Combustion Faults · Gauteng
Cranks, But Won’t Start.
Fuel and Ignition First.
If your generator cranks but will not start, the starter is doing its job and the fault lies in fuel, air or ignition. Air in the diesel lines, a blocked filter, a stop solenoid that stays shut, failed glow plugs or no spark on a petrol set are the usual causes. We prove fuel delivery and ignition on site across Gauteng.
Callout fee waived when you accept our written quote. 1-year workmanship guarantee. See prices
- Fuel and ignition diagnosis
- Diesel glow plug checks
- Petrol spark and carburettor
- Onsite Gauteng repairs
The Fault
What causes a generator to crank but not start?
If the starter spins the engine at a healthy speed and the set still will not fire, the start circuit has done its job. The question now is whether fuel and ignition, or compression heat on a diesel, arrive at the right moment. That is a different job from a generator that does not crank at all.
On a diesel, the usual cause 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 give strong cranking with no fire. Cold-start aids matter too: failed glow plugs or intake heaters leave a diesel turning without firing, especially on standby sets that stand for days between outages.
On a petrol set, we look at spark and mixture. A fouled plug, a failed coil, a flooded carburettor or stale fuel in the bowl will let it crank endlessly. Recoil and electric-start petrol sets show the same faults once the engine turns.
We diagnose this on site for homes and businesses in Johannesburg, Midrand, the East Rand and across Gauteng. We prove fuel delivery and ignition before we strip an injector or a carburettor.
Turns over, will not fire?
Call or WhatsApp 082 057 4605. We diagnose fuel and ignition on site.
Fault guide
Generator cranks but will not start: what it can mean and what to do
If the engine turns at normal speed but never fires, the fault usually sits in fuel delivery, the air supply or the stop solenoid. We check those before we touch the injection pump. This guide separates what you can safely notice from what a qualified technician tests. One symptom never proves that a particular part has failed.
Symptom, likely cause and repair
Find the line closest to what you see. The cause is the most likely one, not a diagnosis: testing confirms it before any part is replaced.
| What you see | Likely cause | Usual repair |
|---|---|---|
| Cranks normally but never fires (diesel) | No fuel reaching the injectors: empty tank, blocked filter or air in the lines | Fuel system repairs |
| Cranks, may puff smoke, never catches | A fuel solenoid that does not open or a fuel pump fault | Fuel solenoid repairs |
| Cranks after standing for months | Fuel that has aged or been contaminated with water | Contaminated diesel |
| A petrol set pulls or cranks but will not fire | A fouled spark plug or a gummed-up carburettor | Petrol generator repairs |
| Cranks slowly and will not fire | Cranking speed too low for a diesel to start, from a weak battery | Battery and charging repairs |
01
What you may notice
- The engine turns over normally but never fires
- It fires briefly or coughs and does not keep running
- The controller reports a fail-to-start after several attempts
- The set started on the last outage but not on this one
02
Possible causes
Any of these can produce the same symptom. Testing decides which one applies.
- No fuel reaching the engine: an empty tank, a closed valve, blocked filters or air in the fuel lines
- A fuel or stop solenoid that is not opening
- Water or contamination in the fuel
- A blocked air filter or intake
- Cold-start aids not working, where the engine uses them
- Low compression or an engine timing problem (less common)
- On petrol sets: stale fuel, a blocked carburettor or no spark
03
What you can safely check
Look and note only, from outside the canopy. Do not open panels, covers, fuel lines or the cooling system.
- Is there fuel in the tank, from the gauge or a sight glass you can see without opening the system?
- Was the tank recently filled, or has the fuel been standing for months?
- Do you see any smoke from the exhaust while it cranks?
- How many start attempts has the controller made, and what alarm does it show?
04
Stop using the generator and call if you notice
- Fuel leaking or a strong fuel smell
- Smoke from the starter or wiring after repeated cranking
- The battery getting hot from repeated starting
If it is safe to reach, stop the generator with its normal stop control or emergency stop, keep people away, and call a technician.
05
What a qualified technician typically tests
These are technician checks, not steps to try yourself. Several involve live electrical measurement, fuel or pressurised systems.
- Fuel delivery from the tank through the filters to the injection system
- Air in the fuel system, and bleeding it where the engine design requires
- Fuel and stop solenoid operation from the controller signal
- Fuel quality and water in the filter bowl or tank sample
- Air intake, cold-start aids and, if needed, compression
06
Common repair categories
The repair follows the test result. These are the services this symptom most often leads to.
07
What to send when you book
- Your suburb and how we reach the generator
- Make, model and kVA from the data plate (a photo is ideal)
- Fuel type: diesel, petrol or gas
- When fuel was last delivered and how long the set had been standing
- Whether it fired at all or only cranked
08
Related faults and services
Not sure which symptom fits? Try the generator symptom finder.
Safety before you check anything
- Exhaust contains carbon monoxide, which you cannot see or smell. Run a portable generator outdoors only, away from doors, windows and vents, and never run any generator in a house, garage or other enclosed space.
- A standby generator set to automatic can start at any moment, when the mains fails or on its exercise timer. Keep the canopy closed and stay clear of fans, belts and the exhaust.
- Generator output, the changeover and the control panel can be live, and some parts hold stored electrical energy after shutdown. Leave panels, covers and wiring closed for us to open.
- The engine, exhaust and coolant stay hot after running. Never open a radiator or coolant cap on a hot engine.
