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. Even the idle air control valv 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

 

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

 

quick question - when you changed out the IAC valve, did you clean the throttle body? there are internal passages that can cause erratic idle problems as you describe. also, you might want to throw in a new O2 sensor, and check for any vacuum leaks. i sort of doubt it's an ignition problem since you've replaced just about everything - i'm assuming you have good spark. have you checked your fuel pressure? i don't think the problem is with the injectors themselves, and since you have replaced the filter, it may be a low fuel pressure issue. finally, what is the condition of the catalytic converter? there maybe an problem there...

good luck - keep us informed -

 

The IAC valve was changed in a shop so i dont now what they did whith TB. I have not tested the fuel pressure yet, perhaps they will do it next week for me.
You hear from me in this case, i promised that!

/Benny

 

Start with a fuel pressure test

 

I dont think its fuel pressure problems because whit that problems i would not have that high CO-content.......or have i?

/Benny

 

yeah but I always start with the basics just to rule them out. High idle could be a vacuum leak.

Something is telling it to deliver more fuel. I agree with Joe C's suggestions myself.

 

But the idling goes down to 400 rpm sometimes before it goes back to 600 rpm. So it goes up and down, up and down....... well i dont know really.

/Benny

 

Are you getting any codes at all?

 

They will check that next week at the shop and then we will see.

/Benny

 

Here's some suggestions. Most erratic idle problems like you describe are caused by air/fuel mixtures that aren't correct and the computer starts hunting and pecking looking for the right mixture. That can be anything from vacuum leaks to o2 sensors, to bad catalytic conv. to a maf/map, egr valves, valve leaks inside the engine.

http://www.misterfixit.com/ruffidle.htm

 

Thanks for the link! My spark plug at the 8th cylinder looked very avful when i take it out of the engine. I think it could be a very big leak at the injector in that cylinder so that the ECM dont know what to do.....and that gives the bad idling. Do you think so to? It could be one reason.

/Benny

 

I agree with the suggestion to check for vacuum leaks. The car might also have dirty injectors.

 

Could very well be your problem

 

It costs almost 700 dollars for a set of injectors here in Sweden so i hope thats the problem. I want start a changingparty. I must go to the problems directly. Corvette parts in Sweden is really expensive. No lets see if their is anyone who think its another problems.

/Benny

 

if you happen to need injectors, contact Jon at FIC (forum vendor) he can set you up with a set of boschIII's w/plenum gaskets for around $200 (US) - international, flat rate, US prioriy mail shipping shouldn't be too bad to Sweden.

with RetiredSFC 97 - start with basics...

 

Alright...thanks!

/Benny

 

i re-read the original post, and notice the cold engine thing. when cold, the engine is in the "open loop" mode, and the engine is running on predetermined parameters. after the temp reaches about 100F, the system goes "closed loop", and the ECM starts monitoring various sensors - O2, MAF, TPS, etc. if the ECM is getting a signal out of the sensors operation range, it should throw a "service engine" light and set a code. maybe i missed it, but are you getting a service engine light, or codes?

 

The SES-light dont light up and the codes if there are any its going to be checked up next week at the shop.

/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