Generator not starting, or cranking but not firing
Stand at the panel, press start, and listen. Everything below depends on which of two faults you have — and getting that split right takes ten seconds and saves several hours.
The split that decides everything
Which of these two is it?
Most time wasted on a no-start is spent bleeding fuel on a set whose real problem was a battery, or condemning a starter on a set that had run its tank dry.
Branch A
The engine does not turn
Nothing, a click, or a slow laboured turn.
- Battery, cables and earth strap
- Isolator and emergency stop
- Starter motor and solenoid
- The controller's start output
Branch B
It turns normally but never fires
Cranking speed sounds right, it just does not catch.
- Fuel supply and solenoid
- Air in the fuel system
- Filters and water separator
- Compression and injectors
Put the controller in Stop or Manual before you open a panel, go near a belt or fan, or touch a battery terminal. Never work on a set left in Auto. Isolate the starting battery before working near rotating parts or on the starter circuit. Treat the alternator terminal box and the outgoing breaker as live even with the engine stopped. Turbochargers, manifolds and exhausts stay hot long after a shutdown. And if the set has been cranked repeatedly the starter will be very hot — let it cool, because a few minutes of continuous cranking will destroy a serviceable starter.
Branch A
It will not crank
Nothing at all — no crank, no click, dead panel
- Battery voltage. 12 V systems sit around 12.6 V at rest, 24 V systems around 25.2 V. What matters more is what happens when you press start: if voltage collapses to single figures the battery is finished. A surface charge reads healthy on a battery with no capacity left — use a load tester if you have one.
- Battery isolator. Left open after the last service. Costs nothing to check.
- Emergency stop. A latched mushroom button kills everything, and so does a break anywhere in the E-stop wiring loop. Twist the button out, then check the loop. Most controllers need the E-stop released and the alarm reset.
- Controller DC supply and fuse. A blown DC fuse looks exactly like a dead battery. Check it before you order one.
- Terminals and earth strap. Corroded or loose battery terminals and a corroded block earth strap are the commonest cause of a no-crank that "was fine last month". Clean to bright metal, remake tight, protect.
One click, no crank
- The solenoid is pulling in and the starter is not turning: volt-drop, a failed starter, or an engine that will not rotate.
- Measure voltage at the starter main terminal while cranking, not at the battery. A healthy battery with a bad cable gives exactly this symptom.
- If battery voltage holds and starter voltage collapses, the fault is the cable or the earth path.
- If supply is good, bar the engine over by hand at the flywheel with the battery isolated. If it will not rotate, stop. A hydraulically locked or seized engine cranked hard bends connecting rods.
Cranks, but slowly
- Weak battery, bad connections, or oil too thick for conditions — and in UAE ambient temperatures it is almost never the oil.
- Heat is harder on a lead-acid battery than cold. A battery giving four or five years in a temperate climate gives noticeably less here.
- A set that cranks slowly on a warm morning has already told you what it will do on the morning the mains drop.
Cranks on manual, never starts on mains failure
- Not a starting fault. The engine is fine; the controller is not being told to start.
- Check the controller is in Auto, check its mains sensing, and check the start signal wiring and the changeover control supply.
- Panel-side work: control panel and AVR repair.
Branch B
It cranks normally but never fires
The engine is being turned fast enough. It is not getting fuel, it is getting air with the fuel, or it has lost compression.
- Is there fuel, and is the tap open? Dip the tank physically rather than trusting the gauge — a failed level sender reading a quarter full on an empty tank is a genuinely common callout. Check every valve between tank and engine, including any a contractor may have closed.
- Does the fuel solenoid energise? On a mechanically governed engine, put a hand on the solenoid while someone cranks. You should feel it pull in and, critically, hold after the crank signal ends. One that pulls in and drops out gives an engine that fires and dies within a second.
- Is there fuel at the injectors? With the engine cranking, slacken a high-pressure line at an injector and look for delivery. Keep hands clear — injection pressures penetrate skin. This is done with a rag and a screwdriver, not a fingertip. No fuel at the injector with fuel in the tank means the lift pump, the filters, the solenoid or an air lock.
- Air in the fuel system. It cranks and cranks, fires briefly, then dies — or it started perfectly until someone changed the filters. Air enters on the suction side, so the leak is at a filter seal, a hand-primer, a union, or a cracked line between tank and lift pump. Bleed at the filter head then at the injection pump, in the order the engine manual sets out, until fuel runs clear of bubbles. If it fills with air again overnight you have not found the leak.
- Filters and water separator. Drain the bowl and look at what comes out. A layer of water under the diesel, or dark slime at the interface, changes the whole job: the fault is in the tank, and new filters will block again within days.
- Compression, if it only fights when cold. A set that starts fine warm and fights cold is telling you about compression, injector condition or a failed cold-start aid. That is a measurement job — a compression test and injectors on a bench. See injector repair and calibration and diesel fuel systems.
