 1973 1.7L bucking skipping backfiring thru engine, 1973 1.7L bucking skipping backfiring thru engine |
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| johnoscar |
 Jul 6 2022, 05:15 PM
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#1
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Newbie  Group: Members Posts: 11 Joined: 23-May 22 From: Westfield, Massachusetts Member No.: 26,569 Region Association: North East States  |
Hi all...my first post. ***** (07-10-2022)Updated at bottom
Original owner 1973 1.7 914 now having engine issues. Engine rebuilt top end at Tangerine Racing 2008-2009. The only real new added different part was pop-up pistons 91mm. Slight bucking since then, but never before. Now gotten significantly worse with skipping and backfiring back thru engine. Car will do 80mph on the highway. Probably still skipping, but too fast to feel. Car is bucking. Most felt when feathering throttle under even small load, Also skipping and backfiring while static and under load So......what have I done............ Replaced throttle switch with new from AA Removed electric connection to throttle switch and drove without change Checked Head temp sensor ohms cold 3600-3700 hot 80-90 Replaced Head Temperature Sensor new from AA without change Trigger points cleaned/lubed replaced without change Swapped trigger points with used without change Replaced distributor cap, points, rotor and reset dwell to 48.5 degrees all new from AA Replaced distributor with 123 ignition without change Timing adjusted to 27 Degrees BTDC Replaced all air hoses new from AA without change Replaced ignition wires new from AA without change Checked all ground wires and connections Ignition harness is original but very flexible without brittle wires Replaced push rod tube seals new from AA Reset valve adjustment to .006 in Swapped ECU with used and drove without change. Swapped MPS with used and drove without change Rebuilt MPS with new beryllium copper diaphragm and drove without change Swapped coil with used and drove without change Fuel pump and hose visually checked with nothing compromised. Stainless steel fuel lines installed with rebuild. Disconnected tach from coil and ran without change Disconnected alternator from relay board and ran without change Fuel filter changed within last 2000 miles New Bosch Ignition condenser wire too short on replacement part (not replaced) All above is done and results are totally without change in the issues I'd be interested in anyone's thoughts. I feel the list is extensive and I have had help with this project from a 50 year experience 914 guy. What have I not done? Where else could the issues be generated? Please feel free to comment on anything within the post!!! ***** Clarification within post Cylinder compression 1=158 2=155 3=165 4=154 (all cold) Don't know what the compression ratio is. Fuel injectors cleaned and measured by Dr Injector and are not the problem according to him. The backfiring is thru the intake. Intermittent. On increase in rpm's even in static position |
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| mepstein |
Jul 6 2022, 05:35 PM
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#2
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914-6 GT in waiting Group: Members Posts: 19,279 Joined: 19-September 09 From: Landenberg, PA/Wilmington, DE Member No.: 10,825 Region Association: MidAtlantic Region 
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| StarBear |
Jul 6 2022, 05:52 PM
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#3
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Senior Member Group: Members Posts: 1,889 Joined: 2-September 09 From: NJ Member No.: 10,753 Region Association: North East States
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Wow. Amazing.
Also amazing a) another original owner (now about 7-8) and after this long your first post. (IMG:style_emoticons/default/biggrin.gif) |
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| johnoscar |
Jul 6 2022, 06:02 PM
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#4
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Newbie Group: Members Posts: 11 Joined: 23-May 22 From: Westfield, Massachusetts Member No.: 26,569 Region Association: North East States |
QUOTE(mepstein @ Jul 6 2022, 05:35 PM)  Check all the grounds on the engine. TY for the reply. That has been done. What has not been done is following ECU to all connective points. |
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| johnoscar |
Jul 6 2022, 06:03 PM
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#5
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Newbie Group: Members Posts: 11 Joined: 23-May 22 From: Westfield, Massachusetts Member No.: 26,569 Region Association: North East States |
QUOTE(mepstein @ Jul 6 2022, 05:35 PM) Check all the grounds on the engine. TY for the reply. That has been done. What has not been done is following ECU to all connective points. |
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| emerygt350 |
Jul 6 2022, 06:09 PM
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#6
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Advanced Member Group: Members Posts: 2,103 Joined: 20-July 21 From: Upstate, NY Member No.: 25,740 Region Association: North East States |
Sounds like a lean condition. Didn't see anything about the injectors. Are they original?
