# 1998 Nissan Maxima problem comes and goes........HELP!



## ldpfeifer (Sep 23, 2010)

My son's 98 Max runs great. He made 3 stops in an hour and a half yesterday shopping. Last stop, he took off and had to floor it to get up to 40 MPH. Erratic low idle,bogging performance. Went 5 blocks to his apartment and parked it. Went out a couple hours later and it ran fine again. I had a knock sensor code, replaced the sensor. Had multiple miss-fires and changed from 20000 mile Autolite to NGK Iridium plugs. New rear Denso coil packs, fronts on order. Pulled the intake plenum to make sure all carbon was cleared out as I got a P0400 EGR code, 20000 miles ago the EGR tube was blocked. Pulled off several EGR parts and tested them, all OK. New PCV valve and tested for vacuum leaks. All new fuel injector seals and replace those little plastic things on the end. Name escapes me right now...pintels? Just put on new pre cats and new cat. New O2 sensors. 211,000 miles on car. I did find a little oil in the center cylinder spark plug rear valve cover hole, the rubber donut was out of alignment and I fixed that. It never seems to do this after it is started, only after it has run for a bit. Of course it never will do it for me and sometimes will go for a week or 2 and it only happens once or twice and then runs fine again. Cleaned the MAF sensor with MAF cleaner. Cleaned the throttlebody with throttle body cleaner. Thing runs great, except for this and a small oil leak from the rear right side of the engine that is always annoying. Any ideas out there, as I really don't want to keep throwing money at this thing. NO CODES OR CHECK ENGINE LIGHT when this happens. I am thinking it is something that is not monitoured by the ECM. Fuel filter is not that old and if it plugged I wouldn't think it would unplug and plug again. Fuel pump in original. I did put in a new ignition switch also. 
Thanks in andvance for ideas.


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## LylePfeifer (Mar 19, 2009)

OK, I gave up and went to see my go to guy when I can't figure things out on my own. George, my guy, said you know it’s been hot and I have been changing fuel pumps for over 2 weeks. In 100 degree temps if you don't keep that tank at least half full, you’re going to be using hot fuel to cool that fuel pump. But I told him I just drove the car 2 hours without a hick up. Let it set 15 minutes and it stored a multiple miss-fire code. He said it did that because the fuel pump is failing, seen a bunch in the last 2 weeks. Get a pressure gauge and drive the car, watch it and see what it does. I went to Oreilly's and rented one. Hooked it up and low and behold, it was supposed to be 35 PSI. 28 PSI was the best it got and if you floored it, down to 15 PSI. If you pull the Vacuum off of the fuel pressure regulator, it should jump up to 43 PSI. Nothing, stayed at 28 PSI. I ordered a new fuel pump, a new fuel pressure regulator just in case and was staring at the cam shaft sensor as it was misting a little oil from the tired o-ring seal. I pulled it out to change the o-ring, cleaned it up and notice a crack from one of the molding holes half way across and right through the metal tab. So I put that on new too. I checked the new fuel pump, 35 PSI and flip the throttle, no change. Rock solid at 35 PSI. I pulled the fuel pressure regulator vacuum line and right up to the max of 45 PSI. Car has been running fine. Now I have to go find George and had him a $50 for 10 minutes of his time. Anyone with car stalling problems, you might want to try the fuel pressure gauge and see where you’re at. George said he has seen as little as 2 PSI low cause all kinds of problems.......I never thought a car that would run for 2 hours solid would have had a bad fuel pump.


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## jdg (Aug 27, 2009)

Common fuel pump failure mode. Common symptoms for said fuel pump failure mode. Bearings/bushings in the fuel pump get hot, go bad, pump mechanism itself slows down, pressure drops, just generally goes to crap.
Knock sensor code gets tripped because the engine is running lean due to the low fuel pressure and the ECU couldn't compensate enough.
EGR code, well, that was probably just a coincidence, but not unexpected given the mileage.
New cats, O2 sensors, and the other parts...again, given the mileage, replacing them wasn't going to hurt anything but the wallet.
"something that is not monitored by the ECM" - True statement. It's only been within the past few years that it's become fairly common for the fuel pressure has been directly monitored by the ECM. Without monitoring fuel pressure directly, the health of the fuel pump has to be either inferred by monitoring other subsystems, or as you did, directly with a fuel pressure gauge.
It happens in all makes/models. I'll say a lot of the time, they're driven by soccer moms trying to squeeze that last 3 miles out of the tank where the fuel gauge has been sitting on "E" all day, before finally giving up and stopping at a gas station.


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## LylePfeifer (Mar 19, 2009)

I'll say a lot of the time, they're driven by soccer moms trying to squeeze that last 3 miles out of the tank where the fuel gauge has been sitting on "E" all day, before finally giving up and stopping at a gas station..................Now that is funny, I don't care who you are.....and so true!

Oh, your right about the knock sensor throwing a code. I changed that our too as I had ordered one for it. It was cracked also.


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