Suddenly hard to depress accelerator?

[Greystroke]

Hi all, over the last couple of days we've noticed our accelerator is suddenly rather hard to depress past a certain point. It moves free and smooth as it always has until about half way down, then suddenly gets really hard, almost like there's a back pressure on it. You can force it down and the engine revs through fine, but what's causing it? I thought maybe we had a boost leak at first as the turbo wouldn't spool more than 4psi, but if you push down hard it works like normal. Doesn't feel like the usual old cable situation, so need some ideas. Cheers.

 

[coldtaco]

cable get a internal failure?

 

[AirheadNut]

Can you disconnect the cable on the engine end and try pressing the accel. pedal? That would determine if the cable is bad or not.

 

[Greystroke]

I'll try that this evening and get back about it.

 

[Greystroke]

Checked it tonight when I got home. With the engine off the accelerator goes all the way down with ease, engine running it goes firm at about halfway again. Can't afford the down time of a mechanic at the moment but this car is starting to get the better of me lately.

 

[AirheadNut]

Bummer. Sounds like an internal problem in the injector pump?

 

[Greystroke]

Put the same info on the troop carrier of Australia Facebook page and got a few more ideas to work thorough. So far I've got;

- Turbo boost leak, compression coming back through valves and creating an over pressure at the butterfly valve. (Doesn't seem likely to me as the butterfly valve in a 12ht is always full open when running, accelerator controls fuel delivery not air)
- Something stuck under the peddle (nothing there)
- Throttle linkage stuck (disconnected accelerator cable and both move freely when engine is not running)
- Bent throttle body or sticking shaft (see first point. This would make ignition and shutdown difficult but no affect while running. Startup and shutdown are working fine)
- Idle up solenoid stuck (in my mind this makes the best sense, all parts of the throttle move freely while the engine is off, making vacuum is pretty much the only thing that changes when running. If it were the injector pump, shouldn't the firmness always be felt even when the engine is not running? The idle up solenoid sits directly on accelerator linkage, if it has seized or is otherwise playing up via vacuum issue, it would be applying constant pressure to the linkage making it hard to move past a certain point)

The last one is what I'm hoping for but will have to wait and see really.

 

[Greystroke]

Update. So the drive into work today was smooth as... I'm at a total loss as to what was causing this issue. I did 3 things recently to the engine none of which I thought would have caused this. 1 put a new gasket on the air intake. 2 cleaned the boost gauge hoses by blowing down them (I'll come back to this). 3 changed the spring in the boost controller.

Number 2 is interesting to me as I have the boost gauge plumbed into a hose which is connected to some sort of valve (can't find any info on it so no clue what it actually does but I think it's a one way valve). This hose is the pressure outlet from the crossover pipe that provides boost pressure to trigger the aneroid on the back of the injector pump. When I cleared the hose I didn't disconnect that valve, I have a feeling I inadvertently forced oil down there and it was interfering with the aneroid. I'll monitor it for a while to see if the problem comes back, might even test my theory later. But for now it seems ok.