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| johnoscar |
Jul 6 2022, 06:10 PM
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#7
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Newbie Group: Members Posts: 11 Joined: 23-May 22 From: Westfield, Massachusetts Member No.: 26,569 Region Association: North East States |
QUOTE(StarBear @ Jul 6 2022, 05:52 PM) Wow. Amazing. Also amazing a) another original owner (now about 7-8) and after this long your first post. (IMG:style_emoticons/default/biggrin.gif) TY for the reply. I am not the maintenance person du jour. Most maintenance has been done by the pros. Now I'm finding lots of parts availability, but no one locally who knows how to fix these cars. So I'm forced to dig in myself as a lowly rated novice. |
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| johnoscar |
Jul 6 2022, 06:13 PM
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#8
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Newbie Group: Members Posts: 11 Joined: 23-May 22 From: Westfield, Massachusetts Member No.: 26,569 Region Association: North East States |
QUOTE(emerygt350 @ Jul 6 2022, 06:09 PM) Sounds like a lean condition. Didn't see anything about the injectors. Are they original? Ty for your comment. The injectors were all proved out by Dr Injector somewhere in the western US. All came up perfect. His comments to me were whatever the problem, it's not the injectors. |
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| wonkipop |
Jul 6 2022, 06:58 PM
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#9
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Advanced Member Group: Members Posts: 4,330 Joined: 6-May 20 From: north antarctica Member No.: 24,231 Region Association: NineFourteenerVille
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i don't want to say this ........but
burnt valve? or an exhaust valve that never sealed properly and its gotten worse and worse. symptoms fit. EDIT well done for being the one and only owner. stick with it. (IMG:style_emoticons/default/beerchug.gif) |
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| emerygt350 |
Jul 6 2022, 07:30 PM
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#10
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Advanced Member Group: Members Posts: 2,103 Joined: 20-July 21 From: Upstate, NY Member No.: 25,740 Region Association: North East States |
QUOTE(wonkipop @ Jul 6 2022, 06:58 PM) i don't want to say this ........but burnt valve? or an exhaust valve that never sealed properly and its gotten worse and worse. symptoms fit. EDIT well done for being the one and only owner. stick with it. (IMG:style_emoticons/default/beerchug.gif) That, sadly, was my next question as well. Have you done a compression test? |
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| 914_teener |
Jul 6 2022, 07:36 PM
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#11
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914 Guru Group: Members Posts: 5,199 Joined: 31-August 08 From: So. Cal Member No.: 9,489 Region Association: Southern California |
QUOTE(johnoscar @ Jul 6 2022, 05:03 PM) QUOTE(mepstein @ Jul 6 2022, 05:35 PM) Check all the grounds on the engine. TY for the reply. That has been done. What has not been done is following ECU to all connective points. Super important. You need to test the FI harness for continuity. All it takes is a DVM (Digital Volt Meter). |
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| johnoscar |
Jul 7 2022, 03:37 PM
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#12
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Newbie Group: Members Posts: 11 Joined: 23-May 22 From: Westfield, Massachusetts Member No.: 26,569 Region Association: North East States |
QUOTE(wonkipop @ Jul 6 2022, 06:58 PM) i don't want to say this ........but burnt valve? or an exhaust valve that never sealed properly and its gotten worse and worse. symptoms fit. EDIT well done for being the one and only owner. stick with it. (IMG:style_emoticons/default/beerchug.gif) TY..... have not yet dug that far |
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| JeffBowlsby |
Jul 7 2022, 03:41 PM
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#13
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914 Wiring Harnesses Group: Members Posts: 8,510 Joined: 7-January 03 From: San Ramon CA Member No.: 104 Region Association: None
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QUOTE(914_teener @ Jul 6 2022, 06:36 PM) QUOTE(johnoscar @ Jul 6 2022, 05:03 PM) QUOTE(mepstein @ Jul 6 2022, 05:35 PM) Check all the grounds on the engine. TY for the reply. That has been done. What has not been done is following ECU to all connective points. Super important. You need to test the FI harness for continuity. All it takes is a DVM (Digital Volt Meter). And be sure to wiggle the harness during your continuity testing of each circuit to see if any circuit is intermittent. I am also happy to check your harnesses at no cost to you other than for shipping, but you will need to remove/ship them to me. |
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| mgphoto |
Jul 7 2022, 04:28 PM
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#14
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"If there is a mistake it will find me" Group: Members Posts: 1,339 Joined: 1-April 09 From: Los Angeles, CA Member No.: 10,225 Region Association: Southern California |
Remove the valve covers, pull the rockers use a straight edge to see if the valve stems line up.
