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1993 nissan maxima rough idle horrible gas milage

I sure hope hope someone can help me.
my daughter has a 1993 maxima SE (3.0 DOHC) that ran ok until one day when she left work and started the car it was running very rough (missing and sputtering).
She had the car towed here and I looked it over,it had a lot of visible problems which I have fixed (cracked coil packs,leaking valve cover gaskets, filthy fuel filter,clogged pcv valve, oil saturated air filter,spark plugs burned down to nubs etc, I replaced all those obviously defective parts) but the car still idles very rough,idles too low RPMs(400-500 rpms),exhaust smells like raw fuel and it only gets 5 miles to the gallon on my last test drive.

I removed the intake manifold to get to the rear fuel injectors to see if they might be stuck open and leaking.The car had been sitting for about 5 days with the battery disconnected and when I removed the first injector there was no fuel in the injector or the rail and no pressure in the rail.
I left the injector out overnight and the next morning there was fuel all over the top of the engine and in the fuel rail.
I put the injector back in and unbolted the rail,I reconnected the battery and turned the key to start the fuel pump.I waited for about 3-4 minutes and did not see any fuel leaking from the injectors.I turned the key off and removed it from the ignition,disconnected the battery and bolted the fuel rail back down.I again removed one of the injectors and there was no fuel in the injector or the rail and no pressure in the rail.After about 2 minutes, with the key out of the ignition and the battery disconnected,I saw fuel start filling the rail and the injector port, so I quickly put the injector back in.

I`m thinking the next step would be to replace the fuel pressure regulator and recheck the injectors for leaks.Am I on the right track here with the pressure regulator? What could be causing the car to suddenly start acting this way, my daughter said the car ran fine on her way to work ( although I hardly think it could have been running “fine” with cracked coil packs,clogged air filter,worn plugs etc)

Any suggestions will be greatly appreciated.

I would check to see if the timing belt/chain jumped a tooth. That would explain a sudden rough running and poor gas mileage due to unburned gas because the valve timing is off.

Given the apparent lack of maintenance, a loose timing belt/chain and/or weak tensioner would not be at all surprising.

Thanks for replying.
That would be my worst nightmare,but I did briefly consider that might be the problem. Since it has DOHC it has 3 timing chains which increases the chance that one of them might have slipped.
I suppose the easiest way to check that is to remove the valve cover on the number 1 cylinder and handcrank the the crank shaft until number 1 is at TDC then look at the camshaft to see if the valves are open or closed?

But what if that bank of valves is still timed correctly and it’s the other bank that jumped? You may have to pull the chain cover and check all the alignment marks.

Maybe the fuel pressure regulator is leaking. That could explain the poor running, bad fuel mileage, raw gas smell out the exhaust, etc.

The car is 21 years old and the rubber diaphragm in the regulator could easily have given up.

Have you checked the fuel pressure, yet? This simple test can eliminate a lot of the guessing. Fuel pressure way above spec is usually a faulty regulator. Fuel pressure good usually points to either bad injectors or a possible faulty ECU.

I dont have fuel pressure gauge,Ill get one this weekend and check the pressure and the timing chain this weekend also.
One other important thing that I failed to mention is that the check engine light has never come on,so Im assuming that whatever is causing the problem is something that is not monitored by the ECU,which is why I havent checked any of the sensors or anything else that is monitored by the ECU, I`m assuming they are all working correctly and will check them as a last resort.

Im really baffled as to why there was no fuel or pressure in the injectors or the fuel rail until after I removed the injector.The battery was disconnected so the fuel pump couldnt have been running so what was forcing the fuel up and into the fuel rail only after the injector was removed?

A '93 model year car uses an ODB-I system, which is not very sophisticated. Basically, it will only set a code if it cannot read a sensor, but lacks the ability to determine if the signal from the sensors is considered reasonable or reliable. '96 and newer cats use ODB-II, that has a lot more ability, including mis-fire detectors that ODB-I doesn’t have. So, working on pre-'96 cars requires a lot more old-fashioned diagnostic work to be done that newer cars.

Thanks for that info I didnt know that. so, the cam position sensor/s could be malfunctioning which could cause symptoms similar to a slipped timing chain and that wouldnt necessarily cause a fault code?
When I check the timing chain if it is ok and hasnt slipped maybe Ill focus my attention on the cam sensor/s


When you get that fuel pressure gauge, bear in mind that your car almost certainly does NOT have a fuel pressure test port. As such, you’ll need to tee into the system, so to speak. Make sure that fuel pressure gauge set has the adapter you need

It does seem clear that you are running very rich - or there is a timing issue.

