Rover SD1 Forum Snippet #10 - Rover SD1 Unusual Efi Solutions
1 - Five minutes is sufficient time for the engine to get get warm/hot so lets look for a heat related issue/quirk with the local Efi wiring connectors to and from any/all of the various components thereabouts because, as connecors warm up so to might the contact resistance of a duff connection change.
Vigorous wriggling of all the wiring and connectors as the fault occurs might reveal a dodgy connection, where simple visual and/or multimeter continuity checks do not.
2 - Five minutes is also sufficient time for the state of battery charge to change after prior cranking loads have drawn loadsa current, causing the amount of charging current through the engine to chassis earth strap(s) to vary considerably as the battery recovers from its temporary discharge.
If those connections are dodgy then the voltage drop across them will vary considerably with charging current and because chassis earth and engine earth may be different, even in a well maintained system, it's worth checking all the key earth connections.
Within this category comes the equally unusual residual earth voltage effect of poor alternator earthing despite the adjustment bolts and adjustment bracket connections which can be faulty due to corrosion and paint, respectively. The cure here is to run a supplimentary earth connection from the alternator body to a convenient engine earth point.
This is also particularly true for the Efi system earth on the grounding stud(s) behind and below the L/H rocker cover. Its whole purpose in life is to maintain a rock steady earth upon which the rest of the Efi system can rely.
To measure such residual earth differentials as suggested above, set a digital multimeter to its lowest voltage range and probe between various solid earth points to detect any problems. eg: between chassis and engine block or between engine block and Efi System Earth.
It is easy to dismiss these suggestions as trifling, but believe me, small changes in voltage on any of the sensor inputs caused by earth differentials is all it takes to upset the mixture equilibrium of an otherwise perfect system. And so the Efi Diagnostic Challenge continues.
And that's not all!
Mentioned earlier was the commonality of rogue air leaks into the inlet system. Yet even the most diligent search will not always uncover one of the more overlooked suspects.
A leaking rocker cover gasket can and will play havoc, to varying degrees, with Efi engine idling and breathing, as well as it's cruising and full load performance.
Not sure if I'm right? Simulate the phenomenon and loosen, but dont fully remove, the oil filler cap from the LH rocker cover and see how the performance is affected.
The moral behind these examples is to be prepared to extend ones thinking laterally to the fringes of probability, consider all the possibilities, imagine the improbable and look for the remote.
If you don't do this yourself, be assured there is virtually nobody left from the original technical workforce who were familiar with our cars in their heyday!
Please feel free to contact me to comment on any of the above.
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Whenever Rover SD1 Efi System faults get beyond the point where, despite even the most diligent of component testing, owners report their Efi cars start and run OK, then shortly thereafter, for some enigmatic reason, simply stop working, or at best, run pretty rough, Commonly then, this is the oft-heard plea:
"My Efi system always begins to play up after five minutes but all the components and the ECU check out OK and I have also tested for air leaks and faulty connections, Please Help?"
Even competent DIY owners can become moggydawed at this stage and rightly so, because they also know that the vast majority (> 80%) of Rover SD1 Efi System faults are caused primarily by air leaks into the plenum chamber and secondarily by electrical wiring and connector problems, and have equally followed them through, yet still contrive to overlook two logical possibilities suggested by the very nature and description of the circumstances.. The clue is in the question!
So, beyond the obvious and diligent checking of the sensor input data to the ECU, which I'm sure they should have fully understood and covered from reading my gospels, they might then consider the following: