Help! Electronic Problem on Idle , HELP HELP HELP

[keremarsan]

Hello and Happy New Year from Istanbul / Turkey ,

Please I need help

Last day I had a veru bad experience with my 1988 corvette ,

After the work, I wanted to start my car, but the feul pump did not work.
I forced the car to start without the fuel pump , it started but after it died ( normal ). I tried this for about 5 minutes.

Suddenly, the fuel pump started and engine started normally,
My problems begins after this time :

- Engine can not decrease the IDDLE , Iddle is between 1000 - 1200 RPM
- The Fuel Consumption gauges does not work ( 0 litre / 100 )
- On the road , sometiomes the car returned to normal condition ( suddenly , it indicates the fuel consumption and then again 0 l/100 )

- No error code stored , no engine service soon lamp indication
- I connected A to B on ALDL , normally , I must to get tree times 12 and to finish retrivieving codes, tree times 12 ( 6 in sum ) I get NOTHING
Someting like, DİAGNOSİS don't work.

When I connected A to B, the Cooling fun must work but it doesnt, instead of that, Air Condition is started ?????!!! Maybe some Shortcut ? ECM error ?

Another interesting thing, after connection A to B on ALDL, I started the car with pins connected (something not to do ) , and the car works perfectly !!!!!

I don't have any Idea what can be my problem.

Event with iddle problem and no fuel cons. indicated, car works totally normal on different throttle , no leak of power , no excessiv consumption.

Please , I am waiting for your suggestion ?

thanks all ,

PS: I think to change IACV and Fuel pump and Fuel pump relay but the problems seems to be a more complicated electronic problem.
All other gauges fontions are normal ( oil pressure, oil temp , cooling Temp, Voltage, RPM , Speed ..... )

 

[vetteoz]

the feul pump did not work.I forced the car to start without the fuel pump , it started but after it died . I tried this for about 5 minutes.Suddenly, the fuel pump started and engine started normally, indication

Engine will not start "without pump".

What you are doing there is cranking long enough to build oil presssure to close the oil pressure switch which runs the pump direct from the battery; not through the relay.The fact that it started means the pump is working OK.
Swap pump relay with cooling fan relay to check if relay is faulty.
If working relay does not run pump when key first turned on, ( should hear it prime ) you have a problem with the control wiring to the ECM or the ECM itself.
Also check wiring at relay plug.Common to have bad insulation leading to faults.

 

[jmccloud]

No fans with ALDL connected

The fans not running when in diagnostic mode may indicate a poor ground for the ECM.

 

[keremarsan]

thank for the help ,
The car is started with not enough fuel without pump , no prime, no pump at all and when the fuel is finish on "fuel rails", it dieds.

Which I can not understand is that there is no ECM error code stored. .....

Thanks

Engine will not start "without pump".

What you are doing there is cranking long enough to build oil presssure to close the oil pressure switch which runs the pump direct from the battery; not through the relay.The fact that it started means the pump is working OK.
Swap pump relay with cooling fan relay to check if relay is faulty.
If working relay does not run pump when key first turned on, ( should hear it prime ) you have a problem with the control wiring to the ECM or the ECM itself.
Also check wiring at relay plug.Common to have bad insulation leading to faults.

 

[keremarsan]

Thank you for your help ,
I will check the connection .... I think , trying to start the engine with faulty fuel pump caused serious problems.

 

[JAKE]

To my knowledge that is no code for a faulty or failed fuel pump. If it goes bad, there's no code to be set.

There are a few ways to test the pump for proper operation. One is to supply 12V to the 'G' terminal on the ALDL. If memory services, 'G' is on the lower row, the last ALDL opening to the left (as you're sitting in the driver's seat.

Another way is to un-bolt the fuel pump relay from the firewall and, using alligator clips you jump two of the pins on the relay. This by-passes the relay and supplies voltage directly to the pump. If the pump them turns on, it's probably the fuel pump relay that's bad.

You jumper terminals 'D' and 'E' on the relay; they should be marked so you can tell which is which.

You can also do the swapping relays trick by connecting the fuel pump connector to a KNOWN GOOD relay.

If it were me, I'd first try disconnecting the battery for about 30 seconds, then, after re-connecting it, see if the problems return.

If '12' blinks three times and no other code is shown, that means that the diagnostic is working and there is no stored SES code to display.

Let's not over-engineer this; it's probably something simple.

Hope this helps.

Jake

 

[keremarsan]

Thanks JAKE,

I will make a summary of the situation :
last night, I checked all the connections and fuses of the sensors.
Suddenly, the car begins to work perfectly : Fuek pump works, fuel pump relay works and everything was okey:

until This morning when same problem returned :

Here is the situation :

When :

Fuel pump works ,

-After cooling temp increases, car can not decrease the RPM ( stays stable at 1100 RPM )
-After Turning off the engine , with A-B connected on ALDL, the can can not begin to diagnosis.
-In these conditions, the car can not show the fuel consumption on display.

Reverse situation :

when fuel pump works ( I write when because, it works sometimes )

- If the car CAN decrease the RPM ( when engine is hot )
- on ALDL , A-B pins connected , car can begin the diagnosis ( only with code 12, but no error code stored )
- and in these conditions, car CAN show the consuption.

Maybe a faulty fuel pump, IACV or fuel pump relay causes this strange situation.

Thank you for your help,

I will begin with changing: fuel pump, the relay and IACV valve, then I will see what happens.

Thanks,

Cheers

kerem