Replaced Injectors.. Still no action in Cyls 3 and 4?
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HT4100 4.1, 4.5, 4.9 Discussion, Replaced Injectors.. Still no action in Cyls 3 and 4? in Cadillac Engine Technical Discussion; Ok, as described in THIS THREAD I have 2 dead cylinders. I agreed at first that it was the injectors ...
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    JeremyG is offline Cadillac Owners Member
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    Replaced Injectors.. Still no action in Cyls 3 and 4?

    Ok, as described in THIS THREAD I have 2 dead cylinders. I agreed at first that it was the injectors but after carefully replacing all 8 with known-good injectors, the same cylinders are not firing. In summary it seems to be intermittant and seems to smooth out under medium to hard accelleration. Very rarely it will idle/cruise so I'm thinking it can't be anything mechanical (something mechanical seems like it would ALWAYS have the problem).

    I've checked all the wires (bought a new set and will replace them but in the meantime just used the new ones temporarily and the problem is still there).

    The coil is giving spark as well, although I just might replace it knowing they aren't horribly expensive (or are they? I know my Durango was only $35).

    I've pulled both plugs and they appear decent, although I'm going to replace them just in case.

    So, what's the next possible problem?

    I do have one current code, IO39 which is suspension so that's obviously not the problem... I DO have a Check Engine light, though... but no other current codes? At least none in the display, I don't know if a scan tool will show any codes that the car itself won't?

    What should I be looking at next? I guess I could do a compression test?

    I just don't want to do any work that's not needed... my theory is fix the easiest/cheapest things first....

    HELP!!

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    100
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    Re: Replaced Injectors.. Still no action in Cyls 3 and 4?

    Sorry to hear that.

    Well, what I can think of are the distributor (including the cap) and/or cylinder related problems. The parts in the distributor related to #3 and 4 may be faulty (electrodes in the cap or rusty tooth for the hall sensor, did you say you replaced the cap??). I would probably do a compression test to make sure the cylinders are fine, if not, that's the problem!

    If the coil is the cause, I think you will get the problem at random cylinders. Although, it is not too expensive, you might want to spend the money for something else...

    Good luck!

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    Stoneage_Caddy's Avatar
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    Re: Replaced Injectors.. Still no action in Cyls 3 and 4?

    like i told someone else(and what 100 said) , check compression before going further

    that person found an issue in the rocker arms and how they are held down(stripped stud i belive) , and that was the second instance ive heard of the problem

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    100
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    Re: Replaced Injectors.. Still no action in Cyls 3 and 4?

    Quote Originally Posted by Stoneage_Caddy
    like i told someone else(and what 100 said) , check compression before going further

    that person found an issue in the rocker arms and how they are held down(stripped stud i belive) , and that was the second instance ive heard of the problem
    >Stoneage_Caddy
    That person said that he appreciated your pin-point advice

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    JeremyG is offline Cadillac Owners Member
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    Re: Replaced Injectors.. Still no action in Cyls 3 and 4?

    Ok, cool... and I hate to ask such a simple question but what compression should I be looking for?

    Man it would suck if I had no compression... I would assume then we're looking at big bucks

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    JeremyG is offline Cadillac Owners Member
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    Re: Replaced Injectors.. Still no action in Cyls 3 and 4?

    Oh another thing a mechanic friend told me is that it's possible that 3&4 are fired off the same wiring for the injectors... that possibly something is wrong in the wires going to the injectors... I'll check that too but for the 10 minutes to do the compression test that will be the next step.

    Will report back probably tonight.

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    Re: Replaced Injectors.. Still no action in Cyls 3 and 4?

    100- i thought that was you ....damn my memory .....

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    Re: Replaced Injectors.. Still no action in Cyls 3 and 4?

    Quote Originally Posted by Stoneage_Caddy
    100- i thought that was you ....damn my memory .....
    Yeah, that person was me. Damn good your memory!

    On compression, unfortunately I don't know what it should be from the manual, but I think it is about 125 psi with WOT if the compression ratio is 9.5... Am I right?

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    Re: Replaced Injectors.. Still no action in Cyls 3 and 4?

    "Minimum, 965 kPa (140 psi) @ 300 rpm. The lowest reading cylinder should not be less than 80% of the highest. Perform compression test with engine at normal operating temperature, spark plugs removed and throttle wide open."

    source: alldata

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    Re: Replaced Injectors.. Still no action in Cyls 3 and 4?

