Fuel pressure issue?

[rb0095]

Ok, just did a fuel pressure test. I'm not sure if this makes a difference, but according to one app on my phone the outside air temperature is 36F according to another the temp is 38F.

With the engine running at idle I got a steady 3.5 bar pressure reading.

Then I turned off the car to see how quickly the fuel pressure dropped. It fell to about 1.8 bar in three minutes, 1.5 bar in about 4 minutes 30 seconds. After 10 minutes it was at about 1.1 bar. 0.85 bar after 15 minutes, and about 0.79 bar after 20 minutes.

Based on the information I can find the pressure at idle is about right. I'm not sure how fast it is supposed to drop after turning off the engine though...maybe someone here can help me answer that.

[gull]

Are these control pressure (valve open) or system pressure (valve closed)? 3.5 psi sounds about right for warm control pressure. With a cold engine the control pressure should start out lower than 3.5 psi and gradually increase over the first couple of minutes the engine is idling. This leans out the mixture as the engine warms, and verifying this can be important in sorting out warm-up problems. System pressure, on the other hand, should be between about 4.5 and 5.2 bar, and shouldn't vary much.

Spec for residual pressure is 38 psi (about 2.6 bar) after 10 minutes, 35 psi (about 2.4 bar) after 20 minutes. But if you know your injectors are leaking fuel then low residual pressure isn't a surprise -- they're gradually depressurizing the system.

[rb0095]

Are these control pressure (valve open) or system pressure (valve closed)?

These are with the valve open. I didn't take the time yesterday to do any testing with the valve closed. I did try closing the valve once to see what it did, the pressure gauge shot up to about 4.5 bar or a little higher if I remember, then the engine died and the pressure immediately dropped to about 2.something bar.


Also, the pressure did gradually increase to 3.5 bar, it did not reach that pressure right away.

Spec for residual pressure is 38 psi (about 2.6 bar) after 10 minutes, 35 psi (about 2.4 bar) after 20 minutes. But if you know your injectors are leaking fuel then low residual pressure isn't a surprise -- they're gradually depressurizing the system.

As I said earlier, I replaced all the fuel injectors in early 2009, it surprises me that they are leaking...but it does explain how quickly the fuel pressure decreased. Is there any way to verify that the fuel injectors are leaking fuel into the engine after shutdown? I know that they spray fuel into the engine when the key is turned on, but based on some of the vacuum issues I've had with this car I am wondering if the mixture was/is set incorrectly on the fuel distributer to compensate for all the false air that was/has been causing a lean mixture. As it is, I am still working on fixing the vacuum leak on the throttle body, haven't had much time with the Holidays and such...either way, I am not confident that the fuel injectors are leaking after engine shutdown.
Based on other information that I can find another part that would affect the fuel pressure after the engine is off is the fuel accumulator and or fuel pump (check valve), are there any tests that I can do to test those parts?

[gull]

OK, then your pressures sound fine, other than the residual pressure.

If they're spraying when the key is on and the engine isn't running, my guess is they're also spraying when the engine is off and there is still pressure in the fuel system, and that would explain your low residual pressure. The injectors should normally *only* spray when the airflow meter plate is lifted, either manually or by air flowing into the engine. If the injectors are known good than it could be the AFM plate is binding and not fully returning (I think you said you already checked that), or the fuel distributor itself has a problem. I know there's a plunger in there that can get hung up and cause problems, but I've never taken one apart so I can't help you there. The Haynes manual does have some info.

[rb0095]

Recently tried the Teflon tape, it seems to have fixed that vacuum leak...I'll do a more in depth check later. I also just re-replaced the idle air screw o-ring. I was trying to adjust the idle speed and noticed that the screw didn't seem to be doing much, discovered that the vacuum leak was back. This time I made sure I got the right o-ring. When I compared the new o-ring to the one I was replacing it was obvious that the older one was too small.

After installing the new o-ring on the idle screw I adjusted the air/fuel mixture. I found that for some reason the test plugs (for dwell/duty cycle adjustment) are no longer working properly. The dwell meter sits at 85...same thing on two different meters. So I adjusted the mixture by ear, just until I find out why the plugs aren't reading properly. Then after I got the everything tuned as best I could I checked the status on my fuel injection issue. The fuel injectors still spay fuel when the fuel pump turns on (key on, engine not cranking), however, the amount that they spray is much smaller. In fact, they almost don't spray...

Then I got an idea...maybe I still have a vacuum leak somewhere that I haven't noticed. A check using a vacuum gage shows that there is a vacuum leak. The vacuum currently reads just under 15.

At this point my assumption that the car has been adjusted rich to compensate for vacuum leaks seems to be correct. Though it is not my only fuel issue as the residual fuel pressure shows; once I find and fix my vacuum leaks, then adjust the air/fuel mixture properly I believe my issue with the fuel injectors will be fixed.

