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Thread: Fuel issues, stumbling misfiring, 320hp Omni

  1. #41
    Hybrid booster
    Join Date
    Oct 2009
    Location
    Robins AFB, GA
    Posts
    645

    Re: Fuel issues, stumbling misfiring, 320hp Omni


  2. #42
    Hybrid booster
    Join Date
    Oct 2009
    Location
    Robins AFB, GA
    Posts
    645

    Re: Fuel issues, stumbling misfiring, 320hp Omni

    I'm back from deployment and decided to update this thread since the issue has been resolved! So the issue was I had a bad MAP sensor and an oiled down fuel regulator. Here's my findings and what I believe happened to cause the MAP to fail.

    The fuel regulator vacuum barb was teed into the PCV vac system. I also found that my PCV valve was cracked, so I went to the parts store and bought a new PCV valve. While I was deployed, I read up on a few threads and such which led me to start suspecting the fuel regulator was one of the problems that I was having. One of the simple tests was to pull the vacuum line off of the regulator and smell it to see if gasoline was present. If there was, then the diaphragm inside likely had a pinhole and needed a rebuild. So, I got home and pulled the vacuum line. I could smell gasoline in the vac line but no actual gas in the line.

    Off to Harbor Freight! Bought a fuel pressure test kit. The billet fuel rail I have on the engine is from FWD-P and it does not have a schrader valve, but it does have an inlet on the drivers side of the rail where you could plug in a second feed line to the rail if you wanted to.. so I plugged the test kit in and started the engine. At idle, the pressure bounced from 43psi, to 55, diving to 30, back to 55, 40, etc.. then dies. I pinched the feed line from the fuel pump shut with some pliers. The idle and the pressure settled around 45psi until the pressure gradually dropped and the engine began to die. Released the feed line, and again, erratic idle and bouncing fuel pressure. Decide to pinch the return line that's on the regulator. Pressure spiked to 90+psi, at which point I quickly released the line. AFR's at this time on the wideband sit steady at 10.0 on the guage. This tells me that the pump is fully working and pressurizing the rail, but the regulator is failing to maintain the pressure.

    In order to remove the regulator, I had to cut the return fuel line(which was replaced with new line) and remove the valve cover in order to get to the phillips head bolts holding the regulator onto the rail, as well as the vacuum line on the regulator. This is where things got interesting. Once the regulator was pulled off the rail and off the vac source, oil started to ooze out of the vacuum barb. Hrmmm...... Pics below! And more continued below the pictures.







    As you can see, when I pulled the top part of the regulator off, there was oil present. In the picture, this is evident from the oil on my fingertips. The last picture is the diaphragm, which is clearly covered in oil.

    So, once the regulator was cleaned, inspected, and reassembled, it went back onto the rail. I re-did the PCV system to where it attached straight into the front of the intake manifold with nothing teed into it. The vacuum line for the fuel regulator was teed into the back of the intake. I believe that oil had enabled fuel to enter the vacuum system, or something along those lines, and it eventually reached the MAP sensor, shorting it out. So, a quick call to Cindy, and two days later, a new 3 bar MAP sensor was at my doorstep.

    Plugged in the new MAP sensor, started the car, immediately noticed a MUCH better idle. Pulled codes just as a check. 12, 13, and 55. 12 and 55 can be ignored. 13 is still a code for MAP sensor. Disconnected the battery for a few minutes to clear the codes. Re-connected the battery and went for a drive. Car drove OK, still a bit sketchy. Got on a main road, and the car drove fine through the RPMS, as I only took it up to 3500rpm. Before, the engine would barely make it over 3000rpm before it would start stumbling. So this is a good sign. Got on a long road, enough to get up to 4th gear. Got the rpm's up and let the boost build. Before, if the boost guage touched 0, the engine would stumble. This time around, I got it into boost but realized it went super lean on the wideband, so I immediately backed off. This was good all around, but rain started to roll in and I was already a bit under the weather, so home I went where I parked it until the next day. Pulled codes, 12 and 55.

    So come to yesterday, I went to a buddies house where he and I first rode around in his new to him 1990 Mustang with a 351 windsor engine. After that, we went to dial in the fuel on the Omni. The G-Valve is set at 18psi, and we found a long road to do 4th gear pulls. I told him that as soon as he saw the wideband go red or go past 14, to tell me to let off. So after a few pulls, we got it dialed down to 11.5 at 18psi and it pulls really strong. AFR's at idle have cleared up to between 13.2 and 14.4. AFR's while driving are between 13.9 and 14.8.

    Went to a burnout car show last night with my wife and friends, didnt participate in the contest, just went to show up in the Omni since people know of it in town lol. But, ended up getting pulled over on the way over there because of expired registration. DIDNT GET A TICKET!! Turns out the cop that pulled me over used to have a CSX, what luck!! Anyways, it's parked in the garage and is awaiting final parts for the next big upgrade. To anyone reading this, I hope this helps out with whatever issue you might be having. Also would like to thank everyone who helped with information in tracking this issue down!

    Later!

  3. #43
    turbo addict
    Join Date
    Dec 2011
    Location
    Hemet,CA
    Posts
    1,636

    Re: Fuel issues, stumbling misfiring, 320hp Omni

    nice fix! always satisfying to actually nail a problem like that..im jealous lol

  4. #44
    Hybrid booster
    Join Date
    Oct 2009
    Location
    Robins AFB, GA
    Posts
    645

    Re: Fuel issues, stumbling misfiring, 320hp Omni

    I wish I could have figured it out when it started acting up back in August when my parents were here for my wedding. I've had it for 2 years here in Georgia and my dad has yet to ride in it since I got it road worthy. But, since my registration is expired, this gives me the chance to finally get my custom license plates!
    NOTAVW

  5. #45
    turbo addict
    Join Date
    Nov 2006
    Location
    san diego, california
    Posts
    1,548

    Re: Fuel issues, stumbling misfiring, 320hp Omni

    NOTAVW

    i like that one!

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