2002 Isuzu Rodeo - Hard starting when engine is warmed up

I have a 2002 isuzu rodeo 3.2 l Starts right away when engine is cold or after short trips. If driven several miles it becomes hard to start. any ideas?

Explain a little better “it becomes hard to start”?? Is the engine cranking slower, or cranks the same speed but takes longer to start??

I’m presuming it cranks ok in both cases, but when warmed up, on re-starts doesn’t catch and run immediately, like it does on cold starts. I’m also presuming after it does start, the engine runs perfectly in both situations. Another presumption, the check engine light is not on, and there are no diagnostic codes stored in computer memory. Mechanics call that a “hot soak” problem. It can be a little tricky to diagnose. You might Google that term, read what it says the most likely culprits are. My guess , one of these

  • a problem with the car’s evap system is purging the canister during warm starts, when it is supposed to wait until the engine is already started & running at a higher rpm. Does it start better on warm starts if you hold the gas pedal all the way to the floor during cranking?

  • the ignition system is failing when the engine compartment reaches a certain temperature, crank position sensor, ignition module, coil packs. Does opening the hood , allowing the engine compartment temperature to cool seem to help?

  • The egr is activating prematurely on warm starts. It isn’t supposed to turn on until after the engine is running. The egr system on most cars is automatically disabled when engine is cold, explaining why this isn’t noticed then. Technicians know how to test the egr system, often they can just look at the egr valve to see if it is opening when it shouldn’t. (Note: Not all engines use egr, don’t know about yours)

  • the engine is running overly lean. when cold the computer injectes extra gas which masks the problem. Ask shop to check fuel trim data.

It cranks the same speed but takes longer to start. I changed the fuel filter and put new plugs but that didn’t help

With a 21 year old engine, there are several possibilities, but I think that leaking fuel injectors are a likely cause of these hard starts when the engine is warm.

The O-rings in the FI system harden and become brittle over the years, and this inevitably leads to leaks. The pressure in the fuel rail drops, gas leaks into the intake manifold, and the spark plugs get flooded with raw gas, resulting in slow starts.

I think new injectors are in your future.

That might be vapor lock.

Have the residual fuel pressure tested.

Residual Fuel Pressure Test
When the pump is turned off or stops running, the system should hold residual pressure for several minutes (look up the specs to see how much pressure drop is allowed over a given period of time). If pressure drops quickly, the vehicle may have a leaky fuel line, a leaky fuel pump check valve, a leaky fuel pressure regulator or one or more leaky fuel injectors. Low residual fuel pressure can cause hard starting and vapor lock during hot weather.


I’m not familiar w/the Rodeo’s engine, but on my own FI cars, the injector o-rings prevent air leaks, not fuel leaks. Air leaks at injector o-rings can cause a difficult to diagnose too-lean condition, so could contribute to OP’s symptom. If injectors are leaking fuel, that would show up in Tester’s suggested test above.

No George.

The 0-rings prevent all leaks.

And I’ve seen fuel leaks much worse than that.


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Interesting vdo. I’ve never seen an injector o-ring leak fuel like that myself. As far as o-rings not causing fuel leaks, I was referring to the theory proposed above that an o-ring leak would leak fuel into the intake manifold & cause overly rich operation. VDC may be referring to an o-ring at the tip of the injector maybe. I’ve never seen that problem. I don’t think my VW Rabbit had o-rings at the tip of the injectors. I’ve never looked at the Corolla’s injectors.

It is sort of puzzling why the fuel would leak out on an exterior surface like that, what with the intake manifold suction tending to draw it in.

Thanks for the info. I was thinking it might be fuel injectors.

The entire fuel system is under fuel pressure!



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Direct injection maybe.