Mechanics

VOLVO 940 ENGINE PROBLEM

1993 Volvo 940 • 250,000 miles

I live in France and have a Volvo Wentworth estate 1993 model that has
served me very well for many years but unfortunately developed a fault
whereby the engine runs after a fashion when the air flow meter is
disconnected but stops immediately it is reconnected!

The fault is not in the airflow meter as it has been changed twice to
no avail, but the local garage mechanics are pulling their hair out
now as it has been with them for six months and they cant find the
fault! They have also changed the cam position sensor and under car fuel pump to no avail!

There are no Volvo garages in this part of France so nobody to ask
about the problem, also this model was never imported to France anyway
so they have no experience of it!

I would appreciate your advice on what other parts should be changed to try and resolve this problem!

Regards
Barry Crofford
AD
Avatar
Guest
January 23, 2013.




Changing parts without understanding the cause is going to be costly and time consuming.

Was any attempt made to retrieve trouble codes?
With air flow connected, were you able to keep the engine running while feathering the throttle?


KHLow2008
Jan 23, 2013.
Sorry to say that I do not know how to retrieve trouble codes!

It is not possible to keep the engine running for more than a few moments with air flow meter connected even with the throttle.
AD


Tiny
Barry Crofford
Jan 23, 2013.
Check the following and let me know what you find. After recording the codes, disconnect the battery negative terminal for a few minutes and reconnect. Remember to connect the MAF. Start engine and after engine stalled, recheck for trouble codes.

FUEL INJECTION & IGNITION SYSTEMS

Fuel injection and ignition systems each feature a self-diagnostic function for fault tracing. A common diagnostic unit for retrieving codes is located in engine compartment, behind left strut assembly. Diagnostic unit is equipped with an LED indicator, activation button and function selector cable. See Fig. 1.

Diagnostic unit output socket No. 2 is used for fuel injection. Socket No. 6 is used for ignition system. Once selector cable has been inserted in correct slot, depressing button once, twice or 3 times selects from one of 3 control (fault tracing) functions.

Faults stored in ECU memory are read by observing LED flashes.

Diagnostic system for fuel injection ECU stores 17 fault codes and ignition ECU stores 9 fault codes. All fault codes contain 3 digits (example: 4-1-3). Since all codes have 3 digits, each code requires 3 series of flashes. A 3-second interval separates each series of flashes.

ENTERING SELF-DIAGNOSTICS

System monitors operation of components and switches. When component or switch is operated according to a set procedure, LED will display a 3-digit code. Failure to display a code indicates control unit has failed to detect operation of component/switch. In this case, fault lies with component/switch or associated connectors and wiring.

Functional check system can also test whether components/switches are correctly wired. For example, it can check whether permanent/magnet generator (engine speed sensor) and wiring are intact if engine fails to start.

Control Function No. 1
(Retrieving Codes)

This function displays any of 17 different fuel system codes stored in ECU memory during engine operation.

Control Function No. 2 (Activating Circuit Breakers)

This function tests fuel system circuit breakers. As it is activated, information is provided through LED in a flash code. This control function is generally used as a double-check after repairs.

Control Function No. 3 (Testing Fuel System Components)

This function tests fuel system components with engine stopped. It consists of a function cycle where diagnostic system activates components. Determine whether component is working by listening or putting a hand on it when it is activated.


KHLow2008
Jan 24, 2013.

AD