Stalling issues - Code 31 (Camshaft Position Sensor)

[MuRCieLaGo]

1991 ZR-1

Hello guys,

I will explain my problem on this thread now.

I just bought the car yesterday and I drove the 800 kms back home.

Intermittent Service Engine Soon light.

When I come to stops or red lights, engine has a hard time going at idle.

50% of time: engine dies. I can start it back (I need to crank a bit longer but it starts).
Other 50% of time: idle goes to 500 rpm, go back a bit higher than 1,000 rpm, bounces for some seconds and then sets to normal idle (800?).

When it is cold, I don't have the problem at all (tested only this morning, can't tell if it is always like that).

Plus, I don't know if it has something to do with that problem, but when I go at WOT at around 75 mph (6th speed), the engine has a hard time going higher in RPM. WOT at 3,000 RPM at pretty much any speed is hard (it bucks, feels like misfires). WOT at 4,000 RPM and higher is nice and smooth.

Seller said:
-Plugs have been changed last year.
-Injectors have been changed last year.

No receipts at all. I know he's a honest guy though, no question there.

Anybody can help me? These LT5s are intimidating, I've a lot of stuff to learn there.

Thanks!

[secondchance]

Originally Posted by MuRCieLaGo

1991 ZR-1

Hello guys,

I will explain my problem on this thread now.

I just bought the car yesterday and I drove the 800 kms back home.

Intermittent Service Engine Soon light.

When I come to stops or red lights, engine has a hard time going at idle.

50% of time: engine dies. I can start it back (I need to crank a bit longer but it starts).
Other 50% of time: idle goes to 500 rpm, go back a bit higher than 1,000 rpm, bounces for some seconds and then sets to normal idle (800?).

When it is cold, I don't have the problem at all (tested only this morning, can't tell if it is always like that).

Plus, I don't know if it has something to do with that problem, but when I go at WOT at around 75 mph (6th speed), the engine has a hard time going higher in RPM. WOT at 3,000 RPM at pretty much any speed is hard (it bucks, feels like misfires). WOT at 4,000 RPM and higher is nice and smooth.

Seller said:
-Plugs have been changed last year.
-Injectors have been changed last year.

No receipts at all. I know he's a honest guy though, no question there.

Anybody can help me? These LT5s are intimidating, I've a lot of stuff to learn there.

Thanks!

Post title says "code 31". Is this the code you are seeing with scanner or using pin grounding method? Faulty or disconnected cam position sensor will exhibit symptoms you are describing.
First check the cam position sensor connector - from cam position sensor on driver side head (on the side) wrapped in 1/4" black flex conduit to a weatherpak plug above the brake booster. If connected, you may need a new sensor.

[MuRCieLaGo]

The code has been scanned with an unknown GM scanner (seems to be worth a lot of money). It showed no signal coming from the cam sensor. Cam sensor has an easy access and is connected. I'm pretty sure there's a way to measure the resistance of it to determine if it is bad or not?

If that's the problem, I'll be glad to pay $200+ for the sensor!

[We Gone]

Time to make your first tool buy and a must for any ZR-1 owner.. A FSM...

I would follow the code, check the plugs maybe ohm the wires. If all is good new Sensor.

[MuRCieLaGo]

I'll test everything related to fire tomorrow. I hope coil packs have an easy access, I don't feel comfortable to pull the plenum yet.

Thank you I appreciate your help!

[secondchance]

Originally Posted by MuRCieLaGo

I'll test everything related to fire tomorrow. I hope coil packs have an easy access, I don't feel comfortable to pull the plenum yet.

Thank you I appreciate your help!

If scanner is throwing code 31, even though connected, I'm pretty sure it's cam sensor failure.
Unfortunately, coil packs are under the plenum. Pulling the plenum, once you do it a couple of times, is no big deal. Especially with coolant passage plugged I can get in and out in less than an hour. It's a ZR-1 ownership initiation.

[Z51JEFF]

CHECK ENGINE LIGHT, bucking and the present throuble code 31 is what my 91 did when the cam sensor died.

[Paul Workman]

Jerry's Gaskets has cam position sensors for $150. You'll want to get acquainted with Jerry - seems like most of us do, sooner or later - for all things LT5-related. (Click on the link and it should take you right to the page w/ the sensor on it!)

I agree w/ Secondchance: Pulling the plenum is "a right of passage" for a ZR-1 owner. All the crap you see on the outside of other motors is hidden under the plenum on the LT5. And*, after installing plugs in the INJECTOR HOUSING coolant ports leading to the throttlebody, and having a long nose "T" star tool or a 4" (~10 cm) Snap-On star extension and a drill makes pulling the plenum off about a 5-10 minute job - about like pulling a carb. (Oh...and get a set (or two) of the plenum gaskets from Jerry too, while your at it!)

