Whistling fuel pressure regulator

Post by **firedane** » Tue Aug 06, 2002 11:56 am

I have a whistling 92 Q45a. Preface- I knew I needed to install new spark plugs, new hoses under plenum, and reseal the rocker covers. Put it all off until the wife left town and didn't need the car. The week before she left she complained about rough idle, no power, and even an occasional stall. I figured plugs, fuel filter and rail clean. Well, I got it all accomplished in about 3 evenings and have encountered the above whistle.

It is coming from the fuel pressure regulator

When I pinch the vacuum hose the whistle pitch changes. I suppose I could do "Dixie" if I tried. Car runs smooth right now as opposed to before the work. However it is a flat dog when I step on the throttle. I need to put a gauge on the fuel rail but it sure seems like the regulator is whistling in its death throes. Anyone ever get this little gem of a problem?

firedaneMedina, Ohio

Post by **firedane** » Tue Aug 06, 2002 11:56 am

Well, I guess I spoke to soon. Went to move the Q and it started very hard. Cranked but no go. Acted like it was out of gas!! Also seems to have developed valve noise (Clatter) at about 2000 rpm. Chain probem was done a couple of years ago. Maybe the regulator is faulty, but I am starting to suspect the fuel pump. How long should the system hold pressure at the rail after shutdown? I don't recall getting a spray when I removed the hoses after it sat for 3 days. I am going to gauge the rail tomorrow and I think I will replace the regulator and the pump regardless of the pressure readings. Both appear to be original and I dont trust them.

firedaneMedina, Ohio

Post by **PalmerWMD** » Tue Aug 06, 2002 11:56 am

I'm itching to post some idle speculation of mine, but I better let the Gurus handle this one..

Fred...

Post by **maxnix** » Tue Aug 06, 2002 11:56 am

Post it, Fred. Your speculations are always well considered.

I am ceratinly not qualified to speculate.

Post by **Q451990** » Tue Aug 06, 2002 11:56 am

I've very rarely heard of a bad regulator or damper. Are you sure the noise you're hearing isn't a vaccum leak? I'm thinking the driveablility problems may be something else, like a bad MAF or CAS connection. Check those at idle and see if the idle speed changes. I'm sure you had a lot of stuff disconnected while the car was apart, so it's always a good idea to go back and double-check everything.

Heath

Post by **Q45tech** » Tue Aug 06, 2002 11:56 am

Never had to replace a pressure regulator or fuel pressure damper. A quick survey shows no one has or heard of one going bad but there is always a first one.

The purpose of the vacuum line is to raise the pressure from 34 psi at 18-19" HG to 43.4 psi at wot 1-2" HG. Incrementally 9.5 psi rise for 17" drop.....1"HG change is 0.55 psi change.

Volume is square root of ratio or roughly 13% more fuel flow without a vacuum vs with. The fuel pump has to increase rpm at WOT so this compensates for that time lag and distance.From idle to around 3500-4000 rpm acceleration not having the extra fuel will be noticeable [maybe?].......it is provided to quench the detonation before it starts and to quickly add fuel before the computer has time to calculate what you are trying to do since the MAF is farther away than the injector it takes a few rpm to transistion.

Post by **firedane** » Tue Aug 06, 2002 11:56 am

Yes, the noise is/was vacuum. I changed the hose going to the regulator and checked the steel tube also. When I pinched the hose going to the regulator, the pitch of the whistle changed. I double checked the hoses as you all are correct, I could have missed a reconnect. The whistle disappeared later in the evening and the rough idle appeared along with the valve-like rattle. On a cold start, it idled smooth, but as the temp gauge went up, it reappeared. Temo gauge at almost exactly middle. Also now stalling at an idle. I have 2 fuel pressure gauges so I will install one inthe rail and one at the rail inlet. I also have a hand vacuum source so I will measure pressure relationship.

firedaneMedina, Ohio

Post by **DAEDALUS** » Tue Aug 06, 2002 11:56 am

A vacuum leak can really confuse the ECU, causing stumbling, hunting, and stalling. As far as the ECU can tell, what's coming in doesn't correlate with what's going out. Aerosols work well in pinpointing. Not sure if that would cause valvetrain rattle, though.

YouTube · Post by **EZcheese15** » Tue Aug 06, 2002 11:56 am

Ok, this is somewhat unrelated, but...

Stock Nissan FPR's do go bad. Infact, mine is bad in my 02 Sentra!! It doesn't hold fuel pressure when the car is shut off. So it takes a long time to prime the fuel system before starting (like 10 cranks sometimes).

