OK, so here goes.
Renault Trafic 2.1L Diesel 1992
Tried to start the engine after 4 months non use over winter. Engine was coughing and trying to start, but never turning over properly.
The longer I tried to start it the worse it got. Eventually it would just crank and not even try to start.
Poor cranking speed
Glow plugs not working
-Tested battery voltage using a multimeter.
Result 12.7V, therefore the battery is fine. I replaced it with one freshly charged from the mains just in case. Cranking speed was improved, but no change in starting.
Sounded like this:
[Poor cranking speed eliminated]
-Tested glow plugs by pointing a hairdryer on full power into the air intake and tried starting. No improvement. Likely indicates that glow plugs aren't the cause.
-Check for voltage at the head of each glow plug when the ignition is turned on. All showed the same pattern of 10.4V increasing to 10.8V before the relay turned them off.
-Double checked glow plugs by testing resistance between glow plug tip and battery ground, got 2.0 Ohms for all glow plugs. Any low resistance, if it's the same for all plugs, should indicate that they're OK.
[Glow plugs eliminated]
-Tried lightly spraying easy start into the air filter in small pulses. Engine turned over as long as the spray was present, and stopped immediately without it. This should be done without waiting for the glow plug light.
The fact that it runs as long as a 'fuel' is supplied, and can ignite the easy start via compression without the glow plugs, indicates that compression is fine and it's a fuel supply issue.
Sounds like this:
p.s. That clanking sound is bad. Lay off if you hear that, it's early ignition of the fuel that does bad things to the engine.
-Went to the petrol station and filled a jerrycan with diesel, as some places will change the mixture depending on the season. I made sure the tank was more than 50% current season blend. I actually did this before any of the other steps mentioned.
-Pumped fuel primer button several times to make sure fuel was getting to the pump. Button became firmer after a couple of presses which shows fuel is in the pipe. Also tried pumping while someone else cranked the engine.
-Tested the fuel stop valve [blue thing in the blue circle] by feeling for a light click when the ignition is turned on and off. I felt the click each time, and lightly tapped it with a wooden hammer both when activated and not activated in case anything was stuck inside.
-Undid nuts fixing fuel lines to injectors [in the red circles] by about 3/4 of a turn. Cranked engine with throttle on max and checked fuel lines for fuel dripping out.
Fuel dripped out of all lines, but a bit inconsistently with occasional gaps.
This indicates air in the fuel supply, or a bust fuel pump. Hopefully the former. It's possible that it's just some air in the top of the fuel pump, as the fuel supply was more consistent in the 2 lines that traced back to the bottom pipes leaving the pump.
-To check this I undid the fuel supply line from the filter/primer to the pump [yellow circle, a bit hard to see], and pumped the primer while holding the other end of the tube in a glass.
Fuel came out, but with occasional splurts of air.
This indicated that air is entering in either the fuel lines, the fuel filter, or the fuel primer.
-I bled the fuel system (method explained later on) and reattached everything to check there were no other problems, and noticed some diesel coming out of the fuel primer button while I was pressing it. Where diesel can come out, air can get in. I listened carefully by the primer and heard a very tiny hiss/squeak, confirming this.
Offending article shown in the second picture. The leak was between the big black button and the metal surround.
[Cause hopefully identified!]
-I reconnected everything and tried starting the engine, and it almost started a couple of times before dying again. This shows there were no other problems in the system other than the air leak.
I then went and bought a fuel primer repair kit for €16 and got to work.
So, to summarise the problem and explain the symptoms:
There was a tiny air leak in the fuel primer that had increased during winter.
This meant that when the fuel pump ran as I tried to start the engine, more and more air got sucked into the tube between the filter/primer and the pump.
The initial diesel with a little air in was enough to make the engine semi turn over, but as more and more air got in less and less diesel did, until it could only crank without starting.
I'll do a separate post with the repair job as this is already fairly long.