990owner]

Yes. In park it revs all the way.

[Q451990owner]

I did the crocodile bypass cable and connected the pin indicated in the picture to ground. The pump became much louder as it was operating faster, yet no difference . The car now chokes at 2,500-3,000 RPM.

In park, the car revs to 7,000 rpm no problem. This issue took all the power away from my car. I don't know what to do. I calle Bosch , the new pump u put , according to them, is the original pump that Infinity puts in the car. They told me that they buy it from infinity.... And all pumps have one speed, the control module gives different current to vary the speed, like a volume control to a speaker... So I think that I already verified it's not the fuel pump, I put a brand new filter and right off the bat same issue...
Could it be a sensor? ( I have a brand new MAF sensor) someone mentioned the exhaust pipe or a muffler clogged.
Any thoughts?

[Q451990owner]

I called a shop, they mentioned computer problem, perhaps water got to it.

Can anyone make sense out of this please? I'm about to junk this car after investing $2500 in it...

[goody90q45]

You mentioned that you cleaned corrosion off the MAF and TPS sensor connectors. Did you do the same to the crank angle sensor (CAS/distributor)? It's located on the driver side of the engine, in front, below the cylinder head.

[Q451990owner]

No I did not. Is there a picture that can show me where that is? All this is new to me.... So many sensors. Could this cause a car that is driving 70mph to lose power above 3,000 rpm?

[goody90q45]

You'll see it where I described. It looks like a smallish distributor with no plug wires going into it. A dirty connector on the CAS can cause idle and acceleration problems so it's worth cleaning it up to rule it out.

[paranoidjack]

Well doesn't sound like fuel pump.

If it does it without load, I very strongly doubt that the fuel pump has anything to do with it.

I know when my MAF was bad (all 3 times!!!!!), the car a) showed DIFFERENT symptoms, and b) would have issues revving above certain rpms.

New Chinese maf from ebay, $40 shipped...or new OEM one for MUCH MUCH more, or used OEM one...

Try it..

[Q451990owner]

I replaces the MAF with a used one from eBay. The rough idle issue has disappeared completely. The engine vibration at 2000 rpm has gone.
But the issue of not being able to exceed 3,000 rpm while driving has stayed. The car simply chokes above 3,000 rpm. In idle no problem.

[Skibane]

Could also be an obstruction in the exhaust system - Plugged cat or similar.

The fact that it revs fine with no load on the engine is interesting - Sounds more like a fuel or air flow problem than an electrical problem.

One other question: If you manually shift to first gear and apply very light throttle while pulling away from a stop, can you gradually get the engine above 3000 RPM, or does it just flat refuse to rev with the car in gear?

[Q451990owner]

Yes, I have tried putting it on 1st manually, and as soon as it gets to 3,000 rpm it chokes. However, I did notice that in the morning when the car is totally cold, for like the first 30 seconds, it lets me rev up to maximum. As soon as the car warms up a little bit , it chokes at 3,000 rpm.
This feels like lack of fuel at high load. But Bosvh swears that it's the correct fuel pump. I've tried to put the pump on high speed by bypassing with a jumper to groung. The pump becomes louder, but same issue. I thought my filter was clogged, I replaced it, and same issue.
I'm beginning to suspect a faulty sensor. Don't know which though. I replaced the MAF with a used one I bought on line, but problem was not solved.

[Skibane]

However, I did notice that in the morning when the car is totally cold, for like the first 30 seconds, it lets me rev up to maximum. As soon as the car warms up a little bit , it chokes at 3,000 rpm.

Normally, the ECM uses the coolant temperature sensor to determine if the engine is cold or hot, and adjusts the fuel mixture accordingly. Cold engine = extra fuel.



If the coolant temperature failed (became an open circuit), the ECM would see a very cold temperature reading all the time - and would enrich the fuel all the time. Result: Poor driveability after the engine warmed up.

Does the exhaust smell normal after the engine is warmed up? Any smell of raw gas?

[Q451990owner]

Exhaust has a strong smell. Not of gas though.

[Q451990owner]

If the coolant temp sensor was bad, how would a poor mixture cause at 3,000 rpm a total choking of the engine? As I play with the gas pedal I can feel the cutoff point. It's like this; if I reach the choking point, and lot off the gas pedal, the power comes back, and sometimes I can get a few hundred rpm more when I let go the pedal and reapply gently. If it was a coolant sensor issue, wouldnt it just be a rough engine at all rpm Rather than cutting off at a particular rpm?

[Q451990owner]

After thinking a bit about the coolant temperature sensor it began to make sense a little bit, because about a month ago I had the mechanic install the recommended transmission radiator that was pegged to the radiator . The guy took the radiator cover out and worked in that area a few hours. So he could have easily disconnected the sensor by mistake.
Can anyone please post a picture of where the coolant temperature sensor is located ? Also one that shows what it looks like.
One question though crossed my mind , if the temperature sensor is disconnected, wouldn't the temperature gauge show cold all the time? Where does it get it's readings? Because the temperature gauge is working perfectly well
Well. Thank you for the idea. I would live to check it out myself, if anyone has a picture that can help me locate this sensor and identify it.

[Skibane]

The temperature gauge uses a separate sensor.

On the Y33, they're both located on top of the engine, in the main coolant passage:

[Q451990owner]

The problem seems to be getting worse and worse.
Apparently, a couple months ago the car was not getting pas 4,500 RPam, then gradually I noticed that when I floor the pedal something weirded is going on, perhaps the transmission. But it didn't matter as I was getting sufficient power.
This lowered to 3,500 when I noticed it more. Then to 3,000 which is when I posted this problem.
Well, now it's down to 2,100. I can't get past 2,100 and that makes it hard to go up hills. I will have to stop using the car till I fix it.

