I'm going to try the 4.1->4.9 conversion - Page 7
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HT4100 4.1, 4.5, 4.9 Discussion, I'm going to try the 4.1->4.9 conversion in Cadillac Engine Technical Discussion; Unfortunately if the battery was reversed, Then you may have more problems. The blower control module is powered all of ...
  1. #91
    aeronca36606 is offline Cadillac Owners Enthusiast
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    Re: I'm going to try the 4.1->4.9 conversion

    Unfortunately if the battery was reversed, Then you may have more problems. The blower control module is powered all of the time so that may be suspect. The cooling fan controller behind the left headlight is also powered as soon as the ignition switch is turned on. This also may be bad. (Expensive and hard to find as it is a one year part) Obviously the alternator could have taken a hit. The radio. The Auto Level Controller. And on. Most of the lower current devices are fuse protected but some of the higher current devices are not (Except for hi amp fusible links)

    I had a simuler problem when i had my Diesel engine replaced. The mechanic that did the switch forgot to connect the second ground to the engine block. When he tried to run the starter, He fried several expensive modules. I saw this happen but could not stop him quick enough.

    Good luck and hope it did not do too much damage.

  2. #92
    ehall's Avatar
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    Re: I'm going to try the 4.1->4.9 conversion

    We didn't try to start it. The headlights were on so we knew something was wrong. I've done it before but this is the first time I remember blowing more than 1 or 2 fuses. I'll work through any other problems that come up but don't expect any (BTW I have a spare fan control module; I bought a mislabeled part on ebay that had the right part num). Stupid battery side posts ... can't see the damn markings

  3. #93
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    Re: I'm going to try the 4.1->4.9 conversion

    Quote Originally Posted by aeronca36606 View Post
    Do the other numbers other than the part number match? If so, You should be able to change the prom from your 85 fwd to the replacement ECM. I do not know this for sure, but many times the computer boards are the same just a different prom. Of course if the boards are different, Then all bets are off!
    If the car is equipped with the VATS system (not sure when Cadillac got this), that alone will require prom replacement as the VATS resistance/voltage values are unique to the ECM's prom.

  4. #94
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    Re: I'm going to try the 4.1->4.9 conversion

    The boards and boxes are similar and of course the 4.1 engine management is the same, however there are differences in the car setup such as the fuel pump and a couple of the sensors. I don't know how much of this is wiring and how much is in the PROM, but I do know that GM wouldn't have changed part number and inventory if they were identical. Even if it does "work" to some degree, it will just make things more confusing and could possibly cause a problems (eg, wrong output voltage to a sensor) so I'm just leaving it alone

  5. #95
    aeronca36606 is offline Cadillac Owners Enthusiast
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    Re: I'm going to try the 4.1->4.9 conversion

    Gm did use a lot of the same computers between different years and models. The proms where unique to the make and model the computer was used in. The difference is in the firmware prom. For instance i had to replace the bcm in one of my 1985 Deville Diesels. I used a bcm from a 1987 Gas Devillle. The computers where the same. The proms where different. Hence the different part number. The board manufacturing numbers where the same. The earlier 1984 Diesel Electronic Control System or DECS computer is different from the late 85 with quite a few different sensors. However the only real difference is in the firmware Prom. You will also notice that the part number for the service replacement computers will cross to several different makes and models and years. They come without the Prom. You are supposed to use your original Prom when replacing the unit.

    I do not know if this holds true with the 2 ECM's you are dealing with though. Further investigation would be required. Good luck with the swap though. I am watching with keen interest to see what kind of results you get. Hopefully it can help someone else down the road.

  6. #96
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    Re: I'm going to try the 4.1->4.9 conversion

    Yeah, that ^^^

  7. #97
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    Re: I'm going to try the 4.1->4.9 conversion

    The ECM boxes have different box numbers. My 85 is 1226462 and the RWD box I got from the junkyard is 1226463. There is something different about them, I dunno what, but I don't feel like doing a spark test to find out. I'll send it to you to play with if you want, I don't need it

  8. #98
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    Re: I'm going to try the 4.1->4.9 conversion

    Here are a couple of pics of the 4.1 vs 4.9 front exhaust manifold. The 4.1 has a flatter manifold which I suppose leaves a little more room in the engine bay although I don't recall any problems with the 4.9 front manifold that is in there now.



    The ports are the same size, but the 4.1 has provisions for the smog pump air supply through the extra flange in the casting--air comes in through the large hole in the top center, then feeds into small pinholes near the exhaust ports (you can't see the pinholes in the pic). These were more or less blocked off so it's unlikely that the smog pump was working as advertised.



    These are the smog pump/AIR parts, minus the hard lines that were bolted the engine (those were destroyed). This is the pump, intake filter canister, diverter valve assembly, and check valve for the cat pipe, plus the soft lines. I will let these go to a worthy cause



    The vacuum pump... the hose coming off the diaphragm with the big check valve drew a vacuum load for the brake booster, cruise control, and cabin accessories (HVAC etc), and the other line went into the throttle body (dumping the vacuumed air into the throttle body, I presume). There is also vacuum blowoff vent down by the diaphragm somewhere. I'm keeping this until I figure out how to hook it up.



    Here's the 4.9 parts I have leftover, plus the distributor. Let me know if anybody wants them


  9. #99
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    Re: I'm going to try the 4.1->4.9 conversion

    ^ Does the idle speed controller work on the 4.9 throttle body?

  10. #100
    ehall's Avatar
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    Re: I'm going to try the 4.1->4.9 conversion

    dunno but I assume so

  11. #101
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    Re: I'm going to try the 4.1->4.9 conversion

    What would you want for it? My dad's car could use one, he's been through all the ones we have already

  12. #102
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    Re: I'm going to try the 4.1->4.9 conversion

    Rodya, I have another one in my parts box that you can have for the price of postage. Send me a PM and we will figure it out.

  13. #103
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    Re: I'm going to try the 4.1->4.9 conversion

    The 2nd ECM showed up in the afternoon mail so I ran down to the shop and plugged it up. With the key in Run position, I got the Service Soon light and Service Electrical light, but not the Service Now light. Also no VFD lights on the fuel or HVAC monitors... dead BCM now? Did some pin-out tests and didn't get good voltage anywhere... arghh the fan motors ran the battery down. Alright get a jumper battery pack and clip it on, good voltage to BCM on the ACC and IGN circuits but not on the battery circuit... fuse is blown? Yes replace the fuse and turn the key... dash lights and all the correct CELs. Crank the key and fuel injectors are firing! Alright!

    So it's on the battery charger now and I'll try to get it buttoned back up tomorrow. Unless something else pops up (haha) I should be able to get it running tomorrow.

  14. #104
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    Re: I'm going to try the 4.1->4.9 conversion

    Damn, so close yet so far! Cant wait to hear the final results. I never would have thought a 4.1 tbi system could possibly even attempt to run 4.9 liters. Now it doesnt seem so unattainable. Good work!

  15. #105
    aeronca36606 is offline Cadillac Owners Enthusiast
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    Re: I'm going to try the 4.1->4.9 conversion

    It is good to here that you are close. Glitches like this are almost a given. Murphy at work! I hope you are keeping a list of parts and modifications. It would be great if this can be duplicated by others. Good luck with the "Revile"

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