- Do not refuel a running or hot generator. If you smell gas at a gas-fuelled set, do not operate switches; leave the area and contact your gas supplier.
Carbon monoxide guidance: US Consumer Product Safety Commission: Generators and engine-driven tools (carbon monoxide).
Send the details on WhatsApp
This opens WhatsApp with a short message already typed: brand, model, capacity, symptoms and suburb. Fill in what you know and send it. Blank lines are fine.
- The data-plate photo is added inside WhatsApp after the chat opens: tap the attachment or camera icon and choose the photo. A link cannot attach the photo for you.
- Take the photo only when the generator is switched off and has cooled down. Do not reach over or into a running or hot generator, and keep away from the exhaust.
- A standby generator set to automatic can start by itself when the mains supply fails. If you are not sure how it is set, photograph the plate from a distance or send a photo of the whole set instead.
Typical repair costs for this fault
Published ranges, last reviewed October 2026. The callout is R400 – R700 in business hours and R700 – R1,400 after hours, and it is waived if you accept the quote. Your written quote after diagnosis is the price that applies.
- Starting fault diagnosis and repair
- R600 – R3,500
- Fuel filter replacement
- R300 – R800
- Fuel pump repair or replacement
- R1,800 – R4,500
- Injector replacement (diesel)
- R3,000 – R9,000
Step 9: book a diagnosis visit.
How We Diagnose
Prove fuel and spark before stripping pumps
- 01
Confirm cranking speed
We check that cranking speed and battery voltage are high enough. Slow cranking is a start-circuit job, not a fuel job.
- 02
Prove fuel at the engine
We test the filters, the lift pump output, air leaks and solenoid operation before we remove any injector.
- 03
Prove spark or glow
On petrol sets we check for spark at the plug. On diesels we test the glow-plug circuit and cold-start aids. We never swap pumps on a guess.
- 04
Repair and run under load
Once it fires, we confirm it keeps running and takes load. A set that only idles is not finished.
Fuel System
This fault often ends in the fuel path
This is the fault where fuel-system repairs earn their keep. A new starter cannot help an engine that already turns. Bleeding out air, restoring lift-pump pressure or cleaning a petrol carburettor is the work that brings combustion back.
If your generator does not turn over at all, start with our no-start guide instead. Mixing up the two 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 we find contamination
Common Questions
Cranks but will not start — useful answers
Why does my generator crank but not start?
Because fuel, air or ignition is missing, not because the starter has failed. The usual causes are no fuel, air in the diesel lines, failed glow plugs, no spark on a petrol set, or a fuel-cut solenoid that stays shut. We find which one before we recommend parts.
Can a blocked fuel filter cause cranking with no start?
Yes. A filter can look wet and still starve the pump. Filters on standby diesels clog slowly, so the engine turns normally until the day it needs a real start.
Do I need new injectors if it will not fire?
Not necessarily. We test injectors only after we have ruled out the fuel supply and air leaks. Fitting new injectors to a contaminated system brings the same no-start back a week later.
My petrol generator smells of fuel while cranking. What now?
Stop cranking and keep flames and sparks away. The smell usually means a flooded carburettor or a stuck float, and more attempts wash the cylinder and foul the plug. It needs a mixture and spark diagnosis, not a stronger battery.
Can a fuel solenoid stop a diesel that is cranking?
Yes. If the solenoid does not open, the engine turns and gets no fuel. We check it together with the filters and look for air in the lines before we condemn the injection pump.
Can low oil make a generator crank and then die?
Yes. Some sets crank and shut down at once when the oil switch is open. The level may be low, or the sender may be giving a false reading. Please do not keep resetting it.
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
- Fuel Solenoid Repairs Shutoff that never releases fuel
- Fuel Pump Repairs Diesel not reaching the engine
- Diesel Injector Service Hard starting and poor spray
- Generator Repairs Full onsite repair service
- Emergency Generator Repair Open 24/7, on site within 1 hour
- Generator Servicing Fuel filters and a proper run-up
- Fuel System Repairs Injectors, pumps and contamination
- Generator Not Starting No crank or no start command
- Diesel Generator Repairs Standby and commercial diesels
- Contact Call or request a quote
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.
What to send before we attend
These details help us plan the visit and bring the right parts. Send what you can on WhatsApp; if you can’t find the model number, we still book the visit.
- Location
- The suburb or site, so the visit can be booked in the right area.
- Make and model
- The generator brand and model, if they are known.
- kVA
- The size printed on the data plate.
- Fuel type
- Diesel, petrol, LPG, natural gas, or dual-fuel.
- Controller model
- The module name on the panel, when it is visible.
- Fault or alarm
- What the set does, and any text on the screen.
- Photos
- The generator, the data plate, and the controller or alarm. Send these on WhatsApp.
Book a Diagnosis
Engine turning, still dead?
Tell us whether it smells of fuel, smokes, or stays completely dry while cranking. That detail speeds up the diagnosis.
- Call
- 082 057 4605
- Message us on WhatsApp
What happens next
- We reply with questions about the generator, or to book a visit.
- A technician comes to you. For a breakdown we arrive within 1 hour.
- The fault is diagnosed on site and you get a written quote. No work starts until you accept it.
Charlie, lead technician: Degree in Mechanical Engineering, Degree in Electrical Engineering, Diesel Plant Fitter. Generator specialists since 2000.