Fuel/Vacuum related issue

[vertigasen]

Ok, this has been an ongoing problem, but I have had multiple things going on at once (KB front seal....). I have been fixing them one at a time, but back to the major issue again.

I have had a fuel and vacuum issue for a little while. I think I have narrowed it down, but I need some opinions before I start tearing everything down again. First, I started having a random misfire. It does not throw codes (infact since I put my engine back together, I have had 0 codes...even for my o2s). The misfire starts after the engine is warm. It is lessened by running the A/C. A secondary problem is that my fuel pressure gradually rises over time until it levels out at about 60.

Here is what I am thinking. The vacuum system is connected to the fuel tank via the evap system. I am thinking that I either have a leak in my gas tank....filler grommet, fuel hat seal (yes, the pump was upgraded almost 2 years ago but this has been going on since around that time). I do have the strong smell of gas for about 2 days in my car after filling it up (30 mins of idling = quarter tank). I checked the Boost-a-Pump....voltage is normal.

My major problem is no codes and the randomness of the misfire. I would figure that if I had a problem with the evap system or gas tank....I would get a code. I also figured that since I do not even have 1 rear o2 sensor plugged in, I would get a code....none.

If anyone has any other sugguestions, I would greatly appreciate them. I am disabled due to the Army, and it is a pain in the ass to do stuff over and over because it takes me forever. If I can do it all at once, it would be great!

Thanks!

 

[wmburns]

IMO, you have come to the right place. Always want to help a member of the service.

If it's OK with you, can we work through some tests? There may be more than one issue going on.

Frankly, there are a lot of cars out there with vapor leaks in the fuel systems that run without any real issues. The usual place for vapor leaks are the filler neck (rusting out) and the filler neck grommet.

But, the vapor angle is actually easy to rule in/out. Find the EVAP purge line coming from the throttle body. The EVAP line is usually easy to spot because it is covered with tons of black soot (remember that gas vapors are hard on rubber parts). There should be a splice located along the lip accross the firewall. Split the junction and plug BOTH ends of the vacuum line. This is important.

This will functionally disable the EVAP system. Expect some new EVAP related DTC codes but that's OK because it's for testing. Drive the car and report if there is any improvement.

Note, do not operate the car for long periods of time with the EVAP system plugged. Doing so will ruin the charcoal canister. Remember, this is just for a quick test.

To me, the more distrubing issue is the unstable fuel pressure. Before we start, I need to understand HOW you are measuring fuel pressure and how the motor is operating at the time.

Can you explain? Are you using an external fuel gauge? Do you have an ODB2 scanner? Can you monitor operational data? It would be a great benefit to be able to cross check the external fuel pressure with the fuel pressure as reported by the PCM.

 

[vertigasen]

I will go into a lot more detail. When I left for Iraq in 2008, I left my car with family for them to watch over, start....all that. I was only gone for about 8 months because of an IED. When I got back, I got my car and it seem to be running fine.

About 3 months later, it just died on me. I checked everything then, and it ended up being the fuel pump. I used both, an external fuel pressure gauge, and an ODBII scanner and the pressure was low....idle 22, max pressure of 28. I replaced the pump with a SVT Focus pump. Pressure was back to normal, and it seemed fine. Winter came in Colorado, and I had my first surgery, so it sat again for about 3 months. By that time, I had my KB. It went in, and as soon as it did....I had a very slight miss, but only at idle. A/C on, and no miss.

I talked to KB, and they said it just happens sometimes.....it shouldnt be a problem. I drove it like that with no problems at all all last summer.

Aug 09, I had my next reconstruction....and some complications afterwards, so it sat from Aug to December. We had a pretty mild winter, so I started driving it again. It still seemed ok, but the miss had become a little more noticable. While cruising on post at 20 mph, I might be at 1500 rpms. At that rpm, I would sometimes notice the miss, but it was completly random. I was still having to clear codes every day for my o2 sensor, but that was the only code.

