83 308 gtsi erratic timing? | FerrariChat
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83 308 gtsi erratic timing?

Discussion in 'Technical Q&A' started by Harta320, Jul 10, 2005.

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  1. Harta320

    Harta320 Karting

    Nov 6, 2003
    169
    Sarasota, FL
    Full Name:
    Bill Smith
    #1 Harta320, Jul 10, 2005
    After doing a major service to my car this winter along with replacing some old and worn out parts,[ injectors, plugs, ignition wires, fuel distributor, ect.] my car continues to run rich with a slight miss at idle (4.0 %co). I just finished testing the the fuel system and all of the preassures are within spec. The car was running rich when I bought it last year.

    Fuel system checking out OK, I moved on to the ignition system. The reason I waited so long to check the ignition is that other than the wires, extenders and the electrical connections I really was not sure what else to try. So for the hell of it I hooked up my trusty timing light and sure enough the timing seems to be jumping around a few degree and you can notice the stumble when it does. Any help here to figure this out would be great? Things I have tried.

    1. I have checked the resistance in the crank sensors and they all checked out within spec. Any chance that after they heat up one is going bad? It might be a loose wire some where but I have yet to find it. Any suggestions about how to test these while the car is running?

    2. The next item could be one of the Digiplex's. Everything I have read says that there really is no way to test these. Any ideas?

    Thanks
    Bill Smith
     
  2. Ken

    Ken F1 World Champ

    Oct 19, 2001
    16,078
    Arlington Heights IL
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    Kenneth
    #2 Ken, Jul 10, 2005
    It only misses at idle? Could it be simply a foulimg plug from running rich, as you say you are? Then when the revs go up driving it clears itself. Did this miss happen with brand new plugs? If so, then I'm wrong and it's something else, like the electronic ignition perhaps.

    Ken
     
  3. Harta320

    Harta320 Karting

    Nov 6, 2003
    169
    Sarasota, FL
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    Bill Smith
    #3 Harta320, Jul 10, 2005
    No Ken, I do not think that is it. I ran the rpm up to about 1800 with the throttle plate screw so I could get a steady speed and the timing jumped around then also. Not that the fouled plugs are not contributing to the miss but I have had this miss from the beginning even with new plugs. This is the second set by the way. Thanks though! I am hoping someone can help me figure this out.
     
  4. Harta320

    Harta320 Karting

    Nov 6, 2003
    169
    Sarasota, FL
    Full Name:
    Bill Smith
    #4 Harta320, Jul 31, 2005
    I finally got around to checking the strength of the spark with a spark gap tester from Auto Zone. My ignition is certainly cutting out randomly and this probably explains why my timing is jumping around. Does anybody know what volatge the QV coils put out? My coils seems to only be putting out 10,000 to 20,000 volts and the spark that is produced is some what yellowish in color. I thought the spark should be blueish? I think my ignition system is weak but I have no idea what to test or try and where to go from here. Any tips would be great.

    Thanks
    Bill
     
  5. Birdman

    Birdman F1 Veteran

    Jun 20, 2003
    6,689
    North shore, MA
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    THE Birdman
    #5 Birdman, Jul 31, 2005
    Bill,
    A flaky TDC sensor (i.e. crank sensor) will certainly do this. Had this problem on my Mondial. If you checked them (there are 3) with an ohm meter and got about 600 ohms DC resistance, then they are probably fine. There is a chance that one could go out when hot though. I would thoroughly clean every connector between the sensors and the ignition ECUs, including the big connectors on the ECUs as well. You ought to be able to narrow it to which ECU/sensor because you should be able to see it with the timing light. Remember that one ECU controls the front bank and the other one controls the rear.

    You can rule out various components by swapping. For example, swap the harnesses to the ECUs and then also swap the ignition wires from the coils to the distributors. This way you are now still sending the right spark to the right plugs but through opposite paths. (You can't JUST swap the harness to the ECU because then the front ECU would have the timing for the rear bank plugs, etc.) Now see if the problem follows the "swap" or stays with the sensor. (If you do the swap and the issue stays on the same bank, it's a sensor or distributor. If you make the swap and the issue goes to the other bank, it's either the ECU, coil, or something between them). It's actually a pretty simple system and chances are very good that it's either a sensor, a connector, a coil or a distributor (rotor). The ECU's themselves seem to be pretty reliable.

    Good luck.

    Birdman
     
  6. carlrose

    carlrose Formula Junior

    Nov 25, 2003
    327
    #6 carlrose, Jul 31, 2005
    Hi Bill,

    I'm sure you've already checked this but: caps/center carbon electrode/rotors? No oil in cap(s) from leaking cam seals?

    On the 328 as I recall there are also a few grounds to underside of the "frame rail" back behind the coils.

    Finally, good +/- battery cable conenctions?

    Not sure this will be of much help. On the 328 one can actually read AC voltage from the RPM/TDC sensors while the car is running; don't know if this can be done on 308QV.

