Corsa engine problem

Bear with me on this, I had various garages, engineers and mechanics work on
my car over the past 6 months, and nobody can solve my problem.

I have a Corsa with a 1.4 NZ engine, 96 model. It runs rough under certain
conditions, i.e. the engine feels like it is hesitating, and I lose power.
This happens when I'm accelerating on the motorway, or driving up steep
hills. The engine management system warning light is also coming on,
especially on the motorway. The engine is fine around town and country
roads. I've had the codes down-loaded and they read "Fuel mix weak" and
"Engine idling slow". Nobody I've tried can tell me why the fuel mix might
be weak.

I have had the engine tested with Sun diagnostics, had the fuel flow tested,
and at a recent MOT the car passed it's emission test with flying colours.
All serviceable components (e.g. filters, plugs) are up-to-date. I have also
replaced the following components, so I know they're not at fault:

1. Distributor cap and rotor-arm (but not the distributor itself)
2. All HT leads
3. Coil and amplifier
4. Manifold Absolute Pressure (MAP) sensor
5. The entire fuel injection unit (including fuel injector, fuel pressure
regulator, idle speed control motor, and throttle position sensor)

The mechanics I've spoken too haven't got a clue, and have suggested I keep
replacing components, but I'm running out of components to replace. The only
idea I have left is to replace the following:

1. Engine control unit - see later in this e-mail.
2. Distributor (which has as integral "Hall-effect" sensor), - although I'm
not sure why this would cause a weak fuel mix.
3. The fuel pump - a friend suggested I might not be getting enough fuel
pressure at the injector unit, even though I've had the fuel flow tested.
4. The catalytic converter might be cracked, causing a back pressure, but
the engine passed its emission test.

I'm getting a bored replacing everything (it's expensive, even with second
hand parts). Does anyone have any ideas?

Finally. today I bought a second hand engine control unit. But when fitted,
the engine wouldn't start, and the engine management warning light flashed
steadily. The obvious conclusion is the control unit is broken, but
alternatively, is there something I need to do I "re-set" a new engine
control unit?

If you've got to the end of this message I appreciate your patience, and
would appreciate any suggestions even more.

- Craig

 

had a similar problem with a 1200 corsa that the wife had( 1997) although I
never got a management light up, it was the inlet manifold gasket.
Vauxhall changed these from the cardboard type to a metal one as they were
having lots of problems.

 

This may sound obvious but have you asked a Vauxhall dealer? Their
Tech2 will give the proper fault codes.

One option is sticking valves. What fuel do you use? I would use a
proper quality detergent fuel such as Shell, Esso or BP. Avoid
supermarket or other cheap non-additive fuels.

 

Thanks for the info.

Had a Vauxhall dealer look at it twice. First time they diagnosed a cylinder
head gasket. Second time they claimed there were no codes to download
(despite the warning light being on for 5 minutes at a time). Next day I
paid an independent diagnostic engineer to download the codes and give the
engine a thorough going over with Sun diagnostics. He claimed the codes
equated to "Fuel mix weak" and "Idling slow", which I've equated to 44 and
35 respectively. The engine is faultless when the car is stationary, and
only faults on the motorway. He suggested either at extensive road test (at
£50 an hour) or hire a rolling road. I haven't tried a second main dealer.
Maybe the one I picked wasn't particularly good.

I use a mixture of Sainsbury's and Shell, and have done since 1998 when IO
bought the car. The fuel I pick doesn't seem to alter the performance.

I had the oxygen sensor replaced a little over a year ago, along with the
exhaust manifold, by a big independent garage who I normally trust. Although
the car ran fine for about 8 months, I think I might get their work checked
out by the main dealer.

 

Get it checked by your "large independent" you *might* have a warranty
come back.
Dave

 

The Reason why your ecu light was flashing on the alternative unit is
because the ecu's are coded to the car and a steadily flashing warning lamp
means the code in the ecu does not match the code of your immobiliser.

 

Have you checked for an air leak?
Check the throttle body base gasket.
Has it got a fuel tank vent valve - if yes block the pipe off and try it

 

Makes sense. Is there any way to re-code the ecu to match the immobiliser?

Cheers.

- Craig

 

Someone hasn't fitted the fuel filter the wrong way around have they?