Fuel pressure issue

Alex_Murrica

SCCoA Member
Hey guys, I just finished putting my car back together after rebuilding the trans, doing an intake manifold and some top end gaskets, replacing the fuel pump and putting some new exhaust pieces on. Yesterday she made her first drive out of the neighborhood and ran great but when I went to start it back up to go home it would just turn over and wasn't even trying to start. I got some carb cleaner and was able to get it to run so I knew it was a fuel issue. I then turned the key on and messed with the fuel lines near the filter and towards the tank and hit the bottom of the tank trying to jar the pump into priming and it did and I was able to get it to run. It drove home flawlessly but this morning I go to start it and the fuel pump is priming every time the key is on, but when I hit the schrader valve it has some pressure initially but after that there's no continuous flow. I'm wondering if there is a check valve stuck somewhere or if my pressure regulator is bad. It's just strange how it's priming and has no pressure after. Thoughts?
 
Still haven't gotten anywhere with this, any suggestions would be appreciated. Car start with starter fluid and runs fine on its own after that but once shut off it just cranks and won't start. Fuel pump and filter have been replaced. Fuel pressure regulator maybe?
 
When you hit the Schrader valve? Like, open the valve and let it squirt out?

If so, I wouldn't expect any continuous flow. The car is supposed to prime once at key on. The fuel pressure regulator allows it to hold pressure until the engine starts. Then a second trigger circuit activates the relay. I think this helps to save the pump from excess wear, and to prevent a massive fuel leak if anything goes wrong.

Have you checked the fuel pressure with an actual gauge to see if pressure is holding? And if the fuel pressure keeps up as you drive?
 
Could be regulator. Did you replace the pump before or after this started happening?

Yes, but it ran fine for a few days before this issue and I've taken the new pump out and put the old one in and it has the same problem.


When you hit the Schrader valve? Like, open the valve and let it squirt out?

If so, I wouldn't expect any continuous flow. The car is supposed to prime once at key on. The fuel pressure regulator allows it to hold pressure until the engine starts. Then a second trigger circuit activates the relay. I think this helps to save the pump from excess wear, and to prevent a massive fuel leak if anything goes wrong.

Have you checked the fuel pressure with an actual gauge to see if pressure is holding? And if the fuel pressure keeps up as you drive?

I haven't checked it with a gauge yet, but the car acts normal once it is started. Do you think it could be a relay? The schrader valve has pressure after it primes and when the car is running. You're saying that I should only get one good squirt after the pump primes?
 
Yep, one good shot of fuel releases the built up pressure in the line, but there is no flow. You NEED to get a pressure gauge on it to see what it is doing. I got a fitting designed to feed NOS systems off the Schrader valve and a cheap pressure gauge and just pull the guts out of the valve and thread the gauge on with a piece of -4 braided line. When you shut it off the pressure SHOULD stay in the line for quite a while, or bleed off very slowly (like over 30 min-1hr maybe). If it does not hold pressure it indicates a problem, bad injectors (sticking open, even if the car runs OK), a check valve in the system, or possibly a regulator. If the car runs WELL I would not think the injectors r the likely problem. I have had regulators diaphrams rip, but the car will run pig rich when that happens, as fuel is pulled into the motor thru the vacume lines:eek: Again, if the cars is running good that is less likely. I am not sure how the check valve is used, or where it is in the SC system.

When you describe the pump as "not priming", do you still hear the pump turn on and run for around 5 seconds EVERY time you turn the key from off to run? I have also had intermittent pump relay failure, where for a couple weeks, banging on the tank would cause the relay to function for a while again (89 MK VII LSC relay in the trunk above the tank). Once running it would run great, but it was a crap shoot as to if it would start the next time, or be fine for a week at a time. Otherwise if you have to do the bang on the tank to get the pump to cycle, you have something wrong with tank/pump (bad electrical connections, just a plain bad pump, possibly junk/sludge in the tank). Speaking of ugly in the tank, have you replaced the fuel filter? Cheep ins, and I always fall back to that one when weird fuel problems come up.