[gull]

Good to hear.
Re the test plug issue -- what happens if you trigger the full throttle switch? You should see a fixed 65% duty cycle. If you do, then the test plug is fine and there's a fault in your oxygen sensor system -- probably bad wiring or a bad sensor. If not then it's probably the test plug.

[rb0095]

what happens if you trigger the full throttle switch?

I don't have a full throttle switch, the 1.6 engine doesn't have one. From what I know they are only on the 1.8 engines...but I may be wrong.

Based on some of the other things that I have noticed in the way its running recently I'm guessing that it's the oxygen sensor. The oxygen sensor is almost two years old now, I'll just replace it and go from there.

[gull]

There's a fairly useful table here that may help your troubleshooting. Obviously you'll want to ignore the rows having to do with the full-throttle switch:
http://www.cabby-info.com/cis.htm
If you disconnect the O2 sensor, forcing it to stay in open-loop, you should see about 80% during warm-up and 50% after that.

I once had a shorted O2 sensor plug that caused it to stay close to 80% all the time; that could be your problem. If the engine runs differently when you wiggle the O2 sensor wiring you have a problem there somewhere. It took me forever to figure out; the car would run great one day and the next it would run so badly it wouldn't get over 25 mph.

[rb0095]

I replaced the O2 sensor Saturday night. Since then the car has been running much better. I'm guessing that the old one went out a while ago and it just took me a while to notice it.

Last night, however, it did something odd. I was driving home from work and noticed that it was idling way too high. When I pulled up to a stop light it was idling at about 2300 rpm. It normally idles a bit high while warming up, then the idle goes down to normal, but last night it stayed at 2300 rpm all the way home (45 minute drive). 2300 rpm is the highest I've seen it idle...I'm looking into the issue today. Probably about time to correct the air/fuel mix anyways. I haven't adjusted it since replacing the o2 sensor.

Also, I have been observing the way my car runs a lot more closely lately and I have found something that seems unusual. My car has a 4 speed transmission, so when I'm going down the freeway at 65 mph the engine is turning at about 3500 rpm. If I drive at 3300-3500 rpm for a good 15-20 minutes then exit off the freeway the car tends to idle high (1700-2000 rpm). Then after driving at a lower speed (around 2000 rpm) for about 5-10 minutes the idle goes back to normal (about 900-1000 rpm). When I drive to work the car is running at about 3000 rpm for at least 15-20 minutes of the 45 minute drive, but I don't notice a difference in idle. Should driving at 3500 rpm for 15+ minutes really make that big of a difference to the idle speed?

I wonder if this issue with the idle is related to fuel pressure/volume. Note that I'm not 100% positive that rpm is the cause of this issue.

[rb0095]

I recently had a good talk with my uncle who is a mechanic. I find it much easier to explain in person my issue to himt. He suggested that my idle issue could be vacuum related. He also suggested that since I already know there is a vacuum leak I should focus on that first and go from there. I'm going to try and follow that advise and not to jump to conclusions without proper testing.

When searching for the vacuum leak today I discovered that the auxiliary air valve is not closing when the engine is warmed up, definitely contributing/causing my vacuum issues.

Thanks, for all the help so far.

[rb0095]

Replaced the auxiliary air valve on Saturday with a working one. The car runs and sounds much better when it is warmed up.

The dwell meter is still not getting an accurate reading on the test plug though...so it's still tuned by ear. Reads a steady 85 on the meter.

Did a vacuum test as well, still reading just under 15 on the gauge... I guess I'll be looking for more vacuum leaks.

[kamzcab86]

It's entirely possible that the test plug has gone bad... mine did: http://cabby-info.com/readings.htm .

Where is the 15 vacuum reading being taken at?

[rb0095]

Where is the 15 vacuum reading being taken at?

Off the vacuum line that goes to the brake booster/vacuum advance on the distributer.

[kamzcab86]

Try taking a reading at the intake manifold. Then increase the RPMs and see what the reading is.

[rb0095]

I haven't had a chance to check the vacuum at the manifold yet, but I'm going to do that today.

I was recently looking through the bently manual I have and realized something that I find odd. My car is a 1980, according the the bently manual the timing on my car should be set to 3 degrees after top dead center (my car currently is, this is where the timing mark is on the flywheel). I also know that most other cabriolets/rabbits are set to 6 degrees before top dead center. Does anyone know why my 1980 should be set to 3 atdc and not 6 btdc?

Would this difference in timing affect my vacuum readings?

Another quick question that is related, if someone in the past put a better/different camshaft in, would that affect where the engine should be timed? I don't know if it has the original camshaft, or much about the engine/car in general before I got it. I just know it is a 1.6 (based on the engine code of YK)