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 toget up to 40 MPH. Erratic low idle,bogging performance. Went 5 blocks tohis apartment and parked it. Went out acouple hours later and it ran fine again. I had a knock sensor code, replaced the sensor. Had multiple miss-fires and changed from20000 mile Autolite to NGK Iridium plugs. New rear Denso coil packs, fronts on order. Pulled the intake plenum to make sure allcarbon was cleared out, 20000 miles ago the EGR tube was blocked. Pulled off several EGR parts and tested them,all OK. New PCV valve and tested for vacuumleaks. All new fuel injector seals andreplace those little plastic things on the end. Name escapes me right now. Justput on new pre cats and new cat. New O2sensors. 211,000 miles on car. I did find a little oil in the centercylinder spark plug valve cover hole, the rubber donut was out of alignment andI fixed that. It never seems to do thisafter it is started, only after it has run for a bit. Of course it never will do it for me andsometimes will go for a week or 2 and it only happens once or twice and thenruns fine again. Cleaned the MAF sensorwith MAF cleaner. Cleaned the throttlebody with throttle body cleaner. Thingruns great, except for this and a small oil lead from the rear right side ofthe engine that is always annoying. Anyideas out there, as I really don't want to keep throwing money at thisthing. NO CODES OR LIGHT.



Thanks in advance.

 

Right off the bat i can tell you that your new coil packs are no good. Aftermarket brands are prone to constant problems, precisely the problems you describe in fact - you will need to return those and get OEM, used is ok here in most cases. You can also buy them new off rockauto if im not mistaken where they are under the brand name Hitachi. Of course its possible that there are other issues but from what you describe it sounds like the car is going into failsafe/limp mode from improper coilpack signals.

I wasnt exactly sure from your post but it sounds like you have at least one bad spark plug tube gasket, if so it will need to be replaced. A felpro brand kit that includes 6 of these gaskets as well as the valve cover gaskets can be found on rockauto for cheap. Bad tube gasket = dirty sparkplug = misfire problems.

Seems like you pretty much have done your homework though so good job on the trouble shooting. Just make sure to stick to OEM parts when it comes to any sensors/electrical units with these cars.

 

If you can say that you have no codes right now, then I'm assuming you've got a scan-tool.

I'd maybe suggest that you operate the car with the scan-tool connected and see if any codes or diagnostic information is provided while the car is in operation.

 

Air issue? It hadoriginal coil packs on it until I changed them out. Yes I have a scan tool. The problem is it hasto be something that is not monitored by the ECM. Fuel pump? Fuel filter isfairly new and I have never seen one plug and then clear itself only to plugback up again. The Denso are used oncertain Maxima engine combinations. Withall I did, it is if I didn't do anything at all as it still runs the same. It has to be something that is notmonitored......as it had all original parts and changing them out did nothingto solve the problem. I hate to keepthrowing parts on it.

 

Sounds like you checked a lot of stuff, but did you check the boot on the throttle body? My 96 did that, with multiple misfire code, and the boot was dryrotted and letting air in after the MAF.

 

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.

 

Your post is a little confusing. Did you install the new FPR that you bought too? Or just the fuel pump?

 

I changed the fuel pressure regulator because when I pulled the vacuum line off, the pressure didn't rise. Most likely due to the bad pump, but I needed to make sure the car was fixed as my son was going to drive it 2 hours home. Still running great.