Problems with the idling!

[Corvetteman]

Fuel problems/Air problems/Electrical problems/ECM problems?

Hi!

My name is Benny and i´m from Sweden. I´m not so good in writing in English but I hope you understand me.
In the summer 2009 I bought my very first Corvette a -86 C4. it´s a ordinary 350 engine with bigger valve in the cylinder head and another cam shaft. After a couple of weeks the problems started. When the engine is cold it start without problem. Very soon the problems begin, the engine idling between 600 rpm and 800 rpm sometimes down to 400 rpm so it almost stops. Sometimes it does. I have to do between 1 to 6 tryies to start it up. Before it runs uneven like I describe before I can hear bangs from the exhaustsystem and the engine dies when I press the gas pedal and it stops. Sometimes I have to shout of the ignition before the enging runs again sometimes I can start it without shout of the ignition. When it starts it idling up to 1400 rpm. After a while it goes down to the ordinary 600-800 rpm (sometimes 400 rpm). The engine can run quite a long time before it stops again. When you are out in the traffic and gas-brake-gas-brake it will stops most of the time and I have to start all over again with the same starting procedure. Not so good.
In the summer 2009 the fuel pump with filter was changed. The ignition was changed from 0 degrees to 6 degrees BTDC………no changes at all. Only a week ago I change spark plugs, spark plugs wire set, distributor cap, distributor rotor and ignition coil without any changes. The spark plug at cylinder eight looks awful to me. I have test the injectors with multimeters……no problems. 16,0 to 16,3 ohm cold and 16,3 to 16,6 warm.
What do you think?
Could it be:
Fuel problems?
Air problems?
Electrical problems?
ECM problems?
Anything else?

I´m very grateful for any help!
I´m hope that the Corvettesummer isn´t over yet!

Regards from Sweden

/Benny

 

[Corvetteman]

CO-content.

I wondering if i have injector problem because the CO-content in the exhaust gas is really high.
2008 was it 0,3
2009 was it 0,6
2010 was it 1,7
Normaly it should be around 0,0 to 0,3. In our old Volvo car from 1990 with the same equipment that is on the Corvette the CO-content is 0,2.

/Benny

 

[vetteboy86]

Hi There Welcome to CAC!

Is your service engine soon (SES) light on? That is the first place to start. Pull any stored trouble codes.

 

[boomdriver]

I wondering if i have injector problem because the CO-content in the exhaust gas is really high.
2008 was it 0,3
2009 was it 0,6
2010 was it 1,7
Normaly it should be around 0,0 to 0,3. In our old Volvo car from 1990 with the same equipment that is on the Corvette the CO-content is 0,2.

/Benny

Is this causing the Service Engine Soon to come on? If so, that means the ECM has a trouble code stored. This will help in the diagnosis.


If its not setting codes, my best guess would be the EGR valve stuck open or possibly a bad MAF relay. The ECM will tell you if it has anything to do with the MAF sensor.

 

[Corvetteman]

No SES!

Its not setting codes for the Service Engine Soon to come on. I dont think its the MAF-relä because i heard that MAF-relay is the same as Fuel pump relay which i have changed and i take the old one and put it in the place for the MAF-relay whitout any changes.

/Benny

 

[vetteboy86]

You might want to verify the SES light works in your car. Does it illuminate when the key is on position motor not running?

Also, You have an identical thread running in the general discussion. I will remove that thread, since this one is getting all attention.

 

[Corvetteman]

You might want to verify the SES light works in your car. Does it illuminate when the key is on position motor not running?

Also, You have an identical thread running in the general discussion. I will remove that thread, since this one is getting all attention.

Yes the SES light works i know that. Sometimes it lights up and then i turn the ignition of and starts again and then the SES light is gone for the moment.

/Benny

 

[sweabe]

From a fellow Swede, välkommen till CAC, you will find this site very helpful, as I have

You say that your number eight spark plug looks awful, what color does it have? Is it firing at all?

I would start by looking back on what you have done, if there are any problems caused by the service parts you have replaced.

// sweabe CCS #777

 

[Corvetteman]

From a fellow Swede, välkommen till CAC, you will find this site very helpful, as I have

You say that your number eight spark plug looks awful, what color does it have? Is it firing at all?

I would start by looking back on what you have done, if there are any problems caused by the service parts you have replaced.

// sweabe CCS #777

The eight spark plugg was really black and full of shit.....
All spare parts that i have changed makes no differense at all.