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| johnoscar |
Jul 7 2022, 06:36 PM
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#15
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Newbie Group: Members Posts: 11 Joined: 23-May 22 From: Westfield, Massachusetts Member No.: 26,569 Region Association: North East States |
QUOTE(emerygt350 @ Jul 6 2022, 07:30 PM) QUOTE(wonkipop @ Jul 6 2022, 06:58 PM) i don't want to say this ........but burnt valve? or an exhaust valve that never sealed properly and its gotten worse and worse. symptoms fit. EDIT well done for being the one and only owner. stick with it. (IMG:style_emoticons/default/beerchug.gif) That, sadly, was my next question as well. Have you done a compression test? compression is between 150-165 per cylinder |
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| mgphoto |
Jul 7 2022, 06:50 PM
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#16
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"If there is a mistake it will find me" Group: Members Posts: 1,339 Joined: 1-April 09 From: Los Angeles, CA Member No.: 10,225 Region Association: Southern California |
QUOTE(johnoscar @ Jul 7 2022, 05:36 PM) QUOTE(emerygt350 @ Jul 6 2022, 07:30 PM) QUOTE(wonkipop @ Jul 6 2022, 06:58 PM) i don't want to say this ........but burnt valve? or an exhaust valve that never sealed properly and its gotten worse and worse. symptoms fit. EDIT well done for being the one and only owner. stick with it. (IMG:style_emoticons/default/beerchug.gif) That, sadly, was my next question as well. Have you done a compression test? compression is between 150-165 per cylinder You might have a valve seat problem that doesn’t show up until the engine is running or hot. Look at the intake valves especially. |
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| nditiz1 |
Jul 7 2022, 06:53 PM
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#17
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Senior Member Group: Members Posts: 1,188 Joined: 26-May 15 From: Mount Airy, Maryland Member No.: 18,763 Region Association: MidAtlantic Region
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Going off of what someone else said about a lean condition maybe there is a vac leak. I might have missed it but I didn't see it in your list to fully check for vac leaks. If you are introducing un metered air it could cause lean bucking and running rough.
Also I know not in the same ball park ad FI, but I had popping through carbs that ended up being a missing manifold gasket only at ~3000 rpm. Under that it was fine. |
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| emerygt350 |
Jul 7 2022, 07:29 PM
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#18
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Advanced Member Group: Members Posts: 2,103 Joined: 20-July 21 From: Upstate, NY Member No.: 25,740 Region Association: North East States |
It could be a vacuum leak. You say you have had issues finding shops to look at it. Maybe snap some pics of the engine and let us take a look.
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| ctc911ctc |
Jul 8 2022, 12:39 PM
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#19
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Senior Member Group: Members Posts: 893 Joined: 9-June 18 From: boston Member No.: 22,206 Region Association: North East States
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QUOTE(emerygt350 @ Jul 7 2022, 07:29 PM) It could be a vacuum leak. You say you have had issues finding shops to look at it. Maybe snap some pics of the engine and let us take a look. (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) There is a guy in the Springfield area - close to you called Hurst Injectors (https://hurstinjectorservice.com/) - GREAT GUY - GREAT WORK, knows Bosch like the back of his hand - the injectors might need a refresh - short money........ If the car sat for a while prior to this FUN - I would STRONGLY suggest starting with the vacuum circuit. Everything connected to the Plenum (box under the Throttle Body - where the throttle cable goes) must be air-tight. The Plenum itself will rust and leak........ I chased the same thing for months and finally checked the vacuum, if there are leaks the car will lose it's mind...... Oh, I am in Arlington - trailer it here and I will troubleshoot for you......N/C |
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| Jmkorfha |
Jul 9 2022, 08:16 AM
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#20
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I'm not a singing grandpa. Group: Members Posts: 58 Joined: 26-October 13 From: Austin, Mn Member No.: 16,569 Region Association: Upper MidWest |
My guess is the condenser.
If I read the thread right, the replacement had a wire that was too short. So you didn’t replace it.(?) Extend the wire and try it. |
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