I know my FPR is bad cuz I swapped it with my brother's (who also has an 02 sentra), and his started having problems, and mine stopped (having problems).

But like I said, take this with a grian of salt. It is most likely not your problem, I just wanted to vent!

YouTube · Post by **EZcheese15** » Tue Aug 06, 2002 11:56 am

Q45tech, I have a question about my previous post that I am wondering if you could answer....(or anybody else who may know)

Like I said, my car didn't hold fuel pressure when the car is shut off. Is this the job of the FPR?? I know the FPR is to increase or decrease the amount of fuel with varying vacuum under different engine loads, but what holds the pressure in the fuel lines after the car is shut off?

I have a returnless fuel system, and the FPR is located in the fuel tank, directly on the fuel pump casing. I swapped the entire fuel pump assembly/casing (including the FPR) to discover something was faulty. I assume it was the FPR, but could it be the actual pump? I have no fuel problems with the car running, only when it is shut off.

Post by **Q451990** » Tue Aug 06, 2002 11:56 am

Is it possible there's another vacuum leak? One good way to check for leaks is to spray carb cleaner or brake parts cleaner around at different areas and look for idle fluctuations. I'm wondering if your AAC Valve (A/K/A IAC Valve) hose is disconnected or split... that's in the same general area. It's also very easy to pinch the o-rings between the runners and plenum.

Heath

Post by **DAEDALUS** » Tue Aug 06, 2002 11:56 am

I REALLY think Heath is on to something with the plenum gaskets if you didn't replace them. At this point they will be hard as rocks and quite brittle too. If you don't put all 8 back in the exact same place and rotation (quite impossible) OR if any of them have cracked/chipped, you will almost certainly have leaks there. Luckily you do not need to do a lot of work to replace them. Loosen all the screws on the plenum, and just pry it up about 3/16"--just high enough to fish out the gaskets. Be careful not to drop any down below.

Post by **Q45tech** » Tue Aug 06, 2002 11:56 am

On a returnless system there is a oneway valve at the pump so if it is not leaking then the injectors are!

On a Q you have the pressure reg feeding the return line, the one way valve at the pump, and injectors to worry about.Plus the WOT fuel pulse dampener which in theory acts as another one way valve to hold the rail pressure isolated from anything that happens prior to the rubber lines feeding the rail....like when you change a a fuel filter.

But the lines spit gasoline [hot disconnect] so these may not work as well as designed.

The Q should hold pressure [at least 20 psi] for days, months, if not years [I'm dreaming here].

On the pressure regulator:The engine vacuum helps pull the spring down [lighten the load against the diaphram which controls the cone shaped return valve.If the spring fails the return will always be open but line sizing and pump strength [volume/psi] is usually enough once it starts but the WOT will be lean since the psi doen't rise but falls with rpm and load.

As I've said we have never replaced one on a Q but the highest engine mileage is around 250,000 we know of. Our 410k Q is on its 2nd engine so it's regulator probably only has 200k....?

Hooking up a pressure gauge and taping it to windshield so you can make sure you are maintaining 43.4 PSI [between fuel filter and rail] at WOT all the way to 6900 rpm is important as the injector opening time is calculated against this and 34 psi would be 13% too lean.!!!!!!!!!!!!!!!!This is EXTREMELY IMPORTANT with a JWT ecu as the injector time is already set 7-10% leaner [than standard] above 5400 rpm. Good way to melt something if fuel pressure drops!

Post by **Q45tech** » Tue Aug 06, 2002 11:56 am

By the way the fuel pressure regulator is sealed in Japan with Japan air pressure. Roughly sealevel!So the fuel pressure will vary slightly as the altitude changes and the engine vacuum at idle and WOT varies.In Atlanta [900' AMSL] the proper engine vacuum [teed at the regulator] is 18.5-19.0 " HG at idle and 34.0 psi fuel pressure.....each psi is roughly 1.45% more fuel.So a lower vacuum engine runs richer but the programming is already so very very very lean at idle.

On Nissans an 11.0 to 1 WOT AF is used to cool the piston crowns instead of the 12.0-12.5 more normal ratio for peak power.A function of the aluminum heads and 4 valves per cylinder and the 20% higher efficiency over American 2 valve iron head units.

Up to a point, too rich a mixture doesn't hurt power production as much as you would think with a 10.2 CR as preignition is greatly suppressed allowing more advance to optimize BMEP.Really depends on the fuel blend and how they cheated that batch.

It will be so nice when individual pressure cell are attached to each cylinder along EG monitoring to optimize everything individually by around 2005.

