S1 V6 auto back on the road at last!! - Problem solved!!

[White Exec]

Chasing Earths: Measured the resistance between the battery -ve and the earthing point behind osf headlamp. It measures about 5ohms - compared to 0.5 ohms on the good gold car. Cleaned up the earth terminals behind the airbox. In summary, when we disconnect the batter +ve, the resistance between -ve battery post to any of the earth points was about 0.5ohms. Connect up the positive, open and close a door, and it jumps to around 30 then falls back to about 5 ohms. Couldn't figure out the reason for this. Certainly linked to the interior/puddle lamps and the electrovavle activating. So this is a difference between the two cars that we can't explain.

Tachometer. : Some strangeness was observed from the tacho - at one point it was stuck in the red rev limiter range whilst the engine was at idle!

So my summary of events: Throttle sensor is now working but makes no difference. Some oddity over the grounding resistance. Steve

Earths
Anything as wrong as this needs urgently sorting. A 5-ohm resistance present in an earth line is enough to produce a huge voltage drop (and stop something working correctly). Most likely is a damaged cable, or a still-dirty ground connection. If in doubt, run an additional known-good grounding connection.

Always difficult trying to measure resistance in connected/powered-up circuits; sometimes easier to measure dropped voltages, and calculate from there. You know this.

Because the resistance changes when doors/lamps/EVs... are operating, this suggests that the cable you are checking is being forced to carry more current (this will aggravate a bad connection or damaged wire), and this will either be in order, OR another wiring route is not present (or damaged), so it forces the first cable to carry its current. (It's akin to the HD earth cable between engine and batt -ve/chassis being defective or absent. When you operate the starter, other light-duty ground cables attempt to supply the starter current, and either overheat or get damaged.)

Meter up the suspect cable, and see how much current it's trying to carry. This might give a clue about what is being temporarily fed when door etc. is opened.

The tacho misbehaviour needs nailing too. I don't have a V6 circuit diagram, but this needs confirmation.
________

I think you're right about this knotty problem, where the cause isn't yet nailed: anything found out-of-range needs sorting. Frustrating one.

[normanlindley]

i noticed the battery voltage was too low on every test, Xm's like plenty of voltage

[Dean]

I really don't believe that this engine is suffering from fuel starvation.

Do you mean you don't think there is a problem with the mechanical fueling side of things or that it is actually receiving the correct amount of fuel at the point of injection?

Adding extra fuel to the intake manually and seeing the engine speed increase dramatically would suggest there is insufficient fuel being injected, I agree this may be an issue that isn't related at all to the fuel system (delivery volume / pressure) but an air mass calculation problem.

I think the test of adding extra fuel proves that the engine is mechanically sound and there are no restrictions to air pumping and so the issue is most likely to be a fuel metering issue but it is of course by no means certain to be the problem.

D

[MTXM]

While I am obviously very grateful all the advice and expertise, as mentioned above the problem has been around for a while and a very great deal of work has been done and time and effort expended to locate the running issue. I am really looking to narrow down the possible cause of the poor fuelling and faulty components, rather than to ever expand the list!

Compression guages are cheap and useful for checking engine condition, borrow or buy one and check the compression, it will show up other problems as well like bad timing, valve damage etc.

I am not sure I want to know about any of those other issues at present Dean and just want to solve the poor running!

I have no faith in the videoed test of pouring fuel into the intake. The rate at which fuel was added would make the mixture totally incombustible in the engine,

Please believe me that the amount of fuel was not that large Mike and it was definitely combusted in the engine.

Most likely is a damaged cable, or a still-dirty ground connection. If in doubt, run an additional known-good grounding connection.

The cable was thoroughly checked and confirmed to be satisfactory Chris and the higher resistance was only present with the battery positive connected, presumably due to a static load from a relay etc.

i noticed the battery voltage was too low on every test, Xm's like plenty of voltage

The battery, while virtually brand new, is a bit depleted Norman due to the car standing idle and the Lexia tests and did eventually fail, while the running voltage was around 13v that I would think is healthy enough.

I think the test of adding extra fuel proves that the engine is mechanically sound and there are no restrictions to air pumping and so the issue is most likely to be a fuel metering issue but it is of course by no means certain to be the problem.

