Help me please
Thread Starter
Drifting
Joined: Feb 2013
Posts: 1,464
Likes: 48
Help me please
My 89 6 spd is not running well. So I did a fuel pressure check. When I turn on the key the fuel pressure is about 10 psi. When I shut the key the pressure goes immediately to zero. If the car is running the fuel pressure is a steady 39/40 psi.I purchased a FP regulator and plan on installing it today. I decided to take a look at the timing. When I disconnect the EST plug the car stalls out, almost immediately. Looking at the back of the intake plenum on the passenger side there are two vacuum ports. One is for the FP regulator and one that has a hose that is about 1/4 inch ID. I disconnect that hose and the car will idle with the EST disconnected. I tried to search what the hose goes to but I could not find a diagram of the plenum that describes the hose or what it connects to. I think it might be the cruise control, checking today. But, what I really do not understand the car has been running fine for over a year. Now I have to disconnect this hose to get it to run. I set the timing to 6 BTC. When I connect the EST it moves to 8 BTC. The fuel pump is new. A few weeks and only a few hundred miles. Thank you in advance.
Heel & Toe
Joined: Jan 2022
Posts: 20
Likes: 7
The hose for that port runs under the plenum to the drivers side and connects to a check valve. The check valve has two hoses connected to it, one for HVAC and the other for cruise control and other vacuum operated items,
Thread Starter
Drifting
Joined: Feb 2013
Posts: 1,464
Likes: 48
Thank you. I kinda thought that is what it did. What I don't understand is the car was running fine. And now it has this problem and if I remove that hose the car idles correctly. This is a recent development. Very frustrating. I am on Guam working for the Navy. I left all my tools home and the auto hobby shop, a garage on base where we rent work space, is only open on Friday afternoon and Saturday. they were closed this weekend. So I have to wait another week to do anything at all.
Thread Starter
Drifting
Joined: Feb 2013
Posts: 1,464
Likes: 48
What I don't understand is why I am not getting 40 psi when I turn on the key. It's like 10 psi. When I start the car I have 39/40 psi steady. I have the vacuum line to the HVAC Cruise control disconnected and unplugged the car idles fine. Timing is 8 before TDC with the EST connected and 6 with it disconnected. If connect the vacuum hose it will stall. I'm going to order a check valve. Thank you all for your help.
Some one on FB mentioned a FP with a residual valve. That does not make any sense to me. Because when I turn the key to run the FP should send fuel and being the injectors have not received a pulse the fuel is trapped between the FP and the injectors.
Some one on FB mentioned a FP with a residual valve. That does not make any sense to me. Because when I turn the key to run the FP should send fuel and being the injectors have not received a pulse the fuel is trapped between the FP and the injectors.
Racer
Joined: Feb 2024
Posts: 268
Likes: 113
From: New York
A few thoughts:
When you key on the pressure should jump up to around 40psi. Although you have steady pressure at idle, your pump may be on the way out.
When you create a vacuum leak it idles. Does the car show any signs of running rich? Black smoke or rich smelling? What do the plugs look like? And what if you create a vacuum leak somewhere else? Like pull the PVC valve out of the valve cover. Or pull the PVC valve out all together. Does it behave similarly to disconnecting that vacuum line?
I wonder if your IAC is working? The ECM should command the IAC to open when your idle drops too low. This would have the same affect as creating a vacuum leak.
Datalogging would be very useful in this situation. Requires a laptop PC, an ALDL to USB cable, some free downloaded software/files and a small learning curve.
When you key on the pressure should jump up to around 40psi. Although you have steady pressure at idle, your pump may be on the way out.
When you create a vacuum leak it idles. Does the car show any signs of running rich? Black smoke or rich smelling? What do the plugs look like? And what if you create a vacuum leak somewhere else? Like pull the PVC valve out of the valve cover. Or pull the PVC valve out all together. Does it behave similarly to disconnecting that vacuum line?
I wonder if your IAC is working? The ECM should command the IAC to open when your idle drops too low. This would have the same affect as creating a vacuum leak.
Datalogging would be very useful in this situation. Requires a laptop PC, an ALDL to USB cable, some free downloaded software/files and a small learning curve.
Last edited by C4industries; Mar 29, 2025 at 08:36 PM.
