Running GREAT and then rough…..hhhhmmmm, engine runs rough at one place in the power band |
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Running GREAT and then rough…..hhhhmmmm, engine runs rough at one place in the power band |
ctc911ctc |
Dec 13 2019, 10:16 AM
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#1
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Senior Member Group: Members Posts: 892 Joined: 9-June 18 From: boston Member No.: 22,206 Region Association: North East States |
-Update -
I removed the TPS, calibrated it as per instructions on the Bird. Here are some pictures. I would like to be able to "RING" this out, not sure what I would be looking for. Though we know that one course is to install a new board and then calibrate. There is little else I could find to assure operation. Any experience with asserting these things are good. Some pics Any ideas would be great! -End of Update- I am a bit befuddled as to which way to go so I decided that the 914W team would like to hear about this puzzle. Background '74 2.0, garaged from '84 until 2018, 22K miles Running since June. Repaired or replaced: Entire Fuel System - tank, lines, injectors, pump, pressure reg Adjusted the valves Removed and rang-out the engine harness, Rebuilt the MPS Rebuilt the Plenum and tested it for leaks - none observed New gaskets at the plenum and manifold at the engine Rebuilt Throttle Body, very minor leaks around the actuator (throttle), New circuit card New Plugs, points, cap and inspected the distributor for all of the regular ailments - super tight. Engine idles great, pulls like a monster - sounds like a German symphony HOWEVER Last night I drove it back from the paint shop on 93 heading south from NH to Boston (lots of beeps from newer Porsches (IMG:style_emoticons/default/smile.gif) (IMG:style_emoticons/default/wink.gif) ) and found that the car started to buck and the engine runs rough when just a small amount of throttle is applied. More Detail If you are doing 55 and want to maintain that speed, it is necessary to apply a small amount of gas to sustain the speed. This is when the cars starts to exhibit this "miss/run-rough" puzzle. If more throttle is applied the bucking stops, the engine is smooth and all is well. Conversely, while de-accelerating there is no bucking. This problem is NOT velocity-dependent, sustaining at 30/40/50/60 will exhibit the same reaction. WHERE WOULD YOU START TO LOOK IF YOU HAD THIS CHALLENGE? |
brant |
Dec 13 2019, 10:20 AM
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#2
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914 Wizard Group: Members Posts: 11,623 Joined: 30-December 02 From: Colorado Member No.: 47 Region Association: Rocky Mountains |
kinda sounds like a TPS issue
the connectors become very brittle did you calibrate the TPS during rebuild? maybe check the wiring again to the TPS |
Spoke |
Dec 13 2019, 11:48 PM
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#3
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Jerry Group: Members Posts: 6,978 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None |
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ctc911ctc |
Dec 14 2019, 08:58 AM
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#4
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Senior Member Group: Members Posts: 892 Joined: 9-June 18 From: boston Member No.: 22,206 Region Association: North East States |
Will be checking the throttle switch (TPS) today,
Completely slipped my mind that Pbanders was all over this, https://members.rennlist.com/pbanders/DJetParts.htm Also, there is an over analysis of same at: https://www.sw-em.com/bosch_d-jetronic_TPS_investigation.htm Where the writer refers to the symptom as MaC or Miss-at-Cruise More to come CTC911CTC kinda sounds like a TPS issue As a quick check, isn't it possible to disconnect the TPS and run it like that just to see if the bucking stops? |
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