Which line is the return
01-31-2011, 08:36 AM
#1
Racer
Thread Starter
Which line is the return
This is on an 87 (with 90 MAP intake).
I have had the intake etc off and like a fool, didn't mark the fuel lines. Now I am not certain which is pressure and which is return coming from underneath. One of them has a diaphragm assembly on it beside the water pump however my FSM (87) doesn't show anything on either line. When the PO did the MAP swap, they bent the lines in such a way as now either will fit either port on the rail.
I can hook the battery up and find out which is feed but would be nicer not to.
By the way, anyone know what that diaphragm thing is?
I have had the intake etc off and like a fool, didn't mark the fuel lines. Now I am not certain which is pressure and which is return coming from underneath. One of them has a diaphragm assembly on it beside the water pump however my FSM (87) doesn't show anything on either line. When the PO did the MAP swap, they bent the lines in such a way as now either will fit either port on the rail.
I can hook the battery up and find out which is feed but would be nicer not to.
By the way, anyone know what that diaphragm thing is?
01-31-2011, 10:31 AM
#3
Team Owner
Follow the fuel line from the fuel filter going forward. The feed line filter will be attached to the inside of the frame rail. It's a PITA to follow it up and over the motor mount and under the exhaust manifold but it will point out the end of the feed line. Some 87's have a filter on the return line, but IIRC, they are forward of the feed line filter.
The stock 87 fuel line feeds into the front end of the passenger side fuel rail and the return line is the one coming out of the pressure regulator (in front of the distributor). That return line sits on top of the fuel rail and goes forward to the bracket that holds both connectors.
For the diaphragm, are you referring to the fuel pressure regulator between the back sides of the fuel rails?
The stock 87 fuel line feeds into the front end of the passenger side fuel rail and the return line is the one coming out of the pressure regulator (in front of the distributor). That return line sits on top of the fuel rail and goes forward to the bracket that holds both connectors.
For the diaphragm, are you referring to the fuel pressure regulator between the back sides of the fuel rails?
01-31-2011, 01:19 PM
#4
Racer
Thread Starter
As mentioned, I can power the pump and see which one has pressure, just a messy way to do it.
On this car, both steel lines coming up to the point of attachment are the same size. 1 is just steel line all the way down to under the engine/frame, the other one has what looks like vacuum diaphragm (without a spigot or vacuum hose) inline on the steel line. I did find something that showed on an F body what was being called an "accumulator" on the pressure line before the rail, maybe what it is.
Again unfortunately I don't know if these lines are 87 or 90, turns out to be a lot more 90 on this car than just the hood, door interior and intake. Rear suspension is all 90, all 4 brakes etc etc. However the motor vin matches the car and is 87, but that doesn't mean they didn't use 90 fuel lines when they switched to MAP, car was hit in right passenger corner. My understanding is the switch to MAP wasn't to go to MAP but because of the 90 interior and dash and the need to switch ECM's to 90 for the wiring..
Not a huge deal, will either follow it or pressurize it if need be.
This 87 mixed 90 is ignorant at best, so many changes for a 90, you have to measure everything and find specs to figure out if you need to order 90 or 87 parts
On this car, both steel lines coming up to the point of attachment are the same size. 1 is just steel line all the way down to under the engine/frame, the other one has what looks like vacuum diaphragm (without a spigot or vacuum hose) inline on the steel line. I did find something that showed on an F body what was being called an "accumulator" on the pressure line before the rail, maybe what it is.
Again unfortunately I don't know if these lines are 87 or 90, turns out to be a lot more 90 on this car than just the hood, door interior and intake. Rear suspension is all 90, all 4 brakes etc etc. However the motor vin matches the car and is 87, but that doesn't mean they didn't use 90 fuel lines when they switched to MAP, car was hit in right passenger corner. My understanding is the switch to MAP wasn't to go to MAP but because of the 90 interior and dash and the need to switch ECM's to 90 for the wiring..
Not a huge deal, will either follow it or pressurize it if need be.
This 87 mixed 90 is ignorant at best, so many changes for a 90, you have to measure everything and find specs to figure out if you need to order 90 or 87 parts
01-31-2011, 01:37 PM
#5
Le Mans Master
87 should have one line smaller than the other, the smaller line is the return. (16mm vs 14mm)
90 would have both the same, as stated before, trace from down below the pass side qtr panel where there is a big fuel filter (if they both have one, the return line will be much smaller size filter/adaptor) and trace up. The one with the filter is the feed.
90 would have both the same, as stated before, trace from down below the pass side qtr panel where there is a big fuel filter (if they both have one, the return line will be much smaller size filter/adaptor) and trace up. The one with the filter is the feed.
01-31-2011, 01:41 PM
#6
Le Mans Master
87 should have one line smaller than the other, the smaller line is the return. (16mm vs 14mm)
90 would have both the same, as stated before, trace from down below the pass side qtr panel where there is a big fuel filter (if they both have one, the return line will be much smaller size filter/adaptor) and trace up. The one with the filter is the feed.
90 would have both the same, as stated before, trace from down below the pass side qtr panel where there is a big fuel filter (if they both have one, the return line will be much smaller size filter/adaptor) and trace up. The one with the filter is the feed.
I have mine off and marked 91. when I get home I will look and post it for ya.
01-31-2011, 08:45 PM
#7
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I just hooked these up on mine. I was surprised to find they are interchangeable at the manifold fittings!
I looked at the regulator at the back of the intake and followed the tube that comes from it to determine the return line. The return line hose is the one with that diaphragm looking thing and I believe is the outer - closer to the passenger side - fitting on the intake (which goes back to the fuel regulator on the intake).
I'm thinking that diaphragm looking thing is some kind of a check or bleed valve to maintain a little pressure on the injectors when turned off so when you go to start it there is not a large volume of air in the lines, etc.
I looked at the regulator at the back of the intake and followed the tube that comes from it to determine the return line. The return line hose is the one with that diaphragm looking thing and I believe is the outer - closer to the passenger side - fitting on the intake (which goes back to the fuel regulator on the intake).
I'm thinking that diaphragm looking thing is some kind of a check or bleed valve to maintain a little pressure on the injectors when turned off so when you go to start it there is not a large volume of air in the lines, etc.
01-31-2011, 09:19 PM
#8
Le Mans Master
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Is there to dampen pulses ( vibration) in the return line
The regulator does that
Easier to look at the supply line to the fuel rails because return comes from reg
In any case the inboard line is alway the supply line on a TPI ;
the steel line from flex hose attachment point goes straight into the rail whereas the return is a long line alongside pass side fuel rail to the reg at rear
In any case the inboard line is alway the supply line on a TPI ;
the steel line from flex hose attachment point goes straight into the rail whereas the return is a long line alongside pass side fuel rail to the reg at rear
Last edited by rodj; 01-31-2011 at 09:26 PM.
