How stock fpr's work

[jeff1234]

All, I have a simple question that can be answered by someone who has a complete knowledge of stock fuel pressure regulators, here it is! When you apply vacuum to the port for that purpose, should the pill attached to the diaphragm move? I placed a small screwdriver in mine and then applied at least 24 inches hg and nothing happens. How are these things supposed to work, when under vacuum and under positive pressure. I think mine is allowing full pressure to the rail at idle.
Thanks jeff1234

[BadAssPerformance]

What is your fuel pressure with it running connected to vacuum?

What is your fuel pressure with the vacuum hose disconencted and plugged?

[tryingbe]

Step 1, get a fuel pressure gauge.


What do you mean by "full pressure"?

[jeff1234]

I really only wanted to know if the disk attached to the dia off of the seat inside the regulator when vacuum is applied to the diaphragm.

---------- Post added at 10:40 PM ---------- Previous post was at 10:37 PM ----------

This reply system isn't working well tonight. (I really only wanted to know if the disk attached to the diaphragm is lifted off the seat inside the regulator when vacuum is applied to the diaphragm.)

[Vigo]

You're saying you have the FPR off the car, and you put vacuum on it and it didnt open? That's normal.

The FPR is set to open at 55psi where you had the screwdriver and ambient pressure on the reference port (the vacuum/boost hose barb). Pulling 24 inches of vacuum (~12psi) just lessens the spring pressure by 12psi. So with that vacuum you would still need ~43psi where the screwdriver was to open it.

So you were nowhere close to opening it. There's no way to open it with vacuum alone.

[cordes]

You're saying you have the FPR off the car, and you put vacuum on it and it didnt open? That's normal.

The FPR is set to open at 55psi where you had the screwdriver and ambient pressure on the reference port (the vacuum/boost hose barb). Pulling 24 inches of vacuum (~12psi) just lessens the spring pressure by 12psi. So with that vacuum you would still need ~43psi where the screwdriver was to open it.

So you were nowhere close to opening it. There's no way to open it with vacuum alone.

Agreed. It would take a heck of a pull on the nipple to open the reg without any help on the other end.

[jeff1234]

That is precisely the information I was looking for. Thank you! I am trying to eliminate the fpr as the source of a rich condition at idle which starts to foul the plugs immediately. I also suspect a previously fouled O2 sensor. The fpr is the more expensive part and it is displaying the same symptoms of an article about an S-10 that fouled plugs, ran rich with sooty exhaust and didn't idle worth a darn. They replaced the fpr and it solved all of the problems. This is exactly what my car did when I restarted it after putting the engine back together after engine damage repair. Previously, the engine had run perfectly. I described what happened to the engine in a previous post. Yesterday before I started this thread I took my fpr to work and applied 24 inches of hg to the reference port and at the same time I put 90 psi on the input side of the fpr. The result was, no output at the port that goes into the fuel rail. Is this consistent with the way these are supposed to operate or does it indicate failure. (by the way, there was no fuel inside the reference port) Thanks for your help!

[jeff1234]

This is the article I read, jeff

www.howstuffinmycarworks.com/Fuel_pressure_regulator.html

[tryingbe]

So, at the end, you still have no idea what your fuel pressure is. Spend the $20 at harbor freight and buy this.

http://www.harborfreight.com/fuel-injection-pump-tester-92699.html

Then you know exactly what your fuel pressure is.

[AZTurbo]

I took my fpr to work and applied 24 inches of hg to the reference port and at the same time I put 90 psi on the input side of the fpr. The result was, no output at the port that goes into the fuel rail. Is this consistent with the way these are supposed to operate or does it indicate failure. (by the way, there was no fuel inside the reference port) Thanks for your help!

The regulator works by allowing bypass of the fuel supply once the target pressure is reached.

Full pressure fuel is fed to the rail, once the pressure is high enough in the rail, the fuel overcomes the diaphragm in the regulator, and returns to the tank through the return line.

