Deville 94 4.9 45 MPH and up problem
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, Deville 94 4.9 45 MPH and up problem in Past Cadillac Vehicle Discussion; Hey there fellow Cadillac aficionados. I bought me a 94 Cadillac Deville 4.9 V8 this past March of this year. ...
  1. #1
    CaptainAmericaUSA is offline Cadillac Owners Member
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    Cool Deville 94 4.9 45 MPH and up problem

    Hey there fellow Cadillac aficionados.
    I bought me a 94 Cadillac Deville 4.9 V8 this past March of this year.

    I've dealt with a few problems since I bought it nothing too, too major.

    I had to replace the battery etc.

    It's in really good condition.

    The problem I am having is once I hit 45 mph it shudders all the way up and beyond 45 mph once the engine gets hot unless I floor it and give it the gas it goes away but if I lightly hold down the gas pedal it's rough.

    I used to have 3 error codes including the check engine light.

    Now the P030 code use to be current and then became history and once I got the throttle body clean it was cleared out of my history and so was the history code P098.

    However after a day the P098 code is showing up again as history.

    In the last two days since the throttle body cleaning the p030 code does not show up as current or history only p098

    Now I also have another code since I've had the vehicle known as P046 as current known as you all know "right to rear fuel bank difference."

    Now that code makes sense to me after using the forms to make logic out of the whole ordeal.

    The previous owner it seems had taken it to a Cadillac dealership once last year in September.

    He basically told them the symptoms of the cause.

    Now on the report it states that the OHMS fuel rail is very low.
    Recommend replacement of all 8 injectors.
    Noted replacement of 2 new ones.
    So the previous owner had 2 already replaced.

    Now I bought all remanufactured fuel injectors for my car online on EBay.

    I plan on switching them out tomorrow.
    Now the ones on EBay say Ford on them.
    Will this cause an issue for my vehicle?
    It stated it was compatible with my vehicle.


    Could the fuel injector imbalance be the cause behind my not so great gas mileage?

    I'm only getting about 13 city instead of 14.

    However since I've had the car the caddy's average fuel has really gone from 13 to 12.9 to 12.8 all the way to a steady 12.6.....in the past oh 3 weeks.

    I should be getting 14 or 15 no?
    I use premium 93 octane due the fact the requires that type and I want to give my woman the best she deserves.

    However sadly I can't say the prior owner did the same seeing how the economy was really bad not that long ago.



    Anyhow those are the only true major things that need to be done right now.

    My other question is... How do I clean the EGR value along with the EGR ports and the EGR mouser holes or are they all the same on the 4.9 v8?

    Also they by passed the air compressor with the serpentine belt. I take it the air compressor must have seized up?

    Is it worth replacing?

    Should I change the fuel filter? Would that help with the gas mileage maybe?

    Also how hard is it to change the rear knuckle bushings on a caddy?

    Is the knuckle bushing only in the front and only two on each wheel in the front or are there two for the each wheel on the back?

    The reason I ask is one of the reports state that I need to fix the rear knuckle bushings they're worn all the way to the knuckle. I was wondering if each control arm needed a bushing meaning two on each wheel or just one.

    If I buy a set of four knuckle bushing do I need to buy another set?
    Or is one set good enough?

    Because the another report stated it also needs new shocks, struts, toe bars ect.

    I can live with the suspension the way it is right now it's not bad unless I'm on the Turnpike.

    I just need to clean the EGR ports since the report stated they are plugged and take care of the fuel injector p046 current code along with the p098 history code and the check engine light.



    I'm also changing the distributor cap and rotor along with the wires and spark plugs.

    Due the fact it looks like the previous owner was looking for a misfire and probed the boots and glued the holes on the plugs shut.


