4.5 running like poop
Cadillac
 

Cadillac Forums | Help Us Help You | Advertise | Cadillac Parts | Cadillac News | Cadillac Classifieds / (Old System)

Cadillac Technical Archive | Cadillac Dealers | Cadillac Reviews | Cadillac Dealer Reviews | Cadillac Vendors

CadillacForums.com is the premier Cadillac Forum on the internet. Registered Users do not see the above ads.
+ Reply to Thread
Results 1 to 9 of 9
HT4100 4.1, 4.5, 4.9 Discussion, 4.5 running like poop in Cadillac Engine Technical Discussion; I have a 1990 DeVille with the 4.5 and it's running like crap. It idles a lot rougher than it ...
  1. #1
    gtm245 is offline Cadillac Owners Fanatic
    Join Date
    Jan 2004
    Posts
    116

    4.5 running like poop

    I have a 1990 DeVille with the 4.5 and it's running like crap. It idles a lot rougher than it ever has and it just sounds rougher and a little louder than before. I just did an oil and filter change about 100 miles ago. Also, I usually use 89 octane with absolutly no problems (believe me I'm very meticulous about my car) but 2 tank fulls ago I filled up with 92 octane. It seemed to run a tiny bit better (smoother and a bit faster), but nothing that someone would notice if they weren't looking for it. Anyway, that was 2 tank fulls ago and on the last tank, about 80 miles ago (a couple days after my oil change), I went back to 89 octane. At first it sounded and felt like it always had when I had run 89 but then it started to get rougher and rougher. It started to get rougher and rougher after I had done a few WOT runs down the highway. Besides the usuall rough idle that I now have sometimes it stumbles for a few seconds after I start it up. All fluids are at the full mark, 2000 miles ago I installed a new fuel filter and air filter, it has a new serpentine belt, and 41,000 miles on it.

    Whats the deal? Is the rough idle and driving from using 89 octane while doing some WOT runs? I didn't notice any audible pinging or knocking. Fresh oil and filter, new fuel filter, the same 89 I've always run without rough idle so I have no idea what's causing this. Someone please help me.

    BTW I think I'll try the 92 octane again once I'm done with this tank of 89. About 11 more gal. to go and then I'll see if it was the gas. Where's BBoblynski on this one.

  2. Remove Advertisements
    CadillacForums.com
    Advertisements
     

  3. #2
    BeelzeBob's Avatar
    BeelzeBob is offline I'm a Cadillac Fanatic!
    Join Date
    Dec 2002
    Location
    Fort Lauderdale, Florida
    Age
    50
    Posts
    9,577

    Re: 4.5 running like poop

    Quote Originally Posted by gtm245
    I have a 1990 DeVille with the 4.5 and it's running like crap. It idles a lot rougher than it ever has and it just sounds rougher and a little louder than before. I just did an oil and filter change about 100 miles ago. Also, I usually use 89 octane with absolutly no problems (believe me I'm very meticulous about my car) but 2 tank fulls ago I filled up with 92 octane. It seemed to run a tiny bit better (smoother and a bit faster), but nothing that someone would notice if they weren't looking for it. Anyway, that was 2 tank fulls ago and on the last tank, about 80 miles ago (a couple days after my oil change), I went back to 89 octane. At first it sounded and felt like it always had when I had run 89 but then it started to get rougher and rougher. It started to get rougher and rougher after I had done a few WOT runs down the highway. Besides the usuall rough idle that I now have sometimes it stumbles for a few seconds after I start it up. All fluids are at the full mark, 2000 miles ago I installed a new fuel filter and air filter, it has a new serpentine belt, and 41,000 miles on it.



    Whats the deal? Is the rough idle and driving from using 89 octane while doing some WOT runs? I didn't notice any audible pinging or knocking. Fresh oil and filter, new fuel filter, the same 89 I've always run without rough idle so I have no idea what's causing this. Someone please help me.

    BTW I think I'll try the 92 octane again once I'm done with this tank of 89. About 11 more gal. to go and then I'll see if it was the gas. Where's BBoblynski on this one.

    Did you check the fuel pressure regulator...????

    Pull the vacuum line off the fuel pressure regulator while the engine is idling and watch the vacuum nipple for several minutes for any sign of fuel leakage.

    Check fuel pressure???

    The fuel did not likely hurt it or cause the problems you note.

    bbob was gone snowmobiling for a few days in Canada. This forum is NOT a full time gig....LOL

  4. #3
    gtm245 is offline Cadillac Owners Fanatic
    Join Date
    Jan 2004
    Posts
    116
    Thread Starter

    Re: 4.5 running like poop

    Fuel pressure is right at specs. so it can't be a fuel delivery problem? Any other ideas?

    Along with the roughness I now have, a while back I remember I started a thread about if I could use 89 octane instead of premium and if you remember I said my car made a weird engine noise that I couldn't describe. Then you (bbob) asked if it sounded like marbles in a can with a rag wrapped around it to muffle it. It kind of sounds like that but I have a better description. See if you can figure this one out. The noise sounds like one of those wind chimes that people have out on their front porch (you know the ones with the different legnth bars that chime when they hit each other). It sounds like one of those except more dull and more muffled. This happens whenever I drive it, not just when I go WOT. Seems to have gotten a little worse after I switched back to 89 and did a few WOT runs with it. Anyway I used to enjoy the nice smoothness and quietness of my engine but now not so much. Anyway, this and my last post is the best that I can describe what my car is doing at this time.

    Could maybe one of these be causing the problem of the rough idle:
    Clogged fuel injector?
    Preignition from using 89 octane?
    Something else?

    What about the wierd noise? I have no clue what that noise is. All I know is it got worse after the oil change and after putting in 89 octane. Thanks bbob for any advice.

