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  1. #1

    Default Weird Surging problem under boost

    I have a 1983 Mercury Capri turbo RS. I have been chasing a surging problem under boost for quite some time. The car has the biggest after-market SVO turbo catalog cam (available circa 1994) along with a ported head and oversized intake and exhaust valves. It has the 83 inline intake which has been port matched but retains the stock throttle body. About 15 years ago it got injectors from an 85.5 SVO and computer and air meter. I have tried multiple computers including an 86 PE SVO computer and the original 83 Capri rs computer. In all cases under boost the car tends to Surge.It then has been more recently updated to have an 88 Thunderbird Turbo Coupe air meter (basically the same as the svo meter but was trying to troubleshoot) and la3 computer. Same results.

    I have it limited currently to only 10 psi and have checked my fuel pressure with it being at about 36 PSI at idle and going up to about 45 PSI under boost. I have disconnected the knock sensor and it helped some but in the grand scheme it made little change.

    I have pulled codes and only have a code for the knock sensor which is unplugged. I'm turning to The Experts for ideas on what to try next and how to isolate the problem. It feels like either the timing is retarding on about a one and a half second interval or the fuel map is coming up and down on the same cycle. The motor is not missing it just seems too lose and then regained power every second to Second and a half.

    Thoughts?

  2. #2
    FEP Power Member SchoolBoy's Avatar
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    Arlington Washington
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    Do you have an intercooler, bypass/blow off valve, what spark plugs, plug gap, base timing with spout disconnected, what kind of boost controller, cap/rotor/plug wires last replaced, stock turbo? Also have you done a compression or leak down test lately?

    Is the 10psi based on a quality gauge?

    Fuel pressure I think should be closer to 40 at idle.
    If you blink at the end of the straight away you'll miss the twisties and what fun would that be!
    1982 Capri RS 5.0L
    Suspension Build http://vb.foureyedpride.com/showthre...tion-and-Build
    1985 SVO 2A & leather. Stolen & Destroyed 2022
    Motor Build http://vb.foureyedpride.com/showthread.php?t=63505
    Dyno stats and exhaust install http://vb.foureyedpride.com/showthre...Dyno-d-finally
    My FMIC build http://vb.foureyedpride.com/showthre...-amp-D-project
    Electronic boost controller and bypass valve
    http://vb.foureyedpride.com/showthre...d-Bypass-Valve
    Opperation SVO Tunes http://vb.foureyedpride.com/showthre...51#post1148551

  3. #3

    Default

    Quote Originally Posted by SchoolBoy View Post
    Do you have an intercooler, bypass/blow off valve, what spark plugs, plug gap, base timing with spout disconnected, what kind of boost controller, cap/rotor/plug wires last replaced, stock turbo? Also have you done a compression or leak down test lately?

    Is the 10psi based on a quality gauge?

    Fuel pressure I think should be closer to 40 at idle.
    It has an 88 turbo coupe intercooler, mounted in the traditionAL spot. No bypass or blow off. I don't recall the plugs or gaps but the baselite timing is at 14 if memory serves me right. The boost controller is a bolt stuck in the waste gate bypass hose... used to have a fish tank valve when I ran more boost (20 years ago).

    Cap and rotor have been replaced with AutoZone replacements. The turbo is off of an 86 SVO Mustang. I have not done a compression or leak down test but based upon how it's behaving it seems extremely Electronics related.
    Last edited by foot2floor; 05-26-2017 at 08:01 PM.

  4. #4
    FEP Power Member SchoolBoy's Avatar
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    Jan 2004
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    Arlington Washington
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    Normally I would agree that is would seam to be electronics related, but given the number of ecu swaps I am leaning on rulling that out unless the main harnes has an issue.

    But I would try 10* base timing, bump the fp to 40, and check plug gap to 32.

    Also I bring up the leak down test because my car was running like garbage for a years I went through alot of the same stuff you did including the $1500 for a fmic. Only to find out on the leak down test that my rings were leaking 50%. Apon tear down we found the piston to wall clearance was twice the maximum. I was really lucky not to have broke a skirt or ring land....
    If you blink at the end of the straight away you'll miss the twisties and what fun would that be!
    1982 Capri RS 5.0L
    Suspension Build http://vb.foureyedpride.com/showthre...tion-and-Build
    1985 SVO 2A & leather. Stolen & Destroyed 2022
    Motor Build http://vb.foureyedpride.com/showthread.php?t=63505
    Dyno stats and exhaust install http://vb.foureyedpride.com/showthre...Dyno-d-finally
    My FMIC build http://vb.foureyedpride.com/showthre...-amp-D-project
    Electronic boost controller and bypass valve
    http://vb.foureyedpride.com/showthre...d-Bypass-Valve
    Opperation SVO Tunes http://vb.foureyedpride.com/showthre...51#post1148551

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