As an update.
The TMAP sensor appears to be producing duff information. When driving
along the manifold pressure goes from normal up to full on (107, heh I don't
know what the scale is) and then back down again. This causes one hell of a
surge from the engine... repeat. Lots. The car is almost undriveable
around town but it's better at a cruise. Not superb, mind...
Is there anything else that can cause this reaction other than a duff TMAP
sensor or the wiring loom? I've cleaned the ICV, no effect (barely any crud
in there either, heh).
Apparently on date Thu, 02 Jun 2005 11:36:26 GMT, "DervMan"
Like you've realised, this is because the EMS is not getting a sensible reading
from the MAP. Either the sensor or the wiring is wrong.
Well sensors are generally either faulty or dirty, and wiring can be
intermittent. Beyond that it's unlikely that the EMS is faulty and you don't
want that to be the case anyway.
One last thing you can try, force a retrain by disconnecting the battery. The
EMS will be reset and will have to relearn all the compensatory thingamies.
It'll run rough for a bit until it does. If it is software related, this will
generally clear the problem, but I wouldn't expect it to help. Remember to
clear the DTC after you've fixed things to see it if comes back, it'll keep
being there until you do and people have been known to replace sensors a second
time when the DTC continues to be reported because they've not actually cleared
Really I have had a few fuel injected cars do this. The last - a granada
became all but undrivable.
It started OK but after 2 mins it began...
It was a multiplug down the drivers side of the engine in this case, it
looked dry, and wd40 didnt do any good either. Left apart overnight, with a
fan heater on low, blowing on it sorted it though. Rain can be enough.
Sensors or EMS systems seldom go intermittent. HT leads can but they do it
worst under load.
Does the fuel pump give constant pressure? it could be failing intermitently
MAP sensor is "Manifold Absolute Pressure" sensor, and it merely senses the
air-pressure in the manifold.
In simple terms : It replaces the old-fashioned airflow-meter - the lower
the manifold's airpressure, the more air is passing through it, so the more
fuel it needs to inject.
It's Kangarooing cos it thinks there's either maximum airflow or no airflow,
so it's injecting Lots/FuckAll fuel.
First, check the pipework. My old 405 had the map sensor mounted next to the
radiator, and it was connected to the manifold with a bit of thin tubing.
The tube split, so I duct-taped it together, and all was well again.
Assuming the pipework is fine, then it's either a duff connection, or a
knackered sensor. If it were me, I'd just replace the sensor and clean the
connection whilst I was doing it - a new one will only be a few quid from
Pressure falls with higher velocity and vice versa.
The above link is from my site and although the example uses divergent
ducts to vary the velocity, the principle is the same.
British Jet Engine Website http://www.britjet.co.uk
Heh, yeah, I know about the Bernoulli effect, but in the inlet manifold the
vacuum is generated by the engine, not by air-flow. When the throttle
plate is closed you have maximum vacuum. When the throttle plate is open
you have a pressure slightly* below atmospheric.
So pressure _is_ higher when more air is flowing... :-)
*the slight drop below ambient is due to the Bernoulli effect, but is
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