 ‘74 2.0 Bucking Only When Warmed Up, Runs great when cool |
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| Jackba |
 Sep 14 2019, 04:15 PM
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#1
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Newbie  Group: Members Posts: 40 Joined: 13-July 18 From: Sacramento Member No.: 22,308 Region Association: Northern California  |
I originally started this as a “Won’t Start” thread and got a ton of help from the group. Prior to not starting at all I had a problem with bucking at all times, not just when warm.
The process of fixing the no start issue was lengthy and included the following: Ultrasonically cleaned all parts of the distributor and oiled the plates Changed condenser Checked points and gap Checked trigger points Checked power to injectors using a noid light Verified normal spray pattern of injectors Checked CHT resistance Removed fuel tank and cleaned sock Verified hoses were not kinked Replaced fuel filter replaced bad relay board Verified operation of relays Checked fuel pressure. Removed and cleaned FI grounds Checked static timing Cleaned near new TPS Replaced fuel pump Replacing the pump fixed the no start problem. Took the car for a quick drive and all was fine. Decided to install a Pertronix ignition module and change ignition wires at the same time. Car is running a 5 year old Beru blue 3.3 ohm coil. Thinking I had everything solved I took the car out for an extended drive last Sunday. For the first 5 miles it ran absolutely great. Better than ever. Then it started hesitating and the hesitation got worse. It started bucking to a point where I didn’t think I could make it home, but I did. Now I’m wondering what else I can possibly do? Any suggestions would be welcome. Thanks, Jack |
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Replies(1 - 7)
| Amphicar770 |
Sep 14 2019, 10:32 PM
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#2
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Senior Member Group: Members Posts: 1,191 Joined: 20-April 10 From: PA, USA Member No.: 11,639 Region Association: MidAtlantic Region 
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Similar experience s couple of years ago. Bucking once warm, Died on road twice but once fully cooled would start right up. Turned out to be a loose connector on rear, right side of engine. Once seated properly, problem never recurred. Is your engine wiring harness original?
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| Jackba |
Sep 14 2019, 11:12 PM
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#3
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Newbie Group: Members Posts: 40 Joined: 13-July 18 From: Sacramento Member No.: 22,308 Region Association: Northern California |
QUOTE(Amphicar770 @ Sep 14 2019, 11:32 PM)  Similar experience s couple of years ago. Bucking once warm, Died on road twice but once fully cooled would start right up. Turned out to be a loose connector on rear, right side of engine. Once seated properly, problem never recurred. Is your engine wiring harness original? Thanks for responding. My FI harness was rebuilt by Jeff Bowlsby a few years ago. Not many hours on it. Are you referring to the 3 FI ground wires on the top rear of the engine case or another location? |
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| rjames |
Sep 15 2019, 10:02 AM
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#4
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I'm made of metal Group: Members Posts: 3,933 Joined: 24-July 05 From: Shoreline, WA Member No.: 4,467 Region Association: Pacific Northwest
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The only time my car ever experienced bucking was when i has an intermittent issue with the relay that was being used for the fuel pump. Swapping it out for another relay fixed the issue.
You said you’ve already checked the board and relays, but it still could be fuel related. It would be helpful if you could determine what the fuel pressure was when it starts bucking to rule out any fuel delivery issues before the injectors. |
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| Jackba |
Sep 15 2019, 01:42 PM
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#5
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Newbie Group: Members Posts: 40 Joined: 13-July 18 From: Sacramento Member No.: 22,308 Region Association: Northern California |
QUOTE(rjames @ Sep 15 2019, 11:02 AM) The only time my car ever experienced bucking was when i has an intermittent issue with the relay that was being used for the fuel pump. Swapping it out for another relay fixed the issue. You said you’ve already checked the board and relays, but it still could be fuel related. It would be helpful if you could determine what the fuel pressure was when it starts bucking to rule out any fuel delivery issues before the injectors. Good thought. Thanks Robert. I’ll do some research on how I can make that happen. Jack |
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| porschetub |
Sep 15 2019, 02:36 PM
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#6
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Advanced Member Group: Members Posts: 4,699 Joined: 25-July 15 From: New Zealand Member No.: 18,995 Region Association: None |
QUOTE(Jackba @ Sep 16 2019, 07:42 AM) QUOTE(rjames @ Sep 15 2019, 11:02 AM) The only time my car ever experienced bucking was when i has an intermittent issue with the relay that was being used for the fuel pump. Swapping it out for another relay fixed the issue. You said you’ve already checked the board and relays, but it still could be fuel related. It would be helpful if you could determine what the fuel pressure was when it starts bucking to rule out any fuel delivery issues before the injectors. Good thought. Thanks Robert. I’ll do some research on how I can make that happen. Jack Not sure if this is any help but had a bucking issue with my first e28 BMW,would run fine on cold start then would stagger and buck occasionally,turned out to be low voltage @ the fuel pump due to a bad connector on the pump relay wiring,10cent connector fixed it but nearly drove me mad in the process (IMG:style_emoticons/default/headbang.gif) . Good luck. |
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| Jackba |
Sep 15 2019, 04:13 PM
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#7
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Newbie Group: Members Posts: 40 Joined: 13-July 18 From: Sacramento Member No.: 22,308 Region Association: Northern California |
QUOTE(porschetub @ Sep 15 2019, 03:36 PM) QUOTE(Jackba @ Sep 16 2019, 07:42 AM) QUOTE(rjames @ Sep 15 2019, 11:02 AM) The only time my car ever experienced bucking was when i has an intermittent issue with the relay that was being used for the fuel pump. Swapping it out for another relay fixed the issue. You said you’ve already checked the board and relays, but it still could be fuel related. It would be helpful if you could determine what the fuel pressure was when it starts bucking to rule out any fuel delivery issues before the injectors. Good thought. Thanks Robert. I’ll do some research on how I can make that happen. Jack Not sure if this is any help but had a bucking issue with my first e28 BMW,would run fine on cold start then would stagger and buck occasionally,turned out to be low voltage @ the fuel pump due to a bad connector on the pump relay wiring,10cent connector fixed it but nearly drove me mad in the process (IMG:style_emoticons/default/headbang.gif) . Good luck. Thanks for weighing in. Any help is appreciated, |
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| Amphicar770 |
Sep 16 2019, 06:13 PM
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#8
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Senior Member Group: Members Posts: 1,191 Joined: 20-April 10 From: PA, USA Member No.: 11,639 Region Association: MidAtlantic Region
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QUOTE(Jackba @ Sep 15 2019, 01:12 AM) QUOTE(Amphicar770 @ Sep 14 2019, 11:32 PM) Similar experience s couple of years ago. Bucking once warm, Died on road twice but once fully cooled would start right up. Turned out to be a loose connector on rear, right side of engine. Once seated properly, problem never recurred. Is your engine wiring harness original? Thanks for responding. My FI harness was rebuilt by Jeff Bowlsby a few years ago. Not many hours on it. Are you referring to the 3 FI ground wires on the top rear of the engine case or another location? Mine was a new Bolsby harness as well. As I recall, single wire I think going to the CHT. It looked like it was on properly but was not. Made sense afterward given running awesome until engine warmed up. |
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