Is this the dreaded 914 vapor lock?, Asking for your ideas and thoughts |
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Is this the dreaded 914 vapor lock?, Asking for your ideas and thoughts |
Artfrombama |
Jul 14 2024, 05:04 PM
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#1
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Member Group: Members Posts: 156 Joined: 21-January 24 From: Alabama Member No.: 27,870 Region Association: South East States |
Drove my 914 to a PCA function yesterday morning, 93f and humid.
After driving on the interstate at 70-75mph for around 45 miles I exited and the motor died. I had enough momentum and coasted into a gas station/convenience store where I topped off the tank and tried to restart the car, no luck. The car would fire, run a few seconds and die then refused to re-start for another 10-15 minutes then the same scenario again. No tools to diagnose or repair. While waiting on AAA for three hours (another story) I would occasionally try to start the car with the same results. Today, car started normally, runs normally. 1974 L-jet, original three bung fuel pump, original location. 500 miles on new tank, sock, filter, ss lines. |
wonkipop |
Jul 15 2024, 07:15 PM
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#2
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Advanced Member Group: Members Posts: 4,611 Joined: 6-May 20 From: north antarctica Member No.: 24,231 Region Association: NineFourteenerVille |
so let me get this right with the test you did.
you unplugged fuel regulator and plugged line and tested and got 43 psi. that means your pump could only muster 43 psi before it was blowing out the back door. a good one will get to about 60-70 psi. thats basically the same test i did on my rebuilt pumps if i understand you right. we were using a guage that had an adjustable tap on it. setting it to values of first 28 then 35 simulating the fpr. it was making it. then we kept cranking it until we got it to shoot out port 3. happened at 60-70 depending on the pump i was testing. additional to the ultimate pressure test the whole deal has to be able to do those two values i posted. theoretically with the fuel pressure regulator plugged in and being tested it should still be able to make the pressures of 28 and 35 in the injector line even with weaker value of 43 max made by pump. its a bit of a close margin but its there. thats if the fpr is good. unless that 43 is not something its able to make consistently. i'm reading your second test again carefully. so you are saying that once again you plugged line before fpr. ie ultimate test of pump against completely closed line. and all it could muster was 14psi. so was blowing out the back door at 14 psi. if so. pump ratshit. probably in that spring thing. either backflowing down supply line frpm tank because rubber tip on pin is rooted or not there or not seated properly. or the spring is catching and the whole jigger is jammed open letting it flow out of the final escape port back to the tank. |
Artfrombama |
Jul 15 2024, 09:52 PM
Post
#3
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Member Group: Members Posts: 156 Joined: 21-January 24 From: Alabama Member No.: 27,870 Region Association: South East States |
so let me get this right with the test you did. you unplugged fuel regulator and plugged line and tested and got 43 psi. that means your pump could only muster 43 psi before it was blowing out the back door. a good one will get to about 60-70 psi. thats basically the same test i did on my rebuilt pumps if i understand you right. we were using a guage that had an adjustable tap on it. setting it to values of first 28 then 35 simulating the fpr. it was making it. then we kept cranking it until we got it to shoot out port 3. happened at 60-70 depending on the pump i was testing. additional to the ultimate pressure test the whole deal has to be able to do those two values i posted. theoretically with the fuel pressure regulator plugged in and being tested it should still be able to make the pressures of 28 and 35 in the injector line even with weaker value of 43 max made by pump. its a bit of a close margin but its there. thats if the fpr is good. unless that 43 is not something its able to make consistently. i'm reading your second test again carefully. so you are saying that once again you plugged line before fpr. ie ultimate test of pump against completely closed line. and all it could muster was 14psi. so was blowing out the back door at 14 psi. if so. pump ratshit. probably in that spring thing. either backflowing down supply line frpm tank because rubber tip on pin is rooted or not there or not seated properly. or the spring is catching and the whole jigger is jammed open letting it flow out of the final escape port back to the tank. Yeh Sunday I got in the car, hit the key and immediately fired and idled great. I didn’t drive the car because it had been raining. Got under the car and checked the fuel hoses from the tank, we’re ok. Hooked up my pressure gauge to the test nipple and read 23psi, clamped the hose before the PR with hemostats and read dead head pressure, 43psi. Then I checked pressure straight out of the pump 14psi |
wonkipop |
Jul 15 2024, 10:53 PM
Post
#4
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Advanced Member Group: Members Posts: 4,611 Joined: 6-May 20 From: north antarctica Member No.: 24,231 Region Association: NineFourteenerVille |
so let me get this right with the test you did. you unplugged fuel regulator and plugged line and tested and got 43 psi. that means your pump could only muster 43 psi before it was blowing out the back door. a good one will get to about 60-70 psi. thats basically the same test i did on my rebuilt pumps if i understand you right. we were using a guage that had an adjustable tap on it. setting it to values of first 28 then 35 simulating the fpr. it was making it. then we kept cranking it until we got it to shoot out port 3. happened at 60-70 depending on the pump i was testing. additional to the ultimate pressure test the whole deal has to be able to do those two values i posted. theoretically with the fuel pressure regulator plugged in and being tested it should still be able to make the pressures of 28 and 35 in the injector line even with weaker value of 43 max made by pump. its a bit of a close margin but its there. thats if the fpr is good. unless that 43 is not something its able to make consistently. i'm reading your second test again carefully. so you are saying that once again you plugged line before fpr. ie ultimate