    Quote Originally Posted by JeremyG
    Oh another thing a mechanic friend told me is that it's possible that 3&4 are fired off the same wiring for the injectors... that possibly something is wrong in the wires going to the injectors... I'll check that too but for the 10 minutes to do the compression test that will be the next step.

    Will report back probably tonight.
    Nope, there is 8 injector drivers in the PCM. They are tied to B+ (battery power, somewhere on the battery power bus from the Maxi Fuses) in 2 groups of 4. The Cadillac 4.9L uses sequential port injection, so for this car, only 1 injector fires at a time. Unlike the the TPI Chevys, where they are Batch fired fuel injection, meaning that groups of injectors are fired at a time (typically 2 groups of 4).

    Do you have a FSM? Did you do the power balance test? It isolates the fuel injectors from the distributor pretty well.

    Tom

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    Re: Replaced Injectors.. Still no action in Cyls 3 and 4?

    No don't have an FSM... I did do the injector disable thru the computer by doing all the stuff up at the climate control area... no change when disabling 3 and 4.

    Is this power balance test hard to do? Are there any online sources of how to do it?

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    Re: Replaced Injectors.. Still no action in Cyls 3 and 4?

    I'll see if I can type it up.

    Did you ohm out the injectors? 12-16 ohms is typical. Lower than that I would consider suspect and they typically continue to drop. Eventually the PCM driver will shut down from overcurrent. When my 3 injectors failed (1, then the next in about 500 miles, then the next in less than that) it went from 10 ohms to 1 ohm in no time. I was wondering if they leak fuel inside causing the short.

    Some other thoughts, can you pull the connectors on the injectors that aren't working? Connect a DVM up to it and measure voltage to ground. One side should be 12V solid, the other should be pulsing, so you might need to look at it on Dwell (6 cyl scale) or AC. See that you ARE getting voltage from the ECM.
    Starting to wonder if the PCM drivers aren't firiing for some reason.

    Would a bad cam sensor bad on 3 & 4's location cause the injectors to just not fire? Basically it works and has good "location" for 1 8 (4) (3) 6 5 7 2, but bad on the 3 and 4 locations.

    Any chance you have a oscilloscope? You can see a lot with them.

    Tom

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    Re: Replaced Injectors.. Still no action in Cyls 3 and 4?

    Wow, very good help... I'm a bit lost but will answer as well as I can...

    These are brand new tested injectors so I didn't see the need to Ohm them out.

    I can maybe possibly get to the connectors... 3 is almost behind the power steering pump so I'd probably have to pull the pump, take off the connector, and put the pump back on... 4 I'll have to look cuz it's in the back side somewhere.

    The cam sensor idea is a pretty good theory... I'll see what I can find out on that.

    I'm almost ready to just take it in because I'm finding with my new job I just don't have the time to mess with it, but man I hate spending money on things that I can do myself...

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    Re: Replaced Injectors.. Still no action in Cyls 3 and 4?

    I wanted to ohm out all the injectors, so I pulled the ECM and connected it up there. Make sure you safe the airbag for this!

    You need to be a contortionist, but it was far easier than pulling the connectors on each injector.

    It doesn't help much for operational checking, but it does help anyone who wants to check the injector impedance without pulling the connectors on each, which can be a real bear.

    Would be nice to swap in a different ECM t rule it out (bad injector driver). Other than time, it would be an easy fix to repair it if you can find the right type of transistor for it.

    Tom

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    Re: Replaced Injectors.. Still no action in Cyls 3 and 4?

    My guess is that you are not getting power to those two injectors for some reason...or the wires from those two injectors going to the PCM are broken along the way.

    It isn't that difficult to pull the wire connectors off those two injectors... with the key on there should be 12 volts on one of the wires in the connector at each injector.

    The injectors are supplied battery voltage directly thru the two injector fuses. The "ground" side of the injector then goes to the PCM. The PCM "fires" the injector by pulling that wire from the injector to ground thus completing the circuit. So...you should find 12 volts at each injector all the time. If that is good, then you willl need to drop the ECM and remove the wiring connector and check for continuity from the two injectors to the ECM. It is possible that the two injector drivers in the ECM for those two injecotrs are failed....a re-man ECM would be the solution then.

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