4.1 v8 injector resistance
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HT4100 4.1, 4.5, 4.9 Discussion, 4.1 v8 injector resistance in Cadillac Engine Technical Discussion; ...
  1. #1
    Bean's Avatar
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    4.1 v8 injector resistance

    I am having a problem with severe hesitation. Here are the stats.

    1982 Cadillac Fleetwood brougham
    4.1 L V8

    When you put the car under load it will hesitate and bogg down once past half throttle. When not under load (park) it will rev up with no indication that anything is wrong. When I have the computer in display mode and am looking at pulse widths or anything else the car really boggs down and makes it almost undriveable. Fuel mileage has dropped a little. I can drive the car as long as I am not in a big hurry (55 mph is top end and takes a mile to get there).

    After researching here and thinking through the problem here is what I have done and what I know…

    Timing is ok
    Replaced ignition coil
    Replaced ignition control module
    New plugs, cap, wires, and rotor within 2 months
    Fuel pressure is 10 and steady
    Replaced fuel pressure regulator
    New fuel pump and filter within 2 months
    Removed and cleaned screens on injectors (they were not bad)
    Adjusted TPS (within spec)
    New MAP Sensor

    Now I have a code 44 (O2 sensor lean)

    I have also checked the resistance on the injectors and they are at .9 (point 9) ohms. I think that is too low. I have been searching the Chilton for exact spects but cannot find them. Dose anyone have the specs handy? Or dose someone have an idea as to the problem?

    Thanks

    Bean

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  3. #2
    noahsdad's Avatar
    noahsdad is offline Cadillac Owners Connoisseur
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    Re: 4.1 v8 injector resistance

    The FSM doesn't list a resistance number either. Since your fuel pressure is good, I'd first replace the O2 sensor. It's cheap and simple. You'll chase a lot of ghosts until you have a known good O2.

    You also might have a plugged cat.

  4. #3
    Bean's Avatar
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    Re: 4.1 v8 injector resistance

    O2 Sensor is new.

    I have considered a plugged cat but this problem happened suddenly. One second I was fine the next I was looking for an interstate exit. Will a plugged cat happen this quickly?

    thanks

    bean

  5. #4
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    Re: 4.1 v8 injector resistance

    If something breaks loose inside the cat it can happen pretty fast. You say the engine is fine when it's not under load? This 44 code is telling you something. Make sure all your connections to the O2 sensor are clean and tight. Disconnect it and check the parameter value. If it's in the normal range (.38 to .63) when unhooked, the problem is likely vacuum or fuel control.

    First move on to air flow restrictions and vacuum. Have you changed the PCV or crankcase breather element lately? That has a surprising effect on the 4100. An open EGR can also cause sluggish performance, but only above 2000rpm.

  6. #5
    Bean's Avatar
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    Re: 4.1 v8 injector resistance

    I'll check the o2 sensor and replace the pcv and crankcase breather in the morning. I'll find an exhaust service center and get the cat checked soon.

    Thanks for the suggestions

    Bean

  7. #6
    cadillac_tech is offline Cadillac Owners Fanatic
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    Re: 4.1 v8 injector resistance

    Quote Originally Posted by Bean View Post
    not in a big hurry (55 mph is top end and takes a mile to get there).
    That sounds normal for this vehicle
    Check the vacuum line to the MAP. It may be cracked or rotted. Most kikely it's a restricted MAP port in the throttle body. Tee into this line and watch for an immediate drop in vacuum to 0" upon opening the throttle hard.

  8. #7
    peteski is offline Cadillac Owners Enthusiast
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    Re: 4.1 v8 injector resistance

    I don't have my FSM handy (and I'm pretty sure I've seen the injector resistance mentioned in there). And 0.9 ohm sounds too low. But I suspect that you're measuring it incorrectly somehow.

    Injectors are fused. Take a look at the fuse values. Normally fuses are selected so that their working current is about 50% of their rated current.

    Again, I don't recall what the fuse value is. If they are 2A then the injectors would be normally consuming about 1A of current. So in this example, 12V / 1A = 12 ohm (injector resistance). If the fuse is 5A then the injector resistance might be 12V / 2.5A = 4.8 ohms. And so on (depending on the fuse value). But it the injectors were 0.9 ohms, they would have blown the fuse.

    It might be possible that your problem is caused by the transmission (not engine), or possibly malfunctioning EGR circuit.

    Peteski

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    Re: 4.1 v8 injector resistance

    An update on some findings. O2 sensor checks in at .48 volts. PCV replaced.

