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HT4100 4.1, 4.5, 4.9 Discussion, Spark Plugs: What do YOU run? in Cadillac Engine Technical Discussion; Sooooo after I let the car cool for a while I turned the key to ON to check for the ...
  1. #46
    Sevillian273's Avatar
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    Re: Spark Plugs: What do YOU run?

    Sooooo after I let the car cool for a while I turned the key to ON to check for the leaking sound and there was none. Interesting. Then I swapped my Bosch III's in and went to the gas station to fill up. The car ran good with no apparent issues and the avg econ says 20.8 after a 12 mile trip.

    Now I hear the spraying sound again from inside the manifold but this time it's coming from the other throttle bore. $#@!. So it looks I had a leaker the whole time but only when hot. At the beginning of this thread I said that none of the injectors visibly leak because I had the rail pulled up with pressure on it. But when I did that, the engine was COLD! Son of a bitch. So I now have 2 full sets of bad injectors and when I get the money I'm due for a SIXTH RnR of the fuel rail and injectors.

    On the plus side, no more hard starts and no more stumble on acceleration which was likely the plugs. I've located some parts to build my own injector test bench so I can pressure test all my injectors both cold and hot. It will consist of a fuel pump, mustang fuel rail, and a small aquarium. I also have a couple commercial hand-dryers that I'll use to simulate hot-soak conditions on the injectors. It will come in handy as long as I dont burn the house down... I cant wait to get started on it... just need to win a few ebay auctions.

  2. #47
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    Re: Spark Plugs: What do YOU run?

    Wow. You sir, are one of the most unlucky fellers I know. Two bad sets? Lame.

  3. #48
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    Sevillian273 is offline Cadillac Owners Connoisseur
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    Re: Spark Plugs: What do YOU run?

    Quote Originally Posted by drewsdeville View Post
    Wow. You sir, are one of the most unlucky fellers I know. Two bad sets? Lame.
    Oh and it gets better! I just lost the instrument panel cluster and DIC today. Turns out the power supply for the vacuum florescent lights burned out. This power supply is built into the board of the IPC so I need a whole new unit. No speedo, gas gauge, odometer, nothin. And worst of all, no onboard diagnostics so no more mileage calculations for my wonderful fuel problem. Luckily I found a used unit on Ebay for $50 but unfortunately odometer mileage is store in the IPC so I'll have to calculate it based on my last recorded odometer reading. The madness never ends with this car!

    [ame="http://www.youtube.com/watch?v=rX7wtNOkuHo&feature=player_embedded"]YouTube- Nelson[/ame]

  4. #49
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    Re: Spark Plugs: What do YOU run?

    you sure about that? I thought I was pretty sure that the mileage is stored in the BCM.

    I went to the local junkyard for a replacement when the ICP went out on my dads '89 Eldorado. His mileage stayed correct after we were done...

  5. #50
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    Re: Spark Plugs: What do YOU run?

    I read that in the Haynes manual. And I've been told it is stored in the back half of the unit which I can transfer to the ebay unit if it isnt damaged. http://www.cadillacforums.com/forums...ster-gone.html

  6. #51
    steelybill is offline Cadillac Owners Enthusiast
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    Re: Spark Plugs: What do YOU run?

    I replaced the BCM in my '85, and nothing changed in the speedo. Forgot what I changed it for. It was a few years ago.

  7. #52
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    Re: Spark Plugs: What do YOU run?

    A brief update - I swapped the IPC with the ebay unit and sure enough, mileage stayed the same so who knows? Unfortunately the ebay IPC display has dimmed quite a bit since I put it in but as long as it stays lit I'm happy. (knock on wood) I swapped the ECM with an original unit from a 91 deville and no improvement.... mileage accuracy is still way off, mileage still around 14, still bogs and stumbles on acceleration. I've almost got everything I need to build my fuel injector test bench. I still need to get an aquarium and figure out what I'm going to do for 12v bench power. I've got several computer PSU's that I may use but I dont know if they can handle a fuel pump... What do they pull? 20 amps? That may be a lil high for what I have.... Meanwhile I've ordered a pulse width generator and a set of injector clips and am still waiting for them to arrive. Gonna hit the pet supply places tomorrow after work for an aquarium and then I can start construction. Once I get leaking injectors out of the equation I'm going to start compression testing both static and dynamic. At this point I wouldnt be surprised if there was something internally wrong with this engine.

