Cold start valve impression
Thread Starter
Racer
Joined: May 2000
Posts: 411
Likes: 0
From: Krakow
Cold start valve impression
I always have problems with fuel economy on my vette. It seems run rich.
Recently I disconnected my cold start valve, and what difference!!!
Car run much smoother and not as loud.
And the best is fuel economy. Recently I run on autobahn and at constant 85 MPH speed instant fuel consumption was 35-31 MPG!
At 110 MPH was 24 - 22 MPG! :eek:
(I have 4A and 2.59 rear)
That almost unbelievable how that engine can be efficient!
Most funny is that MPG is the same at 40 MPH and at 80 MPH. So why drive 40? :lol:
Before I disconnected my cold start valve at 85 MPH economy was only 24 MPG.
So it looks as my CSV was leaking.
If someone thinking that car has poor economy, maybe it is worth simple disconnect that valve and check it.
BTW
I have no problem with cold starts without CSV.
:cheers:
Jerry
Melting Slicks
Joined: Apr 2002
Posts: 3,019
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From: down that one road next to that big tree
Re: Cold start valve impression (jtjerry)
something doesn't sound right about that & i'd check your plugs to make sure you aren't running lean. i've never really researched the CSV on the C4, one reason is i have a 1990 & don't have one. what in the heck are these things good for? were there any changes in the 89+ cars that helped with cold starting? anyone know much about this? i'm curious just for spits and giggles
Thread Starter
Racer
Joined: May 2000
Posts: 411
Likes: 0
From: Krakow
Re: Cold start valve impression (gtsyellow)
I am not expert but think CSV was deleted in 1989. They changed ECM program (more fuel at cold starts) to compensate CSV absent.
I think CSV do not work when car is warm and running, even at WOT. CSV is only for cold starts.
Jerry
I think CSV do not work when car is warm and running, even at WOT. CSV is only for cold starts.
Jerry
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: Cold start valve impression (jtjerry)
With the CSV cold start enrichment was done by an external times; in '89 and later L98s that duty was done by the ECM and the eight main injectors.
That's a good tip on fuel economy; here in the States we can send all our injectors to Rich at Cruzin Performance. He reconditions, flow tests and leak tests them for $8 each.
People are amazed to hear that a car that is running close to 12s gets 31-32mpg highway, especially anyone driving an SUV. :lol:
That's a good tip on fuel economy; here in the States we can send all our injectors to Rich at Cruzin Performance. He reconditions, flow tests and leak tests them for $8 each.
People are amazed to hear that a car that is running close to 12s gets 31-32mpg highway, especially anyone driving an SUV. :lol:
Racer
Joined: Jun 2000
Posts: 428
Likes: 1
From: Friendswood Texas
Re: Cold start valve impression (65Z01)
I've read the CSV is controlled by a temperature sensative switch located just below the throttle body. There's two switches there, the one with the locking connector is the cold start switch. If the coolant temp is below 95 deg F the switch energizes the CSV and it sprays a little extra fuel into the intake. When the temp gets above 95 it shuts off the CSV. Serves the same function as a choke on carberated engines - it runs the engine a little rich until it warms up.
It was replaced by programming in the ECM in later years.
BTW
If the CSV is leaking I would think the ECM would compensate when it went closed loop. It would fire the main injectors a little less to compensate and you would't run rich after closed loop cuts in.
Do a leak down test on fuel pressure to see if is really leaking.
[Modified by Mike263, 5:16 PM 7/20/2002]
It was replaced by programming in the ECM in later years.
BTW
If the CSV is leaking I would think the ECM would compensate when it went closed loop. It would fire the main injectors a little less to compensate and you would't run rich after closed loop cuts in.
Do a leak down test on fuel pressure to see if is really leaking.
[Modified by Mike263, 5:16 PM 7/20/2002]
Drifting
Joined: May 1999
Posts: 1,478
Likes: 3
From: Sacramento, CA Money can't buy happiness - but it's more comfortable to cry in a Corvette than a Yugo.
Re: Cold start valve impression (Mike263)
What Mike 263 said is exaclty correct. One other possibility is that the thermal switch for the cold start valve (CSV) is defective and causing a good CSV injector to be open when the coolant temp is above 95 deg. F.
Either condition, a bad CSV or bad thermal switch would indeed cause the ECM to see a rich condition and lean out the mixture of the main injectors. Depending on how much is leaking and how often it was leaking however, it might just have caused O2 readings to jump far more wildly than normal. Remember the ECM is making mixture changes based on "after the fact" readings of the single O2 sensor which is reading from the driver's side bank only in the earlier C4s. The ECM may have been jacking with mixture far more than it should have in order to compensate. As if you were tapping on the accelerator instead of applying consistent pressure.
Chart A-9 in the GM Manual details how to do a complete cold start valve circuit test.
Either condition, a bad CSV or bad thermal switch would indeed cause the ECM to see a rich condition and lean out the mixture of the main injectors. Depending on how much is leaking and how often it was leaking however, it might just have caused O2 readings to jump far more wildly than normal. Remember the ECM is making mixture changes based on "after the fact" readings of the single O2 sensor which is reading from the driver's side bank only in the earlier C4s. The ECM may have been jacking with mixture far more than it should have in order to compensate. As if you were tapping on the accelerator instead of applying consistent pressure.
Chart A-9 in the GM Manual details how to do a complete cold start valve circuit test.
