Vehicle details: Alfa Romeo Spider
Year: 1998
Symptom: MIL on but no symptoms,
Author: Dave Hill |
Products suited to this case study*
  • Back-pinning Probe Set

  • *At Pico we are always looking to improve our products. The tool used in this case study may have been superseded and the product above is our latest version used to diagnose the fault documented in this case study.

Alfa Romeo Spider | Misleading MIL

The symptoms

The vehicle was a 1998 Alfa Romeo Spider 2.0 Litre Twin Spark that arrived at the workshop because the MIL (Malfunction Indicator Lamp) was illuminated. The vehicle showed no other drivability issues.

Looking for the fault

In this case the first step to take was a simple code read. This revealed the following code and definition:

8 phase sensor circuit

The code would clear and stay clear KOEO (Key On Engine Off) but would return as soon as the vehicle was restarted.

We were informed that the auxiliary drive belt had recently been shredded, so armed with this knowledge, we thought it seemed sensible to check the valve timing.

This test typically takes just a few minutes to set up and perform. With a “known good capture” to refer to for comparison, this is as effective as stripping the timing covers and visually confirming that the timing marks are lined up. The added bonus of scoping the cam and crank reference marks is that it can be viewed on a running engine, when any excessive slack can be seen as “wandering”.

Here are the cam and crank position sensor captures taken both before and after the fix...

Figure 1 : Before

It had indeed jumped two teeth, which was surprising as it ran so well!

Figure 2: After

As mentioned earlier, being able to conduct a dynamic timing test can be very useful.

This time we received a 16-valve Nissan Primera whose engine was idling a little roughly and the rev counter was twitching. A quick scan revealed:

P0300 Random cylinder misfire

After reading plenty about issues with Nissan timing chains, I kind of had an idea what the problem might be.

So out came the PicoScope...

Within minutes the answer was staring me in the face. The obvious “shifting” in the cam/crank relationship is apparent to the untrained eye (must be if I spotted it ). I later removed the cam cover to check on the chain tensioner protrusion. It was approximately 12 to 15 mm and the chain felt very loose.

Talk about trouble codes throwing you off the scent! I wonder how many ignition components have been replaced unnecessarily due to this code.

Here is an example of excessive slack in the timing gear drive mechanism:

Figure 3


5 comments | Add comment

David Barzelay
September 27 2015

Fantastic way to find a source of problems and the best way to fixed is with the fantastic Picoscope tools.

Kyle Tuttle
August 26 2014

Would like to see more.Excellent article.

August 26 2010

excellent article,thanks so much the video is a big help to someone who hasn’t seen this before!

andrew Kevans
August 06 2009

I have a primera p12 in at the moment and have conducted a cam vs crank signal check which looks like the crank is one tooth advanced? the strange thing is there are no fault codes to back this up also when the car first came in it was burning oil and would not rev above 3500rpm but would start and idle fine i checked the valve timing manualy and found the inlet retarded 1 tooth due to the cost of replacing the chain the customer supplied a second hand engine which has exactly the same running problem do you have a correct waveform for a 1.8 p12 primera 2003

April 27 2009

We would also like to know how Pico was hooked also I have a suuny which idling rough tommorow I am going to hook up my Pico will let u know what happened

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Case study: Misleading MIL