So, I just did some routine checks/maintainance on the vette. I swapped the maf sensor, cleaned it and the connections, cleaned up the o2 connections, checked for breaks in wires, etc....then i hooked a fuel pressure gauge up.

Key on, ~45 psi of pressure, then after a few seconds, down to 38. cranking shoots up to a little over 40, then holds at 39 at idle. shoots up when engine in revved. Load test is good. everything seems fine, then I turn the key off and dang! pressure falls rapidly to 20 in less than 10 seconds!

Injectors are new bosch injectors from Jon, so I bet that isn't were the problem is. Fuel pump is a year old, regulator is 3 years old, no leaks in the lines. So, i assume its either the regulator or the check valve on the pump.

If it is the regulator, that may be what has been responsible for the poor running of the car. The check valve wouldn't affect that.

Any way to check just the regulator itself. remove the vac. line and see if pressure jumps? What lines could I pinch that would show the regulator leaking and not lead me to guess between it and the check valve?

 

just did the test again. pulled the vac. line from the regulator while running and pressure jumped from 39 psi to 47 psi, idle picked up slightly and got a hair smoother. I don't know if this rules the regulator out or not though....

One thing that really irks me is the excessive popping out of the exhaust that has been occuring lately. Its every 10 or 15 seconds now and you get a loud pop from one side or the other. That would seem to be fuel related...or maybe spark related.

I bypassed the knock sensor not too long ago and the car ran like a top for 2 days. No popping from exhaust, no stumble at idle, no rough cold starts, pulled like a jet, etc. Now, it runs like.... again.

 

Note that with key on, pump running, pressure is ok. But falls dramatically after pump turns off with key still on.*

Also, car running extremely rich.

 

Turned key on, pinched feed line, pressure held. Let go of pinch, pressure fell to 28, but stayed steady, wouldn't drop any further. hmmm....

cranked car up, pressure normal, turn off, pressure won't fall! WTF!? I can't get the pressure to fall anymore! Its sitting at 39 psi, and its been 3 minutes.

How could this be!? you can't have an intermittent leak, can you?

 

Wait a second...I did this test after the car had been sitting all night. Maybe the lines were just empty? Because it isn't loosing pressure now, car still runs bad though.

Maybe that is why it said to do the test AFTER the car is at operating temps.



:o

 

Have you pinched off the return line to see if pressure still drops? That's one way of eliminating the check valve or pulsator which can also cause pressure to drop.

I was kinda suspecting you'd be back after you bypassed the knock sensor. Even if they are new injectors I'd still ohm them. I'd also re-check timing and think about checking valve lash.

 

yeah, i was wondering how long it would be too.

My fp is holding now, I guess the lines were just empty and they were filling up when I was "losing pressure." duh.

anyhow, timing is set at 10 btdc. The popping from the exhaust makes me suspect a fuel issue (doesn't seem to be the case) or a spark retard issue, impossibe. So...valve lash...thats an interesting thought. I haven't had the valves adujsted once on the car, and its quite noisy up top. Couldn't hurt. I'll give it a shot and see what happens.

 

Most likely problem is the puslator, pressure is leaking around the connections.

Easy to check: remove fuel pump assembly and take the pulsator off and replace with a short piece of fuel line and two clamps.

Then check fuel pressure and see what happens when you turn the pump off. I bet the pressure will stay solid for over an hour.

Let me know what you find out.

LannyL81

 

just fyi, pulling the vac line should cause the pressure to go higher.

 

I had lots of rough idel, starting, stalling and just plain harsh running issues, I replaced the MAF burn off relays and the ECM. All problems are gone and she never ran so well.

 

Jim, I replaced the maf sensor and the burn off module (only one on an '85). But, I haven't tried replacing the ecm yet; i think that is next on the list though.

Right, thats why I was thinking that ruled out the regulator from being the problem. I DO have a fp drop problem, it lost all pressure in a little over 6 hours...but that is probably not an issue, at least, shouldn't be causing the car to run bad.

 

DO YOU HAVE A ECM.I HAVE A GOOD ONE I WILL SELL CHEAP

 

i had similiar problem awhile back, however I was also expewriencing cold start problems ( which led me to injector leak-down) anyways I than I changed, fuel pump, pulsator (oem @145,000), fuel injectors ( needed bigger ones for my new combo), and installed an adjustable regulator, and mine fuel lose is gone! runs perrrfect.

 

Do you have an adjustable regulator? Many of the adjustable one's leakdown like that - doesn't hurt anything just causes a sligthly longer start time.