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Help me diagnose a hard hot-start and stumble problem 700

1989 740GL Auto Trans 110,000mi total miles

I just delivered and dropped off my '89 740 at our AZ condo.

It was running perfectly in all ways before delivery, but almost as soon as it was unloaded from my trailer, it developed a hot start problem, and is developing a stumble when it is either put into gear, or taken out of gear when warm.

When started cold, it starts instantly (less than one revolution)and runs smoothly at once. Hot, unless the throttle is held open a bit (maybe an inch or more) when cranked, it takes forever to fire and run. Even with partial throttle, it cranks for maybe 2/3 seconds (several revolutions)before firing and running. Hot, it take maybe a few seconds before it runs perfectly smoothly. It starts hot like a carburetor-equipped engine where some fuel boiled/percolated into the intake manifold while sitting hot, causing a rich start.

In all cases once running smoothly, it runs like a fine Swiss watch, with no misses, surging, or problems. Hot, however, if shifted from drive to park, it stumbles a second (without dying) before returning to a perfectly smooth idle, which it never did before.

Unfortunately, I don't have access to my "stuff" there, nor can I do TOO much diagnostic work as the HOA is quite strict.

I have a couple of ideas, but I'd rather solicit ideas from the folks here, rather than muddy the water with my possibly incorrect ideas.

BTW, I recently rebuilt the A/C system in this car in anticipation of its new home, installing a Sanden compressor to replace the Diesel-Kiki, along with new hoses, condenser, R-134 clutch switch, and wiring the pusher fan to run anytime the compressor is engaged, and, of course, R-134 refrigerant. I also used a variable orifice (VOV) in place of the fixed one. I am happy to report that even at 113deg in stop/go city traffic, the system is fabulous. Even at idle in traffic, it cools just fine on fan speed 2, and the engine temp needle never wavers a bit from vertical. The only downside is that when the compressor engages the first time in the day, and when the system shuts down, you can hear the VOV groan like a dying cow as the pressures equalize across it. Not sure if that's normal, or just my orifice, but it cools GREAT.








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    Regarding VOV 700

    Hi Bobby C,

    I'd like to comment on the AC.

    Some VOV do make noise during compressor start-up and shut-down. Sometimes it does sound like someone farting. I have few assortment of VOVs here to attest to that. Yes they cool GREAT!

    I've done a few experiments to eliminate that noise. And I think that noise is mostly due to 1) the way it was designed and 2) the Volvo ac system which has no high side port.

    Regarding 1:
    The VOV has a closed end at its exit except for that 4 holes to let the refrigerant out. BTW a normal orifice tube has another fine filter at its exit end. I think this VOV design is to trap any fine particles there. But it could also produce turbulence which causes such noise. I've cut off the pointed end making it an open hole there. ALMOST total reduction in noise (but with loss of particle trap function which in long term might clog your evaporator if yours is the new parallel flow type).

    Regarding 2:
    The VOV stays practically closed (some VOV do permit little flow when closed) unless refrigerant pressure starts building up at its entry end. This means when vacuuming the system (after VOV installation) not much of the entered air could be sucked out thru it. Along with the design of Volvo system which has no high side port this adds more difficulty to achieve total vacuum. As such the noise could also be attributed to presence of residual air in the system. I've done vacuuming for 12 hours and there still some noise left.

    In the end its up to you if you could live with such noise. Yes in the past I've praised VOV performance. But I was running the system with a tube-fin evaporator (for R12) installed by the last owner without me knowing it. But later I found out with original compressor (small pulley diameter 125mm), orifice tube and Volvo's original parallel flow evaporator the cooling performance is much much better (without noise too!).

    Amarin.








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    Help me diagnose a hard hot-start and stumble problem 700

    Did anything ever come of this? I have close to the same issue with little resolution.








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      Help me diagnose a hard hot-start and stumble problem 700

      Have you looked here?

      https://www.brickboard.com/FAQ/700-900/EnginePerformanceSymptoms.htm#NoorSlowHotStartroblemDiagnosisandRepair
      --
      Post Back. That's whats makes this forum work.







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