WOW! Maybe this was the problem!!
Thread Starter
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
WOW! Maybe this was the problem!!
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?
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?
Thread Starter
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
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.
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.
Thread Starter
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
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?
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?
Thread Starter
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
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
Maybe that is why it said to do the test AFTER the car is at operating temps.
:o
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
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.
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.
Thread Starter
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
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.
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.
Melting Slicks
Joined: Nov 2005
Posts: 3,323
Likes: 142
From: Green Valley Arizona
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
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
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Le Mans Master
Joined: Apr 2005
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From: The Old Dominion
Thread Starter
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
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.
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.
Burning Brakes
Joined: Jan 2007
Posts: 853
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From: Slinger WI
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.
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.