I am hopeful that you are correct with this advice Dean that does echo my own thoughts, apart from the last bit!

With regards,

Matthew T.

[MTXM]

I think it is also worth remembering at this point that the engine ran perfectly well before the last removal, which only involved the disconnection of electrical wiring and fuel pipework and the exhaust system, while nothing was changed originally apart from the starter ring and motor. In my humble opinion this should surely rule out issues such as a loss of cylinder compression, incorrect valve timing, and many of the other possible problems suggested, however well intentioned.

Obviously there has been much subsequent interference to replace wiring plugs, sensors etc., which may possibly have introduced other quirks, but the poor running, although worsened, is essentially unchanged. The engine starts eagerly, ticks over well if at slightly lower revs than ideal and a bit lumpy, but will not rev above 2,200rpm - originally it revved up to 3,500rpm.

With regards,

Matthew T.

[White Exec]

I understand the frustration, Matt, really do.

Going back to Steve's diagnosis report:

"Measured the resistance between the battery -ve and the earthing point behind osf headlamp. It measures about 5ohms - compared to 0.5 ohms on the good gold car."

This means that the car's bodywork is not properly connected to battery -ve.

As the Injection ECU - and lots besides - is grounded to body in various places, this means that much of the electronics could be working at something other than a stable battery -ve (0v). Recipe for serious misbehaviour.
It's called an earth loop, and shouldn't be happening. All earth connections should join faultlessly together, usually courtesy of bodywork and the heavy duty battery -ve straps to chassis and gearbox/engine.

As fuelling is electronically controlled, you can't afford to ignore such an obvious electrical fault.

[Dean]

Compression guages are cheap and useful for checking engine condition, borrow or buy one and check the compression, it will show up other problems as well like bad timing, valve damage etc.

I am not sure I want to know about any of those other issues at present Dean and just want to solve the poor running!
With regards,

Matthew T.

If all you have done is removed the wiring, fuel system and exhaust since the engine was running correctly and you have confirmed the exhaust is clear, the fuel system is delivering correct pressure and flow at the rail and that all sensors and wiring are functioning, with correct continuity or voltage and no shorts or open circuits then its time to expand the scope of investigation as that is not where you problem lays.

Your rough idle could very well be a lean mixture because of poor fuel metering, it could be a low idle speed which you are experiencing, it could also be a misfire or uneven compression and in my experience if you have been unable to confirm one cause definitively you must eliminate the other likely causes for the fault to be able to focus on the root of the problem.

I understand you have put an awful lot of work into this frustrating problem.

D

[MTXM]

Thank you for the further comments and sympathy chaps and in response to Chris we did go on to confirm that the bodywork and engine/gearbox earths and associated cables are good. The other bodywork earths including to the ecu have also previously been checked and I must reiterate that the 5ohm resistance on the battery earth appeared to be lost when the positive lead was removed, which may be significant.

My current feeling Dean is that despite earlier investigation I should re-examine wiring and especially in view of recent oddities with behaviour of the O2 and TP sensors, which are rather vital to the correct running. Obviously the wiring is fairly complex and a rechecking of continuities has to be worthwhile, ideally with another pair of eyes. I would not say that the idling is quite 'rough', but the speed is lower than I would expect with perhaps a little hesitation . The misfiring only occurs with sustained attempted full throttle acceleration.

With regards,

Matthew T.

[White Exec]

That 5-ohm resistance between battery -ve and bodywork should not be there, whether battery +ve is connected or not.

If it is there, it means
- bodywork is not properly earthed, ie connected to battery -ve
- there could, under certain conditions, be a voltage between bodywork and battery -ve, which just should not be, under any circumstances

It says that either
- one/more of the earth straps from battery -ve to body is not doing its job, or
- the ? inner wing ? behind o/s/f headlight ? point to which you are measuring is not joined well electrically to the rest of the chassis/body.

[MTXM]

Here are some further definitive earth resistance check readings with comparisons to the gold car. From my interpretation the only disparity is a slightly higher reading on the grey car between the engine and battery earth with engine running and I wonder what that means? Regards, Matthew T.