You need to apply pressure at the fuel-rail side of the regulator while applying your vacuum to the nipple. THEN you should see pressure exit the return-line side of the regulator.

If you reverse it, then the regulator will never open and you won't feel any flow through the regulator. If your description is as I understand it, then it's not a conclusive test. The reg might be good.. it might not be.

[Vigo]

So, at the end, you still have no idea what your fuel pressure is. Spend the $20 at harbor freight and buy this.

http://www.harborfreight.com/fuel-in...ter-92699.html

Then you know exactly what your fuel pressure is.

I dont want to be rude but i recommend this approach too. And, ive gotten that set for less than $10 with coupons.

I agree with AZturbo, by your description it sounds like you were adding pressure to the outlet instead of the inlet, which would have only held the valve closed even harder.

Really, a fuel pressure gauge will tell you everything you need to know about your fuel pressure regulator.

[jeff1234]

I dont feel that anyone has been rude to me in this thread, on the contrary you guys have been extremely helpful. People who have experienced this problem and solved it tend to examine the problem with the benefit of having the solution. Kind of like, here is what to do, just do it. This approach doesn't work for me, I need to completely understand how something works to be able to troubleshoot it. It's what I do for a living and I have been stuck in enough go nowhere thinking loops that I avoid them like the plague. In this case I had no understanding of how this system works and I couldn't make sense out of what I was seeing. I couldn't find anything in my factory materials so I came to you guys. Here is how I understand how this system works. The fuel pump is is applying about 90 psi to the regulator which in turn supplies the fuel rail. Fuel is continuously flowing from the tank to the rail and back to the tank. The flow doesn't change but the pressure at the rail does. It appears to me that pressure inside the rail feeds back to the regulator to cause the diaphragm to open when more fuel pressure is needed and to close when less is needed. Is this correct or is it the opposite? Is the return line sufficiently small enough to cause the back pressure or is there something in the fuel rail that I dont know about, like an orifice or a check valve? I can see where a stuck regulator allowing a constant 90 psi to the rail would apply to much fuel to the cylinder and cause my problem.
jeff

[tryingbe]

I find it hard to believe that the factory repair material does not mention fuel pressure gauge when it comes to diagnosing fuel pressure issue.

You connect the gauge to the rail and you see exactly what the fuel pressure is, and compare to the published # and then you know if the fuel pump and/or fuel pressure regulator is working or not.

If you want to make this more than it needs to be, and make your head hurt while you do not any closer to solving your problem, read on.

Fuel pump supply flow. Flow does change, according to the pressure, and here is a chart. http://www.autoperformanceengineering.com/html/fpspecs.html The excessive flow of fuel is then returned to the tank by the pressure regulator.

Vacuum/boost line signal tells the fuel pressure regulator what pressure to change the fuel to. 1/4 inch fuel return line is plenty enough for a high pressure 255 walbro fuel pump.


"ran rich with sooty exhaust and didn't idle worth a darn." is this what your car is doing? Or is it doing something else too?

[Vigo]

How to diagnose your FPR with a fuel pressure gauge:

The first thing to remember about the fuel pressure regulator is that ambient pressure is 14.xx psi. The second thing is that for engine-off fuel pressure tests you can run the fuel pump by jumping power to the + terminal of the coil.

So, a stock fuel pressure regulator is set to open when there is 55psi ABOVE ambient on the fuel rail side, and ambient pressure on the reference port. So, if you start your car with NO vacuum/boost line connected to the fpr, you should see 55psi of fuel pressure. If you hook the reference line up, the fuel pressure should raise or drop at a 1:1 ratio to whatever pressure is on the reference line. If you have 10psi of boost, it should read 65 psi. If you have 20" of vacuum, it should read 45psi. Remember that ambient pressure is 14.xx psi and 0" of vacuum. Every drop of 2" vacuum roughly equals a drop of 1psi, all the way down to 0psi pressure / 29.xx" vacuum. Most engines do not pull more than 20" of vacuum (a 10psi drop from ambient) at idle, so idle fuel pressure will be around 45 on a good-running motor.

