Prom needed/High speed great, mid to idle speeds terrible.
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RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, Prom needed/High speed great, mid to idle speeds terrible. in Past Cadillac Vehicle Discussion; I have an '84 Sedan DeVille, 4.1 liter engine. Trouble on hwy 500 miles from home. Drove it home. Replaced ...
  1. #1
    gsim is offline Cadillac Owners Member
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    Prom needed/High speed great, mid to idle speeds terrible.

    I have an '84 Sedan DeVille, 4.1 liter engine. Trouble on hwy 500 miles from home. Drove it home. Replaced bad MAT sensor. Was making car run lean, rough below 70 mph, would not idle. Replaced O2 sensor while I was at it because was original. Got new trouble code 52. So replaced ECM (Engine Control Module) Still runs rough at lower rpm and will not idle and still have code 52. Same exact characteristics as I had while out on the road when it first showed up. I am afraid that the P R O M chip is bad and Cadillac no longer sells that. Anyone know where I can get one? Or does anyone have an idea if 52 is a bad ECM or bad P R O M? The 'Service engine soon' and the 'Service engine now' both light up when I read codes on the climate control panel. I think that is pretty much telling me that the ECM is still bad, which leaves only the P R O M since I have a new ECM in now.

    Gerry
    (just replaced exhaust, cat convertor, tires, shocks last year! Only has 124,000 on the clock.)

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  3. #2
    drmenard is offline Cadillac Owners Connoisseur
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    Re: Prom needed

    I just took a look at some stuff and I found a ECM that might be it. It has a service NO. 1224840 ... Does any one know for sure?

  4. #3
    gsim is offline Cadillac Owners Member
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    Re: Prom needed

    Thanks, drmenard. My part # for the ECM is 1226028. The one I put on is a reman. There were no visible numbers on my P R O M, unless it was on the obverse side which is pressed into that plastic frame. Sigh. I had high hopes of getting her running right again. No rust, rarely spent a night outside, chrome great. Seats good and all power stuff works and never have even touched the air or added freon. Never have seen a Deville of that era in a junkyard in the 12 yrs I have had this one. Only saw Fleetwood Sedans, that era and only one of those some 60 miles away from here.

  5. #4
    AElayyat's Avatar
    AElayyat is offline Cadillac Owners Connoisseur
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    Re: Prom needed

    From what I remember about code 52 is that it is telling you that the battery was recentlly disconnected, don't think it means the ecu is bad.

    I think if you have a bad prom or ecu the car would not fire up...? (I'll let the more quilified people verify that).

    Also when you enter diagonstic mode on these cars the service now & service soon lights do come on.

    I think you may have a different problem I would say either fuel system or electrical system.

    Good luck with your project.

  6. #5
    talismandave's Avatar
    talismandave is offline Cadillac Owners Master
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    Re: Prom needed

    Quote Originally Posted by gsim View Post
    Thanks, drmenard. My part # for the ECM is 1226028. The one I put on is a reman. There were no visible numbers on my P R O M, unless it was on the obverse side which is pressed into that plastic frame. Sigh. I had high hopes of getting her running right again. No rust, rarely spent a night outside, chrome great. Seats good and all power stuff works and never have even touched the air or added freon. Never have seen a Deville of that era in a junkyard in the 12 yrs I have had this one. Only saw Fleetwood Sedans, that era and only one of those some 60 miles away from here.
    I have nothing to offer other than to say don't get discouraged, these guys here will get you through this. I am always amazed at the knowledge available here. That sounds like a car worth the wait!

  7. #6
    carnut is offline Cadillac Owners Master
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    Re: Prom needed

    "trouble 500 miles from home" we need a better description. Code 52 is an old (soft) code. Means that the battery was disconnected somewhere in the cars past. Maybe when you swapped out the ECM? When you pull codes, the codes that display 3 times are current ( hard ) fault codes, if they only display twice, they are history (soft ) and should be erased. Do you have a FACTORY service manual? When you transferred the PROM, did you possibly bend a pin? as you inserted it. easy to do! The ECM itself fits many GM cars of different years, the PROM is specific to your year and car type. I doubt you needed the ECM but now is too late. Did you have a hard (3 displays) code for the MAT sensor prior to replacement? What hard codes do you have now?

  8. #7
    gsim is offline Cadillac Owners Member
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    Re: Prom needed

    "Thanks AElayyat and thanks CarNut. Will poke around some more. Today I will spray cleaner into throttle body throat as I run the car. I will also pull the codes again and this time I will count the number of times that they display. OH, I did run a can of fuel injection cleaner thru the thing when it first showed up, hoping that it was maybe a dirty injector. No help, but it was a hail mary being that we were 500 miles from home.