Good luck

Adam
 
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Finally got to testing the fuel pressure with a gauge. When it primes it has 40 psi, once started (still using starter fluid) it holds 33 psi at idle and goes up accordingly with throttle. Once the car is off it still holds 40 psi (its now an hour later and still at 40). So not the pressure regulator. I've also ruled out the relays and inertia switch, I did the Hayne's method of jumping the test connector to get the fuel pump to run. New fuel pump and filter. I've tried everything I can think of related to fuel delivery. I still don't think it's a spark issue because it runs fine after it starts with a shot of starter fluid.
 
Seems odd it came out of the blue...did you check the fuel safety/impact switch in the trunk? What do you know about the history of the IRCM and EEC? Did you check the ignition switch down on the right side of the steering column inside the lower dash? Do you have any angry neighbors that may have messed with your fuel supply?
 
Seems odd it came out of the blue...did you check the fuel safety/impact switch in the trunk? What do you know about the history of the IRCM and EEC? Did you check the ignition switch down on the right side of the steering column inside the lower dash? Do you have any angry neighbors that may have messed with your fuel supply?

Haha, I shoveled most of my neighbors out of the snow this winter I would hope not! I've messed with the safety switch and it's working properly. I don't know of anything dealing with the IRCM or EEC being done. Is there an EEC relay somewhere I could check? I will definitely check the ignition switch, I've had problems with components in the steering column before.
 
I had a similar problem on mine last year. I was carrying a can of starting ether with me in case it wouldn't start. It turned out to be a leak in the air inlet tube at the throttle body. The hose clamp was on cockeyed and it leaked. It would run fine, just didn't want to start unless the engine was cold. Check for a leak between the MAF and the TB. Check the hose and tube that runs over to the left side valve cover.
 
The engine can't run if the EEC relay is bad. No power to EEC, no run. You have fuel pressure it seems at all the normal times and under normal conditions so it would seem it's not fuel delivery. The injectors themselves are ground switched in the EEC. I highly doubt that circuit has failed. It should be noted though that the injectors are supposed to have power at all times the key is on. Check for power at any red injector wire. If they have power, then check for pulsing during engine crank/run. A small light bulb or 12v LED will suffice.

I would say that most likely since you had the top end of the motor apart, you may have an issue with a main harness connector. This is assuming of course that you re-assembled everything correctly, things like the injectors sitting down properly in the heads, inlet plenums sealed properly, IC tubing, etc. If it runs normally when it runs, then most likely it's an intermittent connection issue with a wiring harness.
 
Just checked for power at the injectors and all of them have 12 volts key on. I'm trying to find the ignition switch under the dash now. All the relays I've found seem to be working.
 
Since the motor won't fire during cranking with out external fuel, but then WILL run when key is in run, you need to recheck for injector power during crank, when the key is all the way forward to engage starter. What Dave said about the ignition switch seems very likely, these rigs will do all sorts of weird stuff when the switch in the column goes bad, and dropping power to one circuit it shouldn't sound like one of them

Adam
 
I'm trying to find the ignition switch under the dash now.

The reason I brought it up earlier is that the original switches seemed to have a bad habit of opening up and causing a raft of issues. Remove the two-piece surround where the steering wheel meets the dash (3 screws from below...example is early SC) - tilt the wheel to get them both clear, then look down on the right side of the steering column - see if the switch has coming apart. You'll need a torx bit to swap it out. A new switch is about $10 or so, I think. Example: http://www.autozone.com/autozone/pa...rd/_/N-igp61Z9rigt?itemIdentifier=368100_0_0_

Good luck.
 
The reason I brought it up earlier is that the original switches seemed to have a bad habit of opening up and causing a raft of issues. Remove the two-piece surround where the steering wheel meets the dash (3 screws from below...example is early SC) - tilt the wheel to get them both clear, then look down on the right side of the steering column - see if the switch has coming apart. You'll need a torx bit to swap it out. A new switch is about $10 or so, I think. Example: http://www.autozone.com/autozone/pa...rd/_/N-igp61Z9rigt?itemIdentifier=368100_0_0_

Good luck.

I had one go bad on me before and it fell apart, the one in there now looks ok but I'm going to replace it because it seems very plausible.
 
So just for the heck of it I switched out my 70mm throttle body for the stock one and now the car starts and runs fine. I don't understand but I'll take starting over some throttle response.
 
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