janarvae

Hi all, car is a '91 L98, 87K, with 5 qts Royal Purple 10W-30 motor oil, rebuilt trans, new intake gaskets, oil pressure sensor, oil pressure sender, cap, rotor, Bosch Design III injectors from FIC, etc.

The car drove well today - it was the first time driving it in a long time. My problem is the oil pressure gauge is showing low oil pressure at hot idle. It appears to almost be in the hashed "danger" zone and it slips just a little bit into it at times. However, cruising at 45-50 mph, the pressure shows around 40-50 psi. At cold idle, it's 20 psi or higher. I searched the archives and learned that at 4 psi the oil light will come on and at 0 psi, the fuel pump turns off. I also read that 10 psi/ 1,000 RPM is the general SBC rule of thumb for oil pressure. It doesn't help that the oil pressure gauge has no divisions to make psi estimations any easier. It never went to zero psi though.

The engine also stalled on two occasions trying to start it up. This is a problem I had before the entire transmission rebuild and intake gasket job. I never checked the fuel pressure with a gauge like you guys told me to, mostly because of apprehension of doing it. But now that I've done what I have, I'm not scared of it in the least.

Could low oil pressure cause a start and stall condition? When I gave it gas, it started though and ran fine. So I'm guessing it's a fuel problem (regulator, pump?) at this point, but still would like some reassurance it's not due to a low oil pressure.

I'm going to be fixing a leaking oil pan gasket anyways and if I need to install a new high flow oil pump, it'll be 2 jobs in one. Or should I just add some heavier motor oil and see what happens?

Thanks for your time as always,

Jonathan

rodj

The OP switch is NOT a safety switch to save your engine
OP switch goes closed at 4psi to run the pump in parallel with the FP relay as a backup to relay failure.
If the oil pressure was to go below 4psi then engine should still run on the relay if it was operating correctly.
Maybe fit an mech OP gauge to check exactly what the hot idle pressure is.

Please explain.

You cannot give it gas or "pump" fuel into a EFI systemwhile starting the same way you can with a carb accel pump. Startup fueling is what is programmed in.
However;
if you open the throttle too much ( over a certain % TPS ) while cranking it senses that you are trying to clear a flooded engine and CUTS fuel off until you release the throttle or engine fires.

anesthes

I'm not sure a new oil pump will help. Your clearances are probably just soo large now from wear that your seeing a reduction in oil pressure.

As Rodj pointed out, there is no oil pressure safety switch, there is a "keep the driver from becoming stranded if the relay fails" switch.

Your stalling could be anything, but my first guess is an IAC.

The modified injectors freak me out too. What size were they "flowed" at?

As previously suggested, you should do a fuel pressure and more importantly a volume test. My guess is it's an IAC.

Good luck.

-- Joe

Iroc57

OP and stalling are 2 different issues. The super low OP is probably your idle dipping down too low. The clearance statement is right on the money. Your oil thins out at temp and pressure drops, once you get your idle squared away see where the OP sits at, 10W30 should be fine

janarvae

Where would I connect an OP gauge?

It started up when I pushed down the accelerator while starting. The other 2 times, I did nothing differently, the time it started, I pushed down the accelerator.

The IAC is a new Delco unit. I measured the pintle distance new and it was acceptable. I followed the FSM protocol when installing a new IAC. Injectors are 22 lb Bosch Design III from FIC injectors. LINK

I had read about the clearance issues on older engines.

The stop idle screw on my TB is untouched from the factory. Timing is set at 6* BTDC. What else can be affecting the idle, besides the IAC and other vacuum leaks? It does sound like a rough hot idle. New 02 sensor also.

Thanks,

Jonathan

engle1147

Jonathan,
Check the car for trouble codes again.....it may produce some insights.

rodj

As noted the ECM cuts off the injector pulse over a certain TPS value when cranking.
If it starts with no injector flow that would indicate excess fuel somewhere ; common hard hot start problem with old leaking injectors BUT you have new ones

Iroc57

If you have done the idle set procedure and everything has been cleaned and/or changed this is all that I can think of. This is where I get lost with EFI, when it is not a "simple" fix

Good luck

janarvae

Checked for codes:

ECM - Code 42 (EST) - set-off during timing, I guess I didn't have the battery disconnected long enough to reset it.

ABS - NONE

CCM - Speedo Read-Out:
Module 1 - C 12 (normal, right?)
Module 4 - H 42 (EST again?)

After it displayed Module 1 it had the symbols ---, then after module 4, ---. Then it only displayed 1.0. I believe --- signifies no codes? But then why does it show code 42?