  5. #4
    BeelzeBob's Avatar
    BeelzeBob is offline I'm a Cadillac Fanatic!
    Join Date
    Dec 2002
    Location
    Fort Lauderdale, Florida
    Age
    50
    Posts
    9,577

    Re: 4.5 running like poop

    Still didn't see any reference about checking the fuel pressure regulator for leaking into the vacuum nipple.....check it.


    Just because the fuel pressure is ok does not rule out other fuel delivery problems.

    An injector could be leaking/dripping/stuck open. Loosen the fuel rail mounts and lift the rail up enough so that the injectors clear the intake manifold ports. Energize the fuel pump to build the sytem pressure and watch the injector tips for leaking.

  6. #5
    gtm245 is offline Cadillac Owners Fanatic
    Join Date
    Jan 2004
    Posts
    116
    Thread Starter

    Re: 4.5 running like poop

    No leaking from the fuel pressure regulator into the vacuum line. Pulled out the fuel rail out and turned the ignition to ON position to build the fuel pressure. I waited forver trying to see any signes of a leaky injector, but all are fine. Put them back in, tightened everything up and started the car. Took a mechanics stethescope and listened to each injector to see if any ones were clogged or partially clogged.... they all have a strong loud pulsating rhythm indicating they are working. So if it's not a fuel delivery problem what could it possibly be?

  7. #6
    BeelzeBob's Avatar
    BeelzeBob is offline I'm a Cadillac Fanatic!
    Join Date
    Dec 2002
    Location
    Fort Lauderdale, Florida
    Age
    50
    Posts
    9,577

    Re: 4.5 running like poop

    How about the EGR tubes..??? Have they been cleaned? Open the throttle blades wide open and look down the throttle bores. Those two tubes sticking up at you are supposed to be clean and not full of carbon. Rod them out with a stiff piece of wire.

  8. #7
    gtm245 is offline Cadillac Owners Fanatic
    Join Date
    Jan 2004
    Posts
    116
    Thread Starter

    Re: 4.5 running like poop

    EGR tubes are spotless; didn't need to be cleaned at all

    Anyway I was on empty, so I just put a full tank of 92 octane (I usually use 89 with ethanol) and after a few minutes it started to idle better and when I drive down the road that mysterious noise is much improved. Still happens most of the time but it is barely audible. Can't really notice it unless you strain to hear it.

    Anyway I've never had a bad idle and that loud of a noise when I have used 89 before. I always use 89 from the same Conoco station and have never had a problem until the last tank. I guess our search is over for the bad idle but I'll probably go back to 89 because I hate to spend $30.00 for a tank of gas.

    Still don't know what that mysterious noise is. I swear it sounds like a bearing noise but what do I know....

  9. #8
    BeelzeBob's Avatar
    BeelzeBob is offline I'm a Cadillac Fanatic!
    Join Date
    Dec 2002
    Location
    Fort Lauderdale, Florida
    Age
    50
    Posts
    9,577

    Re: 4.5 running like poop

    Quote Originally Posted by gtm245
    EGR tubes are spotless; didn't need to be cleaned at all

    Anyway I was on empty, so I just put a full tank of 92 octane (I usually use 89 with ethanol) and after a few minutes it started to idle better and when I drive down the road that mysterious noise is much improved. Still happens most of the time but it is barely audible. Can't really notice it unless you strain to hear it.

    Anyway I've never had a bad idle and that loud of a noise when I have used 89 before. I always use 89 from the same Conoco station and have never had a problem until the last tank. I guess our search is over for the bad idle but I'll probably go back to 89 because I hate to spend $30.00 for a tank of gas.

    Still don't know what that mysterious noise is. I swear it sounds like a bearing noise but what do I know....
    If the "marbley" noise went away with premium fuel then likely what you are hearing is spark knock or detonation.

    The 90 4.5 is tuned for premium fuel but will usually run OK on mid-grades of fuel. If it is spark knocking at part throttle on mid-grade it still hints of a problem with lack of EGR flow. If the tubes are clean then possibly the EGR solenoid is failed or the vaccum supply to the EGR solenoid is missing/plugged/disconnected. Tee in a vacuum gauge immediately at the EGR valve vacuum nipple and watch the gauge when you crowd the throttle with the trans in gear iether driving or against the brakes. The EGR valve should get a vacuum signal from the solenoid when you open the throttle. Lack of vacuun to the valve could certainly cause the engine to spark knock on lower grades of fuel at part throttle.

    I assume the engine is quite and runs OK at full throttle...??? If so, the spark knock would only be at part throttle and that would indicate an EGR problem even more.

  10. #9
    gtm245 is offline Cadillac Owners Fanatic
    Join Date
    Jan 2004
    Posts
    116
    Thread Starter

    Re: 4.5 running like poop

    "If the "marbley" noise went away with premium fuel then likely what you are hearing is spark knock or detonation."

    With 92 octane the marbley noise is still there at part throttle but it is barley audible and happens less often. I agree that it is probably related to the EGR system because so far it seems like it is the only culprit. I have run 89 for a long long time with no problem before so this bad idle/noise has to be due to some sort of malfunction as this. Anyway I will check out the vacuum signal thing tomorrow and see what happens.

    BTW at full throttle it purrs like a kitten. No wierd noises or poor performance or anything like that. Sounds/feels so awesome at full throttle. Gotta love an american V8.

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.
If you do not want to register, fill this field only and the name will be used as user name for your post.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Bookmarks

Cadillac Posting Rules

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
Read about Lincoln | Buick | Kia Forte Forum
Need products for your Cadillac? Check out your options at the links below:

custom floor mats | Cadillac Chrome and Black Chrome Wheels | window tinting