What if you DONT see 55psi?

If you see MORE than 55psi, there are only two realistic causes.

It is either a failed fuel pressure regulator or a restriction in the return line back to the tank. Put the vacuum line back onto the FPR with the engine running. The vacuum of the engine at idle should lower the fuel pressure to 45-50 psi. If the pressure drops, it is the fuel pressure regulator. If the pressure does not drop, do one more test. SIMULTANEOUSLY (as close as you can, you'll probably need two people) turn off the engine or the fuel pump and clamp closed (they make pliers for this) the fuel SUPPLY line (it is the larger of the two and does not connect directly to the FPR). If the pressure drops to 55psi and then stops dropping, or slows considerably, it is a restriction in the return line.

What if you have LESS than 55psi?

If you have less than 55psi, it is almost always a fuel supply (pump/filter) problem. Generally when you have less than 55psi at idle, you can rev the motor and the fuel pressure will drop as the load/rpm increases. If the FPR is working correctly, any fuel pressure less than 55psi means the regulator is closed and there is nothing going through the return line. You can verify that the regulator is closed by clamping the fuel return line. If the regulator is closed this will have no effect on the pressure. If it DOES have an effect then that means the FPR is open when it shouldnt be and has failed.

Now, just because you have 55psi at idle doesnt mean you have the proper fuel pressure at all times. Realistically, you need to be able to drive the car in full boost and to high rpm while watching the gauge to verify that you have sufficient volume for your motor. It doesn't matter what gear you are in, as long as you are able to load the motor to achieve full boost. Most of the time this requires either extending the hose on your cheapy fuel pressure gauge, buying a more expensive gauge with a longer hose, or taking your hood off.

While driving in boost, the FPR should be asking for 55psi + your boost setting. If it's 17psi, you should see roughly 72psi of fuel pressure, etc etc. If the number you see is LESS than what the math says it should be, you are running LEAN, risking blowing up, and it is almost certainly a pump/filter problem (very rarely it can be a voltage/ground problem on the fuel pump circuit).

Checking fuel pressure at full boost is the ultimate test of your fuel system. MANY cars will show the right pressure and act properly at all times EXCEPT high-rpm and full boost. So you can pretty well verify that your FPR is working without leaving the driveway, but unless you do the full-boost, high rpm test, you really havent proven that your fuel system is good enough to do its job.

You can also use the fuel pressure gauge to diagnose a hard-start condition that is being caused by fuel pressure leaking down too fast (it should hold at least 20 psi in the system for 20 minutes or something like that). When you turn off the motor, fuel pressure should drop very slowly. Ideally it would drop too slow for you to see it moving. If it is dropping quickly, you can do this test to figure out if the problem is the FPR or the fuel pump. Clamp (only) the supply line: if the pressure still drops, it is leaking past the FPR seat and the FPR should be replaced. Clamp (only) the return line: if the pressure still drops, the check valve in the fuel pump outlet is leaking and the pump should be replaced. Clamp BOTH lines: If the pressure still drops, your injectors are leaking and you should pull the rail+injectors out of the intake manifold to visually verify which are leaking.

[jeff1234]

Vigo, thanks for taking the time to explain these procedures. With the information you have given me I will get the gauge kit and perform the static test. I haven't been running the engine because it just keeps fouling plugs; once they are fouled it only makes the problem worse. The static test quoted below may show the source of my symptoms which are sooty exhaust, very poor idle qualities and missing. These problems clear up with increased rpm as though when there is enough air to match the amount of fuel going into the cylinder it finally burns properly.

So, a stock fuel pressure regulator is set to open when there is 55psi ABOVE ambient on the fuel rail side, and ambient pressure on the reference port. So, if you start your car with NO vacuum/boost line connected to the fpr, you should see 55psi of fuel pressure.

