Miss fire under load

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Miss fire under load

Postby Mohammed30 » Wed May 11, 2016 8:59 pm

Hi I have a seat Cupar it has a strange missfire under load on motorway driving came up with p0300 rNdom missfire p0301 to p0304 cylinder 1/4 miss fires also detected. Wight so far the vehicle had had coils and plugs. Vehilcle had gone out came back with eml on motorway driving under acceleration. We checked low pressure fuel no stable changed low pressure fuel pump. Which is good know also replace pcv valve which was modified and also replaced Evan canister as it was blocked no many miles this vehicle has approx 45k 2008 model. I have scoped the fuel pressure sensor on rail I have 5 volt batter signal 5 volt and earth when scoped and vehicle is revved the maximum volts I get out of signal wire is 2.6 volts surety should I not be looking for 4.5 to 5v please could some body assist me in this. I think I ha pave fuel pressure issue still ecpven adder rep,acing low pressure pump. ???

I can see the missfire with diagnostic machine at idle soon as I wide open the throttle but the missfire can not be felt straight way at idle it can be felt if revs are kept constant but only briefly.
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Re: Miss fire under load

Postby STC » Thu May 12, 2016 8:06 am

Is this Manifold or Direct Injection ? Engine Code Please ?

the maximum volts I get out of signal wire is 2.6 volts surety should I not be looking for 4.5 to 5v

Don't be too swayed by that just for now, If it is "demand controlled" then it may not give "Full Beans" stood still.

Does your Scan tool give you Actual & Desired Fuel pressure ? You could verify the integrity of the FRP by Teeing in a Fuel Pressure Gauge. Don't overlook Fuel Flow !!

You might want to confirm, before you tie yourself up in knots, what type of misfire you have.
What is the upstream O2 doing as it misfires, you could tie in Injector durations, Secondary Ignition ...

You really should stop bolting new bits on it until you find the fault, just makes the job harder and more expensive.
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