Get to about March of this year, something new started to happen......if I got off the gas, say in 4th gear, after about 5 seconds of letting off the gas, the engine would suddenly change pitch to a very deep tone....almost line an engine brake. When that would happen, my AFR would shoot up into the 18-20 range, but 5 seconds later....eveyrthing would go back to normal. About the same time that this started happening, when the engine would get warm.....the fuel pressure would start going up. At the beginning, my pressure would go up to about 40 at idle, and under boost it would still go to about 50. It didnt really run bad, seemed to be causing no problems. Over a month period, it kept going higher. Once it would hit 50, it wouldnt change....boost or vacuum. It ran fine as long as I was not in boost. As soon as I hit boost, it would jerk and buck. My AFR would be in the 9s and my gas mileage went to hell (120 miles on a tank).

Finally, in July, I was coming home from getting dinner, and coasted down a hill in 5th gear towards a stoplight. It did the "engine brake" thing.....and all hell broke loose. My AFR went to 18 (think I need to recalibrate my AFR anyway....but it is not off much) as soon as I gave it more than about 10% throttle. I pretty much blew this off on a leaky front seal on the KB. KB told me how to fix it....so I did. I just got it back together within the last 2 weeks (everything is taking me a lot longer now).

Now thta it is back together, the miss is still there. The fuel pressure is still raising even when I just let it idle for 30 minutes or so. Both, the PCM and external pressure gauge are reading the pressure about the same...within ~2 psi. The miss is there, and it idles fine (other than the miss) regardless of the fuel pressure. Drivability is the issue as the fuel pressure rises. When it is around normal, it drives fine boost or no boost (miss still there at low RPMs). The more I get into boost, the quicker the pressure rises. It starts to stumble in boost after the pressure starts to go over 40. After 50....there is no boost....by that, I mean it kicks and bucks.

That is why I said I think they are related. I think there has been a vacuum leak in the system somewhere, and that has possibly been the issue with the miss at idle. I believe that the miss getting worse and the fuel pressure going through the roof are a product of the same thing....not to mention as this was happening, I started getting the strong smell of fuel in the car....but only after filling up. I had the entire top of the engine apart when I did the supercharger seal, and I checked every line I took off. The EVAP line, is pretty crusty... I did drop the tank when I did the fuel pump install. When I did the pump install, I DID NOT remove the filler neck. The lower neck bracket stayed on, and I just removed it from the fender and left it attached to the tank.....so the grommet was not changed because it never came out of the tank. Maybe, I damaged the grommet? Maybe the hat did not reseal correctly? This could lead to a vacuum issue in the EVAP system.

Sorry, I got a little long winded because I am on some heavy meds tonight.....MS CONTIN, aka Morphine. I hope this helps because I am finally getting fustrated. Thank you for your help!

 

[wmburns]

Did you have the tune modified for the new fuel pumps? If not, a theroy could be may be the PCM pressure to duty cycle table is wrong for the larger fuel pumps. When the PCM is calling for "x" duty cycle, the fuel pumps are creating too much pressure in response.

The pressure builds until the PCM shuts off the fuel (FP duty cycle = zero). Pressure drops. PCM again calls for "x" amount of fuel. Cycle repeats as the fuel pressure spikes over and over.

Your problem is most likely made worse because of the BAP makes the fuel pumps respond as if on steroids.

An external fuel pressure gauge is handy to have but does not provide the full picture. It really needs to be cross checked with the fuel pressure as reported by the PCM. This should remain in the 38-41 PSI range regardless of boost/vacuum. If not, this indicates problems with the fuel delivery. Causes such as bad fuel pressure sensor or disconnected FP vacuum reference line.

OBTW, one of your comments was also distrubing. An external fuel pressure gauge and the PCM fuel pressures should NOT match each other on a boosted application. Why? Because the PCM uses intake referenced pressure (Delta) where as the external gauge reads atmospheric. So if the two gauges are reading the same, that means the fuel pressure sensor is not getting an accurate read on the intake manifold vacuum reference.