    :) Carl
     
  7. Birdman

    Birdman F1 Veteran

    Jun 20, 2003
    6,689
    North shore, MA
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    THE Birdman
    #7 Birdman, Jul 31, 2005
    As for the weak spark, are the plug gaps right? It's possible to have a bad coil, but unlikely for BOTH to be bad.

    Birdman
     
  8. Harta320

    Harta320 Karting

    Nov 6, 2003
    169
    Sarasota, FL
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    Bill Smith
    #8 Harta320, Jul 31, 2005
    Birdman,

    Well, I changed the crank sensors thinking that would solve the problem and no luck. I would have bet money the sensors where the problem. I tried all of that stuff you suggested and all I can figure out is that my ignition cuts out on both banks randomly. I do know that I switched the ECU cables to the digi's and I did not swap the coil leads(never thought about it). The car ran the same. LOL I have been thru the Fuel system about 3 times now and everything checks out. I guess it will be best to start from the top with the ignition system again. I may have a loose wire somewhere that I need to track down. I have checked most all of them already. By the way new spark plug wires and extentions. I rechecked the timing and I checked the compression. 140 psi across the board cold. Not great but I do not think that is to bad either? This is driving me crazy. I thought that maybe one of the coils is weak but from what I have been reading on the net I am now not to sure. I feel like a dog chasing his tale. LOL Please keep the tips coming guys I am sure we can track this problem down.

    Bill
     
  9. Birdman

    Birdman F1 Veteran

    Jun 20, 2003
    6,689
    North shore, MA
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    #9 Birdman, Aug 1, 2005
    Bill,
    Very important...is this an issue with both banks at the same time, or just one bank?

    Birdman
     
  10. Harta320

    Harta320 Karting

    Nov 6, 2003
    169
    Sarasota, FL
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    Bill Smith
    #10 Harta320, Aug 1, 2005
    As best I can tell both banks. I tried to isolate the problem like you described (could have done it wrong) and the timing seems to cut out on both banks with no preticular pattern evolving. I tried running the car on one bank and they both have the same symptoms as the other. Anyway got any ideas?

    Thanks
    Bill
     
  11. Ken

    Ken F1 World Champ

    Oct 19, 2001
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    Arlington Heights IL
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    #11 Ken, Aug 1, 2005
    I can't help specifically, but I've had those intermittant problems before so here's a thought.

    I used to *assume* I knew something was good only to eventually have it be the problem. Take a fresh approach to your car. Pretend it's someone else's car and you know nothing about what's good or bad on it. Troubleshoot it just like you don't know anything about what you've already checked. The problem my arise quicker than you think.

    Ken
     
  12. barcheta

    barcheta F1 Rookie

    Nov 15, 2003
    3,738
    Maryland
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    Jim
    #12 barcheta, Aug 1, 2005
    Have you checked the diverter valve? I've heard this can cause the symptoms you are describing.
     
  13. Verell

    Verell F1 Veteran
    Consultant Owner

    May 5, 2001
    7,022
    Groton, MA
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    Verell Boaen
    #13 Verell, Aug 1, 2005
    The 2 ECUs share a common chassis ground bolt. This has been known to corrode & cause flaky ignition. Remove ground cables, clean connection, coat with Oxy-Solve or similar anti-oxidant compound & reassemble.

    Also believe there's a crimp-on connector on the flat ground braids. They're known to internally oxidize over time. Permanent fix is to replace the cable, altho I've often been able to restore connectivity for a few years by laying the connector flat on something hard & smacking it with a hammer to re-crimp the connection. Don't hit it super hard, just enough so that the metal barely gives some.
     
  14. Harta320

    Harta320 Karting

    Nov 6, 2003
    169
    Sarasota, FL
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    Bill Smith
    #14 Harta320, Aug 2, 2005
    Are you talking about the main ground at the front of the car? I have cleaned that connection a few times (no smack down though) and when I get a chance I plan on running a ground from the Digi's to the batt. just to see if it helps. I have also cleaned the bundle of wires above the drivers side gas tank with no luck. I am starting to think it may be ground related.
    Any idea where the Digi's ground is connected to the frame? OH by the way I tried the ground from the Digi's trick and no luck.

    Bill
     
  15. Verell

    Verell F1 Veteran
    Consultant Owner

    May 5, 2001
    7,022
    Groton, MA
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    Verell Boaen
    #15 Verell, Aug 2, 2005
    I remember seeing a braided ground strap between each of the Digiplexes & a frame stud. Maybe it was something added on, I didn't look for it ina FPC.

    Umm, here's another one to look for:
    Make sure all the sensor leads are well clear of the ignition wires, & if possible, routed at 90 degrees to them. The sensor signals are pretty small & can be over-ridden by the spark discharge being coupled into them with wierd & wonderful results, especially if the ignition lead can swing relative to the sensor lead.
     

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