/Benny

 

[sweabe]

And all other plugs are ok?

Normally one "bad" cylinder shouldn't stall the engine.

You say that it runs better when you first start it up when the engine is cold.

But then suddenly the problems start, I guess it goes into closed loop then.

Maybe you are getting unburned gas into the exhaust and the computer is trying to compensate for to rich exhausts, and then making the fuel mixture to lean so the engine starves.

I would concentrate on cylinder number eight, maybe you should make a fuel pressure test, concentrating on the static pressure to see if you have a leaking injector

 

[Corvetteman]

And all other plugs are ok?

Normally one "bad" cylinder shouldn't stall the engine.

You say that it runs better when you first start it up when the engine is cold.

But then suddenly the problems start, I guess it goes into closed loop then.

Maybe you are getting unburned gas into the exhaust and the computer is trying to compensate for to rich exhausts, and then making the fuel mixture to lean so the engine starves.

I would concentrate on cylinder number eight, maybe you should make a fuel pressure test, concentrating on the static pressure to see if you have a leaking injector

All other plugs are acceptable, not really god but not bad. I think injector 8 leaks a lot because the CO-content is very high.
2008 was it 0,3
2009 was it 0,6
2010 was it 1,7
Normaly it is between 0,0 and 0,3 so you see its very high and i think its a very big leak on cylinder 8. Fuel test...ok i should do it.

/Benny

 

[SPANISHVETTS]

1) clogged Catalytic converter.

2) throttle body leaking air around butterfly shaft

3) distributor problem

 

[vetteboy86]

Swap plug wires from #8 with another cylinder of a similar length. Fuel pressure measurement will determine if you have leaking injectors.

 

[Corvetteman]

Swap plug wires from #8 with another cylinder of a similar length. Fuel pressure measurement will determine if you have leaking injectors.

The wires are new.

/Benny

 

[Corvetteman]

1) clogged Catalytic converter.

2) throttle body leaking air around butterfly shaft

3) distributor problem

1) clogged Catalytic converter. I haven't check
2) throttle body leaking air around butterfly shaft. Maybe its a little leak
3) distributor problem. Thats not changed is the distributor itself, ignition control module and the ignition pickup

/Benny

 

[Corvetteman]

1) clogged Catalytic converter. I haven't check
2) throttle body leaking air around butterfly shaft. Maybe its a little leak
3) distributor problem. Thats not changed is the distributor itself, ignition control module and the ignition pickup

/Benny

Today i´ve check the vacuum and i can´t find any leaks. I adjust the TPS and get 0,57 v idling and 4,50 V full throttle.....not so bad i think.

/Benny

 

[John Robinson]

The wires are new.

/Benny

Even if they are new you could have a bad wire. If one of the ends was not properly installed by the manufacturer. You could always do a continuity check of the wires to eliminate them as a source of your problem. I learned this one time when I had to replace an alternator. I replaced 4 of them in one day before I got one that was good and the parts house confirmed that the 4 were bad when I took them back. A black or rich plug in #8 may not be from excessive fuel but rather from unburnt fuel. Also as said earlier it seems to happen when the ECM goes into closed loop. There are a number of sensors that come into play at that time. All of them must have a solid ground and some of them are using a common ground. Before you start replacing parts be sure that the basics are covered. Since you indicate the wires are new then I would carefully look to be sure that a sensor wire was not pushed against a manifold or unplugged and not reconnected. The same with the vacuum hoses. Oh and finally are the wires on the right plugs?

 

[Corvetteman]

Even if they are new you could have a bad wire. If one of the ends was not properly installed by the manufacturer. You could always do a continuity check of the wires to eliminate them as a source of your problem. I learned this one time when I had to replace an alternator. I replaced 4 of them in one day before I got one that was good and the parts house confirmed that the 4 were bad when I took them back. A black or rich plug in #8 may not be from excessive fuel but rather from unburnt fuel. Also as said earlier it seems to happen when the ECM goes into closed loop. There are a number of sensors that come into play at that time. All of them must have a solid ground and some of them are using a common ground. Before you start replacing parts be sure that the basics are covered. Since you indicate the wires are new then I would carefully look to be sure that a sensor wire was not pushed against a manifold or unplugged and not reconnected. The same with the vacuum hoses. Oh and finally are the wires on the right plugs?

The wires are on the right plug and the problems where the same with the old wire as well. I have just ordered new injectors, lets see if this solve the problems.

/Benny