The concept of fuel pressure being intake referenced is VITAL to the proper operation of any motor but especially in a boosted application.

NOTE, on boosted applications, the fuel pressure sensors fails at a fairly high rate. The boost is hard on the pressure diaphragm. The failure rate is high enough that many ppl recommend have a spare on hand just for trouble shooting.

Also, strongly recommend having the alternator tested for correct output and EXCESSIVE AC RIPPLE. Most autoparts store will do the test for free.

 

[trinity_gt]

Get to about March of this year, something new started to happen......if I got off the gas, say in 4th gear, after about 5 seconds of letting off the gas, the engine would suddenly change pitch to a very deep tone....almost line an engine brake. When that would happen, my AFR would shoot up into the 18-20 range, but 5 seconds later....eveyrthing would go back to normal.

What you describe here sounds normal. In engineering terms, it's known as DFCO -- decel fuel cut off -- and it's the PCM stopping pulses to the fuel injectors. This is basically an emissions-reduction strategy (as well as a bit of a fuel saver.) The PCM will turn the injectors back on when the vehicle speed or engine RPM values reach certain values to ensure the engine doesn't stall coming to a light (for example.) The high AFR reading makes sense since there's basically no fuel going into the engine at this time.

My KB car (running the KB tune/chip) does the same thing. Now, if this is something new, something you've not noticed before, that's interesting because it's something the car should have been doing all along.

About the same time that this started happening, when the engine would get warm.....the fuel pressure would start going up. At the beginning, my pressure would go up to about 40 at idle, and under boost it would still go to about 50.

Sorry if this has been answered but: Where is this measurement being taken? Are you reading an OBD-II scanner or a fuel pressure gauge tapped into the fuel rail?

It didnt really run bad, seemed to be causing no problems. Over a month period, it kept going higher. Once it would hit 50, it wouldnt change....boost or vacuum. It ran fine as long as I was not in boost. As soon as I hit boost, it would jerk and buck. My AFR would be in the 9s and my gas mileage went to hell (120 miles on a tank).

Finally, in July, I was coming home from getting dinner, and coasted down a hill in 5th gear towards a stoplight. It did the "engine brake" thing.....and all hell broke loose. My AFR went to 18 (think I need to recalibrate my AFR anyway....but it is not off much) as soon as I gave it more than about 10% throttle. I pretty much blew this off on a leaky front seal on the KB. KB told me how to fix it....so I did. I just got it back together within the last 2 weeks (everything is taking me a lot longer now).

Now thta it is back together, the miss is still there. The fuel pressure is still raising even when I just let it idle for 30 minutes or so. Both, the PCM and external pressure gauge are reading the pressure about the same...within ~2 psi.

Very strange. As wmburns notes, the two shouldn't read the same. To reiterate, the rail pressure measured by the fuel pressure sensor (the PCM reading) is "corrected" to provide the pressure drop across the injectors. So at idle when you've got 18inHg of vacuum or at 9psi boost, this sensor should always return something fairly close to 40psi. Basically, the PCM always wants the pressure in the fuel rails about 40psi higher than the pressure in the manifold/ports because the injectors' flow is rated at a 40psi pressure drop.

When you screw a fuel pressure gauge into the fuel rail, you're measuring the actual fuel pressure in the rail, "uncorrected." At idle you'd see something like 35psi and at 9psi boost you'd see close to 50psi.

If the two readings are the same it suggests to me that the fuel pressure sensor on the rail is not properly referenced to the manifold pressure. There's a vacuum line connected to that sensor...where's it going on your car?

 

[vertigasen]

Sorry it took me so long to get back to this. I ordered a new scanner....and finally got it in today. I had an older Equus 3130, and it was showing really strange stuff. I upgraded to the 3160...and it is displaying stuff better.

