So After completing a full top end rebuild and reassembly, I got the engine back into the car, wired up (with help from members here) and started her today. Cue LOTS of smoke and crap as everything burnt off (oil, degreaser etc) but essentially started on the button and ran up to temp without issue. Annoyingly, I think I have a vacuum leak as the idle doesn't seem high enough at cold start and my exhaust bypass valve isn't working (whereas it was before) so more digging needed. I think first step will be to check all vacuum hoses...
Having had a play, an air leak would cause the idle to be high, not low. Disconnecting the ICV has a definite effect so its obviously working. Which is more than I can say for the bypass valve. Scratching my head a bit.
Why don't you trouble shoot why your bypass valve is not working, then it might solve the idle issue too. The bypass valve is activated by 0V signal at the electrical switch, which activates a vacuum switch, that provides a vacuum from the accumulator to the valve. The vacuum accumulator gets its vacuum from the engine. Which one of those things is not true?
My thinking also. Shall report back Tomorrow. Thank you for your help with this. It’s beginning to eat at me, especially after all the bloody hard work to get this far
Regarding previous comments: The accumulator is known to go rusty and develop holes. The exhaust bypass solenoid valve is one of two valves in the right hand rear corner of the engine compartment has a black electrical connector (not blue). Unfortunately, it is possible to get the connectors mixed up. Did you disconnect these plugs at any time? Unless you know which solenoid valve is which, you'll have to trace the rubber tubing from the exhaust bypass valve to its corresponding solenoid valve and make sure it has a black electrical connector on it. The bottom outlet on the solenoid valve is the vacuum supply from the accumulator to the solenoid valve. The outlet above it goes to the bypass valve. Image Unavailable, Please Login Your exhaust bypass solenoid valve should have constant 12 volts dc power from relay "M" (5.2 cars) with the ignition on. If your fuel pump is operating, this is a good sign that relay M is ok (as relay M operates relay N, the fuel pump relay). The Motronic ECU provides an earth to operate the solenoid valve at the applicable time.
The bean can is not corroded and I've checked and have vacuum coming into it so that's OK. Have just checked the wiring connections on theTPS and coolant sensors as my suspicion now is that its not getting its signal. Sadly electrics is a black art to me with which I struggle. Will do my best with a multi meter but am far from confident. The diagram above is very helpful Qavion, thank you
You mean that the ECU is not getting a signal from these? Can you, for example, measure the resistance of the coolant sensor (with the engine cold)? Make sure you have the right sensor, there are a few of them in that area. It's easy to mix up the plugs (connectors) during a major. Plug colour is a guide, but the only reliable way of checking them is to carry out continuity checks between the Motronics ECU main connector and the plugs. Sometimes wire colour helps, but you have to pull back the boots on the plugs. I wouldn't recommend this on an old harness. You might split the rubber. Anyway, here's the full ECU harness wiring diagram for the 5.2 car. F355_5.2_Engine_Control_System
Here's a resistance vs temperature chart for the coolant temp sensor Image Unavailable, Please Login Not the easiest to understand. 2500 ohms at 20C?
With the problem you were having earlier where one connector was unidentified in that vicinity, I suggest you go back and ascertain all connection in that area to be correct. This will be tedious.
So, I've rechecked all the connections and they are fine. Plugged in my OBD reader and its thrown up P0123 error code (high voltage TPS sensor). This might (to my mind) explain the poor cold idle (i.e., it doesn't go up to 1200 like it should) and possibly also the lack of exhaust valve opening (which I think reads TPS). So, going to swap out the TPS (which looks a bugger to get to) and go from there. Fingers crossed.
****ing Italians. Decided - what the hell, it ran fine before, so its unlikely to be a bad sensor now. So, swapped the knock sensor and tps plugs, cleared fault codes and hey presto - it runs perfectly! So, my TPS is black and my knock sensor has the grey plug. Obviously given others have differing colours, they just used whatever was within reach... Anyway, thank you to everyone who has chimed in with help and advice. Just need to bleed the brakes and clutch, put the bodywork back on, give it a clean and go for a test drive... Hurrah!!
Thanks for the tip. Someone was asking me a year or two ago what the result of swapping these over would be (and I wasn't willing to try on my own car). Do you know if your bypass valve has been fixed? This would prove it's partially dependent on the TPS (at least on some cars). I do have the same colours on my car (which I have marked in my wiring diagrams), but as you say, not all cars are the same.
If it does not see a TPS signal, the ECU cannot decide if the throttle has been smashed and therefore cannot activate the bypass valve.
More complicated than I thought. The manual doesn't explicitly mention throttle smashing, but mentions "exhaust counter pressure", rpms, and selected gear. Selected gear, I presume, is figured out from "vehicle speed" (gearbox output) and engine rpms.
Bypass valve has always worked fine so yes, its evidently dependent on vacuum (for physical operation), gear selection and trigger from TPS and rpm.
There is a vacuum line on Rhs back, I believe, it kind of sits almost under the subframe sometimes and can get missed. It actually works 9n conjunction with 1 of the solenoids down there. Like Mitchell said lots of this type of connections and easy to miss one.
