RE: Idle problems

Corvette Forums Corvette Classifieds Gallery Corvette News Member List Search Sponsors
Forum FAQ Calendars Contact Us Corvette Recalls TSBs Corvette Timeslips Register Login

RE: Idle problems

Printable Version

Corvette >> Corvette Models >> Corvette C4 Forum >> RE: Idle problems

Page: << < prev 4 5 [6] 7 8 next > >>

Message

<< Older Topic Newer Topic >>

RE: Idle problems - 9/4/2007 4:19:45 PM

rshiver

Posts: 381
Joined: 8/4/2007
Status: offline

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.

_____________________________

"Giving up" is never an option.
..............(o o)
~~~o00o~(_)~o00o~~~

2000 Limited Edition Ford F-350 Lariat 4x4 Dually, 7.3 Liter Powerstroke Diesel
1985 L98 Corvette
1978 Chevy Camaro LT

(in reply to lbelew)

Post #: 51

RE: Idle problems - 9/4/2007 4:47:26 PM

cwb

Posts: 1508
Joined: 5/13/2007
From: eastern NC
Status: offline

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.

_____________________________

Don''t know nuthin''; ain''t never got paid for wrenchin''...
[image]
http://www.stripers247.com/phpBB2/images/smilies/th_icon_stooges.gif[/image]

(in reply to lbelew)

Post #: 52

RE: Idle problems - 9/4/2007 6:30:58 PM

lbelew

Posts: 54
Joined: 7/10/2007
Status: offline

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.

(in reply to cwb)

Post #: 53

RE: Idle problems - 9/4/2007 6:34:20 PM

cwb

Posts: 1508
Joined: 5/13/2007
From: eastern NC
Status: offline

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...

_____________________________

Don''t know nuthin''; ain''t never got paid for wrenchin''...
[image]
http://www.stripers247.com/phpBB2/images/smilies/th_icon_stooges.gif[/image]

(in reply to lbelew)

Post #: 54

RE: Idle problems - 9/4/2007 6:35:54 PM

lbelew

Posts: 54
Joined: 7/10/2007
Status: offline

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

(in reply to cwb)

Post #: 55

RE: Idle problems - 9/4/2007 6:49:35 PM

cwb

Posts: 1508
Joined: 5/13/2007
From: eastern NC
Status: offline

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

_____________________________

Don''t know nuthin''; ain''t never got paid for wrenchin''...
[image]
http://www.stripers247.com/phpBB2/images/smilies/th_icon_stooges.gif[/image]

(in reply to lbelew)

Post #: 56

RE: Idle problems - 9/4/2007 6:55:52 PM

cwb

Posts: 1508
Joined: 5/13/2007
From: eastern NC
Status: offline

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...

_____________________________

Don''t know nuthin''; ain''t never got paid for wrenchin''...
[image]
http://www.stripers247.com/phpBB2/images/smilies/th_icon_stooges.gif[/image]

(in reply to cwb)

Post #: 57

RE: Idle problems - 9/4/2007 7:21:09 PM

lbelew

Posts: 54
Joined: 7/10/2007
Status: offline

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.

(in reply to cwb)

Post #: 58

RE: Idle problems - 9/4/2007 7:33:47 PM

rshiver

Posts: 381
Joined: 8/4/2007
Status: offline

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.

_____________________________

"Giving up" is never an option.
..............(o o)
~~~o00o~(_)~o00o~~~

2000 Limited Edition Ford F-350 Lariat 4x4 Dually, 7.3 Liter Powerstroke Diesel
1985 L98 Corvette
1978 Chevy Camaro LT

(in reply to cwb)

Post #: 59

RE: Idle problems - 9/4/2007 7:43:09 PM

cwb

Posts: 1508
Joined: 5/13/2007
From: eastern NC
Status: offline

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

_____________________________

Don''t know nuthin''; ain''t never got paid for wrenchin''...
[image]
http://www.stripers247.com/phpBB2/images/smilies/th_icon_stooges.gif[/image]

(in reply to lbelew)

Post #: 60