Closed Loop

[Mabolzich]

I'm a happy owner of a 86 Vette. I runs great, but I'm having a code problem. I wants to run in the closed loop mode. I've got a OB scanner and I get no trouble codes. Then the check engine light comes on and I get the closed loop mode. What can I do to fix this problem?:confused

 

[vetteoz]

What is your problem.
you can't read the codes?
or you don't want it in closed loop?

 

[Mabolzich]

Mabolzich

Maybe I'm mis-stating the problem. It's stays in the limp home mode. Is that an open loop?

 

[geekinavette]

You need to retrieve the actual numeric trouble code from the ECM.

Bill

 

[vetteboy86]

I agree, if you are seeing a Service engine soon(SES) light, retrieve the code. That can be done by using a jumper and connection terminals A and B on the ALDL connector. Any type of service manual should tell you that information.

Closed loop occurs when the car warms up and starts to monitor input from the narrow band Oxygen sensor. Until that time the car operates in open loop.

I think a defective Prom can trigger limp home mode. How do you know this is the problem? Does the SES light flash when you turn the key to ign? Also does the cooling fan turn on? It's been a while, but if the SES stays solid, and the fan turns on when key is to ign, then the car will be in limp mode.

 

[Mabolzich]

Mabolzich

Here's the problem, I blew a head gasket, so I took my Vette to a well known tuner. He rebuilt the engine, trans, replaced wheel bearings, bent sway bar, and a bunch of other stuff. The only thing keeping from getting it back is the limp home mode code that keeps turning up. I can't get in touch with him to get the exact code till later, but he dosen't want me to take the car till it's fixed. It's been a while and I want to resolve this issue before I died. I will get the code to you guys as soon as I can. Thanks for your response. :eyerole

 

[geekinavette]

Correct...a PROM error will cause the ECM to go into limp-home mode. What to look for is a single flash of the Check Engine (or Service Engine Soon) lamp when the ignition is turned on, before the engine is started. If there is a PROM error the lamp will just turn on solid without that single flash and it will be in limp home mode. The older ECMs will actually flash the lamp very rapidly if there is a PROM error, later models (MEMCAL equipped) do not do this...but all OBDI models will flash the lamp once upon turning the ignition on as long as the PROM is functioning properly.

 

[JAKE]

You can just use a paper clip, insert it in the ALDL and retrieve the code(s) yourself.

Jake

West Point ROCKS!

 

[Mabolzich]

Thanks for the input. I don't have the car right now, but I'll get the information later this afternoon or tomorrow.

 

[vetteboy86]

Here's the problem, I blew a head gasket, so I took my Vette to a well known tuner. He rebuilt the engine, trans, replaced wheel bearings, bent sway bar, and a bunch of other stuff. The only thing keeping from getting it back is the limp home mode code that keeps turning up. I can't get in touch with him to get the exact code till later, but he dosen't want me to take the car till it's fixed. It's been a while and I want to resolve this issue before I died. I will get the code to you guys as soon as I can. Thanks for your response. :eyerole

If he is a well known tuner, than he should be able to diagnose the problem. If he can't then I would retrieve the car from him.

 

[Mabolzich]

I've been thinking in that direction.

 

[geekinavette]

If he is a well known tuner, than he should be able to diagnose the problem. If he can't then I would retrieve the car from him.

Was kinda thinking the same thing myself...

 

[vetteboy86]

The first thing you need to do is ask him why he thinks it is limp mode. Is it running rough? Is the motor stock? First step is to check the SES light when the ignition is keyed up.