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coil testing ?'s - hesitation problem

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  • coil testing ?'s - hesitation problem

    I'm trying to track down a hesitation problem that isn't necessarily consistant, but it's getting worse. Yesterday the car drove fine for a short distance and shut it down. Got back in and started right up, but when I went to drive, it hesitated so bad I wouldn't move. I could barely rev the motor. So I shut it down and after a minute or two, started it back up and drove it home. No issues.... so this leads me to testing my ignition system. The wires and new, but I am due for plug and cap/rotor, so I also tested the coil.

    The Coil test according to the Koala CD, is termial 15 and 4 should have 8.25K ohms (i have 5.77) and Terminal 1 and 15 should be 0.82 ohms (i have 0.6-0.7 ohms).

    My question is: is this coil operating in an acceptable range? Koala says to replace it if those readings are not met but is there some give in the ohm readings?

    Thanks for the help and if anyone has any other suggestions of places to look for the problem, let me know (i've already searched the forums and have a short list of areas to test, but can always use more )
    90 Corrado/91 M3/01 M5

  • #2
    Has anyone ever tested their coil?

    After doing some more research on the SIG archive, i've found that Koala's rating of 8.25k Ohms is too high for termial 15 and 4, my 5.77 seems to be right in the average of the rest. However, I couldn't find any mention of the acceptable range for the Ohm reading of Terminal 15 and 1.
    90 Corrado/91 M3/01 M5


    • #3
      I'd be looking at
      1, Plug wires. Edit..scratch this if less than six months in factory guide.
      2, Ign cap and rotor.
      3, Fuel pumps.
      These all cause balky hesitation when they get knackered.

      Coils rarely fail although you can't rule out the possibility.. Your steady deterioration suggests a failing electromechanical component, imo.
      Last edited by Mmark; 08-31-2004, 01:20 PM.


      • #4
        What's the service history of the fuel filter?



        • #5
          Do you happen to have an AF gauge? It's a longshot but if you notice it going lean when it hesitates then it's likely fuel starvation issue, if it goes rich it's spark.


          • #6
            I am having nearly the same problem.
            basically the car will start fine and idle fine, it even revs fine, but when I go to drive it as soon as I try to give it some gas it stutters and I dont have any power. The revs will rise slowly but with jolting, like one of the pistons is being left behind.
            I will be checking dist cap and rotor first of all.

            Does anybody know how to test fuel pressure?


            • #7
              Thanks for the responses.

              Mmark- I know bosch coils are suppose to be pretty durable, it's just in my past experience with a 16v VW, it turned out to be the problem to a non starting/difficult start issue so it's something I always test now

              Dean- the fuel filter, just like the rest of the tune up items are of unknown history.

              My short list of replacement items are:
              Fuel filter
              Cap & rotor

              I'm looking to add to that. I may do fuel pumps and relay if needed.

              Mick- I do not have an air fuel gauge, but I do like you're thinking.. i've just found A/F gauges to be pretty inaccurate on a stock engine management unless you're WOT and when it acts up I can't even get it near WOT.
              90 Corrado/91 M3/01 M5


              • #8
                If the hesitation is a heavy bucking, and it settles down when you let it idle...
                1 A large airleak between AFM and ports may be produced when the engine torques to driver's right hand side. This would have the effect of stretching soft intake piping.
                2 fuel filter or pump(s) with inadequate flow.
                (how much gas do you have in the tank?)
                3 The ignition system is failing under load...usually bad wires.
                Does it backfire?

                Have you tested the AFM?


                • #9
                  not heavy bucking.. the car would not move... it wouldn't even rev. This was the worse case that has happened. In the past it was just hesitation when crusing at a constant freeway speed.. it would surge slightly.

                  1. already checked the intake boot - that was my first thought
                  2. Gas is over 1/4 tank IIRC, but it does feel either like either not enough spark or fuel.. It's done the minor hessitation on a full tank.
                  3. They are new wires this spring.

                  I have not tested the AFM, not sure how.

                  The other thing that may or may not be a factor is this car is not daily driven. It will sit for a week or two a time so i'm also thinking it could be a cold start issue (or thinks it in a cold start mode). If the car gets warmed up after a good 30min or so drive, i've never had this issue. It seems to be only on short trips or the beginning of a long drive. My feeling is it's getting worse and will start effecting it longer if not all the time.
                  90 Corrado/91 M3/01 M5


                  • #10
                    For future people searching for hesitation problems, i'll give an update:

                    Replaced the plugs, cap and rotor and no change in hesitation.

                    Replaced the fuel filter and both pumps, problem solved. No more hesitation at high RPM under WOT.

                    I still have to cut open the fuel filter and see if it was clogged, but fuel came out clean from both ends of it.
                    90 Corrado/91 M3/01 M5


                    • #11
                      Good thing you got rid of the hesitation! Did you check whether you had it already solved with the new fuel filter before you put the new pumps in?

                      I ask as the filter is a maintenance part and cheap but the pumps surely are not.

                      Anyone suspecting fuel delivery problems should check wether the problem has been solved by the changing of the fuel filter alone.

                      One check that can be done on the fuel delivery is the following:

                      - undo the fuel return line from the fuel rail that sits on top of the engine
                      - put a length of fuel hose on to the rail and the other end in a measuring container
                      - pull out the fuel pump relay from behind the cover behind the expansion tank
                      - bridge the contacts in the socket in order to operate the fuel pump.
                      - measure the quantity of fuel that's being delivered. It should be 750cc in 30 seconds
                      - if it's less you could perform the same test directly at the pump underneath the car on the left hand side where the pump sits. If the flow rate is ok there (should be slightly more than 1.5l/min) then you have a clogged filter. If it's too low again you need a new pump (or 2 as there is a 'pre-pump' inside the tank)

                      to check the fuel pressure one should hook up the pressure tester in the return line. It should read at least 3.0 bar. If it doesn't, either filter is clogged, or pump/pressure regulator are defective.

                      I had a similar problem once. The culprit was a Motronic with bad solderings for the transistors that run the injectors. Look for hair cracks with a magnifying glass and good light, resolder and you're done.


                      • #12
                        just a comment on the (wideband) A/F guage reading with bad spark:

                        when you get no spark (misses) and therefore have unburnt fuel, the AF guage shows LEAN
                        and not RICH. This is a common misconception.



                        • #13
                          Weak main pump then.
                          Have you reset the CO?
                          Appreciate the update. that way we can learn.


                          • #14
                            I had all the parts so I didn't replace and test in stages (should have in hind sight).

                            I have not reset the CO (don't have the necessary equipment). Next on the list is TB sync, CO level, and valve adjustment which i leave up to my mechanic.
                            90 Corrado/91 M3/01 M5