1999 QX4 miss fire after warmed up and restarted

[brynderwen]

1. I have 100K on my 1999 QX4 and started to get a miss fire after car had already been driven and restarted warm. So I knew it was time to change, plugs, wires, and distributor cap. Thanks to this forum, I was able to get #6 plug out with the short tool and not the long tool. It does run a lot quieter but I am still having this miss fire issue for about the first mile after restarting from a warm engine. Cold start no problem. When I ordered the distributor cap, it was vague as to whether it included the head rotor. Of course, it was not included. I ordered one today and perhaps that is the issue. Any idea?

2. I'm also wondering how hard it would be to replace the keyless entry security door module under the dash way up there back behind the steering wheel area. It slowly started to not work anymore. I replaced FOB batteries and I had the extra one that was never used before and put a battery in it, to no avail. I also did the key FOB reset of the ignition sequence and that didn't help either. Anyone done it before?

This forum has been a wealth of information.
Thank you all.

[VStar650CL]

1. I have 100K on my 1999 QX4 and started to get a miss fire after car had already been driven and restarted warm. So I knew it was time to change, plugs, wires, and distributor cap. Thanks to this forum, I was able to get #6 plug out with the short tool and not the long tool. It does run a lot quieter but I am still having this miss fire issue for about the first mile after restarting from a warm engine. Cold start no problem. When I ordered the distributor cap, it was vague as to whether it included the head rotor. Of course, it was not included. I ordered one today and perhaps that is the issue. Any idea?

The first thing I'd check is the fuel pressure regulator. That's pretty classic symptoms of a leaky one.

2. I'm also wondering how hard it would be to replace the keyless entry security door module under the dash way up there back behind the steering wheel area. It slowly started to not work anymore. I replaced FOB batteries and I had the extra one that was never used before and put a battery in it, to no avail. I also did the key FOB reset of the ignition sequence and that didn't help either. Anyone done it before?

The SEC isn't hard to change and the fobs just need to be reprogrammed afterward, but finding one may be a whole different matter. My understanding is that they've been discontinued pretty much forever. If the relays are getting balky, you may need to find someone to recondition it.

[brynderwen]

Oh boy, A fuel pressure regulator? How do I go about doing that? Do you think I can do it? It feels like it is miss firing after I start it from already been driven 5 miles and within leaving a parking lot or so, it will run smooth again. Same symptom, you think?

I've seen a few, for sale, security modules out of wrecked vehicles on ebay. I just can't figure out how in the heck I can get that unit out of there. It is way up in there, lodged in. Not sure what to take apart to get to it..........

Thanks VStar

[VStar650CL]

Oh boy, A fuel pressure regulator? How do I go about doing that? Do you think I can do it? It feels like it is miss firing after I start it from already been driven 5 miles and within leaving a parking lot or so, it will run smooth again. Same symptom, you think?

Rough running and/or hard starting after a warm soak are classic symptoms for a pressure regulator with a leaky diaphragm. What happens is that residual fuel pressure after shutdown forces fuel through the leak into the vacuum side of the regulator, then it gets sucked straight into the manifold through the vacuum hose when you restart. The rich condition doesn't bother the engine when cold, but once it warms up and wants a leaner mixture, the leak floods it and it runs badly till the extra fuel burns off.

Not sure whether your '99 has the regulator up front on the engine or all the way at the driver rear, they changed over at some point. The ones in front are easy, in back they're a complete PITA. Maybe @mdmellot or one of the other R50 mavens can help you with specifics.

I've seen a few, for sale, security modules out of wrecked vehicles on ebay. I just can't figure out how in the heck I can get that unit out of there. It is way up in there, lodged in. Not sure what to take apart to get to it..........

I looked on eBay using the p/n's from InfinitiPartsDeal and didn't see any. The problem with a used one is, eventually they'll all develop the same issues with worn relay contacts causing intermittent misbehavior. So you might just be replacing one intermittent headache with a different one. I don't recall them being all that hard to replace, I think you just needed to loosen the lower dash panel and maybe the fusebox.

[mdmellott]

Yep. It's at the rear, blocking easy access to removing #6 spark plug, just like a bad penny always turns up. A couple of screws, a fuel line, and a vacuum line is all there is to remove but they are terribly awkward getting to. This page at Infiniti Parts Deal shows the part number and where it is. If you buy OEM, which I highly recommend for this part, don't forget to purchase the tiny o-ring as well.
https://www.infinitipartsdeal.com/parts ... m=164_A001

[MisterH]

My 99 exhibited the same warm start stumble behavior as you describe. It turned out my #2 injector was failing. Since you're at 100K that's also a fairly common part that typically has reached the end of its service life. One way you can help pinpoint an injector problem is to listen to them pulse. Something you can use as a stethoscope will do the job - just listen to the tick-tick-tick of each of your injectors as they open and close. If you find one or more that isn't making a strong, consistent pulse then you've located the culprit.

