SBC 350 Long Crank Before It Fires
TL;DR: A small block Chevy that cranks four, six or ten seconds before it catches is usually losing residual fuel pressure while it sits, and the leak is normally an injector, the pressure regulator or the pump check valve. The next most common cause is a temperature signal that is lying to the computer, so a cold engine never gets its cold-start enrichment. Spark quality, cranking speed, cam timing and compression round out the list. Test in that order, because the fuel pressure hold test is the cheapest one and it catches most of these engines.
What "long crank" actually tells you
The distinction that matters is when it happens. Write down the pattern before you touch anything, because the pattern narrows the cause faster than any parts swap.
- Long crank only after sitting overnight, normal restart when warm. Classic pressure bleed-down. Fuel is draining out of the rail or throttle body while the engine sits, and the first seconds of cranking are spent refilling it.
- Long crank only when hot, fine when cold. Points toward heat soak, fuel percolating in the lines, or an ignition module that stops behaving once it is up to temperature.
- Long crank every time, hot or cold. Points at something constant: a sensor out of range, a pump that never builds proper pressure, low compression, or cam timing that has walked.
- Long crank that arrived gradually over a year or two. Wear. A tired pump, a timing set stretching, rings and valves losing seal.
The Gen I small block is a cam-in-block, pushrod V8, so there are no cam phasers or lash adjusters in the picture to complicate a slow start the way there are on an overhead-cam engine. That is good news - the list is short and every item on it is testable.
Cause one: the engine is not holding fuel pressure
This is the most common answer on a fuel-injected 350, whether it is a throttle-body-injection truck engine or a later Vortec with the central port injection assembly under the intake.
The test. Put a gauge on the fuel test port. Turn the key on without cranking, let the pump prime, then shut the key off and watch the gauge. Pressure should hold and fall only slowly. If it collapses in seconds, you have found your long crank. Confirm the correct pressure specification and the allowable hold time for your year and fuel system in the factory service information - throttle-body and high-pressure port systems run very different numbers, and a figure carried over from the wrong system will send you down the wrong road.
Where it leaks. There are three realistic places:
- Back into the engine, through an injector. A leaking injector or a weeping poppet nozzle in the central port assembly dumps rail pressure into the intake and puddles fuel where it does no good. Often comes with a fuel smell at shutdown and a rough first few seconds. Injectors on an engine this age are a wear item and are worth doing as a set - see fuel injectors and fuel system parts.
- Back to the tank, through the pump check valve. If pressure falls with the engine off but you can trap it by pinching the supply line, the loss is upstream at the pump assembly.
- Through the pressure regulator. A ruptured regulator diaphragm pulls fuel into the manifold through the vacuum reference line. Pull that line - if it is wet with fuel, you are done diagnosing.
The two-minute confirmation. Cycle the key on and off three or four times before cranking. Each cycle runs the pump prime. If the engine then fires immediately, you have proven the problem is pressure at start, not spark and not compression.
Cause two: the computer is getting a bad temperature signal
A coolant temperature sensor that has drifted is a cheap part causing an expensive-feeling symptom. If it reports the engine as much warmer than it really is, the computer trims out the cold-start enrichment and a genuinely cold engine cranks and cranks on a mixture too lean to light.
The tell is a cold-start-only complaint that ignores everything you do to the fuel system, sometimes with an idle that hunts for the first minute. A scan tool makes this a thirty-second diagnosis: after an overnight soak, the coolant temperature the computer reports should agree with ambient air temperature. If the engine has sat all night in a fifty-degree shop and the sensor claims one hundred and forty, that is your fault - and it will often read plausibly once hot, which is exactly why it slips past a quick check.
While you are in there, look at the intake air temperature reading and the throttle position reading at closed throttle. These are inexpensive parts that skew fuelling in precisely the way that produces a long crank. Browse engine sensors for the family you are working on.
Cause three: spark that is present but weak or late
An engine with no spark will not start at all, so a long crank means spark exists. The question is whether it is strong enough and arriving at the right moment.
On a distributor small block, the parts that produce a weak-spark long crank are the cap and rotor, the coil, the ignition module and the pickup coil in the distributor. Corrosion inside the cap and a track burned across the rotor are common on engines that have sat, and both get worse when everything is damp. A failing module is the classic hot-restart complaint: fine cold, then it refuses to trigger cleanly once it has soaked at temperature.
Base timing is worth checking too. Timing that has drifted retarded makes an engine crank longer before it catches and feel soft off idle afterwards. Set base timing using the procedure specified for your engine and year rather than by ear. Cap, rotor, coil and module all live in ignition components.
Cause four: it is turning over too slowly to start
An engine that sounds like it is cranking normally may not be. Marginal batteries and corroded grounds are the most under-diagnosed cause of a long crank on an older truck, because they degrade slowly enough that the owner recalibrates to them.
Load test the battery, then measure the voltage drop across the negative cable to the block and across the engine-to-body ground strap. A tenth of a volt is fine; half a volt is a fault. Starters draw more current as they wear, and one pulling excess current will drag cranking speed low enough that the engine cannot build the cylinder pressure or the spark energy it needs.
