Welcome to the Corvette Forums at the Corvette Action Center!

the good, the bad, and the ugly

L

LarryK 87

Guest
for the last couple of weeks i have been chasing a nagging problem with my idle, on start up the idle is very high 1600+ rpm, thought maybe the Vac. canister selonoid was sticking, so i bypassed it, no effect ( BTW replaced all Vac lines on the engine) there have been no signs of any vacuum leaks else where, I found i could limit the high rev on startup by putting it into flood mode. Last week it learned a new game, AFTER start up ( in flooded mode) if would idle right back where it beloned, i let the engine warm up a bit ( min 100 deg temp) then pull out, Now the rpm as i drive out of the parking lot will, with light throttle, get to maybe 1500 rpm, and refused to drop (a quick blip o the throttle will settle it down again.
So today i decided to pull the TB and really scrub it down, while i was at it i also bypassed the coolant line as well. Now during all this i dropped one of the( actually both ) retainers for the throttle linkage, while looking for them under the car i found a connector of some sort ( with a bracket on it ) just kind of hanging there, with two wires coming off it not connected to anything, the wires look like they have been torn off what ever they where attached to. Now since for the most part the car was/is running ok, so i decided for the time to ignore it. put every thing back togather, hit the starter, and oh man what a differance, prompt, smooth 800 rpm start, clean and solid idled right down to 600.
The good...
Took it out for a bit of a test drive, great in traffic, no stumble no nothing just a rock solid 600 idle in trafic at a stop in gear. so far so good.

The bad...
I have suspected from a few posts here that my trans is going, so a quick drive to the local AAMCO ( nope did not take it there ) turned around started back into traffic with a light throttle and you would have thought the rear end had just lost half it's teeth.
Engine aint idling so good now. Take it to the local Vette place ( 3 -4 mile drive ), his prognosis... Trans is shot ( Torq. converter is what is causing the noise ) and is damaging the trans more every time it does this. Referred me to the shop he sends his trans out to, so off i go. Engine now starts like it used to, High Idle, then calms down ( but no sticking )

The Ugly...
During the drive to the trans shop ( 4-5 miles ) the engine starts running real rough, at stop lights the idle is surging, as i continue the engine gets worse, so i decide to turn around and take it home. Now here is the real ugly part and the question ( finally )
At the next light, the idle is rough ( but not stalling ) and the oil pressure light comes on, idle comes up, light goes off , now at no time did it sound ( or indicate ) the rpm was so low as to drop the oil pressure below the trip point. I pulled into a parking lot put it in park, idle still very rough BUT no oil pressure warning, put it in gear, oil pressure warniing again as the engine surges ( repeated this several times ) Now this only happens with the car in gear and at an idle and never at all while actually moving.

Can The transmmission some how effect the Dash electronics or the ECM to the point of showing an oil pressure warning? ( The Dash was set to display Oil Temp when it first did it ) Typical Oil pressure is 50 PSI.

BTW during the drive home the SES light came on, then whent off when i put it into park in the parking lot, and did not come back on during the rest of the drive home.
 
L

LarryK 87

Guest
TGB&U continued

well pulled a code 44 this AM, Hence the rough running, may have simply lost the O2 sensor at the same time?
 

Ken

Gone but not forgotten
Joined
Jan 30, 2001
Messages
8,236
Location
Hermosa Beach, CA
Corvette
1987 Z51 Silver Coupe
I saw this last night and decided to ponder it for a while before I responded. You still have me stumped, hopefully someone else will chime in before long. ;)

_ken :w
 
L

LarryK 87

Guest
yeah, not really sure what the scoop is. scared to drive anywhere now. really wacked part is i have hard the RPM low enough to stall it ( adjusting the minimum idle ) and never had the light come on.

of course i am making an assumption that it is only a PRESSURE warning, and not oil temp warning as well, or even possibly tied to the trans for temp/pressure warnings.
 
Joined
Oct 30, 2001
Messages
2,273
Location
Glen Burnie, MD, USA
Corvette
1986 Bright Red Coupe
I'm going to ask two dumb questions:

1. Is the oil level actually low? That tripped my pressure light, though while doing a hard corner rather than idling.
2. Is the oil pump OK? When the pump was going bad on my old Subaru (crank-driven pump) it would drop into the danger zone when idling after the car had warmed up. However, during normal driving, or if I held the revs to about 1500, pressure was fine. IIRC (this was 10 years ago) an internal seal had slipped and was allowing oil to bleed back to the sump.

[RICHR]
 
L

LarryK 87

Guest
well one problem is some elements are out in the display, but on particulaly humid mornings enough work to indicate 50+ psi at normal idle. I did check the levels and all is where it belongs, the only differance was the ECM was closed loop ( gener. remains in open loop during my morning drive to work about 4 miles ), running very rich, and only did it while in gear. not to much of an rpm drop between park/nut. and drive maybe 100 rpm at best, no where near enough to stall the engine.

digits where fluctuating so much i could not tell even close to what the pressure might actually have been, so some flakeyness with the oil pump is not entirly out of the question.
 
Joined
Oct 30, 2001
Messages
2,273
Location
Glen Burnie, MD, USA
Corvette
1986 Bright Red Coupe
Just a stab in the dark here and then I'll be quiet.

Aren't the oil pumps on the L98 driven off the distributor PTO? If something has bent/broken/stripped under the distributor, that would cause a rough running and if it's attached to the oil pump as well then that could explain the low pressure.

[RICHR]
 
L

LarryK 87

Guest
yes that is a possibility, and yes the oil pump is driven off the distrib. shaft, which in turn is driven fom the cam. And i have heard of the pin breaking on the dist. shaft and releasing the pump.

So i tried it this morning, idle is smooth, oil pressure is up around
+ 50psi. so took it to work, maintained pressure all the way in ( 4+ miles) idle is 800, no surging. Temps never exceeded 160
hit 2 of the 4 stop lights. No warnings acting exactly like it should.
But it also stayed in open loop didnt run long enough, nor warm up enough to go to closed loop.

So i have a few other possibilities,

problem seems to only occurs when at temp and somthing internal is way out of tolerance or failed, and only shows it'self when at full operating temp,

or The ecm is having a problem in closed loop.

Or the O2 Sensor is way bad, and telling the ecm( when in closed loop) to add more fuel ( the rough idle, and the Code 44 ), This in turn causes the engine to surge so bad the pressure does actually drop breifly enough ( stretching it a bit here )to trip the warning point but not long enough to stall out
 
L

LarryK 87

Guest
well i think most of the problem has been resolved.
1. Bad O2 senser = code 44 rough idle
2. The dash module seems to be the source of the other problem
this afternoon took car home to get lunch, starts, idles ok, Tach idicating 6400 rpm ( at idle ), then starts fluctuating between 2400 and 6400. oil pressure indicating 45 - 55 psi... and surprise... oil pressure warning ( while indicating 45+ psi )

Car had been sitting in the sun most of the morning.

After lunch ( became slightly overcast ) and i left the windows down, dash responds as expected, shows proper RPM and Pressure, and surprise...... NO pressure warning.

What a relief now it's only a dash rebuild
 

Corvette Forums

Not a member of the Corvette Action Center?  Join now!  It's free!

Help support the Corvette Action Center!

Supporting Vendors

Dealers:

MacMulkin Chevrolet - The Second Largest Corvette Dealer in the Country!

Parts/Accessories:

Vetteskins

Advertise with the Corvette Action Center!

Double Your Chances!

Partners

Top Bottom