Problem with 1990 Seville 4.5
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HT4100 4.1, 4.5, 4.9 Discussion, Problem with 1990 Seville 4.5 in Cadillac Engine Technical Discussion; ...
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    83CADMAN's Avatar
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    Question Problem with 1990 Seville 4.5

    I was driving, car was up to temp (208 deg) running great.
    All of a sudden the thing stalls, I coast it off the street and try to restart.
    After a few tries it fires up and I started making my way home.
    When I gave it gas it sputtered like it was running out, (10 gal in the tank)
    I managed to make it about half way home when it decided it was done stranding me with another roadside repair. I found a NAPA about ½ mi away and thinking fuel filter did a quick R&R. It fired right up then died about 4 or 5 timed before it started and held a smooth idle.
    But when I pulled the throttle open it sputtered and popped out the TB like the timing was off or something.
    Any pointers on what to check first?

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    dennis93coupe's Avatar
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    Re: Problem with 1990 Seville 4.5

    Quote Originally Posted by 83CADMAN View Post
    But when I pulled the throttle open it sputtered and popped out the TB like the timing was off or something.
    Any pointers on what to check first?
    This sounds like a camshaft problem. I'd go ahead and check timing, cap and rotor. If everything looks ok there, you'll need to take the valve covers off and look at rocker arms, bent push tubes. If you have a lobe going bad, you will be able to tell if the rocker arm doesn't have same movement as others. I don't remember the 4.5 having an issue with distributor gear, but that's another possibility.

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    Re: Problem with 1990 Seville 4.5

    It has been about 7 years since its last tune-up. Sparkplugs were replaced about 4 years ago along with injectors.
    So I opened up the dist to take a look and it really didn’t look all that bad. I replaced the old brittle internal dist wiring, ignition module, cap, coil and rotor.
    It starts right up and idles sweetly…..throttle up a might and blahhhhh. I took a mechanics stethoscope and checked the injectors…all clicking like they ought to.
    I can get it to rev-up but must do it gradually.
    I havn't pulled any spark plugs yet through.
    Man I hate to think it’s a camshaft, that will junk this car.

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    Re: Problem with 1990 Seville 4.5

    Could be a MAP sensor or TPS issue. Both are used to control fuel delivery especially when opening the throttle. One senses the input from your foot on the pedal and the other senses the resulting change in manifold vacuum telling the computer when and how much fuel to add. OBD-I isnt the most sensitive system - many issues can exist without setting a code.

    I think that if you had a bad cylinder (via bad camshaft, valve, etc) that the remaining 7 cylinders will be able to support higher RPMs albeit quite roughly.

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    Re: Problem with 1990 Seville 4.5

    If it's stalling on throttle then it's probably weak fuel delivery. Check pressure at the test port

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    Re: Problem with 1990 Seville 4.5

    Also maybe a plugged cat....maybe. You will need to do a backpressure test which can be done with the fuel pressure gauge plugged into the O2 sensor. You don't want more than a couple pounds back pressure.

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    Re: Problem with 1990 Seville 4.5

    Been reading up on the TPS for the 4.5……sounds like replacement is something I shouldn’t mess with, It involves stuff like disabling the generator by grounding it using a green test port near by??? My car has an alternator! And selecting PCM override PS 103 ICS actuator…PCM data PD 01TPS sensor….WHAT????? No access to OBD thru CCP!

    How in the world do you test the TPS on this vehicle?
    My books say to use a voltage meter and test with key on, engine not running. But how? Where do you connect the test equipment if the plug must remain attached to the sensor?
    What happens if I unplug the TPS? Will it mess up the ISC settings?

    Fuel pressure check is a good idea. I’ll have to get my hands on a gauge fitting set for GM.

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    Re: Problem with 1990 Seville 4.5

    Quote Originally Posted by 83CADMAN View Post
    Been reading up on the TPS for the 4.5……sounds like replacement is something I shouldn’t mess with, It involves 1232]stuff like disabling the generator by grounding it using a green test port near by??? My car has an alternator! And selecting PCM override PS 103 ICS actuator…PCM data PD 01TPS sensor….WHAT????? No access to OBD thru CCP!

