Combustion Faults · Gauteng
Cranks, But Won’t Start.
Fuel and Ignition First.
The engine is turning. It still will not fire. That points to fuel, air in the lines, glow plugs or spark — not a new starter. We prove delivery and ignition on site across Gauteng.
- Fuel and ignition diagnosis
- Diesel glow plug checks
- Petrol spark and carburettor
- Onsite Gauteng repairs
The Fault
Strong cranking means the starter is not the story
If the starter is spinning the engine at a healthy speed and the set still will not fire, the start circuit has already done its job. The fault is now whether fuel and ignition (or compression heat on a diesel) are present at the right time. That is a different job from a generator that does not crank at all.
On diesel generators the usual path is fuel. Air in the lines after a filter change, a lift pump that cannot hold prime, water in the tank, or injectors that no longer atomise will all produce strong cranking with no combustion. Cold-start aids matter too: failed glow plugs or intake heaters leave a diesel turning over without firing, especially on standby sets that sit for days between outages.
On petrol generators the picture is spark and mixture. A fouled plug, a failed coil, a flooded carburettor or stale fuel in the bowl will crank endlessly. Recoil and electric-start petrol units show the same combustion faults once the engine is actually turning.
We diagnose this on site for homes and businesses in Johannesburg, Midrand, the East Rand and across Gauteng. The aim is to prove fuel delivery and ignition before any injector or carburettor is stripped.
Turns over, will not fire?
Call or WhatsApp 082 057 4605. We diagnose fuel and ignition on site.
082 057 4605What You Might See
Symptoms of a crank-no-start
01
Turns over, never fires
Steady cranking, no combustion sound, no exhaust puff. Fuel is not reaching the cylinders, or there is no spark on a petrol engine.
02
Fires once, then floods
A brief catch then a fuel smell and wet plugs or injectors. Mixture is too rich, a needle valve is stuck, or the engine is being over-fuelled while cold.
03
White vapour, no run
On diesels this can be unburnt fuel from poor atomisation or glow-plug failure. It is not treated the same as overheating steam from the coolant system.
04
Runs only on easy-start spray
If aerosol starter fluid makes it fire and it dies when the spray stops, the engine can run — the standing fuel or ignition system cannot.
Typical Causes
Why it turns but never runs
Air in diesel lines
Loose fittings, a dry filter bowl or a leaking return line lets the injection pump lose prime. The engine cranks with nothing to burn.
Contaminated or empty tank
Standby diesel grows water and sludge. Petrol goes stale. Either way the pump is working on fuel that will not ignite cleanly.
Glow plugs or heaters
A diesel that cranks freely in winter but never fires often has open glow plugs or a failed heater relay — not a dead engine.
Injectors and lift pump
No spray, leaking nozzles or a lift pump that cannot feed the injection pump all look like a “won’t start” engine that is mechanically sound.
Spark and carburettor
Petrol sets: no spark at the plug, a stuck float, or varnish in the jets after the unit sat through several loadshedding weeks unused.
Kill circuit still active
A fuel-cut solenoid or ignition kill wire held in shutdown will crank forever. We prove the cut-off is actually releasing.
How We Diagnose
Prove fuel and spark before stripping pumps
- 01
Confirm cranking quality
We check that speed and battery voltage are high enough. Slow cranking is a start-circuit job, not a fuel job.
- 02
Prove fuel at the engine
Filters, lift pump output, air leaks and solenoid operation are tested before injectors are removed.
- 03
Prove spark or glow
Petrol: spark at the plug. Diesel: glow-plug circuit and cold-start aids. No guess-swapping of pumps.
- 04
Repair and start under load
Once it fires, we confirm it stays running and will take load — a set that only idles is not finished.
Fuel System
This fault often ends in the fuel path
Cranks-but-won’t-start is the fault where fuel-system repairs earn their keep. Replacing a starter will not help an engine that is already turning. Bleeding air, restoring lift-pump pressure, or cleaning a petrol carburettor is the work that actually produces combustion.
If your generator does not turn over at all, start with the no-start diagnosis page instead. Mixing those two paths is how batteries and starters get replaced on engines that never had a cranking problem.
Diesel fuel path
Tank, filters, lift pump, injection pump, injectors
Petrol fuel path
Tank, tap, filter, carburettor, spark plug
Bleed and prime
Air leaks after filter changes are a frequent cause
Related repair
Fuel system repairs when contamination is confirmed
Common Questions
Cranks but will not start — useful answers
Why does my generator crank but not start?
The starter is working. Fuel is missing, air is in the diesel lines, glow plugs are open, petrol spark is absent, or a fuel-cut solenoid is still energised. We isolate which of those is true before recommending parts.
Can a blocked fuel filter cause cranking with no start?
Yes. A filter that still looks “wet” can still starve the pump. Standby diesels that sit between outages clog slowly; the engine turns normally until it needs a real start.
Do I need new injectors if it will not fire?
Not automatically. Injectors are tested after fuel supply and air leaks are ruled out. Fitting injectors into a contaminated system repeats the same no-start a week later.
My petrol generator smells of fuel while cranking. What now?
Stop cranking. That smell usually means a flooded carburettor or a stuck float. More starting attempts wash the cylinder and foul the plug. It needs mixture and spark diagnosis, not a stronger battery.
Still unsure what the fault is? Call or WhatsApp 082 057 4605 for onsite diagnosis.
Related Services
Next steps if it still will not fire
Service Areas
Onsite diagnosis across Gauteng
We attend crank-no-start faults in Johannesburg, Pretoria, Sandton, Midrand, Centurion and across the East Rand and West Rand.
Book a Diagnosis
Engine turning, still dead?
Note whether it smells of fuel, smokes, or stays completely dry while cranking. That detail speeds up onsite diagnosis.
- Call
- 082 057 4605
- Message us on WhatsApp