Need replacement FPR?

[RoughRex]

88 N/A won't start, it turns all day but barely catches if at all.

SPARK is good, new plugs checked individually to fire while turning over.
COMPRESSION test (Poor mans version) appears to be OK.
FUEL:
41 PSI measured after filter -> 56 PSI measured if blocking fuel flow
0 PSI measured on return line with flow unobstructed

The part that bothers me here is that I get 56 PSI while obstructing fuel flow... if the FPR is blocking flow why am I not seeing higher PSI on the feed side? Is it getting forced through the injectors?

[jfaplanet]

Jason, I got a new one here that I bought for a friend that never needed it.

Your welcome to try it and see if it fixes the problem. Working Saturday till 1pm, but should be home later Saturday and most of the day Sunday if you want to pick it up.


Charles

[RoughRex]

Charles... you are the man. PM me your number please, I'll give you a call tomorrow afternoon.

[RETed]

I don't understand your original question...

Where did you "obstruct" flow?
Did you pinch the hose?
Where?
After fuel filter, before injectors?
Between rails?
After FPR?

Think of the FPR as a bleeder, relief valve.
If the pressure goes higher than it's setting, then it allows the fuel (pressure) to bypass.


-Ted

[FRED]

41 psi is close to normal on a car that is not running and only the fuel pump running. Car should start easily with 41. Normal is 37-39 psi on a non running engine.

The 54 psi is abnormal.............but heck, the car isn't even running so it matters not when talking about Starting the engine 'cause 41 is plenty fine for that. Idle pressure is in the 28-32 psi range.

Normally if checking just the pump output you'd install a pressure gauge on the outlet line of the filter (as in dead end the hose using the gauge) then turn the pump on. Normal is in the 70-80 psi range (memory, see book for exact figures).

[djmtsu]

Jason, you only have a few weeks.....

[RoughRex]

I don't understand your original question...

Where did you "obstruct" flow?
Did you pinch the hose?
Where?
After fuel filter, before injectors?
Between rails?
After FPR?

Think of the FPR as a bleeder, relief valve.
If the pressure goes higher than it's setting, then it allows the fuel (pressure) to bypass.


-Ted

My fuel Pressure tester came with a T fitting. I put one end in the hose after the fuel filter and plugged the other end... per my Haynes manual, the pump should produce 57 PSI when the flow of fuel is obstructed, in the example they ran the hosed directly into their pressure gauge but I could not configure mine this way.... I got 56 PSI during my test.

Also per the 'ole Haynes manual, I should get 35.6 - 37.0 PSI on the return line without vacuum. I checked my return line both on the drivers side where it comes out from under the TB and I checked it again directly under the FPR as it shows in the manual.. I got 0 PSI both times with the pump running and no flow obstructions other than the FPR. I even opened the pressure relief on my tester while the pump was running and got nothing coming out.

The problem is that when I test the system pressure by using a T fitting after the filter and with no obstructions other than the FPR.. I only get 41 PSI.

So, I know that the pump will build to 56 PSI if completely stopped up and I know that 0 PSI is coming out on the return line. The question is, where is the rest of the pressure bleeding off if I'm only getting 41 PSI of system pressure? I can hear the FPR hissing so I'm sure there is probably a tiny stream of fuel shooting through it... but I don't know if it's enough to drop 13 PSI. I'm afraid the excess pressure may be forcing fuel through the injectors (Hence why the car won't start) but I would expect it to take more than 41 PSI to cause that.

[RoughRex]

Jason, you only have a few weeks.....

I know... I have been really busy with moving and changing jobs and have been totally unmotivated to work on the car. I am 4 wks into the new job though and things are smoothing out a bit. Plus I AM running out of time :o

[RoughRex]

Dangit.... Nix everything I said.. I misread the f'n manual. 57 PSI is the hold pressure for the pump 5 minutes after shutting it off. I should be hitting 64 - 85.3 PSI with the pump running. I don't suppose you have a fuel pump too eh Charles? lol

Tested before filter and hit 58 PSI...Replaced pump sock and still at 58 PSI.... definitely the pump.

[Pete_89T2]

Dangit.... Nix everything I said.. I misread the f'n manual. 57 PSI is the hold pressure for the pump 5 minutes after shutting it off. I should be hitting 64 - 85.3 PSI with the pump running. I don't suppose you have a fuel pump too eh Charles? lol

Tested before filter and hit 58 PSI...Replaced pump sock and still at 58 PSI.... definitely the pump.

Before you go and replace the pump, did you check the voltage at the pump?

[Mazdabater]

Where is your FPR located? Aren't they supposed to be in the return line?

[RoughRex]

Update, pump replaced... now getting 70 PSI with flow obstructed.

Still getting 0 PSI on return side.

The FPR is located on end of the secondary fuel rail where the fuel return should begin.

I am now getting a trickle of fuel out of the pressure relief valve on my tester when testing the return side... I think my original theory is still the problem, I just happened to catch the pump on its way out too.

[FRED]

Your 88 non turbo fuel, USA version should look just like the jpg attached.

The last thing that is in the fuel system on the engine is the FPR and if the pump is running fuel should pour out of the return line on its way back to the fuel tank as long as the pump is running.

IF fuel is not running out of the FPR on it's way back to the fuel tank then you have something plumbed wrong.

A RX, a stk RX starts with the fuel rail reading 37-38 psi. The 41 psi is not that different and the car should start even if it reads 41psi.

You'd read fuel RAIL pressure by tee'ing in a fuel gauge right after the fuel filter and running the pump. You should see what the FSM states...37-39psi.

I've no idea why your trying to read the fuel pressure on the return side. There should be little fuel pressure there since it's running straight back to the fuel tank.

A 88 non turbo should look like the attached jpg. If you pull the return line off and run the pump fuel should flow out the return line from the direction of the engine.

[RoughRex]

Update... The car is running!

I got the FPR from jfaplanet this evening and installed it... the Haynes manual I have says I should get 35.6-37.0 PSI on the return line without vacuum on the FPR and 28.4 PSI with vacuum... I am STILL getting 0... at this point I'm inclined to believe that the Haynes manual is incorrect.

I'm also inclined to believe that the car wasn't running due to gross stupidity on my part... having initially replaced some very ugly spark plugs, I swapped the leading and trailing wires when re-assembling... the symptoms were the same so I didn't catch my mistake until now. The original problem was the plugs, I'm too stupid to re-attach plug wires correctly.

On the plus side I think I've now replaced darn near every part in the fuel system aside from hard lines and rails...

[RETed]

Good to hear you solved the problem.

The #'s looked good to me, although the "dead-head" pressure was slightly low.
In hindsight, the original fuel pump was on it's way out and replacing it just saved you more headaches later down the line.

The engine should've still cranked, started, and idled even if fuel pressure is off by + or - 10psi. :)

Yeah, I think the manual is wrong - you should not be getting any (or just very slight pressure) *after* the FPR.
If you're getting some pressure after the FPR, that's bad for your fuel system, as you're going to get elevated pressure in the fuel rails!
Not good!


-Ted

[djmtsu]

Good stuff Jason.

Are you caravaning with us or the later crew?

[RoughRex]

My boss just approved that Thursday and Friday off this week.. Since I have the whole day, I'm down for whenever. I'll head out with you guys... the earlier the better!