I may have found the issue with the fuel pressure. After examining the manifold pressure hose and where it goes.....Fuel Pressure Rail Sensor, BAP interface, Boost Pressure Gauge, and KB Boost Bypass, I found one of the connector hoses appeared to be loose. The hose itself looked fine, just the opening was larger than the coupler. I removed that piece all together, and just left the BAP, rail sensor and bypass connected. The pressure did not seem to raise as it did before. I only let it idle about 10 minutes, but it didnt change at all. The pressure on the scanner stayed 38.5 to 40.5. The rail pressure gauge stayed about 26.


Now, to the miss. As soon as the fuel system went closed, the miss started. No codes. Things that were strange......the long and short term fuel trims were all over the place STFT @ idle was anywhere from 11 to -8. LTFT was in the range from 0 to -5. As the misses were happening, it was pulling timing. At startup, it was 21. Once the miss started, it was 22-24, but when the miss would happen (every 1-2 seconds) it would shoot up to 30-33. I will get some live data and post it up, if there is something specific you want to see...just let me know.

I removed the evap line and plugged it on both sides.....10 minutes, no code from that either. That didnt seem to change anything. I got to do all of this a little later in the evening, so hopefully I will have more time this weekend to test a few more things.

 

[wmburns]

Ignore the STFT. For the LTFT to be useful, you have to state what the engine was doing at the time. For example if the LTFT changes from negative to positive values going from idle to load, this tells us something. Mearly stating it does this or that tells us nothing.

OBTW, a LTFT in the range of 0 to -5 percent is actually fairly good.

Consider monitoring the DPFE EGR flow as this could cause your issue. Another option is to remove and PLUG the EGR vacuum reference line and see if it improves. Note, if the EGR value itself is not closing fully, this test will be inconclusive.

Do you have UNDERDRIVE pulleys? Some UD's can cause an unstable CKP signal. As well as an incorrectly torqued crank balancer bolt. The torque procedure is critical. There is a small possibility this could be a bad crank damper. If the damper is old and the rubber isolator is hard and brittle, then the balancer is not really doing it's job. This leads to an unstable CKP sensor output. IMO, this option should be low down on the possible list as my quess is it would get worse at higher RPM's.

The fuel pressure sounds much better to me now. 38-40.5 is acceptable for a return-less system.

 

[vertigasen]

I finally got some time today, and was going to do a compression check and some other stuff. I started it, recorded some live data.....went to upload it, but it took some time because I just rebuilt my computer earlier this morning.

The fuel pressure at startup was right on the dot.....38-40.5. No miss, everything seemed great. About 10 minutes into the idle, the miss started. I ended up letting it idle for about an hour, and recorded live data again right before I killed it. The fuel pressure from the ECU was up over 50 now. I used a multimeter and checked input and output from the BAP ~12v on both.

From things you had said in an earlier response, it is possibly the Fuel Pressure Rail Sensor, or the manifold pressure/vacuum hose. I checked the hose, it is fine and most stuff is removed (see my other post). So that leads me to the sensor.

I will do more testing tomorrow......another compression, leak-down, and a few more.

 

[vertigasen]

Compression test done....and not so good.

1 - 105
2 - 100
3 - 98
4 - 100
5 - 105
6 - 100
7 - 98
8 - 60

I put a cap full of oil in #8, and it jumped up to 90. Guess there is a lot more to do than find out what is causing my fuel pressure to go up. I will add a link here in a few to my live data recordings.

 

[trinity_gt]

Compression test done....and not so good.

1 - 105
2 - 100
3 - 98
4 - 100
5 - 105
6 - 100
7 - 98
8 - 60

I put a cap full of oil in #8, and it jumped up to 90. Guess there is a lot more to do than find out what is causing my fuel pressure to go up. I will add a link here in a few to my live data recordings.

#8 definitely looks hurt (oil helping generally means rings and/or piston sealing.) They all look suspiciously low:

1) Did you remove all 8 plugs before doing this test?
2) Did you hold the throttle wide-open while cranking?

 

[Sonic04GT]

Irrelevant, but where in Iraq were you in '08? I was over there the same time. My buddy is with 10th SFG at Fort Carson and loves it. I wanna get up there some time to do some snowboading.