Excessive pressure here would explain my why my plugs are fouling, beyond that I will have to do more tests to zero in on the cause, but at least I will have a beginning. If there is not excessive pressure then I would look to my O2 sensor. At this point I dont want to plug in the new sensor only to have it foul out again. The present sensor is fouled and may be contaminated with aluminum particles from previous engine damage.

Thanks again for your help!

jeff

---------- Post added at 08:15 AM ---------- Previous post was at 08:07 AM ----------

tryingbe, I came to the forum because I cannot ask a specificly focused question of the factory manual. Thanks for sending the link to the chart, it clarifies things. By th way...

If you want to make this more than it needs to be, and make your head hurt while you do not any closer to solving your problem, read on.

That sentence sounded a little sarcastic to me, is that the way you meant it?

jeff

[jeff1234]

Hello all, I picked up the gauge kit from harbor freight and ran the test. I created fuel pressure by applying power to the coil. The line pressure was 60 psi. I used a mighty vac to apply vacuum to the reference port and it dropped the pressure to 50 psi. Shortly after stopping the test, pressure dropped to about 40 psi. There was a rushing noise in the fuel rail during pump operation,, air bubbles? Anyway, the system is still holding 19 psi seven hours later. My guest is that the regulator is good. Any disagreement? If not the next step is to replace the fouled O2 sensor and try starting the engine again. Along that line of thought, I have been told that the Bosch O2 sensors are junk, any thoughts on that?
Thanks, jeff

[Vigo]

Keep in mind that running 5 psi over where it should be is overfueling almost 10%. As a point of comparison, a 2.5 supposedly uses ~17% more fuel than a 2.2.

I would not rule out that the FPR is contributing to whatever problem you're having.

[jeff1234]

Vigo, Add to that the fact that I have plus fourties. I guess I will try the new O2 sensor, I can probably shut the engine off if it doesnt show signs of clearing up in a minute or so and still not foul out the O2 sensor. If that doesn't do it, I will have to get a new pressure regulator. I cant think what else it might be, nothing changed since my engine problems and all all spark plugs look equally fouled. Thanks for your help. jeff

[Vigo]

It is fouling your plugs at idle? What vacuum does the engine make at idle?

[tryingbe]

Stock computer or aftermarket one?

[jeff1234]

Vigo, The stock cam never made more that 12 in.hg. I am going to put the new O2 sensor in tonight and I will report back to you the vacuum reading. (I have done a reset of the idle) I didn't notice what the best idle is so far, I think I remember seeing 10 in. hg last time I ran the engine. I have the biggest cam that Chris sells on his site and before the motor problems the engine ran, I thought, remarkably smooth without much lope, so the way it is running now is completely different. I really dont know if I will be able to get it to idle at all. I ran the static fuel pump test again last night so as to give you a more accurate description of what it did. With the pump running, it showed 60 psi on the gauge but immediately after turning the pump off it dropped to 55 psi. This is with reference at ambient. After a short period of time the pressure is as described in a previous post.

Tryingbe, I have a stock "87" TII L/M with a chip from Shelgame set up for 20 psi and 40's with an intercooler.

Who is it that says, cheap, fast, reliable, pick any two.They sure have it right with these cars.

jeff

[Vigo]

Well, if the engine only makes 10" of vacuum than 50 psi is the correct fuel pressure at idle with the vacuum hose hooked up.

So, if you are getting 50 psi at idle and it is fouling the plugs at idle, i would suspect a different problem.

However, i still think having 60psi at 0vac/boost is a problem. How much it is impacting your plug fouling, i dont know.

[jeff1234]

Changed the O2 sensor tonight, started the car, gobs of black smoke. Took 20 minutes for garage to clear. Idle at 5 in. hg. jeff

[RoadWarrior222]

Check for leeks.... I hear that sometimes the seeds get in behind a gasket or in a vacuum fitting and force it open.

