Help!! Hard to Start, hesitation on the RPM band

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mshawari1

Member
Messages
648
Location
Riyadh
Greeting!!

After I fix the problem of the 4000 RPM surging by fixing the crank sensor wires, I have another problem:

Symptom:

- Hard to start, three or four long cranking is required.
- From idle if I WOT, it will die for a moment before the revs build.
- After 2500 RPM… it has good power till 6000 but with some hesitation.
- Given it little gas till about 2000 RPM it will die to 1000 RPM and come back again.

I’ve replace (with used parts) the ECU, Coils, MAF, Crank Sensor, Crank Sensor Harness, TPS and check the grounding points.

Anyone have any idea!!! I’m tired……..
 
Here are the things I'd be looking at:

1) Check your fuel pressure at the fuel rails

2) Check that all injectors have a continuous +12 on them while cranking, running, etc. If it's intermittent or a much lower voltage, then you may have battery or cabling problems
 
Hi John,
I find that the fuel pump jumper hose inside the fuel tank leaking too much causing pressure drop.
Now the power is good through the whole band and its start right away from the first crank… BUT,
Just after it start it will idle fine for a second then it seems that the ECU try to fix the mixture and the RPM start to jump from ~ 1200 – 200 RPM. Sometimes it dies and sometimes I notice a black smoke from the exhaust "unburned fuel".
It won't idle fine. Could it be bad oxygen sensors or stuck injector?
 

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Do the oxygen sensor failure cause that…

If I disconnect the sensors totally…. What is the symptom I will see.

Could someone try that before?
 
I would still check the fuel pressure at the rail - it will tell you multiple things. Like whether the pump is pumping enough to maintain the pressure, or whether the FPR isn't doing its job and letting the fuel pressure go too high, etc.

About a stuck injector - that's a possibility. You can try manually "firing" each one individually to see if you get a nice solid "click" when they open/close, but be aware, you'll need to do this with the fuel pump disconnected, or you'll hydrolock the engine.
 
if the ecu has to learn anything which makes it hard to start or a hesitation then
it must be a megasquirt ecu heheheheheh

while u keep changing parts why not sit down and think about afew things
and do some tests

hard to start means usually low fuel or too much fuel

try prime fuel system then turn of pump then start
is it better
try spraying more fuel down throttlebody does it start better

is the car a factory 1uz lexus or toyota or is it a conversion

oxy sensors dont usually cause this
is yr tps adjsuted ok
try starting with and without tps plugged in
same with air flow meter and afew other sensors

there is alot u could have done before u went and changed the parts
end of the day all u need is to think it over logically as the mechanical side is easy
the electrical side is the pain in the asssss and this is where most people go hell for leather and change everything and get nowhere

u should change one part at a time and then do tests hepas of them
then change another part
 


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