Need Help
I thought I had a faulty MAS or Throttle Potentiometer when my 1990 XJ would not go over 2500 RPM. I could put the peddle to the floor, but it would just suck air and slow down until you took your foot off the gas and the engine would run again. I was surprised when voltage test readings showed that they seemed to be OK, but the current from the ECU to the MAS was way too low. All the connections and wires are in good shape. It shows fault 18. I have replaced the fuel filter, checked the wires, plugs, distributor cap and air filter. The car cranks right up and runs fine until you get to 2500 RPM. Do you think it is the ECU?
Thanks,
Chris Heuer

 

"Suck air" or hissing?

Sounds like you should check for a plugged up cat (catalytic convertor) or cats, Chris.

 

I'd get a fuel pressure gauge on your engine. What you describe sounds to me like a fuel pump that can't keep up. And the code 18 fits with that, too. That code sets because the ECM knows that if you open the throttle and the RPM's and air flow don't follow, something is wrong, up pops code 18.

Trick could be right about the cat, but I'd check the pump first.

Cheers,

 

Good stuff Steve,

These fuel pumps cause a lot of issues, masked by a lot of symptoms.