Since my bad injector was on the driver side bank (cylinders 2,4,6) I had to remove the upper intake to get to it. As the others have said, it's a messy job. If by chance you have a bad injector on that bank I strongly urge you to replace those three at once; if not all six. For extra peace of mind, even if you don't have a faulty pressure regulator, it'd be smart to replace that too while the intake is off. You have to remove the fuel rail to get to the FPR so I'm all for replacing high mileage critical parts that are otherwise inaccessible without removing the intake. One other item to check if the intake has to come off is to look at your valve cover gaskets. If they're original, there's a high probability they're seeping oil.

The good gentleman here have provided me excellent tips and guidance should you have any difficulties.

[A1218]

I had the exact same issue late last year. It was indeed the FPR that was causing this problem. I confirmed it by pulling the vacuum hose on it shortly after the vehicle was off and gas squirted out.

[brynderwen]

Thanks guys. Oh man, I tried to look for it this morning and I can't seem to find it. Climbed up like a monkey and looked down near #6. I guess if I use a mirror I could see it. I also have a PO325 code, Knock sensor which I already knew about. Also a PO304 #4 misfire, which I believe was one of the wires I replaced last week, but forgot to clear the computer codes.
Has anyone here tried replacing the FPR without removing the intake manifold?
Would it be okay to drive the Infiniti 1,200 miles as I will have to drive that far for a round trip for Easter, next week.
I picked up the new rotor head today and will install once cooled down.
Great to have such great feedback. Thank you

[VStar650CL]

It's very likely just a pinhole, so the only time it can harm anything is after the engine is switched off and the fuel rails still have pressure. In normal operation the leaky fuel will simply burn off. It may make the engine run rich and kill your mileage if the leak is bigger than the ECM can compensate, but I doubt it will harm anything else besides your wallet.

[A1218]

Thanks guys. Oh man, I tried to look for it this morning and I can't seem to find it. Climbed up like a monkey and looked down near #6. I guess if I use a mirror I could see it. I also have a PO325 code, Knock sensor which I already knew about. Also a PO304 #4 misfire, which I believe was one of the wires I replaced last week, but forgot to clear the computer codes.
Has anyone here tried replacing the FPR without removing the intake manifold?
Would it be okay to drive the Infiniti 1,200 miles as I will have to drive that far for a round trip for Easter, next week.
I picked up the new rotor head today and will install once cooled down.
Great to have such great feedback. Thank you

It’s in a pretty tight spot. To get a Phillips driver on there and exert enough force to loosen the screws and then remove the hose which is on there pretty tight if removing the first time might be extremely difficult.

It is visible with a mirror but you can see the small hose coming up the back into the intake plenum which will give you an idea of where to look.

[brynderwen]

Thanks again for your input guys. When I removed the distributor cap and replaced the new rotor head, I could see the intake manifold better. It looks like it is attached down the middle and there are a few other bolts holding lines up here and there a few hoses to undo and I might be able to flop it over to the left side to get to the FPR. Does that seem feasible? And I agree, I should replace both valve cover gaskets while in there. $142 for the FPR and a few bucks for the o-ring. Would I have to replace the manifold gasket? It doesn't get any oil on it, usually, and it looks clean. I would need a 6mm allen socket to remove manifold. Any ideas?
Your information is very helpful and understandable.

[MisterH]

Thanks again for your input guys. When I removed the distributor cap and replaced the new rotor head, I could see the intake manifold better. It looks like it is attached down the middle and there are a few other bolts holding lines up here and there a few hoses to undo and I might be able to flop it over to the left side to get to the FPR. Does that seem feasible? And I agree, I should replace both valve cover gaskets while in there. $142 for the FPR and a few bucks for the o-ring. Would I have to replace the manifold gasket? It doesn't get any oil on it, usually, and it looks clean. I would need a 6mm allen socket to remove manifold. Any ideas?
Your information is very helpful and understandable.

So you've verified that you have a bad FPR? If so, you're probably not going to be able to replace it without removing the intake; and yes, you will need to replace the intake gasket. Here's a link to one of the best descriptions of how to remove the upper intake on the VG33e engine that's in your car. Even though this video applies to the Xterra, the engine is the same and the issues you'll have to contend with are identical:

https://youtu.be/U86sfPwvioQ

Good luck!

[brynderwen]

Thanks MisterH,
No I have not confirmed it is the FPR. Not sure how to actually diagnose if it is bad. Watching that video looks like the coolant hoses in the back are a pain in the you know what.

[A1218]

Thanks MisterH,
No I have not confirmed it is the FPR. Not sure how to actually diagnose if it is bad. Watching that video looks like the coolant hoses in the back are a pain in the you know what.

You can pull the small vacuum hose at the back of the intake plenum and see if gas is in there after a few minutes of shutting down the engine. Pretty easy to do.

As for the hoses its not as bad actually. The 90 degree hose is still available to purchase so you can just cut it if you cannot get it off, but I got it off without much trouble without cutting. There is a straight one too that also wasn't too hard to remove.

One thing I would be careful with is the EGR valve. I removed mine the first time by loosening the two smaller bolts that holds it onto the plenum with a horseshoe like bracket. The second time I took off the plenum I tried loosening the flange nut and it snapped right off, even after soaking and heating it. Had to get a new EGR valve and the pipe going to the exhaust manifold.