    Question about the EGR. When I reach under and push up on the diaphragm (cold running engine) I get a small change in the engine sound. Just a little sputter and that is it. Should I have a bigger response? The EGR is cheap at around $70 so I could just change it anyway?

    The map tube is fine. I removed both ends, one under the dash and at the back of the throttle body. Then I put vacuum on it and it held with no leaks. I did clean the MAP port on the throttle body anyway and checked for vacuum at the map port, all checks out.

    As for the injector resistance. It is at .9 ohms. I checked it again and was very careful to make sure I was not crossing my leads to something else. The fuses to the injectors are 3 amps. According to ohms law I should be blowing fuses if the voltage at the injectors is at 12v (could the computer be regulating a lower voltage?). My best guess is the duty cycle of the injector acts in a way to lower the total amperage of the circuit. Yes the circuit will have a spike that will exceed the amperage of the fuse but is it so fast that the fuse will not burn out? Do not know for sure, electronic circuit theory was a long time ago!

    I still have plans for an exhaust shop and am in the process of locating a spare set of injectors for a trade out.

    Thanks for all the help,


    bean

  10. #9
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    Re: 4.1 v8 injector resistance

    I am not sure about 4100, but a 4.9 engine would nearly stall or stall. If it does not - not your EGR valve but rather EGR passages are plugged, so that opening the valve does not make much difference.

  11. #10
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    Re: 4.1 v8 injector resistance

    0.9 Ohms seems to be too low, but if it is out of spec, I think your problem should have appeared at low load condition as well.

    Isn't it a TBI engine? I remember that I was able to see gasoline spray when I took the big vertical tube that goes over the injector assembly. Maybe a visual inspection tells you something?

    About EGR, if it is not working right (either open or close all the time), I think it would be either very unstable idle, if it even keeps running, or pings like crazy at higher load. I am not sure if problem you described would be caused by a bad EGR.

    Good luck!

  12. #11
    Bean's Avatar
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    Re: 4.1 v8 injector resistance

    I have checked the egr tubes. They are a little dirty and I will clean them soon. I put a little vaccum on the egr valve itself and it works and can hold a vaccum.

    This is a TBI engine and you can see the spray but I have no idea if there is enough spray or if the spray pattern is atomized enough. I have no way to test injectors.

    I am also looking for vaccum leaks and hope to find out if the cat is clogged next week.

    I am hoping to have more time next week to troubleshoot.

    Thanks to everyone for the help

    Bean

  13. #12
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    Re: 4.1 v8 injector resistance

    If the engine is at normal idle, fully depressing the EGR diaphgram should make the engine run really rough (almost stall).

    I still say that 0.9 ohm is too low. Could your multimeter be out of calibration? Check some known low resistance device (maybe like a 4 or 8 ohm speaker). Does the meter reflect the true speaker resistance?

    I'll try to find the injector resistance spec and post it here.

    Peteski

  14. #13
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    Re: 4.1 v8 injector resistance

    A 4 or 8 ohm speaker will not measure 4 or 8 ohms resistance. That number is the impedance. Most speakers have a DC resistance lower than their impedance.

    Edit:

    I just measured 5 speakers here with my fluke 77. 3 of them had resistance within 10 percent of the impedance. 2 were about 30 percent low. So a speaker isn't a standard but sure could test a meter to see if it is broken. That was a good idea

  15. #14
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    Re: 4.1 v8 injector resistance

    Checked the my meter it is ok. I did find a spare set of injectors and they tested low as well.

    For now I have to put the car aside for a couple of days, Grandma has to move into a nursing home and needs family support. I'm sure I will still be working on the car but it will be after nidnight and I will not be able to get too serious until Grandma gets settled.

    As always thanks for the great help,


    Bean

  16. #15
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    Talking Re: 4.1 v8 injector resistance

    PROBLEM SOLVED!!!

    First off a very big thank you to all who helped. The problem was simple, it was the rubber connector between the fuel pump output and the sender.

    With the help of this board I troubleshot everything I knew and somethings I did not know and found nothing, I was about to stuff a rag into the gas thank and light it. I was looking at the bill from the automotive service place that looked at it first and started asking myself if they really did what they said. One of the things they said they did was a test the fuel pressure, which they reported as fine 8 - 10 psi. Since I did not personally witness this nor did I test it myself I took their word for it. That was a bad mistake! Off I go to get a fuel pressure tester and I found only 4 psi of pressure. Drop the fuel tank to check the fuel pump and found the bad hose in the tank. Fuel pressure is now a steady 12 psi and holding.

    Once again Thanks for the help,

    Bean

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