[Vigo]

There is no way the fuel pressure would be the cause of your issue at this point.

There are only a few things that can cause the car to run THAT rich. One of them is a failed coolant temp sensor, so i would check that. If it runs better with it unplugged than plugged in there is a definite problem there, so try that.

Is the car giving you any codes at all through the check engine light?

[jeff1234]

Hello Vigo, I will try that, but I wonder which sensor you mean, the one in the head or the one at the waterbox by the thermostat. Should there be a variable resistance reading at that sensor?
I also wonder if a bad map sensor could do this. I have the GM one and I disconnected the plug and took some readings at "B" pin and "C" pin in the plug. B=4.96 5 volts C=5.03, I dont remember how they are supposed to read but it seems odd that there would be 5 volts at both input and output.
jeff

[jeff1234]

Vigo, no codes, just 55.

[jeff1234]

Vigo, Coolant temp switch reads 31.1 K ohms, it's 22 degrees here today so probably good. jeff

[Vigo]

The coolant temp sensor is the two wire sensor next to the thermostat.

The other temp sender does nothing but run the gauge and cant cause the car to run badly.

[jeff1234]

Hello all, I bought myself a new Mity vac, mine was old and didn't hold vacuum well enough to maintain steady pressure. I tested the map sensor to see if it would hold vacuum; it did so I started the engine and sure enough the engine ran and idled much better. I had applied a steady 15 in. hg and the fuel rail pressure was at 55psi, as it should be. I determined that the problem is with a faulty map sensor solenoid. It was the one thing I changed when I put the engine back in the car. It was an entire solenoid manifold that I got from one of the guys that I had cleaned up and painted to make it look good, guess I will put the old setup back on. I am glad I am seeing a light at the end of the tunnel on this problem. I need to retime it now and reset the idle again. Thanks for all of your help it was appreciated and in the end certainly led me to find the answer.
jeff1234

[RoadWarrior222]

I had applied a steady 15 in. hg and the fuel rail pressure was at 55psi, as it should be. That don't sound right. You pulled 15" of vacuum below atm or pushed 15" over atm? .... 'coz it should only be 55psi at atmospheric(ish)

[jeff1234]

My bad, 15 in hg @ map, engine off, power applied to coil 55psi @ fuel rail. Does this sound correct. Thengine is running correctly when started. Jeff

[tryingbe]

Vacuum should be apply to the fuel pressure regulator when testing.

[jeff1234]

I was half asleep when I wrote that. It got me thinking though so I went out and started the car and applied 12 in hg directly to the map, the fuel pressure read 55psi. Does this sound right?

[tryingbe]

I was half asleep when I wrote that. It got me thinking though so I went out and started the car and applied 12 in hg directly to the map, the fuel pressure read 55psi. Does this sound right?

Stop apply vacuum to the MAP sensor when testing FUEL PRESSURE REGULATOR.

APPLY THE VACUUM TO THE FUEL PRESSURE REGULATOR.

[jeff1234]

Tyingbe, I did that this morning, heres the results. At 15 in hg the needle was vibrating between 50 and 52 psi if I understand Vigo's explanation the pressure should be about 48 psi.

[jeff1234]

Update, I bought an accufab fuel pressure regulator from Chris, this solved the problem. My FPR was bad. I am glad to be past this problem, thanks, everyone for your advice and assistance. Special thanks to Vigo for taking the time to provide technical descriptions.

[cordes]

Glad you solved the issue. Problems with FP can be tricky to diagnose sometimes.

