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 |
ctc911ctc |
Dec 13 2019, 04:50 PM
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#3
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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 |
Excellent idea!
Yes, I did calibrate and cleaned (rebuilt) with a 914Rubber circuit board. I will double check that it is a 2.0 and not a 1.7 and the other errors I have read about. Thanks Brant! (IMG:style_emoticons/default/pray.gif) 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 |
rjames |
Dec 13 2019, 05:03 PM
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#4
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I'm made of metal Group: Members Posts: 3,928 Joined: 24-July 05 From: Shoreline, WA Member No.: 4,467 Region Association: Pacific Northwest |
Verify fuel pressure
Make sure MPS is calibrated for your engine. If it was rebuilt (even if it matches factory stock #s) it likely needs calibration. |
ctc911ctc |
Dec 13 2019, 07:58 PM
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#5
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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 |
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mark04usa |
Dec 13 2019, 11:42 PM
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#6
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'70 1.7 Tangerine Group: Members Posts: 351 Joined: 14-September 09 From: Austin TX Member No.: 10,805 Region Association: Southwest Region |
I would start with thoroughly checking the ignition system, as a more likely suspect to eliminate first. Had a similar intermittant problem that was due to points wire pinched under cap... (IMG:style_emoticons/default/beerchug.gif)
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Spoke |
Dec 13 2019, 11:48 PM
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#7
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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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#8
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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? |
ctc911ctc |
Dec 14 2019, 03:21 PM
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#9
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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******
Started the car Disconnected the TPS Drove the car The hesitation was MUCH worse, the bucking was about the same. Disconnecting the TPS made the entire situation worse though the drive was just around the block. As per PBanders: Track Wear: Over time, the wiper track for the accelerator function will wear. Wear will be especially high at moderate to light throttle angles, corresponding to part-load cruising. Click here for a link to a 60X photo of accelerator track wear. While this TPS track is still good, the re-deposition of gold worn from the contact fingers by the wiper can be seen, and eventually will become sufficient to bridge the traces. This wear causes arcing and poor contact, resulting in the car "bucking" at a constant throttle angle. "Bucking" is a fairly common complaint and is almost always due to track wear. Check by disconnecting the harness plug to the throttle switch and driving at a constant throttle angle under part-load. If the bucking is gone, it's due to the switch. As I mentioned earlier, if you go to http://www.914world.com/ and search for user "davesprinkle", he's made a kit to replace the worn circuit board that restores your TPS to like-new condition. I have a new card from 914Rubber in the car and I am pretty certain the card wipers are connecting to the card correctly. I will take a closer look at this tomorrow. I will also retest tomorrow (too much rain today for a highway check) to make certain that the bucking is gone even though the acceleration is very poor. The barely accelerates until I hold the peddle about 1/2 way for a few seconds and then the engine starts to run strong after a prolonged response to the peddle. Any ideas appreciated. Thank you! 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? |
ctc911ctc |
Dec 15 2019, 05:42 PM
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#10
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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****** Started the car Disconnected the TPS Drove the car The hesitation was MUCH worse, the bucking was about the same. Disconnecting the TPS made the entire situation worse though the drive was just around the block. As per PBanders: Track Wear: Over time, the wiper track for the accelerator function will wear. Wear will be especially high at moderate to light throttle angles, corresponding to part-load cruising. Click here for a link to a 60X photo of accelerator track wear. While this TPS track is still good, the re-deposition of gold worn from the contact fingers by the wiper can be seen, and eventually will become sufficient to bridge the traces. This wear causes arcing and poor contact, resulting in the car "bucking" at a constant throttle angle. "Bucking" is a fairly common complaint and is almost always due to track wear. Check by disconnecting the harness plug to the throttle switch and driving at a constant throttle angle under part-load. If the bucking is gone, it's due to the switch. As I mentioned earlier, if you go to http://www.914world.com/ and search for user "davesprinkle", he's made a kit to replace the worn circuit board that restores your TPS to like-new condition. I have a new card from 914Rubber in the car and I am pretty certain the card wipers are connecting to the card correctly. I will take a closer look at this tomorrow. I will also retest tomorrow (too much rain today for a highway check) to make certain that the bucking is gone even though the acceleration is very poor. The barely accelerates until I hold the peddle about 1/2 way for a few seconds and then the engine starts to run strong after a prolonged response to the peddle. Any ideas appreciated. Thank you! 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? (IMG:style_emoticons/default/icon_bump.gif) |
JeffBowlsby |
Dec 15 2019, 07:21 PM
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#11
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914 Wiring Harnesses Group: Members Posts: 8,501 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. |
ChrisFoley |
Dec 16 2019, 09:57 AM
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#12
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I am Tangerine Racing Group: Members Posts: 7,924 Joined: 29-January 03 From: Bolton, CT Member No.: 209 Region Association: None |
I've experienced similar symptoms when the MPS was adjusted a bit too lean. At some areas in the fuel map it gets lean enough to cause slight misfire.
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914_teener |
Dec 16 2019, 10:14 AM
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#13
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914 Guru Group: Members Posts: 5,197 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
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#14
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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 |
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
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#15
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Jerry Group: Members Posts: 6,978 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
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#16
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914 Wizard Group: Members Posts: 11,623 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 |
ctc911ctc |
Dec 17 2019, 01:55 PM
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#17
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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 |
What changed right before detecting the bucking? Really nothing.
The car had not been driven since 1986. We got it working but could not drive it since I did not have a clear title - after 6 months of working this, I was able to get the gov here in Mass to provide a title. The first stop was the paint shop, on the way there I took side roads, all stop and go. Since I was not sure as to the car's operation I did the shakedown on side roads, no faster than 35-40. On the way back I took the Interstate and cruised between 55 and 65. The car ran great until I was trying to maintain a constant speed and then the bucking would start. Will check next: grounds Fuel Pressure Wiring to the ECU from the TPS (have done this before) Trigger points and operation Ignition system (complete) Last, I found the Tech Tips 700 book very helpful - thank you George! Thank you Brant! 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 |
brant |
Dec 17 2019, 02:12 PM
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#18
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914 Wizard Group: Members Posts: 11,623 Joined: 30-December 02 From: Colorado Member No.: 47 Region Association: Rocky Mountains |
Over there we 5 years did you flush the tank and replace the lines???
Someone suggested restricted fuel lines or a plugged fuel filter Those highway miles would require more fuel and hypothetically could highlight a fuel flow (lean) problem |
Spoke |
Dec 17 2019, 02:42 PM
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#19
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Jerry Group: Members Posts: 6,978 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None |
Will check next: grounds Fuel Pressure Wiring to the ECU from the TPS (have done this before) Trigger points and operation Ignition system (complete) Also check the CHT sender. For overall operation of DJET, you should check the AFR although this requires installing an oxygen sensor in the exhaust. I did this on my 1.8L DJET when I first got it running. Turns out it was running very lean and I had to adjust the MPS. |
JawjaPorsche |
Dec 17 2019, 02:54 PM
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#20
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Advanced Member Group: Members Posts: 3,463 Joined: 23-July 11 From: Clayton, Georgia Member No.: 13,351 Region Association: South East States |
I got a Jeff Bowsley FI harness. Solve a lot gremlins including bucking.
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