ECU diagnosis

An increasing number of jobs refered to us are for ECU diagnosis.

This is often due to the expense of the new unit, or to confirm the diagnosis of another garage.

We can't test ECU's on site, but there are a number of tests that can be carried out, these tests simply prove what its not, until you are left with what it is. In many cases the ECU.

Due to the coding and immobiliser functions within modern ECU's it is sometimes better to repair the old unit.

A few simple procedures such as a global scan, for codes in all modules, not just the suspect ECU or modules as they are now known.

Check power supplies, grounds and primary signals if these are satisfactory then it's a good chance the ECU is at fault.

Many of the vehicles we test for module failure have wiring and connector faults, not ECU failure.

In this case a Landrover was refered to us for a second opinion, the owner did not trust the diagnosis or the the repair estimate.

A quick scan of the modules (results shown above) produced a number of codes.

Checking grounds, connections and lives proved satisfactory, all the primary signals to the ECU were present however there was no injector output.

As it was the holiday season, the ECU repair facility sent a un-locked ECU for the owner to use over the holidays. The repair will prove less costly than the new ECU the owner was quoted by the previous garage, plus having seen for himself that a replacement unit has fixed the intermittent non start he was more than willing to trust our diagnosis.

Not so Noble

Had a call to look at a Noble M12 GTO 3 R, not sure what this is.....nor was I.

A bit of reseach and I was in the picture, a British performance car built in small numbers.

Powered by a ford v6 as found in the mondeo but with 2 small differences twin turbo's.

The car in question had a running problem.

It was impossible to test drive the vehicle effectively due to the weather conditions, but it appears to be over boosting.

A new turbo has been fitted, this is the most likely cause, incorrect waste gate pre-load.

We suggested the shop check both turbo's and adjust accordingly.

They reported back informing us they had found a seized wastegate, however the car is booked on the rollers to confirm diagnosis.

More to follow......

Non Start after repairs

We are often called upon to advise other garages when they can't fix vehicles.
This reinforces the training need.
It is often impossible to diagnose vehicles over the phone but we can suggest procedures to garages.
This was a classic example;
The vehicle in question had been repaired in another shop.
After remedial work the car refused to start.
The only fault code 52 related to the ECU permanent memory.
The shop had sent ECU's away to remove immobiliser function, replaced transponders and receivers for the keys. But now was at a dead end.
We suggested checking fuses, however after a short time we were informed all the fuses were found to be ok.
So we suggested checking EARTH paths for the engine ECU.
The next call thanked us for our help, and enquired about courses in the near future.

Common Rail

Diesel common rail has been around for a while now and we are starting to see more and more problems with these systems.
This being the case we use a number of different techniques to diagnose problems.
The pump is the heart of the system, one quick test we perform is cranking pressure generation.
These pumps have to deliver around 250 bar during cranking or the engine will not start.
So this test can be carried out using a scan tool, or scope.
I prefer the scope as I like to measure the time taken to develop this pressure.
The different systems have similar rise times and it can be a good indication of system functionality.

This example from a cp1 Bosch system fitted to a Peugeot Hdi shows a pressure rise of less than 1 sec. You can see the pump strokes contribute evenly this is a good pump, with good primary supply and no excessive leakage from the high pressure components.

Serial Data analysis for DUMMIES.

The ability to graph serial data makes analysis easy.

In this example the CTS output is being monitored to check for the cause of a 17704 fault code.

The code relates to a cooling system malfunction, and the ECU monitors the CTS for this code so its a good place to start.

We were expecting an error in temperature reporting or thermostat failure.

We were not disappointed.

Fuel Trim in action

There are plenty of articles and much is spoken of Fuel Trim analysis.

However the message has got confused, after attending seminars by 'experts' I was alarmed at the level of miss information.

Looking at oxygen sensor readings will show trends, however the Trim will continue to adjust fuelling so fuel problems are effectively masked, ensuring correct catalyst operation. So much so that the O2 sensor could show normal response, despite abnormal conditions.

One 'expert' suggested measuring response time of the pre cat sensor after over run as a method of measuring short term fuel trim, utter nonsense. The response time will depend on many variables, the biggest being the distance from the exhaust valve that the sensor is positioned. The quanity and temperature of the exhaust gas content will also effect the response time. How can a 1.1 N/A expect to have the same response time as a 2.0 turbo.

Another misleading piece of advice was the true condition is always reported by the post cat sensor. While this has some foundation, the post cat sensor will report on the effectiveness of the catalyst, so should show less oxygen than the pre cat in a correctly fuelled engine. If the catalyst is faulty the post sensor may indicate a lean condition, that simply does not exist.

The best way to evaluate the trim is to use serial data, comparing long and short term trim at different engine load and speed sites.
Forcing the engine lean (on overrun) and rich (on snap throttle) will show oxygen sensor response but little about trims.

Burnt Out

I was called in to look at a Ginneta G50 race car that was burning out relays.

Used in the British GT Championship it would start and run fine but would burn out its relay before the end of the race resulting in a DNF.

A new pump and a few different relays had been tried, but the fault remained.

I used a amps clamp to test current draw, on the control and output sides of the relay.

I discovered that the control side of the relay had abnormal current draw, but where was the resistance, classic cause and effect diagnosis.

The effect = burnt out relay.

The cause = excessive resistance in the circuit.

A quick check with the scope(image shown above) showed higher than acceptable volt drop on the earth circuit.

This after prolonged used caused the relay failure, replacing a section of loom had this GT4 back on the grid.