  8. #53
    the recluse is offline Cadillac Owners Connoisseur
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    Re: Spark Plugs: What do YOU run?

    I'm right there with you with this WHOLE thread. I've been fighting injector bs for a year now and I really feel it blew my headgasket. I've pulled fuel rails some 5 or 6 times myself.

    Found this tidbit online: http://www.lindertech.com/dirty_dzn.htm

    Ours are listed #3 and #8 respectively.

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    Re: Spark Plugs: What do YOU run?

    Yeah I've seen that page. I've actually had more trouble with non oem injectors. With the originals, one simply shorted out with the rest close behind so I pulled them out and that was the end of them. Then I bought a reman set of bosch III's from Ebay, ran them for 4 months until they started to leak(but i didnt know it then because they only leaked when hot) Then onto a set of Allante injectors that leaked even worse only when hot. Now I'm back to the bosch's simply because they dont leak as bad but I'm still getting 14mpg. All of this is because the price of new injectors is so ridiculous.

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    the recluse is offline Cadillac Owners Connoisseur
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    Re: Spark Plugs: What do YOU run?

    Quote Originally Posted by Sevillian273 View Post
    All of this is because the price of new injectors is so ridiculous.
    Agreed.

  11. #56
    the recluse is offline Cadillac Owners Connoisseur
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    Re: Spark Plugs: What do YOU run?

    I just got the MSD injectors in the mail and they have the Rochester Products (RP) logo on the side; which is OEM replacement, right? I know they all get lumped into one company Delphi, Rochester, and Multec and I hope they work for a little while...

  12. #57
    justin4yu is offline Cadillac Owners Member
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    Re: Spark Plugs: What do YOU run?

    A to hot ignition can cause stumbling, put a regular coil in line instead of the excell and see if that helps

  13. #58
    Bobby Eyes is offline Cadillac Owners Member
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    Re: Spark Plugs: What do YOU run?

    I have an '84 coupe DeVille 4.1, can anyone reccomend the best spark plugs I can use on it?

  14. #59
    stickpony is offline Cadillac Owners Member
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    Re: Spark Plugs: What do YOU run?

    iridium autolites

    ive been reading this entire thread...i think your fueling problem could be a small vacuum leak in your throttlebody gasket...spray some carb cleaner at the base of the throttlebody all the way around it, see if the engine idle drops a little when you do that....

    also, this constant business with changing out injectors, changing spark plugs, etc...the issue is elsewhere. have you checked to see if you are getting a constant 12v to your power steering input on the ecm? if not, it will cause a constant rich condition but not set any codes...the power steering switch cuts the 12v only when there is power steering cramp at idle and the ecm richens the fuel mixture to compensate so you can turn yoru steering weheel easier at idle... BUt if the switch is bad, and doesn't allow the 12volts through during normal driving conditions, the ecm will constantly think the power steering is cramped...the computer doesn't always throw a code either when this happens....

    also, your reman computer might be for a 91 or later deville/seville, since they have the same part number, but different memcal(chip)... i would take the chip out of your orgiginal stock computer and put it into the new computer....


    also, have you considered the fact that maybe you have bad compression on one or more of the cylinders? there is alot of ground you have not covered.. but you keep changing the variables by just changing out parts... you need to go back and start over with the basics...

  15. #60
    daniel58 is offline Cadillac Owners Fanatic
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    Re: Spark Plugs: What do YOU run?

    Well I'm going to jump in here, I have had these problems with my 90 Deville. Stumble, running rich, stalling etc. Someone informed me after the fact that the 4.5 uses 16# injectors not 19# mentioned here. The 19# injectors just aggravate your problems. In addition I had installed a new Bosch O2 sensor which was operating but not correctly, this also aggravated the problems. After changing the plugs 4 times and changing pretty much the intire ignition system and all of the injectors (new 19# aftermarket) I put new OEM AC plugs and O2 sensor the old original injectors and the car runs like it should. I also had the instrument cluster and speedometer fail just after this work, battery goes dead and the car blows fuse #7 repeatedly, natuarally this being a Cadillac this was caused by the AC compressor clutch coil failure. Old school logic just does not work, you will be chasing your own tail on these cars. Try OEM parts or the old stuff you removed and see what happens, it worked for me.

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