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Thread: Fuel Injector problems - again

  1. #1
    Junior Member
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    Fuel Injector problems - again

    I had John Hervey clean my injectors 7-8 months ago, after the car had been sitting for several years. He warned me that I would have additional problems, but as soon as I got the injectors back, I ran a spray test, and they looked very good. But then, after a good warm-up, I found coolant leaks, which led me into the VOD for a leak, and also behind a rusted fuel-tank cover plate for some other leaks, etc. While in the VOD I introduced a vacuum leak, with corresponding futile attempts to counter it with A/F adjustments. The car was back-burnered again for several months.

    The end result showed up in a spray test I just ran today. My first test gave me a 3-to-1 variation in highest to lowest flow rate. The second test narrowed that down to 1.6-to-1, however the second test was also inconsistent in the order of the injectors' performance. What's worse is that the injectors don't 'sing' like they should. I searched for actual flow rates in the DMC manual and in a Bosch book that I have, but neither seemed to provide any figures. I did find a thread on here from a couple of years ago that mentioned 6 oz/minute/injector. I'm getting nowhere near that - maybe 20-25% of that.

    The car will start, and idle up to about 2200 RPM, beyond which it stumbles. Here is some other relevant data:
    System pressure - 4.9 bar
    Control Pressure Warm - 3.8 bar

    Should I get these injectors cleaned again, or get new ones? I might have thought new ones, but they cost more than I realized, and I did read some discomforting things about Chinese imitations. As I said, I did not have a problem when I had these cleaned originally by John, but I suspect I will get an even sterner warning if I go back to him again.

    Thanks
    Robert
    1981 DeLorean #1890
    1976 Datsun 280Z
    1968 Pontiac Le Mans convertible

  2. #2
    DMC Midwest - 815.459.6439 DMCMW Dave's Avatar
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    Location:  Crystal Lake IL

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    First be sure to completely clean the fuel system, replace anything that is suspect. If there is anything coming apart (i.e. tank parts, accumulator, filter) you'll just plug up a new set of injectors. That's an expensive lesson.

    Replace the injectors. I've never had much luck cleaning them. I've replaced a lot of "cleaned" injectors.

    I probably posted the 6 oz/minute number, it's what I've always considered "good". Also important is uniformity across the range of opening, i.e. test the flow at wide open, but also at 50% push on the flap and at a very small flap opening. I've seen injectors that flow OK wide open but not at low flow, and you'll get pretty strange operation if they are not balanced across the whole range. Yours sound like they are just overall plugged. That's pretty strange if they were really good not long ago, which is why I'm suspicious about how clean you got the system.

    One more thought - if this was a "back from the dead" car 8 months ago, wasn't cleaned all the way, you put new fuel in the car and it's been sitting since then, it's likely that more junk has broken loose inside the fuel lines/tank and plugged it all up again. At the initial rebuild, did you replace the accumulator, filter, pump, and antiseptically clean the gas tank?
    Dave S
    DMC Midwest - retired but helping
    dswingle@DeLorean.com

  3. #3
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    Last spring, I 'unstuck' the fuel pump (merely by running on good, full 12 V outside the tank) but did not replace it, removed all fuel, cleaned the tank thoroughly with acetone, and replaced the filter. I did not replace the accumulator. The car ran - barely - at which point I did the first spray test before sending the injectors off to be cleaned.
    Robert
    1981 DeLorean #1890
    1976 Datsun 280Z
    1968 Pontiac Le Mans convertible

  4. #4
    DMC Midwest - 815.459.6439 DMCMW Dave's Avatar
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    Quote Originally Posted by DMC1890 View Post
    Last spring, I 'unstuck' the fuel pump (merely by running on good, full 12 V outside the tank) but did not replace it, removed all fuel, cleaned the tank thoroughly with acetone, and replaced the filter. I did not replace the accumulator. The car ran - barely - at which point I did the first spray test before sending the injectors off to be cleaned.
    It's likely that the accumulator has disintegrated and the rubber from that is plugging everything else up. It apparently goes right through the filter. Best thing now would be to replace the accumulator and filter, re-check the tank, and while they are out flush the lines with acetone before putting in the new parts. No shortcuts! Don't run acetone thru the fuel distributor!

    Recall that this is a circulating fuel system, so if what I'm describing is happening you'll probably find more junk in the tank now.
    Dave S
    DMC Midwest - retired but helping
    dswingle@DeLorean.com

  5. #5
    Junior Member
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    Thanks Dave, I had attempted to replace the accumulator last Spring, but I could not remove it with my available wrenches. Then I assumed that since I don't have a rest-pressure issue that the accumulator was OK. I'll try again to remove it.
    Robert
    1981 DeLorean #1890
    1976 Datsun 280Z
    1968 Pontiac Le Mans convertible

  6. #6
    EFI'd dn010's Avatar
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    You should get a new pump while you're at it. $50 on eBay and you know its new. Put your old pump in by the jack as a "spare". It is easier to remove the console and disconnect the accumulator lines available from above than below. You'll find an access hole covered by a rectangular piece of plastic.
    Last edited by dn010; 01-08-2018 at 11:35 AM.
    -----Dan B.

  7. #7
    Delorean Guru
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    Before you do anything try filling the tank with fresh fuel and a can of Techron. If the injectors were OK months ago that may do the trick. If not they will have to be cleaned or replaced. I agree the tank should be wiped out again. You may still have junk in it. Injectors don't go bad from bad fuel in 8 months unless you did not clean the system well. I also suspect you have other problems from when you did your other work.
    David Teitelbaum

  8. #8
    Junior Member
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    Thanks Dan for the accumulator access hint.

    Thanks David T for the other tips.

    I'll report back when I get this resolved.
    Robert
    1981 DeLorean #1890
    1976 Datsun 280Z
    1968 Pontiac Le Mans convertible

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