The Q is pretty wasteful [10-15%] of fuel at WOT and would never make it in NASCAR were every drop per HP counts. But its cooling system is too small to carry away the heat if it wasn't for the work done in vaporizing the excess fuel.

But nobody I know rates an engine on fuel comsumption at WOT!

All passenger cars use this strategy -- excess fuel at WOT and turbos are twice as bad!

Post by **firedane** » Tue Aug 06, 2002 11:56 am

Well, the fuel rail inlet pressure seems ok. About 37psi at idle, jumps to 42-44 after regulator vacuum disconnect. At about 11-1200 rpm there is a drop to about 31psi that seems to hold steady. I replaced the plenum gaskets with new ones. I am going to check the rail pressure at the front between the 2 sides tonight and lift the plenum and check that the gaskets are in place. With the metal insert rings in the gaskets, I would think that one would notice if a gasket slipped. Before torquing down, I used an o-ring pick and checked to see if they were in place. Each one seemed to rotate in the hole around the ring. I am really hesitant to run the throttle up to far because of the valve clatter. I am beginning to think that I missed something really basic here. I will check the AAC valve hoses also. The big hoses below in the rear were a bear to connect. Maybe something is wrong there causing a really big vacuum leak. The car won't idle half the time right now. If I hold the throttle to about 1200 it seems smooth though. No misses or stumbles. :toilet I am ready to flush my ASE certs and beat my head against the wall!! Time for alcohol and a break, then look at it again.

firedaneMedina, Ohio

Post by **Professor_Mike** » Tue Aug 06, 2002 11:56 am

Have you tried checking around possible leaks with a stethescope? Also there is a hose behind the throttle body at the rear that is prone to leakage, it's a 90 degree hose that goes from the plenum to a pipe.

Post by **firedane** » Tue Aug 06, 2002 11:56 am

Yeah I found the EGR tube to throttle body hose. Little bugger was hard as a rock. Also the last mechanic in kinked tke metal tube. I replaced the tube partway with a piece of MPFI hose and routed it next to the AAC supply tube. That way it misses the fuel rail. I just took the plenum back off in preparation for the chain job. Looked at hoses and gasket again. I founf no evidence of mistakes. I have decided that the chains and guides are goibg in regardless unless I find bent valves. The last time the motor was open was about 5 years ago in Houston. I cannot say id both sides were done, or with the right parrts. So I will make sure it is right while I have the time and the wife has a spare car.

firedane

Post by **DAEDALUS** » Tue Aug 06, 2002 11:56 am

I've finally confirmed what I've been fearing for a while now. My fuel pressure just past the filter is 35-36 psi at all RPMs up to 5000. Filter is only a few months old. What is the pressure loss between the filter and the injectors? More simply, what must the fuel pressure from the pump be in order to enable 43.5psi at the injectors?I will order the pump tomorrow. I'm hoping my controller is OK, but there's no way for me to test it directly that I know of. I will test the pressure again at the filter and the fuel rail after replacing the fuel pump next weekend.

Post by **firedane** » Tue Aug 06, 2002 11:56 am

Unplug the vacuum hose to the regulator and test again. The loss of vacuum is hat send the pressure up. (i.e. wide open throttle=low vacuum). I had 2 gauges hooked up, one just past the filter and one between the fuel rails. I saw no difference in the pressures. If there are no restrictions, the pressure should be equal. I put in an Airtex pump that I purchased through my shop. I called the factory and checked to make sure it was set up to handle the variable voltage put out by the pump controller. It is important to use an OEM pump or one that has the same engineering design and specs. I have not had the car rumming yet, still replacing parts on my way out from the timing chain job!! Plug for Infiniti of Scottsdale here- Great service, good price break for NICO members, and they don't look down on the home mechanic. Got pulleys, bolts, and screws in better time than my local dealer could supply. Next Day Air from Arizona to Ohio was $15.00. Reasonable to me.

Good luck

Firedane

Post by **DAEDALUS** » Tue Aug 06, 2002 11:56 am

I thought the pressure before the regulator would be at least as high as the pressure required at the rail. That is, shouldn't the pressure before the regulator be at least 43.5psi at WOT? The regulator doesn't affect the pump operation, does it? I'll be studying my manual tonight, as I sip Mississippi Mud.

Whistling fuel pressure regulator

Whistling fuel pressure regulator

Whistle stopped-now rough idle etc.

Pad your post count! I just did.

Thanks for replies

Vacuum leaks bad!

That might be it

Fuel pressures/plenum gaskets

Hi Prof. Mike

Rail Pressure

Nissan Forums

Infiniti Forums

Datsun Forums

Technical Forums

Classifieds / Marketplace

Nissan Motorsports

General Forums