When you had the injectors out, I’m not sure your check for leaking was complete. If the rail had gone completely empty and was at zero pressure, in order to fill and pressurize the rail you would have needed to cycle the key on and off a whole bunch of time. If the car isn’t cranking/running, the pump only cycles on briefly and cycling once won’t fully repressurize the rail. (Once you get your hands on a pressure gauge you can certainly verify/check).

The part about the fuel rail filling with the key off and battery disconnected is just plain odd. I don’t know what to make of it.

Either way, I would leave leaking fuel injectors on the table. The pressure regulator is easy to check by just pulling the vacuum line and checking for liquid fuel - there shouldn’t be any. The car would need to have been running just prior to this.

I would also do a basic check of the coolant temp sensor. This can easily be done with an ohmmeter since those generally just work by resistance - lower when cooler / higher when hotter. You’d need to dig up the resistance specs someplace.

Even on OBDII systems the error detection is not perfect. There is a lot of tolerance built into the programming - random errors / blips flow around the systems regularly. Most of them are random little blips. Many things operate within a given range. So for most of the monitored systems, its not as simple as “error/no error.” The tolerances for error, then, means that things can be out of spec enough to cause problems, but that it hasn’t triggered the PCM’s programming for calling it an error.

Today I pulled the valve covers and the timing chain covers,turned the crankshaft by hand until #1 was at TDC,the timing marks lined up correctly and the chains were nice and tight.When I removed the rear valve cover I did smell gas,but the smell went away pretty quick and I didn`t see any gas.

I removed the connector from the coolant temp sensor and saw a lot of green corrosion.(I could just clean it but they are cheap so I`m going to replace it and clean the connector)

I pulled the fuel rail up again and cycled the key on and off about 25-30 times,to build pressure in the fuel rail, and none of the injectors showed any signs of leaking.After I bolted the rail back down I removed the fuel pressure regulator to check if there was pressure in the rail, there was pressure but I can`t say for sure how much.

I got new gaskets (valve cover,intake,egr gaskets) some new vacuum hoses (all of the hoses are brittle and some of the hoses I removed, to take the intake off, broke.) and a coolant temp sensor on Ebay.I going to go ahead and put everything back together next week. I might get a new O2 sensor too if I find one cheap on Ebay.

After I get it all back together I`ll get a fuel pressure gauge and start checking some other things too.
( TPS,MAF,IACV,Cam position sensor,fuel pressure regulator)

I only found 1 oxygen sensor on the car (screwed into the side of “Y” pipe under the car)
I also noticed that the car doesnt have a catalytic convertor. There is this braided wire collar type thing (like this: welded onto the "Y" pipe and then just a straight exhaust pipe running to the back of the car.I assume that someone didnt want to pay $1 million to buy a new catalytic convertor so they removed it and put a straight pipe on.
We dont have to get emissions tests where I live so im not going to bother putting a catalytic convertor back on unless it`s needed to make the car run properly again.

You could have removed the vacuum line from the fuel pressure regulator to see if there was any gas in it.
A vacuum can also be pulled on the regulator to test the diaphragm.

Just to update y`all on the situation,
I replaced the O2 sensor,temperature sensor,the MAF,PCV valve, and a used TPS, put the intake manifold back on,with a new gasket,reconnected all the hoses and wires etc, and it runs good now.

I replaced them all at the same time so I dont know if it was just one of those things that was malfunctioning or a combination of 2 or more of them. It idles smooth at 700 RPM, no missing, and theres no fuel odor coming from the exhaust.

I have a new problem now,
I noticed a puddle of oil (at least a coffee cup full or more of oil) by the inside of the front passenger tire.
I asked my daughter if she noticed any oil leaks when she had the car and she said: oh yeah it leaked a lot but I would just put a quart of oil in every 2-3 days and some stop leak now and again and it was fine.
All you can do is roll your eyes when someone says that.

The leak is on the passenger side of the engine where all the belts and pulleys are, I guess Ill check the oil pan gasket,oil filter and crank seal to see whats leaking.
Its odd that I didnt see any oil puddles before now, maybe all that stop leak she put in there finally burned up or leaked out? Hahahaha
This is getting to be a never ending project.

( Total expenses so far for parts is about $250 +/- $10, new coil packs for $5 each, new MAF for $20, gotta love Ebay)

Try the crankshaft sensor down neat the oil filter. It tells the timing of the engine to the computer.

5 years late and obviously didn’t even read the whole thing. Running problem fixed.

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