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1984 400i Auto- Engine Loading-Up Below 3000RPM- Help!

Discussion in '365 GT4 2+2/400/412' started by Jasonberkeley, Aug 26, 2021.

  1. Jasonberkeley

    Jasonberkeley Formula 3
    Silver Subscribed

    Apr 23, 2017
    1,209
    NW Corner, CT
    Full Name:
    Jason Berkeley
    Hi All,

    Couldn't seem to find another thread on this, so apologies if this is duplicative!

    Took the car out today for the first time in a couple of weeks. Hot and humid day. About 92 degrees.

    Drove it about 15 minutes to the store. Ran great. Sat for ten minutes while I picked-up a couple of things, then fired it up and left.

    Immediately started missing at low rpms. Fealt like it was loading up with too much fuel to me. Never eexperienced this before. If I got on it to "clear it out" or downshifted the GM three-speed auto to 2nd gear, and kept the revs above 3,000rpm, it ran fine. But if I came to a stop sign and got going again, same thing would happen.

    Does anybody have any experience with this issue or ideas?

    I've had the entire fuel system rebuilt 2-3 years ago. New injectors. New fuel pumps. Rebuilt fuel distributors and rebuilt warm-up regulators. Been running like a top up until today.

    Any help is appreciated!

    Thanks,

    Jason
     
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  3. sebackman

    sebackman Karting

    May 19, 2010
    110
    Europe
    Hi Jason,

    I have had two things bugging my car the last few years.

    One is the fuel filters. With so much ethanol in the gas nowadays they crumble internally and need changing at least every 5 years. Maybe they work fine at high flow but not on low? I changed both my pumps and filters last year and while I was at it I drew a new power feed direct from the battery via a new relay/fuse, triggered by the old feed. When I opened my old filters they were completely destroyed inside. They were maybe 10years old but the cars has not covered many miles so it is really being exposed to the ethanol that gets them. I'm in Europe and don't know how it is in the US and probably they were changed with the fuel pumps "a few years ago". They are cheap so maybe worth a go.

    A second problem that plagued my car was the distributor ignition advance being stuck. I had a similar problem as yours albeit reversed, ie was fine on low revs but no go when increased. Mine is also a 400i with a single distributor at the back of the block. I also refurbished the whole injection system with new injectors, filters, pumps aso, when this became the problem.

    As the distributor is driven from the engine there is a rubber seal on the drive shaft to preventing oil to enter the distributor from below. Over time this dries out/ get worn so oil can enter. With high voltage from the rotor/cap this oil (mist?) turn into brown muck that clogs the moving parts in the centrifugal ignition advance. Maybe yours is stuck on high advance.

    I took mine out and cleaned all of it and put in a new seal. Now she runs just fine. Its a little fiddly but not complicated. I will do a full write up soon with pictures for anyone else wanting to do it themselves. There is also a thread in here with very helpful advise from other members.

    Open the distributor cap and use a flashlight to look down into the distributor and if it looks like very rusty inside it is the "brownish muck", as the house is aluminum. This may very well not be at all was is the problem with your car, just an idea.

    I'm running a MDS ignition box so if you are on the original Dinoplex that could also an issue. Most of them does not age well :) . -Or too wide spark plug gaps so the ignition power is not enough at lower revs. I found that too wide spark plug gaps with the MSD box consumes cap and rotor so I'm on 0,7mm gaps which works fine even if MSD recommends +1mm. Caps and rotors have become very expensive even if Jag caps is a cost efficient alternative.


    Kind regards
    //Rob
     
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  4. capcgn

    capcgn Karting

    Oct 7, 2006
    131
    Germany
    Please check your fuse board for brown spots. Maybe one zylinder bank is missing because the board has a burned connector and it turns the fuel pump or the ignition for the bank off
     
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  5. Ak Jim

    Ak Jim F1 Veteran
    Rossa Subscribed Owner

    Dec 23, 2007
    5,853
    North Pole AK
    So after you drove for a while did it improve? How about the next day? Just wondering if it’s a vapor lock or heat soak issue. Next time after driving try opening the hood. Typically under hood temps peak 15-30’minutes after shutting the car off.
     
  6. Jasonberkeley

    Jasonberkeley Formula 3
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    Apr 23, 2017
    1,209
    NW Corner, CT
    Full Name:
    Jason Berkeley
    Hi Guys-

    Thanks for all of the suggestions.

    I recalled that I had an issue a few weeks ago with the car starting, and the relays down at the fuse box making some funny noises. I had pulled the 'T' fuel pump relay out then put it in back in and it fired right up.

    I replaced that relay with a new one (purple plastic newer Bosch part- I believe the new superceeding part number is 0332 209 151. Drove the same route and routine the next day while it was just as hot and humid, and ran fine.

    Rob- the fuel filters were replaced when all of the other fuel system work was done. I had read about the seals failing on the distributor on here, and I think this winter I will pop it open as you suggested and replace the seal as a preventative maintenance item and clean it up. If you wouldnt mind posting the write-up with pics that would be greatly appreciated! I am indeed still running the Dinoplex, which is always in the back of my mind!

    Capcgn- I will for sure give the board a close inspection as well. This is a good suggestion- thank you.

    Jim- I always open the hood when I get home, but typically don't do it when I park at a store or go somewhere. I think maybe I just shouldn't drive it when it's north of 90 and so humid out!

    I'll keep you guys posted on how it's running when I take it back out again later this week!

    Thanks again!

    Jason
     
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  8. Jasonberkeley

    Jasonberkeley Formula 3
    Silver Subscribed

    Apr 23, 2017
    1,209
    NW Corner, CT
    Full Name:
    Jason Berkeley

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