test of pump against completely closed line. and all it could muster was 14psi. so was blowing out the back door at 14 psi. if so. pump ratshit. probably in that spring thing. either backflowing down supply line frpm tank because rubber tip on pin is rooted or not there or not seated properly. or the spring is catching and the whole jigger is jammed open letting it flow out of the final escape port back to the tank. Yeh Sunday I got in the car, hit the key and immediately fired and idled great. I didn’t drive the car because it had been raining. Got under the car and checked the fuel hoses from the tank, we’re ok. Hooked up my pressure gauge to the test nipple and read 23psi, clamped the hose before the PR with hemostats and read dead head pressure, 43psi. Then I checked pressure straight out of the pump 14psi yeah when its idling the vac line to the fuel pressure regulator reduces pressure to 28psi - all it needs for idle. so the pump is able to just make that pressure. sort of, against the fuel pressure regulator. enough for it to idle anyway. would have been interesting to give it a bit of stick and see what happens. its got to make 35psi in that circumstance. a bit more stress on it with a hard dead head pressure and its just blowing the relief port open on the pump. it really should be able to climb all the way to somewhere in that vicinity of 60psi before it lets go. really sounds like the spring bit inside that port is all wrong. that little cap on the pump head that is made of soft aluminium holds it all in. from memory its two springs. one inside the other. its like a two stage thing. one spring keeps it against the injector feed port when the pumps off and closes off the port so the injector line keeps pressure. the fuel pressure regulator keeps it pressured at the other end. normal operation of pump can compress that spring and allows delivery to the injector line. the other spring comes in to play when the pressures rise in the pump head and it gets forced further out. that spring resists up to about 60 psi and then gets compressed enough to open the third port, the so called return port. sounds like spring is kaput somehow. when you say you were checking the pressure straight out of pump. which hose or port where you connecting to. was that the third port. the so called return port. straight out of pump it should be able to do the equal of your dead head test. 43 psi. thats at the delivery port. ? |
Artfrombama |
Jul 16 2024, 07:06 PM
Post
#5
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Member Group: Members Posts: 156 Joined: 21-January 24 From: Alabama Member No.: 27,870 Region Association: South East States |
so let me get this right with the test you did. you unplugged fuel regulator and plugged line and tested and got 43 psi. that means your pump could only muster 43 psi before it was blowing out the back door. a good one will get to about 60-70 psi. thats basically the same test i did on my rebuilt pumps if i understand you right. we were using a guage that had an adjustable tap on it. setting it to values of first 28 then 35 simulating the fpr. it was making it. then we kept cranking it until we got it to shoot out port 3. happened at 60-70 depending on the pump i was testing. additional to the ultimate pressure test the whole deal has to be able to do those two values i posted. theoretically with the fuel pressure regulator plugged in and being tested it should still be able to make the pressures of 28 and 35 in the injector line even with weaker value of 43 max made by pump. its a bit of a close margin but its there. thats if the fpr is good. unless that 43 is not something its able to make consistently. i'm reading your second test again carefully. so you are saying that once again you plugged line before fpr. ie ultimate test of pump against completely closed line. and all it could muster was 14psi. so was blowing out the back door at 14 psi. if so. pump ratshit. probably in that spring thing. either backflowing down supply line frpm tank because rubber tip on pin is rooted or not there or not seated properly. or the spring is catching and the whole jigger is jammed open letting it flow out of the final escape port back to the tank. Yeh Sunday I got in the car, hit the key and immediately fired and idled great. I didn’t drive the car because it had been raining. Got under the car and checked the fuel hoses from the tank, we’re ok. Hooked up my pressure gauge to the test nipple and read 23psi, clamped the hose before the PR with hemostats and read dead head pressure, 43psi. Then I checked pressure straight out of the pump 14psi yeah when its idling the vac line to the fuel pressure regulator reduces pressure to 28psi - all it needs for idle. so the pump is able to just make that pressure. sort of, against the fuel pressure regulator. enough for it to idle anyway. would have been interesting to give it a bit of stick and see what happens. its got to make 35psi in that circumstance. a bit more stress on it with a hard dead head pressure and its just blowing the relief port open on the pump. it really should be able to climb all the way to somewhere in that vicinity of 60psi before it lets go. really sounds like the spring bit inside that port is all wrong. that little cap on the pump head that is made of soft aluminium holds it all in. from memory its two springs. one inside the other. its like a two stage thing. one spring keeps it against the injector feed port when the pumps off and closes off the port so the injector line keeps pressure. the fuel pressure regulator keeps it pressured at the other end. normal operation of pump can compress that spring and allows delivery to the injector line. the other spring comes in to play when the pressures rise in the pump head and it gets forced further out. that spring resists up to about 60 psi and then gets compressed enough to open the third port, the so called return port. sounds like spring is kaput somehow. when you say you were checking the pressure straight out of pump. which hose or port where you connecting to. QUOTE was that the third port. the so called return port. straight out of pump it should be able to do the equal of your dead head test. 43 psi. thats at the delivery port. ? I too believe the problem is with the bypass, the pump runs, doesn't leak just no pressure. Pump is headed back to the rebuilders for round 2. Ordered a Pierburg (sp?) from the jungle site to get the car going for the 3+ weeks it's going to take to get my 0 580 463 009 original back. |
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