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  #1  
Old 11-16-2010, 12:58 PM
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Question Fuel pressure regulator

1991 420 SEL. My fuel pressure regulator is currently off the car due to other work. I connected my hand held vacuum gauge to the rubber hose on the end and there was zero hold. Is this normal? Or should it hold vacuum?

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  #2  
Old 11-16-2010, 01:17 PM
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That is just a vent line that will put fuel into the breather system instead of leaking it onto the hot engine in the case of a regulator failure.
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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE
104.980
Milled & ported head, 10.3:1 compression
197 intake cam w/20 advancer
Tuned CIS ECU
4 ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff
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  #3  
Old 11-16-2010, 02:53 PM
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Dave, I suspect your fuel pressure regulator is shot because the vent line only comes into play if the diaphragm fails directing fuel into the breather hose. It's possible that too great a vacuum could have ruptured the diaphragm, but more likely it had failed before that.
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  #4  
Old 11-17-2010, 09:45 AM
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Fuel pressure regulator.

No. It's not a vent line. It's a vacuum line. The opaque hard plastic kind with little rubber ends. The reg. comes with a built in rubber nipple that the hard plastic vacuum line attaches to. The other end connects to a two teat (tit) temperature switch on the intake manifold. (The red one) The other tit connects a vacuum line to the throttle body that lives under the intake manifold. At least thats the way mine is plumbed.
I was hoping that someone who owns a hand held vacuum pump could just walk out and connect the pump to the rubber nipple on the reg. and let me know if theirs hold vacuum or not. The reg. MB P/N is 043 816 10 13.

TIA, Dave
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  #5  
Old 11-17-2010, 01:23 PM
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That is plumbed wrong. The line from the pressure regulator should go directly to the breather hose in the passenger side valve cover.
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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE
104.980
Milled & ported head, 10.3:1 compression
197 intake cam w/20 advancer
Tuned CIS ECU
4 ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff
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  #6  
Old 11-17-2010, 04:13 PM
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Quote:
Originally Posted by duxthe1 View Post
That is plumbed wrong. The line from the pressure regulator should go directly to the breather hose in the passenger side valve cover.
Thanks. I got my "wires" crossed. The red top temp switch vac line goes to the EGR valve. (I think) The fuel reg. vac line (and "they" used vac line) goes to a side nipple on the breather hose from the valve cover to the air cleaner. But the question remains. Should the fuel reg. hold vacuum like say the EGR valve? Or, is it really a vent?
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  #7  
Old 11-17-2010, 07:18 PM
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Posts: 4,101
It is a vent, nothing more. If the diaphram ruptures, the fuel that leaks will need a place to go, that place is the breather hose in the right valve cover.
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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE
104.980
Milled & ported head, 10.3:1 compression
197 intake cam w/20 advancer
Tuned CIS ECU
4 ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff
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  #8  
Old 11-18-2010, 09:02 AM
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Quote:
Originally Posted by duxthe1 View Post
It is a vent, nothing more. If the diaphram ruptures, the fuel that leaks will need a place to go, that place is the breather hose in the right valve cover.
Thanks, sanity check SAT.
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  #9  
Old 11-18-2010, 10:16 AM
david s poole
 
Join Date: Mar 2005
Location: dallas
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that line is not even vacuum it is depression[maybe 1/2 inch vacuum] with engine running.it is there as a safety in case the diaphram ruptures,which i have never seen happen.
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  #10  
Old 11-19-2010, 07:24 AM
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Quote:
Originally Posted by david s poole View Post
that line is not even vacuum it is depression[maybe 1/2 inch vacuum] with engine running.it is there as a safety in case the diaphram ruptures,which i have never seen happen.
Thanks Dave. Had my "wires" crossed.

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