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Fuel pressure high

10K views 31 replies 8 participants last post by  chartmaker 
#1 ·
So i started my car earlier today after it sat for 3 hours. The engine was immediately loping and misfiring for some reason. I didnt think to connect my scan tool at the time, but after driving for a little bit it stopped. I plugged in to see if I saw anything unusual. At the end of the trip I saw I was getting 60psi of fuel pressure (both actual and desired) just sitting at idle. I revved it and it didnt change. It was around 80 degrees out. Any ideas why it wanted so much pressure? I dont get it.
 
#3 ·
Interesting info. I didnt see any codes but it very may well have been running lean on startup for whatever reason. At the time of reading though, LTFT 1 was -3% and LTFT2 was .05%. I didnt see what inlet air temp was at. Wonder if a hose or gasket is leaking temporarily and then sealing up. Ill check the data stream on the way home and see if anything stands out.
 
#4 · (Edited)
Yeah, nothing out of the ordinary this time other than voltage was at 12.06V after 6 hours. I really need to figure out if there's a problem with this charging system or not. The car seems to alternate between running perfectly fine and "wtf".

I don't know if it's relevant, but before I started it and was getting the crappy running, I was getting static pops through my speakers as soon as I turned the key to run.
 
#5 ·
Hmm none of this makes sense. Warm air has less dense oxygen. Adding more fuel to compensate for higher air temps throws fuel to air ratio off farther. Generally when you have warm air you want less fuel because oxygen density is less. Your fuel trims long term should be close to zero which they are. Does your scanner tell you engine load percentage? My Solis ultra does.
 
#6 ·
Maybe the computer ups the pressure to compensate for the faster rate of evaporation of the gasoline in high temperatures? I'm not knowledgeable enough of the physics to say for sure.

And yes, my scanner does have the ability to read engine load. What would I be looking for? I think the issue stems from whatever was going on when the car was first started, as the idle was going up and down. When it went down an obvious miss was felt. 29 misfires were logged while I was sitting in my parking spot. After a short 5 minute drive and getting off the highway, the idle was back to normal. The 60PSI value was observed idling in my parking space at work. Engine felt normal and tach was normal. The trip home was uneventful as well. I would suspect vac issues but I've never seen one that intermittent, so the next item of suspicion for me at least, is IAT or MAF. I was not able to see the IAT reading when it was acting up. When I was able to see it, it was normal and matched the ambient temp. Fuel pressure on the trip home stayed at 40PSI the whole time.

I guess all I can really do is hope it misbehaves again and log every relevant parameter I can think of, unless anyone has any ideas?
 
#7 ·
Static pops in the speakers is an electrical issue. It's possibly 1 of the 3 alternator phases is failing intermitantly. This will confuse the PCM.
What is the battery voltage under these conditions:
1. Idling?
2. Idling, headlights on?
3. 2000rpm, headlights on?
4. 2000rpm, headlights offf?
5. Engine off?
While testing note if popping sound occurs again and what rpm.
 
#14 · (Edited)
I just ran a gamut of tests to try and figure this out. Fuel pressure was 60PSI the entire time of testing, and it's only 74F outside. IAT held around 88F the entire time. ECT read between 92 and 99C (at which point the fans kicked on)

1: 14.05
2: 14
3: 14
4: 14
5: 12.49

Bonus round - AC Volts across battery posts
Engine off: 27.1
Idling: 29.8
2000RPM: 30.0

All the information I had updating in ForScan:

LTFT1: -0.39%
LTFT2: 3.12%
STFT1: 2.82%
STFT2: 2.92%
Total Number of Misfires: 40
ECT: 92C
Fuel Rail Pressure: 60.3PSI
Fuel Rail Pressure Desired: 60.3PSI
Throttle Position: 18.43%
Module supply voltage: 13.69V
Idle Air Control: 38.02%
Throttle position sensor voltage: 0.94V
Desired Idle Speed: 704RPM
Actual revolutions: 706RPM
IAT: 88F
Mass Air Flow: 3.78 g/sec
BARO: 1.02Bar
Spark advance: 12.50* (at 2000RPM it was 40 degrees)

Another thing I noticed was while revving it to 2000RPM, the misfire counter started going through the roof. Holding it for just 20 seconds put the count at over 150. I checked Mode 06 and it wasn't constrained to any particular cylinder, it was spread over them all. I'm sure I would have gotten P0300 if I held it long enough. I don't see this same effect while driving though, which is interesting. I also went over the whole engine bay and typical problem spots with propane and watched the short term trims. Couldn't get anything conclusive. The vac lines to the FPM were intact and not leaking.

So wtf am I dealing with here lol? Bad crank sensor? Bad MAF unit? I'm honestly stumped. :angry:
 
#8 ·
Look at the engine temp also.
PCM uses ECT to adjust fuel pressure for richer cold temps along with IAT.
As 4 wheel said and also could be grounds, connections or even battery issues. I've had several batteries with internal connection fails that were intermittent.
 
