HELP please! car running poorly

Ok, i've tried a few things already, the car used to drive fine, pulls well through the rev range to redline, now car is hesitant and sounds rough and lost alot of power 4k+

ive changed plugs, leads, distributor cap and rotor arm, fuel pump. also cleaned injectors.

nothing significant has happened between running well and like a bag of hammers..

any suggestions on what to check next please would be greatly appreciated.

Thanks, Dean.

Here's a few ideas:


Are the ignition leads on the right way round?
Fuel contamination or blockage?
How did you clean the injectors?
Have you reset the mixture after fiddling with the fuel system?

just cleaned them with carb cleaner. how should i have done it?

yes the leads are correct,

fuel blockage? how could i check?? started loosing power on the motorway, halfway through a trip.

i never reset the mixture, but i tried adjusting it when i  lost power, it is now back to original setting…  the car started to run poorly halfway through a 90 mile trip, this is why i dont know what it could be.

so i would also assume fuel is not contaminated as i drove 80miles previous on same tank.

thanks, dean

Could be overheating then, or something like the head gasket (unlikely tho unless there's other symptoms?)

Fuel contamination - can only really be 100% checked with a fuel pressure test.

If its a slight power drop during a long trip, I'd go for overheating though, so check the cooling system out.

the loss of power started mid trip, but now it is constant from cold, dont think its head gasket as water and oil ok, also spark plugs look identical.

ok, tried a few things, now i'm thinking maybe, inlet manifold cracked, or inlet manifold gasket?

also could it be the fuel pump, or fuel pump relay?  what symptoms would i look for, for a fault with these?

thanks Dean

deanosupremo said

ok, tried a few things, now i'm thinking maybe, inlet manifold cracked, or inlet manifold gasket?

also could it be the fuel pump, or fuel pump relay?  what symptoms would i look for, for a fault with these?

thanks Dean

Its very unlikely to be a cracked inlet manifold, they are strong and don't 'crack up'. Its also unlikely to be an inlet manifold gasket - at high load, the inlet is under less vacuum, so you'd see LESS of a performance issue here, compared to idle etc.

Again unlikely to be fuel pump (you've just replaced it!). Fuel pump relay? Either works or doesn't, really.

Its possible its an vacuum leak of some kind, and then the car has been 'compensated' so it idles okay but the fault shows up at high speed. But….unlikely in my mind.

Basically, you need to check the mixture and I'd also do a fuel pressure test too.