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HT4100 4.1, 4.5, 4.9 Discussion, Rough Running 4.9 - Please Help ! in Cadillac Engine Technical Discussion; OK, so I think I found out where that open line went to. Thank you dennis93coupe and cctgene for the ...
  1. #16
    Moms95DeVille4.9 is offline Cadillac Owners Member
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    Re: Rough Running 4.9 - Please Help !

    OK, so I think I found out where that open line went to. Thank you dennis93coupe and cctgene for the diagrams. It seems that it went to the Evaporative Emissions Canister. At first I didn't think so because it was so far away from there (behind the engine), but in the end I found one open port on the canister and the open line smelled of gas after I uncapped it. And the line does travel up along with the fuel lines, as the diagram indicates from cctgene. Rerouting my line (hopefully) "back" to the canister wasn't difficult but neither was it necessarily easy. Someone must have re-routed the line behind the engine intentionally at one point because it didn't get there by itself. And I can't understand why anyone would do that!!! And it must have been that way for many years (my parents haven't had the car in a shop for many years. The only thing my Dad does is change the oil filter and oil with synthetic every 3500 miles). Interestingly, the line wasn't long enough to reach the canister; it was like 2 inches short. I figured that I might not have used the same routing as the factory. I used a new, longer piece of vacuum/fuel hose for the connection and now it is on. I haven't driven the car around yet but I started it up and nothing blew up or set codes. Does that all sound reasonable?

    And while car is not missing badly like before I did all the work, it still doesn't idle as silky smooth as before. It feels quite "lumpy", if that makes sense. And it ran silky smooth from the time it was born in 1995 until about 3 to 5 months ago. I'd like to get that "silkiness" back, so I'm going to buy the Factory Shop Manual and I'm also looking into buying a used Engine Control Module (Powertrain Control Module). I'm also going to test the MAP sensor, the Throttle Position Sensor, the EGR solenoid and the EGR valve, if I can. From what I've read, those seem to be likely culprits.

    I just wanted to let everybody know what is going on and, as always, I welcome any comments or recommendations.

  2. #17
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    Re: Rough Running 4.9 - Please Help !

    The vent line was 2 inches short because it connects to the tank pressure control valve rather than the charcoal canister itself. There should be another short hose that connects the two together. At least that's the way my 92 4.9 is set up.

  3. #18
    Moms95DeVille4.9 is offline Cadillac Owners Member
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    Thumbs up We fixed it !!! (Finally) Rough Running 4.9 - Help!

    After replacing the fuel injectors and driving the car a few times I determined that the new fuel injectors that I installed 1.5 weeks ago did seem to solve the strange miss. But the car was still idling poorly, and running roughly at lower rpms.

    Everyone told me to get the Factory Service Manual in order to start diagnosing everything, so I found one at a great price. While looking around online I found a used computer for $40 delivery included and decided to splurge.

    Well, they both came today. I unplugged the old computer and plugged in the "new used" one I bought. I started the car up and it was immediately obvious that the car ran smoothly again, like the day it rolled out of the factory. YEAH!!!

    So I think the original poor running condition was a combination of both a few fuel injectors and the PCM (ECM). So the only work that I feel was completely unnecessary was the installation of a new distributor I got from Autozone for $100; that was when I thought it was either the Hall Effect switch or the ignition control module.

    The only thing that remains is to time the distributor correctly and maybe re-learn the ISC (though the idle seems at a reasonable level).

    I finally went through Dad's receipts for work done to the car (he saves all that type of stuff) and the car had a new GM ISC installed at 54,000mi by a dealer for a total of $310.

    Mom has to start driving Dad to his chemotherapy tomorrow, so just in time.

    Thank you again everyone for all your help. Not only were you all great, but it meant a lot to me to not feel alone in dealing with it.

    Sincerely,
    Dave

  4. #19
    Moms95DeVille4.9 is offline Cadillac Owners Member
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    Original PCM Remanufactured by General Motors ?????

    One more thing of interest: after removing the old and ORIGINAL PCM "computer" that was in the car, there was a sticker on it that read "Remanufactured by General Motors". My Dad doesn't ever remember a Cadillac dealer doing anything with the computer, he doesn't remember any recalls being performed, and he has no receipts for a replaced computer or anything having to do with the computer at all.

    So we are thinking that the car might have rolled off the production line with a remanufactured PCM. It isn't a big deal but I'm curious: could the car have been sold new with a remanufactured PCM or is it more likely that the dealer did a recall (or something) without telling us?

  5. #20
    ehall's Avatar
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    Re: Rough Running 4.9 - Please Help !

    Maybe a PROM upgrade and the dealership just swapped the box instead of trying to replace the chip

  6. #21
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    Re: Rough Running 4.9 - Please Help !

    Hard to say how it got there in place of the factory installed unit, might have been a campaign they never said anything and just changed it out. I know from looking in my C body parts book, (predeccessor to your Mom's 95) and only a reman PCM and BCM were listed in the catalog. There was no part number for a new unit and they were only listed without the PROM chip.

  7. #22
    Moms95DeVille4.9 is offline Cadillac Owners Member
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    Re: Rough Running 4.9 - Please Help !

