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'89 5th Ave. - New drama!!!

Discussion in 'F-J-M: Volare, Diplomat, etc, 1977-89' started by goair99, Mar 29, 2017.

  1. goair99

    goair99 Member

    Update: Busy week! She starts right up cold now, no problem. Remember, I filled up the tank with Shell V-Power 93 and added my usual Lucas ethanol treatment.

    So this tell me that she does not like being run with a near empty tank. I still get the surging while under WOT and medium acceleration...All rubber vacuum lines are fresh and in there proper places. I will have to check out the hard plastic lines soon.
  2. AHBGuru

    AHBGuru Member

    Basic diagnostics first:
    Air, spark, fuel.

    - Clean air filter.
    - Champion copper plugs, RN12YC, .035 gap. 7° +/-2° BTDC timing (ESC hose off and plugged at carb). 650 RPM curb idle, 800 step-up, 1200 fast. Check timing chain for stretch, check harmonic balancer for slippage, check vacuum advance for proper function (raise RPM gradually up to 3000, total timing should be 52°+ BTDC).

    - The fuel system on F/M/J cars seems to be the only real problem area. Check the main 5/16" feed line from stem to stern for leaks and overall condition. Replace leaks with short lengths of EFI fuel hose and screw clamps. 1/4" return line is supposed to help reduce vapor-lock. Nylon sock on end of fuel pickup tube is often missing or blocking the tube. Fuel pumps on LA motors often don't give any warning before expiration, but occasionally may send a signal at higher RPM - though the tall gears in retail M bodies don't typically get into those engine speeds. Replacements only seem to last a year or so, regardless of brand.

    Your rebuilt Holley 6280 may or may not have the ethanol-resistant seals and gaskets. Unless you know for certain what you have, run the good stuff.

    - Lean Burn.

    Never a more controversial subject in these cars.

    From 1981 on up, the system actually had two names (components): Electronic Spark Control and Electronic Fuel Control. The computer contains both circuit boards and runs the whole show from that. With a 28 year old car, the computer is the last thing to diagnose, after you've checked out your tune-up areas first. Then check all vacuum hoses and even sensor and solenoid connections for leaks/continuity. What was true in 1989 is still true today - 95% of the time, the computer isn't the problem. However, the next myth to bust is the cost of that computer: most 2bbl computers for sale through Rock Auto are a good bit less than $150. You cannot hack the car with a 2 or 4 bbl electronic ignition conversion for less than twice the price of that computer, if you're using new/rebuilt parts. Plus, you gain ZERO in performance and mpg if the car is already running fine. Rick Ehrenberg's Tech Archive is full of those kinds of horror stories.

    As Valiant mentioned, the 2bbl cars often carbon up at the crossovers, and one may have to yank the intake and take it in for a good rogering.

    For the A998 transmission, it originally called for the 7176 fluid, now superceded by Mopar +4. Use that with a new filter, the new Mopar rubber gasket, adjust the bands and kickdown rod per spec. It wouldn't hurt to regrease the rear axle bearings and use a good Valvoline pumpkin fluid.
    Front hubs take Mopar Green Snot grease. Adjust them up tight. Timkens for replacement.
    Make sure the caliper ways are filed smooth. Firm Feel carries every conceivable suspension part. It's easy to set these cars up good and tight, but they will not ride well afterwards. I had one Fury that I had so tight, you'd feel it if you drove over a dollar bill.

    Lastly, one "mod" that *is* definitely worth the expense is a Canadian Y-pipe