#9 ·
Thanks guys. Ill get back to you on the voltage mesurements. The alt and battery are fairly new but we all know that means crap in todays world. This morning I noticed something though. The car sat overnighy for 12 hours. outside temp was 69F. I started it and it started fine, but the IAT was reading 80F and stayed there for several minutes. It took almost 8 minutes of driving for it to reflect close to the actual temp. Is that right? Something tells me no.
 
#11 · (Edited)
Pic of my volts, I keep this as a reference as to compare for future checks. This DOHC G-4 with 130A alt. The actual volts should be trimmed by the PCM on '02 and later, by the regulator pre '02. Program is higher volts when frist started then lowered after a few minutes, thus to restore the discharge of starting and resting since last running. Then the volts are adjusted based on the predicted battery themperature. Hotter is lower charging volts. That is the normal expected battery needs. In my case, the brake pedal is not pushed.

In my case, I just want to know if my Alt is doing it's thing with load. Note, in this case, gear is "N". I have an adapter that I plug in the power port, the lower plug with the "12V" cover. The cig lighter may or may not work as it may or may not always make contact with the plug in device.

-chart-
 
#10 ·
Did you check the vac line going to the fuel pressure/temperature sensor?

IAT will always read higher than ambient temp if the engine isnt 100% cooled down, such as sitting overnight. Check IAT after the engine hasnt run for 8+ hours and see if it matches with ambient temp.
 
#12 ·
No, I did not. I will check that right now while I do the other tests.

And thats what im saying, it sat for 12 hours overnight, and IAT was reading over 12 degrees higher than actual ambient. 80F versus around 68F for outside temp at 6:30 AM. Doesnt seem right.
 
#15 · (Edited)
I can hook up my computer on my 2006 this evening and see my fuel pressure with engine hot. I am thinking 60 psi isn't really that high or abnormal. I thought fuel volume was a cross between injector pulse width and fuel pressure. Could your injectors be partially restricted and some Techron help out.

I gave up trying to figure my charging system. I rebuilt my old alternator at 130k because flickering lights. Ran a JY alternator for a few months which I partially rebuilt with new slip rings for practice. I was in the high 14s voltage wise when the lights were flickering. I truly believe the PCM causes the lights to flicker. I get a steady voltage and instantious drops as a normal trace. I seem to remember 1/2 volt drops. With both alternators. It did this for at least three years.
 
#16 · (Edited)
I can hook up my computer on my 2006 this evening and see my fuel pressure with engine hot. I am thinking 60 psi isn't really that high or abnormal. I thought fuel volume was a cross between injector pulse width and fuel pressure. Could your injectors be partially restricted and some Techron help out.
I started this out wondering if that was the cause of the terrible running and misses. As I've uncovered though, something else is going on here
 
#20 ·
Voltages are good and consistent regarding charging at steady 14volts.
Resting battery voltage should be 12.6 volts. This could be meter error or a battery cell starting to fail.
Cell voltages can be checked by placing the probes into the cells if the caps are removable. 2.1 volts is normal for a charged battery. The + post to cell and - post to cell should add up to the same as the others. Variation more than 0.05 volts is a cell going bad.
Your bonus readings on AC volts seem high. There should be zero AC volts at battery with the engine off though. This is likely a meter problem since a 28 volt AC voltage on a 12 volt battery is way out of range v

As mentioned in another post, the fuel pressure regulator diaphragm can fail and increase fuel pressure.
 
#21 · (Edited)
Voltages are good and consistent regarding charging at steady 14volts.
Resting battery voltage should be 12.6 volts. This could be meter error or a battery cell starting to fail.
Cell voltages can be checked by placing the probes into the cells if the caps are removable. 2.1 volts is normal for a charged battery. The + post to cell and - post to cell should add up to the same as the others. Variation more than 0.05 volts is a cell going bad.
Your bonus readings on AC volts seem high. There should be zero AC volts at battery with the engine off though. This is likely a meter problem since a 28 volt AC voltage on a 12 volt battery is way out of range v

As mentioned in another post, the fuel pressure regulator diaphragm can fail and increase fuel pressure.
Data says, the fuel pressure is doing what the PCM tells it to do. The FPM and the sensor are slaves to the PCM. Chance of sensor or FPM remote at best. If the PCM calls for higner than than expected, then there is a reason.

Any concerns about voltage should begin with wire maint. All grounds need to be removed ,cleaned, and re-seated. You could test by measrueing volts from the neg bat post to the: engine block, fender, firewall common post. Any over 100mv represent issues. Similar pos post to the mega fuse.

Visual is a clue as in the pic from the JY. But lots of bad stuff hide in plain sight. Common things in the JY for good cars being donors. Bat cables, coilpacks cracked and bulging. Oil in the air cleaner etc.

-chart-
 
#25 ·
Negative to engine looks like it's bad. I had fluctuating readings on the battery cable tracking down a erratic crank issue on my son's car.
Large size battery cables should have rock solid readings. Cables fixed the son's car which is a '05 24v
 
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