    The 'Trouble 500 miles from home' was the same as now. Once warmed up, would not idle. Once warmed up, would not re-start without starter fluid. Ran as if it was starving for fuel at lower speeds and all the way to 60 MPH. At 70 MPH it was as smooth as could be. At that speed I could not tell that I had a trouble. To me that eliminated leaky line/pinhole, etc or fuel pump and fuel filter.

    All that I have for reference is a Haynes manual. It shows a code 52 as either ECM box or P R O M chip bad for all models including v6, HOWEVER it did NOT include the Deville. I could not find a number assigned for a Deville for ECM failure in my book. I finally took that to be a typo. Reason being is that it also said that if 'service engine soon' and 'service engine now' lights came on while I was getting codes, that indicated either ECM or P R O M failure.

    I think that disconnecting battery wipes stored codes clean or at least according to my Haynes book it does. I will run it and check codes this AM. The codes do not come on unless the car is being cranked or is running. Just turning on the key and pressing the 'warmer' and 'off' buttons will NOT bring up codes. The car has to be running or cranking. I recall that when running a fuel delivery trouble 3 yrs ago. Could not get codes to come up until I cranked it. ( On that one, it was the fuel hose knocked off of the fuel pump by an attempt to siphon gas from it some 3 weeks earlier.)

    Gerry

  9. #8
    carnut is offline Cadillac Owners Master
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    Re: Prom needed

    Every 84 Cad I've owned will display codes, key on, engine off. Are both injectors spraying when its running? That Haynes manual needs filed in the trash. I would verify that the MAP (manifold absolute pressure) hose is intact as it goes from the connection on the throttle body to the MAP located by the ECM underdash. That hose clips onto a long fender brace, passenger side underhood, and travels thru the dash to the sensor itself. Without MAP reference the car can run poorly. Verify vacuum is present at the throttle body connection, they can plug up with carbon. Spraying cleaner thru the throttle body is a waste of time. The spray of fuel above the throttle body itself cleans the throttle body bore and throttle blades as the car runs.

  10. #9
    gsim is offline Cadillac Owners Member
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    Re: Prom needed

    Thank you, Carnut.

    My car has never, ever displayed even one code unless either running or cranking. I have had it for 12 years. I will look into the hoses anyway tho. I did tighten the alternator belt while we were out of town so I will look real good around that area to see if I did something to it. Did not have any trouble that day tho. And my wife says that this trouble came in on her once BEFORE we ever left town. It ran perfectly for 4 days while we were out of town tho. When I replaced the ECM, I did see two vacuum things behind the glove box liner adjacent to the ECM itself. One had a vacuum hose running to it from the area of the heater core/evap core region. Other side had no hose on it at all, but I carefully looked around with a flashlight and felt around in that area as well and never could find a hose that was disconnected. I have done no work in that area, so I have no reason to think that it suddenly fell off and disappeared. I will look again though just to be sure. Both of these vacuum devices are switches with about 2 or 3 wires on each and both are mounted on a small bracket back-to-back. As I said, one has a hose that is intact and one does not have a hose on it at all, but has 2 or 3 wires going somewhere. I thought that it was maybe for an option that my car did not have. Regards Haynes manual I could not agree more. I tried to get factory manual at our library but all three are overdue for a long time now, and the librarian thinks that they will never be returned. I will look for one on eBay.

    Kindest regards and thanks again,

    Gerry

  11. #10
    carnut is offline Cadillac Owners Master
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    Re: Prom needed

    You are describing the MAP and BARO sensors behind the ECM. The alternator belt usually becomes loose once the smog pump belt is loose. Notice that the alt belt only runs around the water pump pulley. If the smog pump belt is loose, glazed, or worn out, it will cause the alt belt to squeal or slip causing low voltage at any RPM above idle. Tightening just the alt belt will not correct the slippage. Best practice is to loosen the alternator then tighten the smog belt, then retighten the alt. belt.

  12. #11
    gsim is offline Cadillac Owners Member
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    Re: Prom needed

    Thank you, carnut. All belts are new as I did replace the water pump last winter. There was no hint of any trouble after that. Have just re-checked once more and all belts are properly tightened. Alt belt on my car is strictly run from the water pump hub as you said and yes the smog pump drives the water pump via its belt. The MAP hose does go from where you said directly to the MAP sensor next to the the ECM and those wires are firmly attached to the plug and the plug is on tight. The other one that you said is the BARO sensor looks as if it has never had a hose on it. Maybe it reads barometric pressure through that neck/nipple that looks like it was made for a hose? There is no stray unconnected hose there. I am wondering if maybe my low speed jet is just in trouble? There are only two jets so I figured that one was for cruise-high speed and one was for cruise-low- idle speeds. When the rpm is up, both have a steady stream of fuel vapor and when it stumbles, both are interrupted more, but it seems that the one on the passenger side is more sporadic than the one on the driver side. Also it will periodically run up to a higher rpm and then stumble back down, all without any input at all. This is while it is sitting and supposed to be idling. I had to back out the throttle lever stop near the idle control motor in order for it to idle at all without someone in it keeping it going with the foot feed. So if it was running right, it would be idling way too fast now. Again, the car runs super smooth at 70 mph and above and begins to get rough and surge and wane around 60 and below. Worst is low speed while going uphill. If car is warmed up, it cannot be re-started without starter fluid!

