Sentra SE-R, NX2000, G20 Tune-up and Maintenance Bible

Nissan 2.0 Engine Maintenance Bible

By:RED_DET

Well folks here is your guide to making your pride and joy run at optimal performance. Starting with common problems and solutions:

PROBLEM: Erratic Idle and jumping idle, some other symptoms are also: sluggish performance, real bad mileage, injector leak malfunction code, o2 sensor voltage stuck at 800 mv or so.

Affects: Sentra SE-R, NX2000

One thing you may want to check is that the idle was set correctly. The AAC valve is supposed to regulate the flow of air at idle in order to keep the engine at ~800 rpm.My 93.5 G20 used to have a quirk that disconnecting the TPS would not fully close the AAC valve as it should.I would attempt to adjust the idle per FSM instructions, but turning the idle adjust screw would not affect the idle at all because the AAC valve was still operating and keeping the idle at 750rpm.Sometime after my 60k tune-up I reset the computer which seemed to have eliminated this quirk.

The best way to see if you have this problem is to warm the car up, turn the engine off, disconnect the TPS, and start the car back up.Hopefully, the idle will be at about 750rpm.If so, disconnect the AAC valve while the car is still running.If the idle stays constant, your idle is set correctly.If the engine stalls or the rpm’s drop, your idle may be set incorrectly.

Another cause of poor idle is exhaust gas recirculating back into your intake.A faulty EGR is the most widely known culprit but there is another source that can potentially choke your engine, the PAIR(AIV). This is that EGR looking device mounted on the front of the engine close to the radiator.It’s whole purpose is to allow fresh air into the exhaust stream at idle.On a stock set-up it takes this air from the intake just past the air filter.The PAIR(AIV) has reed valves in it that are supposed to allow air to be sucked into the exhaust stream and prevent exhaust from flowing back into the intake.Unfortunately, the reed valves on my unit are warped due to the heat of the engine and don’t prevent backflow of exhaust gas.

If you want to check the PAIR(AIV), open your filter box while the car is idling.There should be a port on the left hand side of the upper half of the box.You should be able to feel a vacuum on that port if it’s functioning right. If not, you can feel puffs of air coming out of the port, and it will sound just like an exhaust leak.

PROBLEM: Fuel pump failure, causing the car to be inoperable.

Affects: Sentra SE-R 91-93

All US built 1991 and 1992 Sentras (B13)
All US built 1993 Sentras through serial number 730388
[the serial number is the trailing digits on your VIN plate]

“Nissan has assigned Campaign Number 93-U3005 to this Campaign”

Dealer Responsibility:
It is the Dealer’s responsibility to make the correction listed in the Bulletin on each vehicle within the affected VIN range of this Campaign, except those that have had a fuel pump replaced after 1-1-1993, which enters the Service Department, regardless of where it was purchased.This includes vehicles purchased from private parties or presented by transient (tourist) owners and vehicles in Dealer inventory (new or used).

The dealership can bill Nissan for parts and 0.7 hours of service time.

Two fuel pumps may have been used:JECS brand, gold in color, no replacement needed;Bosch [garbage] aluminum color – replace it.Both have the manufacturer imprinted on the case as well.

If the Fuel Pump is a BOSCH type, remove and replace it with a new, countermeasure BOSCH pump, P/N 17042-Q5601BC.

PROBLEM: Surge and hesitation between 1500 and 3000 rpm

Affects: All ’91 – ’93 SR20DE (Sentra SE-R, NX2000 and G20)

If the usual tune-up procedure doesn’t take care of the problem, disconnect the EGR valve and plug the vacuum hose leading to it from the BPT valve. Take the car out for a ride, making sure to drive in the same manner that typically causes the car to surge and hesitate. If the problem is no longer present, chances are good that you’re experiencing the infamous “EGR Problem”.

Remove both vacuum hoses from BPT (right-most disk shaped object behind valve cover). Remove the two philips screws on its top. Push the BPT back toward the firewall. You should see a rubber hose running between the bottom of the BPT and a metal tube. Remove the BPT and rubber hose from the metal tube and set them aside.

This metal tube is connected to the EGR passage and, ultimately, to the exhaust manifold. Exhaust manifold pressure, via this metal tube, operates the BPT valve which regulates the vacuum to, and the opening of, the EGR valve. The less exhaust manifold pressure – the more the BPT valve opens – the more the EGR valve opens. The more exhaust manifold pressure – the less the BPT valve opens – the less the EGR valve opens. Carbon may block this metal tube which causes the BPT to not operate properly (if at all) which causes the EGR valve to operate uncontrollably.

Wait until the car is cold, then spray some carb and choke cleaner into the metal tube to soften up the blockage. Used a stiff piece of wire (a long chunk of 8 gauge wire left over from the big car stereo install will do) to ream out the tube. (*Note: DO THIS WHEN THE CAR IS COLD!! Carb cleaner and a hot exhaust don’t mix well.*) Take note of how far you have pushed the wire into the tube before you pull it out. Lay the wire along side the BPT tube to gauge how far down the tube you have gone. When you’ve pushed the wire far enough down the tube to have reached the EGR tube it intersects, you’ve probably removed all of the blockage(s)

Wait about 10 minutes for the chemicals to evaporate. Start the car and hold your finger in front of the metal tube. You should feel a steady stream of exhaust coming from it. If not, try cleaning it again.

While you’re waiting for the chemicals to evaporate, now would be a good time to remove your EGR valve and clean the carbon deposits from the plunger and seat. I find that the carbon build up eventually gets bad enough to hold the EGR valve slightly open. This changes your base idle speed (TPS disconnected) and can also cause a rough and wandering idle as well as possibly causing your car to stall when you push in the clutch.