    Well, it has been a week and it continues to run perfectly smooth. So I feel confident that it was both the PCM computer and the fuel injectors. Boy, does that engine pick up and go nicely when it is running correctly. I love the torque and the smoothness. Mom and Dad are happy again. I'll try to remember to give an update after a few months.

  8. #23
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    Re: Rough Running 4.9 - Please Help !

    Thanks for the follow-up

  9. #24
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    Re: Rough Running 4.9 - Please Help !

    Nice write up.
    How's the car running??

    BTW where did you get the computer?

  10. #25
    Moms95DeVille4.9 is offline Cadillac Owners Member
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    Re: Rough Running 4.9 - Please Help !

    The car continues to run perfectly.

    I don't know if it is related, but the check engine light came on 3 days ago and I haven't had time to take a look at it yet. After I did all that work I never set the timing correctly (jumping the connector under the dash, etc), so I hope it is something simple like that.

    I found the computer on eBay for $40 delivered (and with guarantee).

  11. #26
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    Re: Rough Running 4.9 - Please Help !

    Thanks for the update. Your DTC dash codes ought to reveal why you get the CE-Light.

    Keep us up to date. This was a very informative thread !!

  12. #27
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    Re: Rough Running 4.9 - Please Help !

    HeyMoms95Deville, I was so inspired by your thread that I deiced to finally go to a local Pick n' Pull and get an
    engine computer.

    The 92 Eldo was stripped of it as was a 92 Seville so I found two 92 DeVilles.
    One Deville had a bit of oxidation on the 'puter retaining bolt and the engine parts had been ignored.
    The other had no oxidation on the computer retaining bolts and it had a recent DMV temp operating permit on the window. Plus the 4.9 L engine had been hit up and the injectors pulled, so I figured this car had had some updates.
    Lo and behold, I pull the computer and its a new replacement. Not the original factory but the same part no. 16132240 as my '92 Eldo.
    So I feel fortunate. ($50 plus tax etc).
    Now it will take me couple of weeks to swap and see if that smooths my idle.
    I have an idle/missing problem. very slight and have done all the due diligence.
    Normally I don't like to throw parts at a problem but your story was so close to mine (idle part) that I decided to move on what had been on the back burner.

    I'll post an outcome when time permits the swap.

    BTW besides disconnecting the battery, was there any other thing you did before/after swapping 'puters?
    Did you have to do the idle learn after?

    EDIT: after referring to my FSManual I do have to do the idle relearn as well as clear codes. The PROM (MemCal) in my Deville unit is for a Deville only so I have to swap my Eldo MemCal prom into the new computer also. I cross refernced rockauto ac/delco prom part numbers and they were different.

  13. #28
    Moms95DeVille4.9 is offline Cadillac Owners Member
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    Re: Rough Running 4.9 - Please Help !

    I did NOT do a "re-learn" of the Idle Position Sensor (IPS). I simply unplugged the old computer and plugged in the new one. Night . . . to . . . day. With the new computer plugged in it ran perfectly smoothly and idled where it was supposed to.

    I finally got the code from it though ------> P048 and P052.

    So it seems that the EGR system is not not quite right. (?) It makes me wonder if it has to do with me plugging that "mystery" line back into the Evaporative Emissions Canister. Maybe someone unplugged it for that reason? Or does it have to do with the EGR valve? Does anybody know? Or could the fuel injectors be causing it? My parents say they don't care, since it runs perfectly, has lots of power and the fuel consumption seems correct. I'd like to leave it perfect.

    Let me know what you think! And thanks again.

    Sincerely,
    Dave

  14. #29
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    Re: Rough Running 4.9 - Please Help !

    Hey, I figure that if one does not disconnect the battery before swapping computers, there is a better chance that the idle will still be ok.
    The manual requires the idle learn after replacing the computer and or eprom (memcal).
    Anyway, the procedure is easy and it is meant to assure that you don't get idle surges while slowing down etc... possible danger.

    The PO52 (same as EO52) simply states that the PCM memory was reset. After a couple of ignition cycles it ought to become PO52 history.

    The P048 (same as E048) tells ya that "EGR system fault"

    among other things, you can manually lift the EGR valve diaphragm after engine reaches greater than 80 deg centigrade coolant temp.
    with air filter asembly off, and engine idling, reach both hands under the EGR valve in order to lift the underside diaphram. This out to cause the engine to stall. That simply tells ya the diaphragm seems OK and/or there are not excess carbon deposits.

    the next tets are vacuum tests and testing the EGR solenoid vacuum.

    An easy vac pre-test is to examine all the vac lines for the valve and solenoid and also look at harness connection for solenoid.
    You may have a small hairline crack somewhere...

    the solenoid has a funky filter on the end of it. Foam like packing foam. Yours may already be cooked off. Try removing the solenoid and looking at the bottom nipple where the filter attaches to make sure it is not clogged.

    What kind of gas mileage you all getting CITY, Hiway, City-Hiway combined?

    I did replace my computer with the junk yard one. The only difference was the ED36 and ED37 data readings seemd to change from slightly rich for both injector banks to slightly lean for both injector banks.

    The sublime missing/idle discrepancy remained the same.

    (I need to check my MAP next before suspecting injectors, since I have done all other points.)
    My gas mileage varies, it can be 13-14 pure city driving, to 16- 18 mixed city/hiway and a bit better pure hiway driving. Otherwise the engine operates fine and starts up right quick.

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