    Any help on getting my engine to run smooth and take care of the 2 error codes and the check engine light hiccup is gladly appreciated.
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  3. #2
    mc_marto's Avatar
    mc_marto is offline Cadillac Owners Fanatic
    Automobile(s): 1991 Cadillac Sedan deVille
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    Re: Cadillac Deville 94 4.9 V8 45 MPH's and up problem

    Your shudder at 45 MPH is most likely caused by your torque converter trying to lock up. I was pin-pointing the same thing on my Deville last summer. I tried a snake oil - Dr. Tranny's Instant Shudder Fix. Surprisingly it did work. I still get shudders occasionally, but they are very mild and go away quickly. You are going to get a little shudder when your torque converter locks up, by default, and when going up hills around that speed. That's normal. I also had taken the vacuum modulator out of the transmission and decided to run the engine, and the result was I lost almost 2 quarts of fluid - I filled it up with Dexron VI. So, I recommend you get the fluid and filter changed in your transmission and upgrade to the Dexron VI fluid.

    It's worthless to clean the EGR valve. Just clean the throttle body and the EGR passages in there.

    If your injectors are leaking, or there is a restriction in the flow, you are going to get worse mileage. Change those out and see how it is. Also, your fuel filter, if clogged could be restricting fuel flow.

    Another place to look for is your oxygen sensor. I think you probably have two. I replaced mine last summer. The reason - it was lazy and not responding quickly. I replaced it and saw an improvement in mileage.

    Last tip - be careful how you accelerate. If you want to be pinned to the seat every time you accelerate then 12 MPG is good actually. Another good driving habit is timing your stop lights and using the brakes as little as possible, and sooner rather than in the last moment. The reason - the more complete stops you have, the more power your engine needs to put out to just get your heavy car going.

    I hope these things help you!

    Martin

  4. #3
    bigm57ict's Avatar
    bigm57ict is online now Cadillac Owners Connoisseur
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    Re: Cadillac Deville 94 4.9 V8 45 MPH's and up problem

    Quote Originally Posted by CaptainAmericaUSA View Post
    Now the P030 code use to be current and then became history and once I got the throttle body clean it was cleared out of my history and so was the history code P098.

    However after a day the P098 code is showing up again as history.

    In the last two days since the throttle body cleaning the p030 code does not show up as current or history only p098
    P030 (ISC RPM out of range) and P098 (High RPM P/N to D/R Shift Under ISC) usually means your ISC (Idle Speed Control) motor is dying or malfuntioning. This can be intermittant. I suppose a TB cleaning could help, but you probably need to replace the ISC.

    Been there. Done that. (twice)

    Quote Originally Posted by CaptainAmericaUSA View Post
    I should be getting 14 or 15 no?
    I use premium 93 octane due the fact the requires that type and I want to give my woman the best she deserves.

    However sadly I can't say the prior owner did the same seeing how the economy was really bad not that long ago.
    The main purpose of using premium fuel is to prevent pinging. It really doesn't help with fuel economy.

    Quote Originally Posted by CaptainAmericaUSA View Post
    Also they by passed the air compressor with the serpentine belt. I take it the air compressor must have seized up?

    Is it worth replacing?
    Are you talking about the A/C compressor?
    Is it worth it? If you want Air conditioning, I suppose it would be. One possible side effect is - with the compressor bypassed, the belt no longer wraps around the water pump pulley. It contacts much less of it. This may or may not cause problems.

    Quote Originally Posted by CaptainAmericaUSA View Post
    Should I change the fuel filter?
    Certainly couldn't hurt. Not a bad idea if it hasn't been changed before.

    Quote Originally Posted by CaptainAmericaUSA View Post
    Would that help with the gas mileage maybe?
    No.


    Quote Originally Posted by CaptainAmericaUSA View Post
    Also how hard is it to change the rear knuckle bushings on a caddy?
    The bushing, itself, is not designed to be changed. They say to replace the whole upper control arm, which comes with bushings installed on it. Unfortunantly, they also say this part is no longer available. Your best bet may be to have a suspension shop fab something. I've been putting this off on my car for this reason, so I'm not sure what the best fix is.

    Good luck with your new Cadillac and keep us posted on the progress.

    Beautiful car! I love the color.
    I also appreciate the fact that is has the proper whitewalls and they are clean!

  5. #4
    brougham is offline Cadillac Owners Master
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    Re: Deville 94 4.9 45 MPH and up problem

    The shuddering sounds like a lockup problem like mc_marto said.
    Your gas mileage is really going to vary depending on how you drive and where. The only way you could possibly tell anything is wrong by the gas mileage is if you drive the same routes in the same traffic every day and suddenly see a big drop in gas mileage. Going from 13 to 12.6 is nothing.

