throttle pot, or not?
Discussion
The very day I sat and thought how lucky I was to have a reliable wedge.....
Started the car up('89 350i) from cold and all was not well. Felt just like fuel starvation. Once hot the idle revs (usually 900) hunted rapidly between 5-600 with a regular beat, if that makes sense, and felt like it would stall any minute but didn't. Problem disappeared then came back with a vengeance. Car shudders like mad on a light throttle, improves with a bit more welly but still holds back.
For a few years now the car has cut out when hot and engine restarted - typically if I stop for petrol.Turn engine off, fill up, restart and then it stalls, but rights itself after a few high revs.
Does it sound like the throttle pot and what readings am I looking for when testing it?
Thanks...........
Started the car up('89 350i) from cold and all was not well. Felt just like fuel starvation. Once hot the idle revs (usually 900) hunted rapidly between 5-600 with a regular beat, if that makes sense, and felt like it would stall any minute but didn't. Problem disappeared then came back with a vengeance. Car shudders like mad on a light throttle, improves with a bit more welly but still holds back.
For a few years now the car has cut out when hot and engine restarted - typically if I stop for petrol.Turn engine off, fill up, restart and then it stalls, but rights itself after a few high revs.
Does it sound like the throttle pot and what readings am I looking for when testing it?
Thanks...........
white said:That sounds like vapourisation in the fuel rail. This is not uncommon with a hot engine and clears as soon as the pump has purged the rail with fresh fuel. My 4lt did it during the hot spell recently when stopped and restarted shortly thereafter.
[snip]
For a few years now the car has cut out when hot and engine restarted - typically if I stop for petrol.Turn engine off, fill up, restart and then it stalls, but rights itself after a few high revs. ...
Sorry I can't comment constructively on your main question though.
Streaky
Thanks for the replies so far. I'm fairly sure it's a fueling problem - I,ve just been to pick it up from the garage and it ran faultlessly until the cold-start injector had done it's job and then it started misfiring again. It idles almost as if only one bank of injectors was working. It'definitely not the ignition module, or the throttle pot which is giving me 0.28v closed - 4.4v fully open. This is my only car at the moment so any suggestions would be appreciated.
You should be able to feel the injectors firing if you hold a finger on them. Failing that, pull off the rubber boot, and poke the leads of an LED into the two terminals. Although dim, you should be able to see if the LED lights with the firing pulses. You have to try the LED both ways as they're polarised. Still not sure? Hang an oscilloscope on the injectors...
With the ignition on but the engine off, if you flick the throttle open quickly, you should hear a click as all the injectors fire. This is the 'foot-down' signal asking for extra fuel.
Check the fuel rail presure: obtain a small pressure gauge scaled, say 0-5 bar with a pipe tail on the inlet. Disconnect the fuel pipe from the cold start injector and plumb in the gauge. Fire up the engine. You should get about 2.5 bar, which holds once you switch the engine off. This will tell you the pump is OK and nothing leaking unduly (injectors sometimes dribble).
Also, remove the pipes from the auxiliary air valve and look through it with the ignition switched on (engine cold). It will take a few minutes but you should be able to watch the blade close off the orifice.
Try changing the ECU water temp sensor. It's only about 12 quid from Range Rover.
Ian
With the ignition on but the engine off, if you flick the throttle open quickly, you should hear a click as all the injectors fire. This is the 'foot-down' signal asking for extra fuel.
Check the fuel rail presure: obtain a small pressure gauge scaled, say 0-5 bar with a pipe tail on the inlet. Disconnect the fuel pipe from the cold start injector and plumb in the gauge. Fire up the engine. You should get about 2.5 bar, which holds once you switch the engine off. This will tell you the pump is OK and nothing leaking unduly (injectors sometimes dribble).
Also, remove the pipes from the auxiliary air valve and look through it with the ignition switched on (engine cold). It will take a few minutes but you should be able to watch the blade close off the orifice.
Try changing the ECU water temp sensor. It's only about 12 quid from Range Rover.
Ian
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