  13. #12
    carnut is offline Cadillac Owners Master
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    Re: Prom needed

    Those are not jets, those are injectors. They should spray equally at all times. I recommend a fuel pressure test. Again, what codes are being displayed? If the belts are tight, you should NOT be able to rotate the alternator pulley by hand against normal rotation (engine off) If you can rotate the alt. pulley at all then the smog pump belt is loose still.

  14. #13
    gsim is offline Cadillac Owners Member
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    Re: Prom needed

    Thank you, car nut. Old timer's terminology. I am aware that they are injectors but still I will call them jets. They go sporadic when the engine stumbles down and gets to running rough. That could be electronic trouble too since that is what governs their volume, etc. It runs very well at 70 MPH and above. I figured that would eliminate fuel pump, fuel line leakage, and fuel filter. It will run for hours at 70 or more without any indication of trouble. From 60 mph down it progressively gets worse and going up a grade, that is amplified.

    I thought that maybe a fuel pressure test would be good, but that even better might be a voltage test across the leads on the two injectors? I can put an analog voltmeter across them, one at a time and observe the voltage as the thing runs. I set the idle up to the point where it will at least stumble along and not quite die. Every so often it surges and runs RPM up right after nearly dying, all by itself with no input. There might be a volume measuring sensor in the intake somewhere that is on the fritz.

    Regarding codes, I still get the exact same reading, and I only get it with the thing running. It is as follows:

    1.8.8 52 1.8.8 52 7.0 If I keep pressing the two buttons down it will read 7.0 repeatedly after that. I suspect it it telling me that it has displayed all of the info it has. And as soon as the very first code comes up (1.8.8) both the 'SERVICE ENGINE SOON' and the 'SERVICE ENGINE NOW' lights come on. The Haynes manual says that is a sign of either ECM or P R O M failure. What can I say? I can find no other literature hereabout to refute that, and the local Cadillac dealership guys were sympathetic, but could not help me. They told me that after Cadillac became 'Government Motors' they sold all of their paper manuals on older cars to one person who came and loaded up all of the books before they relocated to their present place.

    Belts are properly tight and the Alt cannot be turned whatsoever, and really could not even before I tweaked it while in Indiana.

    So I will proceed with the voltage test this AM on both injectors and look to see if it wavers/dips down or spikes when it stumbles and tries to die. Fuel pressure will be a problem being as I will need to match the fuel pressure test port with something threaded. Wish it would take a spark plug thread tester as I have two of those.

    Thanks again,

    Gerry

  15. #14
    carnut is offline Cadillac Owners Master
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    Re: Prom needed

    If you push OFF and HI at the same time, and hold them depressed, once in diagnostics, it will eventually display 0.0 meaning all codes are erased. Code 52 is a soft (history) code. Erase it. 18.8 means all digit segments can display, 7.0 means you are at the end of troubles codes display. With the air cleaner off and the adapter under it off the throttle body, look very closely at the 2 injector harnesses as they pass under the adapter. I've seen where they get pinched or partially cut there. That could account for the sporadic spraying. If I recall correctly the injectors operate at 5 volts or less, so a digital meter would be best. Both Service lights will and should display while in diagnostics, this is a designed in "bulb" test to make sure both will illuminate. Please hold off further checks until you get a factory service manual!!! There were at least 5 on E Bay yesterday. There cannot be any logic to your diagnosis without this book.

  16. #15
    gsim is offline Cadillac Owners Member
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    Re: Prom needed

    Thanks, Carnut. Today I took an analog VM and read across both injectors. I was a steady 2 volts DC while it was running. Although the engine alternately ran fast and rough stumbly slow, the voltage remained the same. Once it died, the voltage on the Driver's side injector died too. However on the passenger side injector, the voltage stayed the same after the engine died. It may be that is the low speed one, if there is such a thing? Made me think that I have no ECM/PROM trouble.

    Regards codes, I have never tried to hold down OFF and HI. My book said OFF and Warmer was the way to do it and I did it that way. I will try to look at it the way you say to see if it will read codes at all.

    Regards the manual, I would love to buy one. Just yesterday I was on eBay and typed in 1984 cadillac auto repair manual. I was taken to a page with lots of old caddy parts and several Haynes books. At that time, I never saw even one factory repair manual. I will try again and will type in cadillac factory shop manual and see if I have as good luck as you did.

    Thank you, Carnut.

    Kindest regards,

    Gerry

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