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Thread: Troubleshooting A Fuel Problem

  1. #1
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    Default Troubleshooting A Fuel Problem

    A friend of mine, just had an odd thing happen with his car, it's running an HP system. Long story short, he had the vacuum line come off his fuel pressure regulator and by looking at his learn table, the ECU threw 100% of fuel all over the map to keep the AFRs in check. Further, he said it lost fuel pressure at some point, which in my opinion just added to the Learn Table adding so much fuel to the base map. His close loop and Learn settings are still 100% across the entire map.
    I stopped by to give him a hand and see if we could figure out what was going on. Aside from the added fuel, everything else looked good, although it was running like crap. He did not have an unmodified copy of the original tune, so I told him that I was pretty certain that a short drive would straighten things out, but it never really came around. He then got a hold of the original tuner and reloaded the dyno tune, to start fresh without a corrupted fuel map, this didn't help either.
    I was starting to think that maybe he had some corrupted files, but before we decided to flash the ECU he decided to have his injectors cleaned & flowed. Low & behold, they were in really rough shape and needed cleaned. At least 4 of them appear to have been stopped up pretty bad. The weird thing is that it was able to idle at a steady 13.5 AFR, but any load at all and it bucked pretty bad.

    After finding out that half the injectors were plugged up, I started thinking about what I could have been looking at in the software to have pointed to that. The only thing I can come up with, is that if we knew what the injector pulse width was at idle, before the injectors became plugged, maybe it would have shown that in the fuel tuning data monitor. Any thoughts on where to look to determine such things without paying to have the injectors checked?
    Last edited by Rick90lx; 06-05-2015 at 09:20 PM.
    93 Notchback, 383ci SBF, Highports, 80mm turbo, custom cam, TH400

  2. #2
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    When you have a tuned fuel map, you should only see a few percent change from day to day (based on weather and how well the temperature correction factors were tuned). If you should happen to see a bigger change than the original tune, then you have a problem. I also tell people to see what kind of injector duty cycle they see at WOT. As an example, if you were only at 65%-70% at WOT, and suddenly you see that you are at 75%-80%, you might have a problem with the injectors.

    Also, if you have had a problem fairly quickly after a tune, then you obviously have an issue in the fuel system itself. Just a few of the things we commonly see causing issues:
    People using E85 with rubber lines (it needs to be PTFE hose), the E85 breaks down rubber hose.
    People who use E85 and don't drive it daily, the longer you park it, the more it corrodes stuff.
    If you park it for more than a week at a time you should flush the system out by running it on gasoline for a few minutes, after it gets up to full operating temperature.
    People with old lines, they do deteriorate over time and come apart internally.
    People with foam in their fuel cell, the foam comes apart, and ends up in the injectors.
    People who put "dirty" fuel into their tanks, or who don't have a proper fuel filter, E85 is commonly full of small dirt & metal particles.
    Even when you buy it in a barrel, typically a good fuel filter solves this. Gasoline from a station that has very old tanks often contains a lot of sediment as well.
    People who run Alcohol and don't flush the fuel system with gasoline after use.
    We see a lot of clogged injectors from people who don't know that you have to flush all the alcohol out, and run gasoline through it every time you shut down for the day.
    -Scott
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  3. #3
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    Normally that was the case, but the loss of fuel pressure in boost, plus the low fuel created the issue, as far as I could tell. That makes sense. Unfortunately, we didn't have that information, and any attempt to tip-in resulted in it going extremely lean. That's what was odd, the car was tuned long ago, and all was good until it ran low on fuel and blew off that line. You would think securing the line & adding fuel, and it would be good to go, as long as there were no mechanical problems. This was only run on Turbo Blue or pump 93, and has the proper pre & post filters. That's part of what it made it so odd. Anyway, thanks for the response, I was on the right track with checking injector pulse width. I'll have him keep track of it for future reference. It had to have been a noticeable change to keep the proper AFR on four good injectors.

    Part of my response was in the quote. Sorry, posting from my phone and I didn't have the patience to do it correctly on this little screen.
    93 Notchback, 383ci SBF, Highports, 80mm turbo, custom cam, TH400

  4. #4
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    Quote Originally Posted by Rick90lx View Post
    After finding out that half the injectors were plugged up, I started thinking about what I could have been looking at in the software to have pointed to that.
    The Learn Table is a very good diagnostic/troubleshooting tool. Significant new changes means something is wrong. When my ECU was finished self-tuning, I transferred Learning To Base, and smoothed the Base Fuel Table using the Fuel Graph. I actually did this a few times. Now my entire Learn Table has values less than ±4%. So whenever I look at it, I know there shouldn't be any values greater than this (or else something is wrong). As S2H mentioned, the injector Duty Cycle % (as viewed on the Data Monitor or Datalogger) can be a very similar diagnostic/troubleshooting tool.
    http://forums.holley.com/showthread....7370#post47370 (Closed Loop & Learn Table - Especially posts #2, #6 & #11.)
    http://forums.holley.com/showthread....2523#post62523 (Holley EFI Tuning Tips & Information)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  5. #5
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    Thanks for cleaning up my post Danny. Normally there weren't any significant changes in the Learn Table, only a +/- 5% or so. We attributed the large spikes in Learning, to running out of fuel on a pass. It wasn't until we fixed the known problems, that we started looking for something more. Thanks again guys!
    93 Notchback, 383ci SBF, Highports, 80mm turbo, custom cam, TH400

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