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#16
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Finally got the videos sorted and some of them uploaded.
https://www.youtube.com/watch?v=oZ8XQAew-Ok I pulled over 1/2 a block from an on ramp, shut the engine off with the elec vac pump running then started the camera to show the sound of the pump running (gauge at 15" HG {0 to 8" HG is green, 8 to 15 is yellow, 15 to 28 is red}). Started the engine and merged onto on ramp traffic with impatient drivers behind beeping. The gauge in front of the vac gauge is a boost gauge. As you can see, during cruise it is at around 10 to 12 " of HG, hard acceleration drops it down to 8" of HG. Shifts were smooth with no clunks or flaring. Braking was normal and does not show on the gauge (unless I pump it many times in succession). I have since routed the cable from the pump inside with a cig. lighter plug so I can manually turn off/on the pump. During a steady cruise, if I turn off the pump, the reservoir vacuum drops from 15 to 10 " HG in around 15 seconds. At 10" of HG, shifts are still normal. When it goes below 6" HG is when the shifts get rougher. If I set the vacuum switch to 11" HG to turn the pump on, it may limit the duty cycle of the pump to be a practical system IMO. I did this elec vac pump test because mach4 says it is not viable for automatic transmissions just to see for myself if true. My results says otherwise. I dunno what's different in his setup. Different vac pump? Different reservoir? Differences in VCV and transmission modulator? Different leakage rate in the system?
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked |
#17
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The trade off of designing a large custom vacuum system vs the minuscule chance of a mechanical pump grenading just did not pencil out in the end - particularly since vacuum pumps are easy to inspect and rebuild should bearings start to fail. I don't deny that it's [I]theoretically possible[/] to run at 15", but the safety margin is just too thin for my taste. For me, your test does nothing but reinforce my decision to abandon the concept of an electrical vacuum pump for automatic transmission MB diesels. As others have demonstrated, for a manual transmission MB, it's definitely a viable solution. Of course, everyone is entitled to a different view and different design parameters and the risks associated with operating at different safety margins. This is good data - thanks for sharing. Definitely helps us all learn and understand what's going on.
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#18
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2004 F150 4.6L -My Daily 2007 Volvo XC70 -Wife's Daily 1998 Ford F150 -Rear ended 1989 J-spec 420SEL -passed onto its new keeper 1982 BMW 733i -fixed and traded for the 420SEL 2003 Volvo V70 5 Speed -scrapped 1997 E290 Turbo Diesel Wagon -traded for above 1992 BMW 525i -traded in 1990 Silver 300TE -hated the M103 1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one 1979 Silver 300D "The Silver Slug" -Sold |
#19
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I might go the electric route if the mechanical pump in my E290 ever goes out. Since I have the 722.6 transmission I don't have to worry about vacuum bleed for the transmission.
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2004 F150 4.6L -My Daily 2007 Volvo XC70 -Wife's Daily 1998 Ford F150 -Rear ended 1989 J-spec 420SEL -passed onto its new keeper 1982 BMW 733i -fixed and traded for the 420SEL 2003 Volvo V70 5 Speed -scrapped 1997 E290 Turbo Diesel Wagon -traded for above 1992 BMW 525i -traded in 1990 Silver 300TE -hated the M103 1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one 1979 Silver 300D "The Silver Slug" -Sold |
#20
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This is just a test to satisfy my curiosity. I am not ready to pull the mechanical pump and replace it just yet unless it decides to grenade and the engine survived.
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked |
#21
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Sorry I missed that little detail
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#22
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On which side of the main line did you tee in? Pump side or brake booster side?
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked |
#23
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My pump is rated at around 7 amps @ 12 V, however when I measured current, it was 3 amps. Maybe my ammeter was off, but even at 7 amps, it's not a big honkin pump.
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked |
#24
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I tapped in by temporarily disconnecting "other consumers (c)". EGR is disconnected as is "blue saucer", so this would be a direct port into the main line. My current vacuum gauge is tapped in there too.
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#25
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There is a check valve between the brake booster and pump in my hard vac plastic line. Are there no difference in pressure on either side?
I moved the tee for the vac gauge to the inlet of the vac reservoir. At idle, I am seeing 17" HG now, 2" higher than when the tee was at the VCV. Reving the engine does not drop the vac now, whereas vac would drop when the gauge tee was at the VCV. I have not taken it for a drive yet with the new gauge location.
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked |
#26
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A relatively small vacuum leak can have significant results. When one of my hvac vacuum pods tore, it made shutdown difficult.
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#27
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked |
#28
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The first gauges screen is one I took just now showing vacuum at idle and the second one is one I took some time ago on a hard pull. Note - 1241 F EGT and 9.9 psi boost. Also note the fuel pressure differential - the first one is after stretching the overflow spring. And finally the 146 intake temp is just heat soak from having sat for 10 minutes after getting back from a trip around town.
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#29
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked |
#30
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Once I determined that the VCV continually bled vacuum (and not just bleeding vacuum down to the level required to send the simulated throttle position to the transmission) and the capacity of my electric vacuum pump was not capable of maintaining vacuum within a reasonable duty cycle (30% or so) I abandoned the project.
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