News

Emissions, Miss, Misfire, High HC

Discussion in 'Technical Q&A' started by Sandahl, Aug 23, 2008.

  1. Sandahl

    Sandahl Rookie

    Dec 1, 2006
    6
    I've picked up a lot of great advice here on FerrariChat. I'd like to contribute this experience to add it to the record for (hopefully) others' benefit.

    My car is a 1988 Mondial 3.2 Cab, almost 23,000 miles on it now. I picked this car because I wanted a "mechanically simple Ferrari" (if there is such a thing), in-car belt/clutch service, and much to some people's amazement I've always liked the look. Sure, I'd rather have a 355 or 360 but this was my level of comfort with purchase and maintenance cost.

    Every year here in Austin, TX at least, we have to get a safety inspection and a relatively simple smog test (fast and slow idle for about 90 seconds I believe). Last year the car passed emissions easily with numbers somewhere in the 1/10th-of-the-limit range here, so this year I somewhat naively assumed I could just drop it off and get the same results and I used the closest gas/inspection station.

    I dropped off the healthy-as-ever car and waited 5-6 hours for the call to pick it up with the inspection completed. Instead I got a call indicating that the car had failed smog and I needed to pick it up. They showed me how it had exceeded the standards for HC, something like 600ppm when the limit was 200. Last year of course it was in the 20's. I mentioned this and they rudely suggested that shop must've been fraudulently testing. Disgusted already, I paid the cashier, walked out to the car and started it up and I was greeted with a lawn mower level of engine smoothness at idle due to some kind of miss. Attempting to rev the engine sounded as though 2 or 3 cylinders were not contributing their share. Walked back to the manager, kept my cool and asked why it seemed to be running on less than eight and wasn't like that when I dropped it off, and he shrugged and said something to the effect "we just test 'em, take it to a Ferrari shop." So with this dead end and some unknown problem I took the car on the short 1-mile drive home, not knowing what they might have done to it at all, but knowing they were not going to help me.

    I set to work immediately and tested for one-ignition-bank-down first (both working), then checked all the plug wires and extenders which all checked out - at least this confirmed that each cylinder was firing at some point so it was looking like a miss albeit a somewhat random one. Next I checked the classic frequency valve/o2 protection relay to no avail and began rebalancing the idle between the throttle stop screw and the large bypass screw which seemed to help slightly. Over the course of an evening and test drives it appeared that things had improved, but the miss was still relatively frequent below say 2400 rpm in a car that will pull smoothly from 1000 rpm WOT in fifth gear if you want it to because CIS/K-Jet cams are pretty mild. I also took off the air cleaner cover and made sure that the CIS airflow sensor "piston" was moving freely.

    Noting that continued driving seemed to improve things I started to suspect (and hope) that the plugs had been loaded up due to too much idling at the service station. How much was too much I don't know, but it could've easily been two hours if they started it up and got distracted.

    I also guessed that a long period of idling may have run down the battery since the alternator's charging ability is minimal at idle and probably insufficient when the radiator fan kicks on, which in Texas in the summer is most of the time if the car's sitting still - this would also contribute to misfire with a low voltage to the ignition boxes. Sure enough, the battery took a 2-3 hour charge at 10 amps to reach full charge state. Subsequent driving continued to improve the miss situation until it had completely disappeared. I let the car sit a week because it was now past due for an inspection sticker and then put the battery charger on it to see how the battery had fared and it was still fully charged.

    Next came a visit then to a different inspection station, this time supervised... The results came back as I originally had assumed: HC PPM in the 20's, other numbers well within standards, an easy PASS.

    In hindsight, the long idle theory is pretty obvious but it certainly was not initially due to the zero information I got; just dropped off a healthy car and picked up one with a big problem.

    Here's my misfire checklist:

    1. Frequency valve buzzing?
    2. Both banks firing?
    3. Plug wires + extenders ok?
    4. Spark plugs clean?
    5. Battery fully charged?
    6. Idle speed controls set appropriately?
    7. CIS airflow "piston" moves freely?

    These covered my situation, but if they had not I would've also checked out:

    8. Distributor caps and rotors
    9. Ignition crank sensors
    10. Ignition modules/coils

    If these all checked out it'd be onto bigger and potentially more expensive items, probably start with a compression check, then cam timing and fuel system but I think the consensus is that most misses are ignition-related.

    Please add anything I might've overlooked. Thanks for all the info I've gathered here over the years!
     
  2. f355spider

    f355spider F1 World Champ
    Rossa Subscribed Owner

    May 29, 2001
    16,988
    USA
    Full Name:
    Hugh G. Rection
    #2 f355spider, Aug 23, 2008
    Last edited: Aug 23, 2008
    While I agree your hypothesis may be correct (I'm certainly no technician), it is also possible that your alternator may not be up to snuff, and have a failing voltage regulator. It would be worth having the electrical system (battery and alternator) load tested to eliminate this possibility. Most auto parts stores will hook up a computerized tester that will do a series of tests, and print out a report. Free. ;) Call around in your area. Generally they will need access to the battery to attach the two leads.

    Weak battery or faulty alternator can contribute to a number of running maladies.
     
  3. Artvonne

    Artvonne F1 Veteran

    Oct 29, 2004
    5,379
    NWA
    Full Name:
    Paul
    I really dont believe we can expect these cars to charge as well as other "normal" cars, say for example a Mustang if left to idle. A Mustang has an operating range from around 800 rpm to about 5500 rpm. The 308 has a range from about 800, to nearly 8000. Because they dont want the alternator to overrev, they set the engine drive belt pulley ratio to peak the alternator rpm with peak engine rpm. As you can see, the 308 has a 10:1 speed range from idle to peak engine speed, whereas the Mustang is about 6:1. This in effect is to say the Mustang alternator spins faster at idle and would then have more output, simply because the 308 has a wider operating band.

    In any event, leaving an exotic car in the hands of ignorant people you dont know is asking for trouble. I would seriously never let the car out of my sight. You really should find a copy of "Ferris Beulers Day Off", and watch it a few times.
     

Share This Page