    How in the world do you test the TPS on this vehicle?
    My books say to use a voltage meter and test with key on, engine not running. But how? Where do you connect the test equipment if the plug must remain attached to the sensor?
    What happens if I unplug the TPS? Will it mess up the ISC settings?
    In order to this you need the test harness. There are other ways to do those tests and adjustments. I doubt this your problem for now.

    Quote Originally Posted by 83CADMAN View Post
    Fuel pressure check is a good idea. I’ll have to get my hands on a gauge fitting set for GM.

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    Re: Problem with 1990 Seville 4.5

    They just call it a generator in the manual... dont worry about it.

    I have the same year and model as you and I assure you that you CAN access OBD through the instrument panel. You can do the entire TPS procedure through the dash in fact. No need to mess with the DVM, grounding the alternator, etc. The numbers you posted are wrong for the seville/eldo's diagnostics anyway. Looks like you are reading from a haynes book!

    A few months back I posted a detailed explanation of how to navigate the menus from the dash.... I'll try to find it again. In the meantime, I would chase down the fuel pressure both with key on engine off, and while running - observing the gauge when the engine dies.

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    Re: Problem with 1990 Seville 4.5

    Got my hands on a fuel pressure gauge set this morning and hooked it up.
    The results were:

    · Key on, engine not running….. 2 lbs
    · Engine running………………. 2 lbs gradually increases to 12 lbs (hard starting)
    · Engine stalled………………… 12 lbs then slowly drops (dies on rapid throttle)

    Not sure what it means, Can’t find what the fuel pressure is supposed to be.
    Using a Chilton’s and a Hayne’s. Neither one is much help for this year car.

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    Re: Problem with 1990 Seville 4.5

    Should be 34 to 38 psi!!

    Fuel pump.

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    Re: Problem with 1990 Seville 4.5

    I did finally find a reference to Fuel Pressure in one of my books; for the 4.5 it states 12 to 14 psi???? Considering the source…..
    That’s a far cry from 34 to 38 psi!!!
    Could it be the pressure regulator? It is up-line from the test port.
    Since the spark plugs were 5 or 6 years old I pulled the front 4, two of them broke, all had a gap of .070 and were brown in color. I guess it’s about time.
    Any tips on changing the rear bank’s spark plugs? Compression test?
    Last time I paid to have the plugs done, but the times are a little different now, so I guess I must get greasy.

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    Re: Problem with 1990 Seville 4.5

    This is what I hate about the haynes and chilton - the info is way too general. There are two 4.5's, '88 to '89 with TBI and 1990 with MPFI like the 4.9L. I could be wrong but I believe that spec is for the TBI 4.5. Either way you need 34 to 38.

    I suppose the FPR could be bypassing too much fuel back to the tank but I've never heard of this. Not sure how you could verify it other than putting a test plug in the return line on the rail side and observing key-on pressure. (engine off)

    On the plugs: http://www.cadillacforums.com/forums...ml#post2730262 Post #3. Its not fun but its do-able.

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    Re: Problem with 1990 Seville 4.5

    With the pressures being sluggish to change and low on start up i would suspect a clogged fuel filter or a clogged line. You could also have a bad fuel pump. The pressure should come right up to full immediately and stay there through the entire engine power band. Should only vary a small percentage. If there is an obstruction of fuel flow and the engine uses it faster than it can be delivered, Then the pressures will be low and fluctuate. A failing fuel pump can also result in readings like these but fuel pumps generally either work half way decent or fail totally.

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    Re: Problem with 1990 Seville 4.5

    Your fuel pressure regulator will lower the fuel pressure when your engine is running. You might pull the vacuum hose on it and see if there is fuel coming out of the vacuum port. That would at least tell you if you have a blown diagphram in the regulator. I seriously doubt it would lower your pressure that much. I agree with Aeronca, change your fuel filter first because you should anyway. Check the pressure and make sure if the pressure is low you aren't losing fuel from an injector stuck open. It would be filling your intake with gas and I would think you would notice that. Make sure you don't have a kinked fuel line also, I saw that happen once.

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