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On boost stumble - '86 Turbo

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Old 06-12-2018, 10:17 PM
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dsulliv6
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Default On boost stumble - '86 Turbo

Hello - I get an on-boost fuel cut-off or stumble, but only in 4th and 5th gears at highway speeds. Car accelerates very well from stop, and from 1st through 3rd gears. When I'm driving at highway speeds, and get on the throttle in those higher gears, it feels like a rev limiter is trying to cut in intermittently. Loose connection? Fuel pump or filter gummed up and not able to maintain fuel flow at speed? Otherwise the car drives strong, and fantastic at all other speeds. At steady-state cruise on highway it's fine. Only when I get deeper into throttle in upper gears do I get this cut-off or stumble. Perplexed what it might be?

Any help with common fuel or rev limiter issues would be appreciated.

Cheers,

Dave
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Old 06-13-2018, 08:38 AM
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Humboldtgrin
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Plug wires?
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Old 06-13-2018, 11:09 AM
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If you are still runnig the stock DME chip, but you have a test pipe (in place of cat converter) or you altered any of the boost control functions then you could be hitting the overboost (overload) protection built in to the DME chip.
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Old 06-13-2018, 01:13 PM
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dsulliv6
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Car is all-original OEM equipment, outside of replaced parts for service. No mods. AFAIK, OE replacement parts were used for servicing the vehicle in it's lifetime - and the copious records I was given with the car seem to indicate that's true.

If it was plug wires, wouldn't I get the stumble at all RPMs/gears? Only occurs at highway speeds.
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Old 06-13-2018, 07:17 PM
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Amalgamated Tom

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I'd put money on a weak ignition -- bad wires, cap, rotor, and/or plugs --your money, not mine, but still... When running in lower gears, the load isn't as great, so the ignition is still strong enough to jump the gap on the plugs. In higher gears under full load, at some point the spark isn't strong enough to jump the gap and/or the spark finds itself an easier path to ground (via bad wires, etc.).
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Old 06-14-2018, 09:03 AM
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87944turbo
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FWIW I had this issue with Magnecor wires. Went back to stock wires, problem solved. Just like yours, issue only presented itself under load at highway speed.
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