    It looks like a nice car. Love the chrome wheels.

  6. #5
    dennis93coupe's Avatar
    dennis93coupe is offline Cadillac Owners Connoisseur
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    Re: Deville 94 4.9 45 MPH and up problem

    How do I clean the EGR value along with the EGR ports and the EGR mouser holes or are they all the same on the 4.9 v8?

    Best way I found is to remove the throttle body and then the EGR valve. Clean the old gaskets off real good and install new gaskets after you have cleaned out the tubes. Blow through the tubes if possible to make sure they aren't clogged.

    I'm also changing the distributor cap and rotor along with the wires and spark plugs.

    Due the fact it looks like the previous owner was looking for a misfire and probed the boots and glued the holes on the plugs shut.


    Good idea changing those, you should never pierce a spark plug wire or boot.

  7. #6
    rodnok01's Avatar
    rodnok01 is online now Cadillac Owners Connoisseur
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    Does sound like convertor issue, try it in drive(3rd or D not OD) and see if it goes away. The convertor won't lock up in drive IIRC.

  8. #7
    CaptainAmericaUSA is offline Cadillac Owners Member
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    Thread Starter

    Cool Re: Deville 94 4.9 45 MPH and up problem

    Update.
    The fuel injectors fixed my fuel problem and the spark plug change along with rotor cap and wire for disruptor cap fixed my shudder I believe. It got my check engine light to go away and it also took away the P046 error code as current into history.

    However a bunch of past codes that are history are stored in my computer for whatever reason.
    My fuel millage it went up to all the way to oh 14.6 avg by the time I got home from a long country drive the other day.

    Prior I had got the fuel treatment from Valvoline and also got the coolant changed since AutoZone sold me the wrong liquid for engine coolant for my Caddy which I kept telling them they were wrong but no!
    So anyhow I also used Seafoam prior to the Valvoline treatment and it help some which I used half a can in the tank. Prior to the Seafoam when I first got the Deville I used Lucas.
    Not too long after I tried some of the snake oil Dr Tranny I think helped somewhat not bad stuff at all.

    The shudder is so slight at 45 that it goes away long after.
    Once I hit 40 mph I switch to 3rd gear no shudder at all. Smooth driving on 3rd.

    Prior to changing out the fuel injectors and the spark plugs, 3rd gear help with the shudder to where it was not bad.

    Now with everything no shudder what so ever at least nowhere close to what it was and if does happen it's only at 45 or 50 and so slight that it's not even remotely an issue really . I still however switch it to third gear at 40 mph and up no matter what.
    It seems more in the suspension then anything now. Which I have to change out a lot such as spring coils and shocks and struts etc.
    I plan on changing out many things over time especially the transmission filter and oil along with replacing my catalytic converter this coming month which I think is on its way out right around the next bend here soon on my next few long trips.
    The catalytic converter was spewing out what looked like hot vapor that you see on the road in a long hot day where you see the thermal heat rise off the road. It also at one point looked liked like a tiny poof of light smoke came out from underneath it.

    I'm going to one day also replace the torque convertor since it also sounds like it maybe a main cause for future problems eventually down the road.

    Well anyhow thanks for all the help everyone! I hope to restore this vehicle and have it for another 30 years God willing.



  9. #8
    amunderdog is offline Cadillac Owners Connoisseur
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    Re: Deville 94 4.9 45 MPH and up problem

    "one of the reports state that I need to fix the rear knuckle bushings they're worn all the way to the knuckle. I was wondering if each control arm needed a bushing meaning two on each wheel or just one".

    There are four
    rear only
    uppers and lowers

    They press in and out
    I sent my knuckles out to a shop with new bushings.
    The mechanic said it was rough and charged me accordingly.

  10. #9
    drewsdeville is offline Cadillac Owners Master
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    Re: Deville 94 4.9 45 MPH and up problem

    Not sure how it can be rough... they simply press in and out. A decent ball joint press and an impact wrench makes it a 10 minute job once the knuckles are out of the car...

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