Some additional notes:

-The speedo drive gear has slipped off - the stealership sold me the wrong one! The TC is NOT locking up now. Also, speed is 0 mph at all times. I'll remove the tailshaft and replace it with the correct one that should arrive today. At the same time, I'll fix that pinion seal leak and change the diff. fluid.

-RPM is way off - need to fix tach. Thinking of installing a '92 or '93 instrument cluster in there.

-Although RPM is still off, I can see that the Oil PSI and charging rate increase and decrease with RPM. I noticed that that tach is undulating about 100 RPM. Is this normal? It rises a little and then falls and Oil PSI and charging volts match it.

-Oil PSI is still low at hot idle.

-Still having a start and then stall issue. It doesn't happen every time though.

-Should I reset the IAC again?

Thanks again,

Jonathan

janarvae

ttt

rodj

For the 1990 and 1991 Corvette, the modules are

Module "1", the CCM
Module "4", the ECM

http://www.corvettebuyers.com/c4vettes/codes.htm

janarvae

Thanks, I had printed out that same sheet and used it to pull the codes. But what I'm confused about is the CCM code - C12. I think 12 means no codes, at least in the ECM, right? I looked through the FSM, but CCM codes start at 13. And the code 42 will be reset soon as it was set off by the timing protocol.

Thanks,

Jonathan

RichS23

Any luck with Oil Pressure issue?

bjankuski

I need to clariy something in this post. If you push down the accelerator to roughly 1/2 throttle or less more fuel is added at start-up. Once you get past 3/4 throttle the injectors are turned off to clear a flood. If pushing down the throttle slightly you are adding more fuel at start-up.

The oil pressure may be low due to many issues but I would guess it is due to excessive engine clearances (wear) or a worn out pump. Your cruising oil pressure is not low so I do not believe the engine is worn to the point of requiring a rebuild. You could add a HV pump to increase oil pressure and it will not cause any problems.

engle1147

I think the speedo sensor may be part of your stalling issue....with no VSS vehicle speed sensor feedback your car's ECM/PCM is having a hard time adjusting the correct injector pulse width for a given situation. Get a new gear/gears installed in the tranny for VSS pickup and go from there.

383vett

If you think your speedo cluster is inaccurate, maybe the cluster is displaying an incorrect oil pressure reading. Screw in a gauge in place of the oil temp sending unit above the oil filter. Also, try opening up the throttle blades by adjusting the setscrew by 1/2 to 1 turn and see if that helps the stalling. You'll have to recheck the tps sensor. Slightly low oil pressure at idle might be ok as long as you have 50 lbs or so at speed. Change from 5-30 to 10-30 or 10-40 and see if that changes the pressure.

janarvae

New speedo gear was put on. A PITA to do on the car, but I did the differential pinion seal and fluid change at the same time (I'll make a thread about that with all the pictures I have). The speedo is accurate as verified by GPS.

I have a 1992 cluster coming in the next day or so. I did hook up my new OBD I cable and using TunerPro RT, I was able to monitor the RPM, IAC counts, and many other parameters in real-time. I found that the idle RPM, with the factory tamper-proof idle stop screw still intact, was 600 RPM. The IAC counts fluctuated at idle a bit, so I'm going to check more into that. This is for an automatic also. I have an oil pressure gauge and fuel pressure gauge now, so I'll run some tests and report back.

The car still has a low oil pressure problem at hot idle, but my biggest concern now is that it takes 2-3 times to start cold. The starter is a rebuilt AC Delco/Nippodenso. It cranks the 1st time, but doesn't start, then it'll start the second time, but stall quickly thereafter. The third time, it'll finally start, sometimes with a little help from the accelerator pedal. To me, it sounds like a fuel pressure problem. Possibly the regulator or pump? They are new FIC Bosch Design III injectors, so I don't think I'm getting leakdown?

See above.

Thanks to all again,

Jonathan

383vett

When you say it takes 2-3 times to start, how long are you cranking for. Just 1or 2 seconds or longer? At this point, you really need to hook up the fuel pressure gauge (just like checking the air in a tire). This will tell you if your fuel pump or pressure regulator are doing their job

Redeasysport

Sounds like your FP relay is going bad and the OP is too low to provide the needed secondary path to keep it on IMHO.

janarvae

I'm cranking for maybe 3-4 seconds each time. It always used to start up in a second. I'll hook the gauge up sometime this week when I have more time.

I'll check that out too.

Thanks,

-Jonathan