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914World.com _ 914World Garage _ 1973 1.7L bucking skipping backfiring thru engine
Posted by: johnoscar Jul 6 2022, 05:15 PM
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
Posted by: mepstein Jul 6 2022, 05:35 PM
Check all the grounds on the engine.
Posted by: 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. 
Posted by: johnoscar Jul 6 2022, 06:02 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.
Posted by: johnoscar Jul 6 2022, 06:03 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.
Posted by: emerygt350 Jul 6 2022, 06:09 PM
Sounds like a lean condition. Didn't see anything about the injectors. Are they original?
Posted by: johnoscar Jul 6 2022, 06:10 PM
Wow. Amazing.
Also amazing a) another original owner (now about 7-8) and after this long your first post.
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.
Posted by: johnoscar Jul 6 2022, 06:13 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.
Posted by: 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. 
Posted by: emerygt350 Jul 6 2022, 07:30 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.
That, sadly, was my next question as well.
Have you done a compression test?
Posted by: 914_teener Jul 6 2022, 07:36 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).
Posted by: johnoscar Jul 7 2022, 03:37 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.
TY.....
have not yet dug that far
Posted by: JeffBowlsby Jul 7 2022, 03:41 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.
Posted by: mgphoto Jul 7 2022, 04:28 PM
Remove the valve covers, pull the rockers use a straight edge to see if the valve stems line up.
Posted by: johnoscar Jul 7 2022, 06:36 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.
That, sadly, was my next question as well.
Have you done a compression test?
compression is between 150-165 per cylinder
Posted by: mgphoto Jul 7 2022, 06:50 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.
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.
Posted by: nditiz1 Jul 7 2022, 06:53 PM
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.
Posted by: 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.
Posted by: ctc911ctc Jul 8 2022, 12:39 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.
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
Posted by: Jmkorfha Jul 9 2022, 08:16 AM
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.
Posted by: johnoscar Jul 9 2022, 10:09 AM
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.
you are correct. the condenser wire from bosch was too short. called george at aa. the posts about the condenser wire are about 2 years oid and he didn't know anything about it. he had to ask someone in his repair garage, but did confirm,
since, i have replaced the distributor with 123ignition, without any change.
Posted by: johnoscar Jul 9 2022, 10:14 AM
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.
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
ty. didn't know that. i'll follow up on what he does. your offer is more than kind and appreciated very much. i may be in contact with you....too good to pass up.
Posted by: emerygt350 Jul 9 2022, 03:16 PM
Wouldn't there be no spark if it were the condenser?
Posted by: ChrisFoley Jul 10 2022, 08:57 AM
ctc911ctc has a 2L engine. The 1.7L plenum is different, and not prone to cracking as the 2L unit is.
Posted by: johnoscar Jul 10 2022, 02:42 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.
That, sadly, was my next question as well.
Have you done a compression test?
cyl1=158 cyl2=155 cyl3=165 cyl4=154 all psi (all cold)
Posted by: emerygt350 Jul 10 2022, 05:40 PM
Those numbers are great. That really only leaves peripherals. Get on the vacuum lines. Get us pictures.
Posted by: ctc911ctc Jul 11 2022, 07:28 AM
Chris,
Good to see your post - hope all is well - it has been a long time since I owned a 1.7, I was not aware that the plenum was different,
Thank you,
ctc911ctc has a 2L engine. The 1.7L plenum is different, and not prone to cracking as the 2L unit is.
Posted by: Highland Jul 11 2022, 01:52 PM
Chris,
Good to see your post - hope all is well - it has been a long time since I owned a 1.7, I was not aware that the plenum was different,
Thank you,
ctc911ctc has a 2L engine. The 1.7L plenum is different, and not prone to cracking as the 2L unit is.
Is the type 4 2L bus’ plenum similar in shape to the 1.7L plenum? If so, why did they elect to use a different 2L plenum design on the 914?
Posted by: wonkipop Jul 11 2022, 04:24 PM
Chris,
Good to see your post - hope all is well - it has been a long time since I owned a 1.7, I was not aware that the plenum was different,
Thank you,
ctc911ctc has a 2L engine. The 1.7L plenum is different, and not prone to cracking as the 2L unit is.
Is the type 4 2L bus’ plenum similar in shape to the 1.7L plenum? If so, why did they elect to use a different 2L plenum design on the 914?
i could be wrong about this -
but the bus 2.0 L was either twin carb (in most of the world except the USA) or if EFI it ran L jetronic. the VW version for the bus came a few years after the 2.0 developed by porsche for the 914 which is D jetronic. porsche designed a fairly unique intake plenum and throttle body for the 914 2.0 the one that is on the VW 2.0 is more like the intake plenum and throttle body on the 1.8 L jets or the 2.0 912E.
Posted by: johnoscar Jul 11 2022, 05:20 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).
Jeff....does your site have a diagram of what wires at the ECU go to which wires at the other end??
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