A stubborn ECU?

Fellas, my Puma has developed a very strange problem: ever since it had a new ECU installed, it has had problems maintaining the right RPM. One chap here told me to follow the ECU reset procedure, and sure enough it worked. Thing is, though, whenever I put petrol the issue returns. The revs become wobbly and to make it worse, when I'm driving down hill, at very low speed, if I happen to need to make a sharp turn, the car shuts off. This is dangerous...Resetting the ECU solves the problem temporarily, but I'd like to fix this definitely. Any thoughts?

I can't offer much help/advice but I will comment what I can...

The ECU 'shouldn't make any difference.. as long as the ECU you got came from a car with exactly the same spec as your car - A/C, PAS.. etc... although it seems strange that these problems started after the ECU was changed...
I would check the specs of your car and the specs of the car the ECU came from first.

If the issue appears after fuelling, there may be a problem with the evap system/purge valve. Maybe see if you can check to see if the valve is closed fully when it is not powered - possibly on idle but I don't really know when the valve is opened by the ECU. You could try and power it from an external power source to see if it opens correctly, but I don't know whether it is 5V or 12V.
If the valve is stuck open, it will be drawing fumes from the tank making it run rich causing idling issues.

Also, if it cuts out when steering, there may be a problem with the power steering pressure switch or it's wiring. Most common problem with that circuit is the wiring. It is subject to a lot of abuse and moisture under there and one of the wires often breaks somewhere near the plug/connector.
The pressure switch is situated (on a 1.7) on the steering cooler pipe, somewhere near the air condition pump (if you have A/C).
If the wire breaks or the circuit goes open circuit it stops the ECU from knowing when the steering is under pressure, then stopping the ECU from increasing the revs to compensate for the extra load on the engine.

I made quite a few edits to that post.. may be worth reading it through again!! :funny:

Valuable info, chap. Will get on the case right away and report on my findings later on.

Edit: The ECU is exactly the same as the old one. The only difference is that the immobilizer of the old one was transplanted to the new one.

Looking at a wiring diagram (again, for a 1.7) the purge valve is powered from the fuse box (violet wire), so I would guess it is 12v powered. It is the grounded through the ECU (black/orange).

Wiring is for a 1.7 as I don't have access to diagrams for a 1.4

EDIT: 1.4 is possibly the same.... have a look here, kindly posted by another member: viewtopic.php?f=47&t=33991

Thanks for going to the trouble of checking the diagrams, Cherry. I have the wiring diagrams for the 1.4. It does seems like it's 12V. Tomorrow I'll figure out a way to test the canister purge valve.
Meanwhile, my preliminary inspection of the power steering pressure switch revealed that while the wires seem to be ok, the sensor itself seems to have taken a couple of strong whacks in the past. The metal ring has a gash on it. Even if it does not solve the problem, it might be a good idea to replace it. Does this require changing the power steering fluid? Is this a part that requires a genuine Ford (quite expensive, I believe) or will an aftermarket one suffice?

Just get a secondhand one that is good. I guess IanG is still in business? No need for replacing the steering fluid, but be fast as some will drip out while you replace the steering switch...

Wild E. Coyote said:

Just get a secondhand one that is good. I guess IanG is still in business? No need for replacing the steering fluid, but be fast as some will drip out while you replace the steering switch...

Click to expand...

Thanks, chap. Just one more question, if I may: given that I can't always replicate the problem (now the car won't shut off where it once did...) is it more or less symptomatic of a bad pressure switch?

The pressure switch should operate at outmost steering angle telling PCM to raise the idle. If you don't turn steering wheel all the way, the pressure switch is jobless. So I guess, if you don't use the steering and the revs go all over the place, it is not the problem.
Are you sure you don't have a vacuum leak at inlet? Given the age of our cats, that would be my first point of suspicion...?

Wild E. Coyote said:

The pressure switch should operate at outmost steering angle telling PCM to raise the idle. If you don't turn steering wheel all the way, the pressure switch is jobless. So I guess, if you don't use the steering and the revs go all over the place, it is not the problem.
Are you sure you don't have a vacuum leak at inlet? Given the age of our cats, that would be my first point of suspicion...?

Click to expand...

TOday it happened again. Going down hill, low speed, tight/slow corner at the end, car shuts down...
I have no idea how to check for a vacuum leak? Listen for a hissing noise?

Tight corner would imply lots of steering lock? That would indeed point out in direction of the pressure switch.

Please, don't take this personally and the wrong way, but the questions you are asking and the problems you are facing have been covered on this excellent forum over and over many times. Just use the search function and read; everything has been written already...

Cheers,