Definitive FPR test?

[StereoInstaller1]

Guys, school me on Fuel Pressure Regulators.

I am assuming there is pressure in the fuel rail when the car is off. I am also assuming that a leaky injector will then dribble fuel into the motor (or at least into the intake) when the car is off.

I want to know why my car has been very hard to start first thing in the AM, then spews tons of grey smoke when it does sputter and bitch into life...and then starts and runs just fine for the rest of the day.

This car has always started beautifully and ran like a top from first try on remote start for years, then it started a little of this "hard start" crap and has steadily gotten worse, now to the point that remote start is useless...so spoiled by coming out to a nice warm car, this crap is pissing me off.

This coming week I will have my injectors tested and resealed as needed, and I already did a new FPR with some improvement, but certainly not "fixed".

R3V, share your knowledge!

Thanks,
Luke

[xwill112x]

get the specs on it...get a gauge and blip the throttle when its running...if it increases according to rpm/load/vaccum then its working.

[xwill112x]

maybe your fuel pressure isnt at spec as well, it should be pumping out like a quart of fuel in 30 seconds. if it passes that test, get a hookup for an exhaust analyzer...if your HC's are high, then its likley you have a leaky injector.

[StereoInstaller1]

I am gonna run it through emissions this week, they use a dynamometer, so that should show the hydrocarbons pretty nicely in use. As well as it runs, should be no issue...but...

The "is it working" is not the answer I am looking for: I want a definitive answer of how to test. Running it on a car is NOT it.

[redhatpat]

You can hook up a fuel pressure tester to the line coming out of the fuel rail. Run the car to get the pressure up, then clamp off the hose coming out of the FP tester and the hose coming out of the FPR. The only place for the pressure to bleed off will be the injectors - unless the FPR diaphragm is leaking, in which case you can easily check the vacuum hose coming out of the FPR for any gas.

I just did this for my car, same thing hard to start after it sat for a time. I picked up some rebuilt injectors from ebay for a good price.

[jlevie]

There are a fuel things that will cause hard cold starts. With respect to the fuel system, a bad FPR or a bad pump check valve will allow rail pressure to leak down. As will leaking injectors. In this case I think I'd suspect injectors first. Short of pulling the injectors you can check for their leaking down by letting the car sit overnight, pulling all the plugs and having someone crank the engine. If there's a strong smell of fuel, or fuel sprays out of the cylinders the injectors are leaking.

Loss of rail pressure from a bad FPR or check valve doesn't cause much of a problem if the fuel pump(s) are working properly. With good pumps the fuel rail will come up to pressure ins a few turns of the engine, But worn pumps cause long cranking before the pressure is high enough for the engine to start.

[StereoInstaller1]

Fresh pump, in fact, this nonsense kinda started with the fresh pump.

As I said, I swapped the FPR and it got better, just not better enough.

I can get injectors cleaned/inspected/matched/resealed locally here for $12/ea plus parts, but testing is free. I think I am gonna grab a spare set (I have 3 or 4) and see if I can do a nice, fully fresh set...just to make sure. The old gal deserves it!

I wanna drop off my set of S50 injectors anyway, get them all fresh for the swap.

So none of you guys have mentioned sucking on the vacuum line? Is that just a retarded test or what? I know from how nicely it runs it can't be that bad, and it is ONLY an issue when it sits overnight...WTF?

[u3b3rg33k]

Sounds like a problem I had. My car would take a lot of cranking to start it after it sat for more than a few hours. It turned out to be leaky injectors. That causes two problems:
1: more fuel than there should be in the cylinders
2: fuel rail would lose its prime, and would have to refill and pressurize. I could smell fuel at the tailpipe while cranking and yet it had trouble starting.

There's a common misconception that the fuel system retains meaningful pressure after the car is shut off. That is immaterial (there is no pressure reservoir, so the only pressure that can be present is held by the rubber fuel lines themselves). What does matter is that the system can pressurize instantly when the fuel pump is powered. If it has air in it, the air must be purged (via the FPR) before it will operate properly. Since I swapped out my injectors for refreshed ones, the problem has not returned. I can now let the car sit for a full week and it will start up as readily as if I had turned it off moments before.

The FPR is an exceedingly simple device. It's sole purpose is to maintain constant relative pressure according to manifold vacuum. Your car should start up properly regardless of the vacuum signal present at the FPR. The only time I've seen one catastrophically fail was on an iX with a clogged return line. The FPR broke, and allowed fuel to pass into the intake manifold via the vacuum line, causing the car to run stupidly rich, get about 5 miles per gallon, and fuel was running out of the airbox. It still started up just fine.

[StereoInstaller1]

^...thanks for the input, useful stuff there.

Me thinks a fresh set of injectors will kick its butt.

Off to Renton Injector...I will report on their service.

Luke

[StereoInstaller1]

2 spare sets of cute little blue injectors off to the injector people...we shall see.

[StereoInstaller1]

Little update: Local shop that said $12 each will do a 100% guaranteed full rebuild on them...for $150.

I have good used sets, but all flowmatched and such would be nice, as in better than new.

Wonder if it is worth it on single pintle injectors, or should I find another set of small 4 pintle?

[u3b3rg33k]

I spent about $150 for the whole nine on my set of six OE injectors - I think a single new injector from BMW runs about the same.

[StereoInstaller1]

So what do you think, rebuild these single pintle or find a set of 4 pintle? Am I going to see an advantage, or even quieter? I only care about smooth, car is bone stock and gonna stay that way, only excellent maintenance as of now.

You should see the mud in the brake/clutch system...yuck.

[u3b3rg33k]

In my opinion, M20 injectors aren't that loud. At least, not when compared to everything else under the hood that makes noise. Might as well go with what the ECU is set up for unless you can come up with a really convincing argument to do otherwise.

[browntown]

When idling, if I pull off the vaccuum hose off the fpr, the car runs better. HA! How does 12$ an injector equal 150$?