HT4100 SES light @ low RPM, much stalling & near stalling
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HT4100 4.1, 4.5, 4.9 Discussion, HT4100 SES light @ low RPM, much stalling & near stalling in Cadillac Engine Technical Discussion; My 85 fleetwood with an HT4100 is having some serious problems. Performance was never good (at all), but within the ...
  1. #1
    BrentNewland is offline Cadillac Owners Member
    Automobile(s): 1985 Cadillac Fleetwood FWD
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    HT4100 SES light @ low RPM, much stalling & near stalling

    My 85 fleetwood with an HT4100 is having some serious problems. Performance was never good (at all), but within the last week the car feels like it's on its last legs. It started off with stalling if I quickly pressed the gas while at a stop (not flooring it, but 1/4-1/3 throttle). It then proceeded into nearly stalling when letting off the brake at a full stop (with an occasional stall or two), followed by that combined with some near stalling at all speeds, occasionally during throttle. I'll be driving, then it'll sound like the engine died (though power steering and such still work). Then I give it a little gas and it's fine for a minute or two.

    I've replaced the spark plugs and wires within the last two months. I've also replaced the fuel filter within the last six months, as well as the battery within the last four. I had the timing set in January after replacing the timing gears (although I don't know at what timing, most likely stock - BTW, what is recommended? 11 BTDC?) I've changed the oil twice in the last six months, and replaced the O2 sensor within the last 9 months (with less than 4 months of driving). Last time I checked the distributor, the cap and rotor both seemed to have plenty of life left in them, though the distributor gear was a little worn.

    I didn't have the ISC motor connected (because I can't find the idle air control screw to set the idle, so the ISC goes out of range trying to compensate, and it was overheating my car); I connected it before leaving work in hopes that it would keep it from stalling (it didn't). Having the ISC disconnected throws a constant SES light; once I connected it, I found that at low RPM's (all speeds) and when it almost stalls it comes on. Increasing RPM sends it away.

    I haven't pulled the codes yet (all the parts stores are closed now, and my digital dash is dead so I can't pull the codes). I'm thinking it's the fuel pump, since I can kill it on demand by flooring it when I'm at low RPM. I don't have a pressure gauge that'll connect to the schrader valve, although I've custom made one that should connect at the fuel filter (which would be easier to see anyways).

    I had one small vacuum line connected to the cruise control arm that was loose (keeps coming loose, too short), and two hoses connected to the air cleaner assembly. After reconnecting these my brake light came on, but my brakes work fine.

    Any thoughts?

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  3. #2
    awadecki is offline Cadillac Owners Enthusiast
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    Re: HT4100 SES light @ low RPM, much stalling & near stalling

    If it dies when you gas it quickly--or wants to--then it's probably the fuel pump. This will also (obviously) cause a serious lack of power condition. Pull out one of your plugs and inspect it. I bet it's a white-tinged color from the engine running lean (i.e. too hot).

  4. #3
    BrentNewland is offline Cadillac Owners Member
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    Re: HT4100 SES light @ low RPM, much stalling & near stalling

    I replaced the fuel pump yesterday (a grueling eight hour task - BTW, if you can't get the tank back in place, make sure the fuel pump connector is to the back side of the tank and not on top). It helped a bit with performance, but it has the same problem.

    What might it be? I had the timing set in January. Could the distributor be just loose enough to slowly rotate and change the timing, or could I have jumped time? Could I have bad spark plugs? Could my exhaust be plugged?

  5. #4
    guidematic's Avatar
    guidematic is offline Cadillac Owners Fanatic
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    Re: HT4100 SES light @ low RPM, much stalling & near stalling

    #1, get the codes out of it. You can't do anything without doing that first.

    #2, consult with the shop manual as how to diagnose fopr these conditions.

    Simply throwing parts at it just because you think it may be this or that gets expensive and frustrating.

    Mike

  6. #5
    ehall's Avatar
    ehall is offline Cadillac Owners Connoisseur
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    Re: HT4100 SES light @ low RPM, much stalling & near stalling

    I had a cold stumble that went away after I put some Lucas fuel treatment in the tank. Probably not your problem but it's a cheap effort.

    I would fix your ISC though. The stop screw is behind the ISC assembly. Remove the torx screws holding the ISC bracket to the throttle body, and you will see the stop screw right there.

  7. #6
    BrentNewland is offline Cadillac Owners Member
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    Re: HT4100 SES light @ low RPM, much stalling & near stalling

    @#4: Can't pull the codes, no digital displays (see first post). Went to Autozone and they said they couldn't get any codes out of the OBD-I port.

    I've put BG44K in right before a full tank of premium fuel, and it didn't make any difference.

    And every cause I can think of that's non-pump related... can't really test those myself any other way. I don't have any timing lights, I'm not pulling all the spark plugs again (number one and all of the back ones are almost impossible to get), I haven't seen any way to check for plugged exhaust (other than removing it), and I have no digital displays. I had suspected the fuel pump was bad since I bought it, so I replaced it (and it fit all the symptoms). Hell, I could have bad injectors or no vacuum.

  8. #7
    BrentNewland is offline Cadillac Owners Member
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    Re: HT4100 SES light @ low RPM, much stalling & near stalling

    Fuel - Feed (pump, fuel filter, line, injectors), vacuum
    Air - Inlet, air filter, butterfly valve, exhaust (catalytic converter, muffler)
    Spark - Spark plugs, timing (gears, chain, distributor (cap, rotor, coil, gear)), plug wires

    Sorry for the double post, just making a diagnostics list of stuff to check.

  9. #8
    BrentNewland is offline Cadillac Owners Member
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    Re: HT4100 SES light @ low RPM, much stalling & near stalling

    Well, I was driving back from picking up my paycheck, and all of my problems suddenly stopped. I've been having to apply some gas when stopped to keep the engine from stalling, and every once in a while I let off the gas at lights to see if it still dies. It had been dying up until then (in the same trip), but it suddenly worked fine. The SES light also stopped coming on. I no longer had hesitation during driving, and flooring from a stop doesn't kill the car. It started overheating shortly thereafter (the light came on, lots of stop and go traffic), but I got out of traffic right after that and cooled the engine down.

    Not sure why the problem disappeared, but I'll take it. We'll see if it lasts.

  10. #9
    Chicano-Mexicano's Avatar
    Chicano-Mexicano is offline Cadillac Owners Fanatic
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    Re: HT4100 SES light @ low RPM, much stalling & near stalling

    Quote Originally Posted by BrentNewland View Post
    Not sure why the problem disappeared, but I'll take it. We'll see if it lasts.
    That is the secret of the 4.1 it has all kinds of problems but it chooses when it wants to show them (usually when your one the highway doing 65) but I digress, best of luck to you and may you one day be able to do a 4.5 swap and put that overs sized aluminum paper weight called the 4.1 out of its misery.

  11. #10
    BrentNewland is offline Cadillac Owners Member
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    Re: HT4100 SES light @ low RPM, much stalling & near stalling

    Sorry for the lack of update, but the next time I drove the car the problem returned. I'm leaning towards plugged cat fouling the O2 sensor and both causing the problem together, but it's going to the mechanic. I don't have time to screw around with it.

  12. #11
    BrentNewland is offline Cadillac Owners Member
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    Re: HT4100 SES light @ low RPM, much stalling & near stalling

    Alright, I have another bit of info I noticed that might help diagnose it. When I have the lights on (night driving) and the engine starts to stall, the lights dim. Also, when it starts to stall the stop engine/oil light comes on.


    Any advice welcome, it's getting worse!

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