Running GREAT and then rough…..hhhhmmmm, engine runs rough at one place in the power band |
|
Porsche, and the Porsche crest are registered trademarks of Dr. Ing. h.c. F. Porsche AG.
This site is not affiliated with Porsche in any way. Its only purpose is to provide an online forum for car enthusiasts. All other trademarks are property of their respective owners. |
|
Running GREAT and then rough…..hhhhmmmm, engine runs rough at one place in the power band |
ctc911ctc |
Dec 13 2019, 10:16 AM
Post
#1
|
Senior Member Group: Members Posts: 893 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? |
JeffBowlsby |
Dec 15 2019, 07:21 PM
Post
#2
|
914 Wiring Harnesses Group: Members Posts: 8,513 Joined: 7-January 03 From: San Ramon CA Member No.: 104 Region Association: None |
Looks like a lot of wear on those traces, to my eye.
Clean them with an eraser and spray the traces with DeOxit spray. You can test the continuity between each circuit with an ohmmeter to verify that the TPS is doing its job. |
914_teener |
Dec 16 2019, 10:14 AM
Post
#3
|
914 Guru Group: Members Posts: 5,200 Joined: 31-August 08 From: So. Cal Member No.: 9,489 Region Association: Southern California |
Looks like a lot of wear on those traces, to my eye. Clean them with an eraser and spray the traces with DeOxit spray. You can test the continuity between each circuit with an ohmmeter to verify that the TPS is doing its job. +2 on that board. I'd probably replace it. Also +1 on the MPS... or kinked fuel line. |
ctc911ctc |
Dec 16 2019, 07:31 PM
Post
#4
|
Senior Member Group: Members Posts: 893 Joined: 9-June 18 From: boston Member No.: 22,206 Region Association: North East States |
Though the card is new, I might get the 45-year-old card back and put it in (IMG:style_emoticons/default/dry.gif) (IMG:style_emoticons/default/dry.gif) (IMG:style_emoticons/default/dry.gif) ..........curious how worn the new one looks, even though it only has 60+ miles on it - all of the wipers are scratching at the same rate - does not look too bad with the naked eye.
As to Fuel pressure - would this cause the bucking at maintaining speed but not when accelerating? I will start the debug list - my next stop after verification of pressure will be ignition. Thank you Teeners! CTC911CTC Looks like a lot of wear on those traces, to my eye. Clean them with an eraser and spray the traces with DeOxit spray. You can test the continuity between each circuit with an ohmmeter to verify that the TPS is doing its job. +2 on that board. I'd probably replace it. Also +1 on the MPS... or kinked fuel line. |
Spoke |
Dec 16 2019, 09:31 PM
Post
#5
|
Jerry Group: Members Posts: 6,985 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None |
Though the card is new, I might get the 45-year-old card back and put it in (IMG:style_emoticons/default/dry.gif) (IMG:style_emoticons/default/dry.gif) (IMG:style_emoticons/default/dry.gif) ..........curious how worn the new one looks, even though it only has 60+ miles on it - all of the wipers are scratching at the same rate - does not look too bad with the naked eye. You did a test which seemingly exonerates the TPS: Disconnected the TPS The hesitation was MUCH worse, the bucking was about the same. A main function of the TPS is to give the injectors extra pulses for acceleration so hesitation would be expected. But w/o the TPS in the circuit, the bucking was about the same. This would seem to eliminate the TPS from being the culprit. |
brant |
Dec 17 2019, 09:17 AM
Post
#6
|
914 Wizard Group: Members Posts: 11,625 Joined: 30-December 02 From: Colorado Member No.: 47 Region Association: Rocky Mountains |
Though the card is new, I might get the 45-year-old card back and put it in (IMG:style_emoticons/default/dry.gif) (IMG:style_emoticons/default/dry.gif) (IMG:style_emoticons/default/dry.gif) ..........curious how worn the new one looks, even though it only has 60+ miles on it - all of the wipers are scratching at the same rate - does not look too bad with the naked eye. You did a test which seemingly exonerates the TPS: Disconnected the TPS The hesitation was MUCH worse, the bucking was about the same. A main function of the TPS is to give the injectors extra pulses for acceleration so hesitation would be expected. But w/o the TPS in the circuit, the bucking was about the same. This would seem to eliminate the TPS from being the culprit. I agree.. seems like something else is causing the bucking I have also always understood that unplugging the TPS would test the trace circuits and I have experienced this test working on my car. I would follow Chris' advice. testing the MPS, the CHT, and wiring loom would be my next move.... was there any work done to the car right before the problem started? I always like to start sleuthing with the last thing touched |
Lo-Fi Version | Time is now: 23rd May 2024 - 10:42 AM |
All rights reserved 914World.com © since 2002 |
914World.com is the fastest growing online 914 community! We have it all, classifieds, events, forums, vendors, parts, autocross, racing, technical articles, events calendar, newsletter, restoration, gallery, archives, history and more for your Porsche 914 ... |