This cannot be the temperature gauge, I'm suspecting more like a catalytic converter clog gage or some exhaust pipe clog.

Any ideas what can be choking my car slowly more and more?

[Q451990owner]

It turns out that a fuel pressure meter under stress while driving revealed drop in pressure to 10 psi when flooring . The tank , new tank revealed rust. I'm treating the tank with acid and changing the pump to an airtex , I had Bosch .
I am also getting the plenum job and replacing the remaining injectors .

AAMCO has provided me with a free diagnostic and charging me $325 labor to do all this. This is an amazing deal. I got the parts at rock auto , each injector is $41 with a $15 core refund, so end price for GB remanufactured injectors is $26 each.
The acid wash is $120 done at a radiator shop.
In a week I will know... Can't wait to see this car perform

[qship96]

trying hard to stay positive here for you,but i just do not see this job going well for you at AAMCO.

There are about 40 small custom molded hoses under that plenum that are a real challenge to work with- most,if not all,will be dry rotted due to age and the heat and will crumble and need replacement as soon as they are touched while removing the plenum.....and the complete kit of these hoses{parts only} is right around $1,000 from a Infiniti dealer,and due to many of them being custom shaped to fit,are not available at your local napa or rock auto type stores.Just the labor to do the under plenum work takes 5-7 hours for an experienced infiniti specialist who has done this exact job on this exact model car.....aamco has no idea what they are about to get into.

Regarding the fuel pressure issue,it is much more likely your fuel pressure regulator has failed VS your brand new bosch pump being the root cause..........stop guessing and throwing parts at a problem trying to solve the issue!

[OwnerCS]

Where are you located? We may know a competent shop in your area. Qship is right.. You don't go wandering off into death valley (e.g. under plenum) without having some experience to draw on or it can be a disaster.

[Q451990owner]

We will see. Perhaps you are Right. They got the fuel Pump out in minutes. I am going out of town for a week and will see what they did when I come back.

[Q451990owner]

And if there are 40 hoses in bad shape under the plenum then it's time to change them. This car is just another car, and the mechanic there is very smart and knowledgable. I don't see harm letting him try this job. Other places charge $400 for the plenum job, so it can't be as complicated as you describe. The correct number of hours according to the book is 3.5 hours, they looked it up.
Again, I will see what they do. I have to be positive about it. I hope you are wrong.

[Infinitiguy19]

I have never attempted the under plenum job, I may need to on my 1994 Q45a. But be sure your "Mechanic" or Technician is able to do the job. Has he ever worked on a car like yours before? What makes has he worked on? This isn't a job for the local gas station garage. You might end up paying them to learn how to work on your car. The whole reason I got into working on cars is because idiots/"know it alls" around me all thought they knew what they were doing.

[Q451990owner]

The guy has the work manual for the car, he is a master mechanic, he pinpointed my fuel pump issue very professionally. He even took apart my exhaust system with fatalities to rule out a clog. He checked the transmission, that's what AAMCO know well. I also downloaded the 2 step by step manuals from this site, printed them, and left them with him. At the end it's just another car job with screws and plumbing. He may end up spending mor time than he ever imagined, but he will get it done, I have confidence that he has the know how. But if not, then no. What can I do? If I have to throw this car away, I will.

[silverQ]

i posted in one of your other threads 1990-q45-gradually-over-2-months-cannot ... 81946.html

is most likely MAF or Crank Angle Sensor or related wiring and connectors. looks like you said the maf was replaced so if a good part.. leaves CAS. fuel pressure check is quite easy on this car can plug into the line past the fuel filter on the side of motor. also pull the vacuum line to the fuel pressure regulator at back of motor and look for fuel should pour out if bad.

Fuel System
Fuel Pump Pressure @ Idle
Vacuum applied at fuel pressure regulator 34 psi
Vacuum released at fuel pressure regulator 43 psi
from q45.org

Yesterday I tested the fuel pressure to find the following results.
1) Ignition on at 44 PSI.
2) After start up, pressure settled down to 34/35 PSI.
post fuel-pressure-test-t504230.html

so 10psi drop is normal

fuel injector and knock sensor testing from q45.org
http://www.q45.org/ohminjectors.html

all injectors should read the same top the tenth of an ohm hot or cold or something is failing
unless you have a dead miss the injectors are okay and this will not limit rpms anyway trust me. drove on 5 cylinders around town for years since was my only car.

bought full set of injectors from rockauto by gb reman not sure if it worked out well; had a few soon fail. problem is engine plenum may have to be removed again to correct. new injectors are going for $685 full set oem on ebay. http://www.ebay.com/itm/BRAND-NEW-GENUI ... 0965746376

some people have switched to the phase two they are a bit cheaper and quite possible a more reliable design is fairly easy swap i hear.
see 94-96-style-injectors-on-90-93-q-inform ... 99119.html (pics are gone maybe msg someone)
have had the phase I design them fail one after another and even in groups (used).

with a misdiagnoses and having things replaced on this car that are not broke gets expensive fast with parts and labor. car usually ends up with a mechanics lien, gave up on, or results in more problems than before and a broken car. when under the plenum to not change the knock sensors and related harness would be a shame. bad ks or harness drops engine power by a third.

tidbit from post in other thread "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."

FSM source now with earlier models http://www.nicoclub.com/FSM/Q45/

best wishes