164Q and LS fuel rail pressure

velocedoc · #1 (**permalink**) 07-14-2005, 08:47 PM

What is the fuel pressure for the 164 LS and Q models? I measured the fuel pressure before the regulator and got 10 lbs. After the fuel regulator I got 35 lbs at 2500 rpm and 45 lb. at idle. Is this enough?

**Alfisto Steve** · #2 (**permalink**) 07-14-2005, 10:29 PM

If you mean after regulator on return line to tank you got 10 psi and before regulator as in fuel rail pressure line in or at short line into fuel regulator from front rail, that sounds about right. Fuel Pressure at idle with vacuum hose to intake disconnected is 42 to 47 psi. With vac hose reconnected pressure should decrease about 7 psi at idle to 35 to 40 psi then increase when throttle opens and intake vacuum drops.

If you mean after regulator on return line to tank you got 10 psi and before regulator as in fuel rail pressure line in or at short line into fuel regulator from front rail

velocedoc · #3 (**permalink**) 07-15-2005, 07:10 AM

I took the incoming fuel line off before the regulator and that is where I got the 10 lb. pressure which would be from the fuel pump. The 35-40 lb pressure was at the fuel rail where the cross over return pipe was behind the regulator. I can now see where the increase came from because I forgot to disconnect the vacuum line to measure the highest pressure. Sounds like things are ok in the fuel department. Thank you for the response.
Christopher Boles
1995 Q

**Alfisto Steve** · #4 (**permalink**) 07-15-2005, 09:31 AM

Chris I am sure fuel pressure is OK but your definition of before fuel regulator and 10 psi has to be after pressure regulator outlet side which is return to fuel tank and from fuel pump. This is residual bypassed pressure that regulator bleds off back to tank.

Fuel pump pressure comes into fuel rail/fuel dampner above timing belt cover near dog bone engine top mount that has to be the 42-47 psi feeding engine.

velocedoc · #5 (**permalink**) 07-15-2005, 10:18 AM

This is what I measured...45 psi at idle and 35 at road speed. I am probably sure this is ok pressure, and to be on the safe side, being it looks original... I will replace the unit, then there is not questions.

BlackAlfa · #6 (**permalink**) 07-15-2005, 11:17 AM

While we are talking about fuel, just want to give another reminder!

If your fuel injection rubber hose does not look only a couple years old, soft and flexible, REPLACE them !!!

We took our "new" 91L (211K) to NYC and we smelled fuel when we got there. Yup, there's a dripping leak at the regulator connection

! I cut the old hose shorter and made a temporary fix (hose was hard so it was not a good fix). We drove around Brooklyn Saturday and went to a few parts store, they either didn't have any FI hose or the longest one I can get is 18"

! 18" is not quite enough for the hose that goes to the firewall. Anyway I bought that and also some non-FI rated hose as backup. Luckily, we made it back to Boston without any more noticable leak. I have ordered a few feet FI hose from IAP and they were put in last night!

Still need to do the couple short sections behind the engine some time

!

Bob

alphalvr · #7 (**permalink**) 07-30-2005, 02:44 PM

i have just fitted (almost complete) a fuel pressure gauge in the car, ive had it working and remember it being around the 50psi mark while driving but when its fully funtional in next few days ill let you know my fuel pressures
but it sounds fine.

evilgidget · #8 (**permalink**) 10-30-2005, 10:13 PM

Correct me if i'm wrong here, but am I correct that the hose on the left side of the engine bay that passes over the timing cover & straight to the front rail is the one that you measure the pressure from? Also, is my assumption that just turning the key to "on" without starting the car should get approx 40lbs pressure at that point pretty much immediately? Just wondering as my current hard start/driveability problem has got me to checking fuel pressure & at that point all i'm getting is a shade under 10lbs and it's not fast getting there...

**Alfisto Steve** · #9 (**permalink**) 10-31-2005, 03:33 AM

No unless somebody has hard wired pump you do not get fuel pump to run by just turning key on. I just bought a 164 this year where that was what was done. I rewired it correctly.

Also had hose come off in tank so had no fuel pressure one day while driving car.

Hose on top of timing belt cover is pressure hose to inlet of fuel rail and if system OK you will have trapped pressure in that hose at all times so engine can start right up.

Fuel pump starts to run when you start engine. If you only get 10 psi at inlet side of fuel rail I suspect cracked short hose in tank.

Shade tree mechanics sure can screw up a 164 by jeery rigging systems they know very little about.

evilgidget · #10 (**permalink**) 10-31-2005, 05:20 AM

Fuel pump runs constantly. Knowing some of the other repairs the PO's mechanic has done in the past, it doesn't surprise me.

Split hose makes sense. I have a suspicion that there was air in the system when I measured, and the pressure took a good minute of fuel pump whining to build up to it's 10lbs...
I was hoping to change the fuel filter just to eliminate that, but I ran out of light after work. Doubt it's that anyway as it's only been a month since I changed it.

Will try to pull the pump tomorrow & have a look.

Thanks Steve.

**Alfisto Steve** · #11 (**permalink**) 10-31-2005, 08:14 AM

Pump in tank so you have to pull front wall carpet in trunk to get to access plates. If you have a ski boot it comes out with front wall carpet and you can work through ski boot from back seat too. There is a black plastic 2 piece cover over tank then a round tank cover with 8 bolts probably with small allen heads.

Note two Plastic pipes under a metal bar. One is pressure one return note ends color coded. Remove bigger rubber hose to vapor cannistor, smaller hose to vent and disconnect electrical connector.

Tricky to lift pump assembly out of tank do not break basket that stainless steel straps are attached to.

Use SAE30R10 submersible fuel injection hose if possible as you probably will find either cracked 1 1/2" hose with fabric outer lining (OEM type installed) or a flabby improper rubber hose if previously replaced.

Basket should have a good antiviration pad on the bottom. Be sure tank and filter screen inside basket clean.

I also use small rubber orings under head of cover bolts to ensure gas fumes do not enter trunk after reassembly.

picture of pump parts:
http://www.alfabb.com/bb/forums/show...ight=fuel+pump

I found my pump hard wired to a wire run from fuse box cigarette lighter power bar to pump wire under right corner of rear seat. It would turn off with key and on as soon as key turned on. At least they put in an in line fuse in wire. I bet you PO mech did something similiar because car was hard to start due to little or no fuel pressure.

evilgidget · #12 (**permalink**) 11-01-2005, 01:28 AM

Short hose turned out to be split end to end. I think the fuel pump was running constantly because there plain & simply wasn't enough pressure in the system. Notably my tank was different from what I think you US people have as my tank is plastic & has a screw-on plastic retainer ring for the pump. Much cursing before it moved...

All is well, now just have to replace all the other fuel lines in the car to clear up the fuel smell. And readjust the AFM as the increased fuel pressure has now resulted in black smoke again. A minor adjustment to fix that, then i'll have to....

(it never ends, does it...)

Thankyou

**Alfisto Steve** · #13 (**permalink**) 11-01-2005, 02:59 AM

Adjustment on AFM is for idle bypass screw and should not be much help for black smoke under power. Recheck your fuel pressure and plugs to see if you have another injector leaking.

Be sure fuel pressure regulator is adjusting pressure to about 40 psi and vacuum hose to intake is hooked up and will cause pressure to drop and rise about 7 psi when throttle opened to drop vacuum

Also check adjustment on min/max switch on throttle body that is clicks between 0 to 1 degrees for min setting to be sure it shuts off fuel on decel. It also has wide open throttle switch in it to enrich fuel at max WOT. Use a meter to check between pin 2 and 18 and 3 and 18.