[BadAssPerformance]

+1, glad its fixed :nod:

[jeff1234]

Well, I thought it was fixed. I attempted to do the final adjustments for idle etc. and found that I still couldn't get it running properly; it was still putting out gobs of black smoke and the longer I tried to adjust it the worse it got. I was frustrated, but I had suspected all along that I was looking at more than one problem. I spoke with Chris at T/U and mentioned that the distributor wasn't in the same place it used to be. He suggested that perhaps my timing belt had slipped a couple of teeth. I went back and checked but discovered that it all looked ok. In the back of my mind I always wondered if the cam timing was affecting the problem. I decided to check compression. My old compression tester was junk so I went to harbor freight and got myself a new compression tester kit. I installed on #1 and cranked the motor over. Only 70 psi in #1, WTF. On a completely new head this shouldn't be so I pulled the front off the motor to make sure all of the marks lined up; they did and the cam gear was straight up. I decided to try changing the cam position. I moved the #1 exhaust lobe towards the exhaust valve, reassembled and tested compression. It was 30 psi, even worse so I moved the #1 intake lobe back towards the intake valve, this resulted in a reading 150 psi, Yay!! I reassembled everything and started the engine. No more black smoke, 15 in hg at idle, great throttle response and a smooth idle. I then timed the motor, set the AFPR and the idle. It's all good. It really is fixed now and I'm happy I found the solution because I was really getting discouraged. Obviously, with such low compression and lazy cam timing the engine couldn't run well enough to properly burn the fuel. Another lesson learned.

[Vigo]

Wow. Unfortunately that is one of the inadequately-documented things that can screw up these cars.. mixing and matching cams and gears. The cams arent even really identifiable without finding real specs and measuring them yourself, and some of them are the same profile machined advanced or retarded versus another version, and then some of the cam gears have the keyways cut so they advance or retard a cam vs the gear that came on it.. so it's POSSIBLE to cobble something together that's like 10 degrees off without realizing it. :(

Glad you got it fixed!!

[cordes]

I'm glad to see that you figured it out too. Here's a video for the next time you need to set the cam timing.


http://www.youtube.com/watch?v=czWD10D_Ff0

[jeff1234]

Thanks for the video. Some positive aspects of this whole deal is that I got needed tools and I got an AFPR, which I was trying to cheap out on (lol). It's clear to me that this particular piece of equipment is really necessary. I have also decided to get a fuel pressure gauge set-up to make tuning more accurate. I wonder if the 150 psi is to much compression for a 20 psi engine and if so would backing out of the cam advance a little lower it?
jeff

[Vigo]

Retarding the cam will lower your static compression reading (i.e. your compression at cranking speed, like 300 rpm.)

Compression numbers are a reflection of your volumetric efficiency at the RPM you take them at. At cranking speed the piston is moving so slowly you get pretty much perfect cylinder filling.

If you do a running compression check you will see that the number changes depending on rpm, which reflects the changes in your VE. I think you have to take the check valve out of the gauge/hose to do this.

Point being, your 300 rpm numbers dont tell you a WHOLE lot about what's going on at 3000 or 4000 rpm. If you are concerned about getting detonation at higher rpms and in boost, you should get your hands on something to monitor the stock knock sensor, like an old OTC 2000 scanner (which are cheap) or any kind of scanner that hook up to that car. If you do pick up knock counts and are already showing good or on the rich side on the wideband, you could try taking a little timing out of that area in your calibration to see if it goes away. If you continue to get knock counts even with some ignition retard, or if you are getting knock counts in higher rpms, farther away from the peak torque rpm, then you may have bigger problems. But i dont think a 150 reading at 300 rpms means you are going to have issues. I just did a compression check on a completely stock, untouched 85 turbo motor with low miles and got 150psi.

[jeff1234]

Hey all, here's an update on the fuel pressure problem. The car is up and running, I am driving it every day but Shelgame is building me a new cal. He believes that I have a set of injectors that were spec'd for +fourties but are closer to +45's. This may explain why in fourth and fifth gear the car really fly's but in the lower gears when you step into it it falters. I am really enjoying driving this car, I have been working on it since 2005. I am looking forward to cleaning up the interior (paint, dyes, new headliner etc. and finally a repaint. jeff