The happy camper

By Frank Massey | Published:  13 September, 2017

It’s only when you visit the past that you realise how far the journey to the present has taken us. Some time ago Martin, a very good friend of mine from Londonderry, sent over a set of very early EVL Bosch injectors.

This injector pattern started life around the late 1960s and ran through to the mid 1980s and was used by Ferrari, Volvo, Opel, and many others. The set supplied to me came out of a VW camper van, and like many from this era were badly rusting and contaminated from in-tank corrosion. At the time fuel lines and tanks were made from untreated mild steel, and filtration did not meet current standards of 5 microns, or 2 microns with the latest HDEV 6 injectors. The biggest single cause of wear and failure was water ingress in gasoline due to condensation and external ingress.

The injectors were in a bad condition, sticking, blocked, and dribbling. I started the cleaning process with an external pre-clean ultrasonic tank before risking contamination in our ASNU bench. Several cleaning sessions later, with a varying degree of improvement, we arrived at a fully serviceable set.

I posted them back assuming it would be the last of my involvement. I should have known better. Martin and Matthew at Conlon motors have been involved with our training programme over many years. I travel over there several times a year for onsite training, and you have guessed it, waiting for me on my last visit was the camper van.

It was running extremely rich, blowing blue smoke. You could taste the emissions. If you have ever followed a vintage car you will know what I mean. This is where a trip down memory lane started.  I have not worked on this system for many years.  In fact it was on systems like this that our current-day diagnostic processes were developed.


Possible causes
So, let’s roll the dice. A rich mixture, possible causes?

  •  High fuel pressure, nominal value 2/2.5 bar
  •  Electronic control error, nominal hot injector delivery open time 2.2m/s
  •  Uncontrolled delivery past the injector


Considering my knowledge of the injector condition and hoping further contamination had not entered the system, together with the fact I did not have my fuel pressure gauges with me,  I elected to go for electronic control error.
The first step should be to understand the critical components in forming the fuel calculation values. Bosch LE is a pretty basic system; a NTC coolant sensor, nominal value hot 1v, air vane meter, nominal value at idle 1v, throttle position switch, and ambient air sensor in air vane meter, nominal value 20º 3v.

Always simplify your first steps to ascertain what the problem is. So, my first measurement was injector open time, this was approx. 12m/s at idle.  This value represented full throttle load. My next test focused on the coolant sensor which was correct. The idle, full load switch was ok, directing me to the major load calculation component, the air vane meter.
Experience reminded me of historical problems. For example, ignition backfire through the induction system nearly always distorted the vane causing sticking and severe over-fuelling. Placing my finger in the vane aperture confirmed the vane was free, but the spring pressure was too weak.


Spring tension
The penny drops! The previous problem of blocked injectors had been compensated by adjusting the vane spring tension. This was a common tool for subtle tuning, but not a blunt instrument for error correction. How do you adjust the spring? It’s quite simple really; increase tension until the injector open value reaches 2.2m/s. I also set the air bypass bleed to a 50% position. So far so good, engine now much smoother, with no blue smoke. Time for the gas analyser. Not unexpectedly, it registered high CO. The problem of course was fuel oil contamination. An oil change reduced the CO value to an impressive 1% with HCs of 100ppm.
What relevance has this on current systems? Everything! It’s the process and discipline that’s evolved into diagnosing today’s more complex systems. I often find myself saying to training course delegates: “Don’t complicate problems, apply common sense and logic.” Things have changed dramatically. Today’s skill-sets are found in several key areas; the ability to interpret serial data, a thorough understanding of system knowledge and component responsibility. It is vital to have the ability to evaluate oscilloscope and various pressure measurements.

I have missed out the most challenging of all; the dark arts of software intervention. I should acknowledge that given 50 years of experience, the ability of diagnosis and test functions through a serial platform is staggering. I am of course referring to VM level access. Nothing else comes close.
 
Further information
Please contact Annette on:
01772 201 597 or email enquiries@ads-global.co.uk.

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