Reassemble the system, hook your EGR valve back up and take your car out for a ride. You should find that the problem is gone and your local smog police will give you an award for being a law-abiding smog free citizen once more.

I make checking the metal tube and cleaning the EGR valve a part of every tune-up and/or oil change.

red arrow EGR valve, yellow arrow BPT valve.

TPS Voltage Adjustment

Imagine that this picture is what the back of your TPS wiring harness looks like as it’s plugged into the TPS:

—–
|A|
——–
|B||
——–
|C|
—–

What you need to do is get a DVM and hook the positive lead through the back of the harness into “B” and hook the negative lead through the back of the harness into “A”. It’s easiest if you straighten a couple of paper clips (I used my wife’s sewing needles…she nearly killed me) and shove them into the openings and hook onto ’em with alligator clips, but *DON’T* let them touch. Turn the ignition on (don’t start the car) and check the voltage between “A” (-) and “B” (+). It should be between 0.45 and 0.55V. If it’s not, you’ll need to loosen (but not remove) the two screws or bolts that hold the TPS to the throttle body. Rotate the TPS until you get the proper voltage and tighten the screws, making sure it doesn’t go out of adjustment when you tighten it down. As a final check, open the throttle all of the way. You should read around 4V. If so, great! If not, uh…my condolences.

Ford guys adjust the TPS to “fool” the computer into thinking the throttle is opened farther than it actually is. It supposedly works, but it never made much sense to me. It seems that the ECU would think that WOT is achieved at a certain voltage (like 4V on ours) and going farther than that doesn’t do any good. It would also seem that if the TPS is “turned up” too high, the ECU would never see the correct voltage for closed throttle (like ~0.5V on ours) and the idle would be all screwy. But they claim it works and claim to have back-to-back 1/4 mi runs to back it up. It sounds like a good question for Jim or Clark at JWT.

MAF Sensor Grounding

The MAF sensor is located just past the air intake. You’ll need to pull back the rubber cover to expose three wires. On mine, the outer two were orange, the middle one is white. The middle pin is where we need to get a voltage reading from (with the engine idling). Take the positive lead of the voltmeter and make contact with the middle wire. The negative lead should be pressed to one of the ground connectors on the engine block, near the firewall, right behind the fuel injectors. You might have to look hard to see them, just look for a bolt with several black wires running to it. Took me a while to spot it myself, several vacuum hoses in the way…

The voltage read should be less than 9mv (.009v), if it is above this value, the sensor needs to be regrounded. To do this, a wire needs to be run from the middle pin to the ground lug. You’ll need to remove the connector from the MAF to get a good angle on it. On either side of the connector is a small opening for a small flat blade screwdriver. There is a wire that runs around the connector to hold it in place, you need to pry this wire outwards, then move the connector back a bit. Do one side, then the other, and it should pop right off. I’d never seen this type of fastener before, once you have it off you’ll see what I mean.

You’ll want to solder a new wire to the middle pin, make sure you get a good connection. Then, run the other end to the ground lug. If you want to do the job right, you’ll want to get a connector from Radio Shack or other electronics store that has a ring that you can crimp the wire to. I don’t remember the size of the bolt, so I’m no help there. I just looped my wire around the bolt twice and put it back on. I may go back and fix it up nice some other time.

Once the sensor is regrounded, the voltage should drop significantly. Mine was at around 11mv, after the fix it went down to less than 2mv.

Advancing The Timing

# Warm up engine to regular operating temp, and ensure idle speed stays below 1000 rpm.
# Run engine at 2000 rpm for 2 minutes under no-load [in neutral, no accessories on]. Race engine 2 or 3 times under no-load, then run engine at idle speed. [this heats up the oxygen sensor so it is working]
# Turn off engine and disconnect throttle position sensor (TPS) harness connector. [It’s on the side of the throttle body facing the firewall – driver side of the engine, down low and past the brake master-cylinder]
# Start engine. Race engine (2 – 3000 rpm) under no-load, the run at idle speed. [You may have trouble keeping it running with the throttle sensor disconnected. Depending on where your timing is set, it may stall. If so have someone sit in the car and press the gas *very slightly* to keep it running. Don’t rev it up or you will not get an accurate timing reading/adjustment. Keep it at idle speed, about 800 rpm]
# Check ignition timing with a timing light. It should be 15 degrees plus or minus 2 degrees Before Top Dead Center. [The timing mark at the extreme left (counter-clockwise) is zero degrees. There are lines at 5, 10 and 20 degrees to the right of it. There is a wide paint mark from 13 to 15 degrees, which the factory probably set yours to. Eyeball 17 degrees between the marks and that’s what you want.]

From the 1991 Technical Bulletins, Beginning with April 1991 production,
the ignition timing mating mark has been changed as shown below.
NEW marks at -5,0,5,10,13,white paint,15,20 B.T.D.C..
OLD marks at 0,5,10,15,20 B.T.D.C..

#If not, slightly loosen two bolts holding the distributor, and twist it [toward the front of the engine to retard, toward the cabin to advance] to obtain the desired timing. [Recheck the setting after tightening the bolts!].
#Shut off engine and reconnect throttle sensor.

That’s it. The trick is to set it to the extreme limit of the specification – 17 degrees. You’ll get noticeably better throttle response there. Advanced timing helps power, but can cause knocking or pinging. The EFI computer *should* “hear” this and back off the timing to prevent engine damage, at which point it may run worse than if you had kept the timing conservative. Mine didn’t benefit from going beyond 17. I always run 91 octane or better gas too, which lets you push the timing farther without trouble.

*you need to rev the motor past 3000 rpm 3 times for the motor to lock the timing (after disconnecting the TPS)*