There's nothing scary about the LT5. It is different and requires certain techniques and sealants, etc; different; not intimidating, and actually FUN to work with, if having the right tools and the FSM!

Welcome to the club! You've come to the right site for "all things ZR-1!

Paul

[Dynomite]

Originally Posted by Paul Workman

after installing plugs in the INJECTOR HOUSING coolant ports leading to the throttlebody, and having a long nose "T" star tool or a 4" (~10 cm) Snap-On star extension and a drill makes pulling the plenum off about a 5-10 minute job - about like pulling a carb. (Oh...and get a set (or two) of the plenum gaskets from Jerry too, while your at it!)

Paul

Concur with Paul

Removing Plenum (including the 10 minute Plenum Removal)

Injector Housing TB Coolant Blocking

Jerrys Plenum Gasket

Originally Posted by MuRCieLaGo

I don't feel comfortable to pull the plenum yet.

Just Do It
Get the right tools handy and we will be here as you go.....just post up any questions as someone will answer within a few minutes usually.
If a Torx bolt does not want to move....take it easy and post up as you do not want to strip the heads of any Torx. Same goes with metric bolt. Usually not an issue however except on Injector Housing Coolant Manifold Bolts if you decide to Block TB Coolant.

And.......when you get Plenum Off....there are some simple things to do list including Valley Drain Cleaning, Starter Solenoid Reconditioning, Tightening Crank Case Cover Bolts, Checking Vacuum System for Leaks...........all of which only take a few minutes each.

You can even take a Pressure Washer to the Valley after the coils and starter have been removed.

[MuRCieLaGo]

Originally Posted by secondchance

If scanner is throwing code 31, even though connected, I'm pretty sure it's cam sensor failure.
Unfortunately, coil packs are under the plenum. Pulling the plenum, once you do it a couple of times, is no big deal. Especially with coolant passage plugged I can get in and out in less than an hour. It's a ZR-1 ownership initiation.

Originally Posted by Z51JEFF

CHECK ENGINE LIGHT, bucking and the present throuble code 31 is what my 91 did when the cam sensor died.

I removed the cam sensor and went to test it in a well-known electrical shop where I live. Cam sensor works fine.

Originally Posted by Paul Workman

Jerry's Gaskets has cam position sensors for $150. You'll want to get acquainted with Jerry - seems like most of us do, sooner or later - for all things LT5-related. (Click on the link and it should take you right to the page w/ the sensor on it!)

I agree w/ Secondchance: Pulling the plenum is "a right of passage" for a ZR-1 owner. All the crap you see on the outside of other motors is hidden under the plenum on the LT5. And*, after installing plugs in the INJECTOR HOUSING coolant ports leading to the throttlebody, and having a long nose "T" star tool or a 4" (~10 cm) Snap-On star extension and a drill makes pulling the plenum off about a 5-10 minute job - about like pulling a carb. (Oh...and get a set (or two) of the plenum gaskets from Jerry too, while your at it!)

There's nothing scary about the LT5. It is different and requires certain techniques and sealants, etc; different; not intimidating, and actually FUN to work with, if having the right tools and the FSM!

Welcome to the club! You've come to the right site for "all things ZR-1!

Paul

Alright, I'll remove the plenum then. I thought it was a harder job. Unfortunately I don't have the FSM. Is there a digital copy of a 1991 somewhere? Thanks for the welcome words, I really appreciate this forum.

Originally Posted by Dynomite

Concur with Paul

Removing Plenum (including the 10 minute Plenum Removal)

Injector Housing TB Coolant Blocking

Jerrys Plenum Gasket



Just Do It
Get the right tools handy and we will be here as you go.....just post up any questions as someone will answer within a few minutes usually.
If a Torx bolt does not want to move....take it easy and post up as you do not want to strip the heads of any Torx. Same goes with metric bolt. Usually not an issue however except on Injector Housing Coolant Manifold Bolts if you decide to Block TB Coolant.

And.......when you get Plenum Off....there are some simple things to do list including Valley Drain Cleaning, Starter Solenoid Reconditioning, Tightening Crank Case Cover Bolts, Checking Vacuum System for Leaks...........all of which only take a few minutes each.

You can even take a Pressure Washer to the Valley after the coils and starter have been removed.

I'll remove the plenum this afternoon. However, I need to search for how to test the injectors (that's the next thing I need to test I guess). Haven't found some good, easy explanations yet.

Thanks Dynomite for the complete answer!