Idle problems - Page 3

You could very well have a bad fuel pressure regulator. Try unplugging the vacuum line to the regulator while it's running, the pressure should go up a little, and see if the idle smooths out any when you unplug it. Let us know what the results are.

quote:

ORIGINAL: lbelew

Thanks again guys. Wondering if a slight rattle in my catalytic converter can cause my idle problem. Also hooked up a pressure gauge to my schraeder valve and am reading 28psi, a little low. When I plug the return line I get 70psi. If I run the car with the return line returning the fuel to a gas can I get 28psi. What do you think.  No codes present but still erratic idle a low power off the line and crappy cruise performance. No surges at power but not alot of power.

 
The TPI article said proper fuel pressure had to be confirmed under three circumstances.
 
I don't remember what each tells ya', but obviously each readin' is important...
 
Early c4's have an exhaust resonance problem at 2000 - 2200 rpm. I doubt it's tied to the motor tune problem.

Just unplugged the fuel regulator and pressure went from 28 to 38psi, still rough idle though. Do you think the noisy cat could trip the knock sensor. Thanks.

quote:

ORIGINAL: lbelew

Just unplugged the fuel regulator and pressure went from 28 to 38psi, still rough idle though. Do you think the noisy cat could trip the knock sensor. Thanks.

 
Yeah possible, but I still doubt that's what's goin' on here...
 

Do you think its my fuel pressure regulator based on the psi increase.

quote:

ORIGINAL: lbelew

Just unplugged the fuel regulator and pressure went from 28 to 38psi, still rough idle though. Do you think the noisy cat could trip the knock sensor. Thanks.

 
OKAY...
 
I just went back and looked at the TPI article. It says 43.5 is proper pressure for most years of TPI.
http://www.corvetteforums.com/upfiles/5243/89F34528C1E141548C7EB4DAF97A25E6.jpg
http://www.corvetteforums.com/m_37283/tm.htm

43.5 with NO vacuum.
 
...and 1 psi drop for every 2 inches of vacuum. You got a 10 psi difference, which means 20 inches of vacuum (20 INCHES OF MERCURY IN A BAROMETER).
 
AIN'T NO WAY. Check your reading again. If the numbers you got are right, that's the problem...

I've got a 15-18 inch's of vacuum on my motor. If I had 20 inch's, the change from 28 to 38 is just right( 1985 had 40psi unlike the 1986 and later.) or am I missing something here. What is the normal reading for vacuum on a 1985.

Mine runs fine with 32 psi fuel pressure. If yours didn't smooth out when you unplugged the vacuum line then I feel like you have something else causing your problem. Try this....loosen the bolt thats holding the distributor down just enough so you can turn it. Crank the car, then turn the distributor both ways (raise and lower) just a little and see if it runs any smoother. be sure to mark the distributor somewhere so you will know where to set it back if this doesn't help any. Thats basically how I found my problem. My timing was set too high, which BTW was set by mr goodwrench.
 
Hope your engine hasn't jumped timing.

quote:

ORIGINAL: lbelew

I've got a 15-18 inch's of vacuum on my motor. If I had 20 inch's, the change from 28 to 38 is just right( 1985 had 40psi unlike the 1986 and later.) or am I missing something here. What is the normal reading for vacuum on a 1985.

 
Yeah, BUT, the article says when you plug back in the vacuum line to the regulator, you will get a 1 PSI drop for every 2 inches of vacuum.
 
You're gettin' a 10 PSI difference, which means a 20 inch swing in vacuum. That's way off!!! A hurricane doesn't cause that much variation in barometric pressure
 

I've varied my timing from the recommended 6 btdc to 12 btdc. It runs smoother the further I advance it but the best running timming makes her ping. Reading the service manual they say I should have 34-39psi fuel pressure, I've only got 28 with vacuum. What kind of reading do you have on yours without vacuum. Also wondering if my cat is creating a backpressure issue. Thanks.  

I have about 37 psi with the vac unplugged. Listen to your exhaust, is it making a hissing sound if so I would suspect a clogged cat.  Have you tried un plugging your sparkplug wires one at a time to see if you have a cylinder misfiring? Have you done a compression test on all eight cylinders?

Another pressure reference in the article, page 6, 3rd column, near the bottom:
 
below 35 psi, you get poor air/fuel mix, and idle and driveability problems. Is this the problem???

1990 with same problems should I try the same fixes or is the cars different? Can only get about 12 degrees advance before engine stumbles badly?

On L98 engines the timing should be set at 6 degrees BTDC with the timing set connector unplugged. The timing set connector is located beside the distributor on the passengers side, it's a single, (brown and black I think) wire coming out of a wiring harness. Be sure to reconnect it after the timing is set.

Well guys, the saga comes to an end. Found the consolidated ground on the drivers side head had a nut that was close to vibrating off, tough to see, but still visible. Appreciate all of the good advice and a special thanks to rshiver.

Congratulations man, glad you finally got it, now go and enjoy your Vette.
 
Cheers

quote:

ORIGINAL: rshiver

Congratulations man, glad you finally got it, now go and enjoy your Vette.

Cheers

 
I told you !!! Wouldn't listen to me tho', huh? Noooooooooooooo... Vacuum leak, huh? Where did you get that idea anyway? Comic book? Horoscope? Psychic hotline???
 
 

....THANK GOD THATS OVER WITH

quote:

I told you !!! Wouldn't listen to me tho', huh? Noooooooooooooo... Vacuum leak, huh? Where did you get that idea anyway? Comic book? Horoscope? Psychic hotline???

 

quote:

ORIGINAL: rshiver

quote:

I told you !!! Wouldn't listen to me tho', huh? Noooooooooooooo... Vacuum leak, huh? Where did you get that idea anyway? Comic book? Horoscope? Psychic hotline???

 
It's a joke.

No doubt in my mind man, BTW..... Happy Birthday!!!

quote:

ORIGINAL: rshiver

No doubt in my mind man, BTW..... Happy Birthday!!!

Thanks!

Yeah... Humor's a little dry sometimes...

I was on that guy's motor from the beginning there, and was wrackin' all two brain cells on it tryin' to get a solution on it there. 

Yeah...I know what you mean, I've seen one other case where it was a bad consolidated ground, it was on an 86 Chevy pickup and it had about 3 or 4 ground wires that bolted to the thermostat housing and a couple of them had broken. But it never crossed my mind at all to check that...DUH!. Oh well...live and learn.