Read the alarm first
What the panel is telling you
Read the alarm and the event log before you do anything else. Some no-start alarms name the fault outright.
| Panel says | What it usually means |
|---|---|
| Fail to start | The controller cranked for its configured attempts and never saw firing speed. Fuel, starting, or speed sensing. |
| Crank attempt 1 / 2 / 3 | It is counting attempts. Watch what the engine actually does on each one — that is the diagnosis, not the count. |
| Loss of magnetic pickup | The controller cannot see engine speed. The set may be running fine and being shut down by a blind controller. |
| Charge alt failure | The battery charging alternator is not producing. Belt, alternator, or the excite wire. The set runs until the battery flattens, then will not start again. |
| Emergency stop | The button, or a break in its wiring loop. |
| Locked out | A shutdown has latched. See generator locked out fault. |
| ECU red / amber | The engine's own ECU is refusing or complaining. See ECU warning lights. |
The fault that looks like a no-start and is not
Loss of magnetic pickup produces a set that appears not to start when it is in fact starting perfectly well. The pickup reads the flywheel ring gear; if it has failed, or its air gap has drifted, or its screened cable has chafed, the controller sees zero rpm, decides the start failed, and cuts the fuel. The engine you can hear running is being shut down by a controller that cannot hear it.
Stop — do not keep cranking
Five reasons to put the key down and call
- The engine will not turn by hand
Seizure or hydraulic lock. Cranking it harder is how the damage becomes permanent.
- Coolant or fuel in the oil, or a rising oil level
A leaking injector, an injection pump seal or a head gasket. Do not run it.
- It fires with a knock and stops
Stop, and leave it stopped.
- Any burnt smell from the alternator terminal box
That is a winding fault, not a starting fault.
- It has been cranked for several minutes
Starter and battery are both being destroyed, and unburnt fuel is sitting in the cylinders and exhaust.
Why it happened
Why standby sets fail to start here
Almost every no-start we attend on a standby set traces back to one of three things — and all three are consequences of the set sitting still rather than running.
The battery
Not charged, not maintained, or simply old. UAE heat shortens battery life materially, and a charger that has quietly failed or been unplugged leaves a set that looks ready and is not.
The fuel
Warm, part-empty tanks make condensation; condensation makes water; water in a diesel tank in this climate makes microbial growth. That blocks filters, corrodes tank floors and pushes abrasive debris through injection equipment worth far more than the fuel.
Time, not hours
A set running twenty minutes a month never reaches a running-hours service interval, but its coolant inhibitor, rubber, fuel and battery degrade on the calendar anyway. The failure appears on the one day the mains actually drop.
What prevents all three
A test start under load, and a maintenance regime that works on the calendar rather than the hour meter. Interval by interval on the maintenance checklist, and the servicing itself on preventive maintenance.
Before you phone
What to have ready when you call
Send it to +971 50 767 9050 on WhatsApp. We can usually tell you before anyone travels whether it is something you can put right on site — and if it is, we will say so.
The machine
- Genset make, model and kVA
- Engine and alternator nameplates
- Controller make and model
- Running hours, and when it last ran successfully
The fault
- Which branch you are in — does it crank or not?
- A photograph of the alarm screen and event log
- Battery voltage at rest and while cranking, if you have a meter
- What changed before the fault: a fuel delivery, a service visit, a power cut, a new load
What comes to the workshop in Industrial Area 15 and what is fixed where the set stands is set out on generator repair and service. Planned work and quotations: jacob@abradiesel.com.
Common questions
No-start faults, answered
My generator cranks but will not start. What is the most likely cause?
Fuel, in some form: an empty or isolated tank, blocked filters, a fuel solenoid that is not energising or not holding, or air in the system after a filter change. Check the tank physically, check the solenoid operates, then check for fuel at an injector while cranking. If all three are good and it still will not fire, you are looking at compression or injectors — and that needs measurement rather than guesswork.
My generator will not crank at all. Where do I start?
Battery voltage while cranking, the battery isolator, the emergency stop and its wiring loop, and the controller's DC fuse — in that order. Between them they account for the large majority of no-crank faults. A single click without rotation points to volt-drop, a failed starter, or an engine that will not turn.
How do I restart a generator after an emergency stop?
Release the mushroom button by twisting it out, then reset the alarm at the controller. If the panel still shows emergency stop with the button released, the fault is a break in the E-stop wiring loop rather than the button itself. Before restarting, find out why the button was pressed — if someone stopped the set for a reason, that reason is still there.
Can I keep cranking until it starts?
No. Continuous cranking overheats the starter, flattens the battery and fills the cylinders and exhaust with unburnt fuel. Follow the engine manufacturer's crank and rest pattern, and if it has not fired after a few attempts, stop and diagnose. Repeated cranking turns a cheap fault into two expensive ones.
What does "charge alt failure" mean on the panel?
The battery charging alternator on the engine is not producing output. The belt is slack or broken, the alternator has failed, or the excite wire between it and the controller is broken. The set will run on the battery until it flattens and then will not restart — which is why this alarm is often the reason behind next month's no-start.
The engine runs but there is still no power. Is that the same fault?
No, that is a different page. The engine side is fine and the fault is in excitation, the AVR or the windings. Go to generator running but not producing power.
Related
Where to go next
Generator will not start and the site is off supply?
Call or WhatsApp. Tell us whether it cranks, and send a photograph of the controller screen and the data plate. Open 7 days, 07:00–20:00.