Cause five: the engine has lost its seal or its cam timing
If fuel, spark and cranking speed all check out, compression itself is on trial.
Compression and leakdown. Test all eight holes with the throttle held open. One low cylinder against seven good ones is a valve or a gasket. All eight low and even is rings, or a cam that has moved. Follow with a leakdown test to find where it is going: out the exhaust is an exhaust valve, out the intake is an intake valve, into the crankcase is rings, into the cooling system is a head gasket. Head gaskets and the rest of the sealing package are in gaskets and seals.
Timing chain stretch. The original small block timing set is a known wear item, and the factory nylon-toothed cam sprocket used on many of these engines shed teeth as it aged. A stretched chain retards cam timing, which softens cranking compression and makes the engine slower to fire. It also lets the distributor - driven off the camshaft - wander in relation to the crank, so ignition timing goes with it. Check for slack by turning the crankshaft and watching how far it moves before the rotor responds. If it has stretched, replace the whole set rather than the chain alone: timing chains, gears and tensioners.
Vacuum leaks. A failed intake manifold gasket, a cracked brake booster hose or a leaking PCV grommet leans out the cold start when the engine can least afford it. Smoke test before condemning anything expensive.
Test order that saves the most time
| Step | Test | What a failure points to | Effort |
|---|---|---|---|
| 1 | Key-cycle prime three times, then crank | Fuel pressure bleed-down | Two minutes, no tools |
| 2 | Fuel pressure gauge, hold test after prime | Injector, regulator or pump check valve | Low |
| 3 | Vacuum line to the regulator - is it wet? | Ruptured regulator diaphragm | Low |
| 4 | Coolant temperature reading after overnight soak | Temperature sensor out of range | Low, needs a scan tool |
| 5 | Battery load test and ground voltage drops | Battery, cables, grounds, starter | Low |
| 6 | Spark quality, cap, rotor, coil, module | Ignition wear or heat failure | Moderate |
| 7 | Base timing check | Timing drift or distributor position | Moderate |
| 8 | Compression, then leakdown | Rings, valves, head gasket | Higher |
| 9 | Chain slack check at the rotor | Stretched timing set | Higher |
Do not jump to step 8 first. Most long-crank small blocks are solved between steps 2 and 4, on some of the least expensive parts on the engine. Budget roughly an hour of shop diagnostic time to get through the first five steps, and a further hour or two if it goes as far as compression and leakdown.
Frequently Asked Questions
Why does my Chevy 350 crank for several seconds before it starts, but only in the morning? Because it is losing residual fuel pressure while it sits. The first seconds of cranking are spent refilling a rail or throttle body that drained overnight. Prove it by cycling the key on and off three or four times to prime the pump before cranking - if it then fires straight away, the fault is a leaking injector, a leaking pressure regulator, or a failed check valve in the pump assembly.
Can a bad coolant temperature sensor cause a long crank on a 350? Yes, and it is one of the most commonly missed causes. If the sensor reports a cold engine as warm, the computer removes the cold-start enrichment and the engine cranks on a mixture too lean to light. After an overnight soak, the coolant temperature the computer reports should match ambient air temperature. If it does not, replace the sensor before chasing anything else.
Is a long crank a sign my 350 needs a rebuild? Usually not. Rings and valves that have lost enough seal to cause a hard start also show up as low, even compression across all eight cylinders and as oil consumption or blowby you would already have noticed. Run compression and leakdown tests before accepting that answer - fuel, sensor and ignition causes are far more common and far cheaper.
Does a stretched timing chain make an engine hard to start? It can. A stretched chain retards cam timing, which lowers cranking compression, and because the distributor is driven off the camshaft it drags ignition timing along with it. Check for slack by turning the crankshaft and watching how far it moves before the rotor responds. If the set is worn, replace the chain and both gears together.
Why does my 350 start fine cold but crank a long time when hot? That pattern points at heat rather than fuel drain-back. The usual suspects are an ignition module that stops triggering cleanly once it has soaked at temperature, fuel percolating in lines or a throttle body sitting over a hot manifold, or a starter drawing enough current when hot to drag cranking speed down. Test the ignition module hot, not cold, and watch cranking voltage during a hot start attempt.
Should I replace all the injectors or just the leaking one? On an engine old enough to have a leaking injector, do the set. The others share the same age, the same fuel and the same heat cycles, and the labour to reach them is identical whether you change one or eight. Confirm the correct application against the manufacturer's catalogue for your exact year and fuel system before ordering.
Sources
Written from the Core Powertrain Parts technical team's field experience with the GM Gen I small block V8 across carburetted, throttle-body-injection and Vortec central-port applications, our internal engine-family reference for cam-in-block pushrod V8 layout and camshaft-driven distributor drive, and this store's own fitment and product taxonomy. All fuel pressure specifications, pressure hold times, base timing values and procedures, sensor resistance and voltage tables, compression and leakdown limits, fastener torque values and part numbers should be confirmed against the current GM service information for the specific year, engine RPO and fuel system, and against the manufacturer's catalogue and installation data for any part being fitted.
Parts for this engine family: SBC 350 parts and the wider small block Chevy engine parts range. Free shipping on orders over $70. Fitment questions: sales@coretransmissionparts.com.