weird 3.9 idling

Hi,
just to keep it alive, more news after refitting everything to place.
First of all I discovered the mysterious relay+fuses are part of the front screen heater circuit. I picked it on a picture in the manual and then confirmed by operating the switch and feeling the relay vibrating. It could be somehow related to Efi as the ECU senses the ON/OFF of this relay to put up RMP and compensate for electrical load.
Presently the fuses are removed so the relay can be switched + the switch light comes on, but there is no load.
However, when everything was back I started the engine again and…surprise… back to 1500 RPM idle. No oscillations but high RPM. Waited until engine reached running temp but idle remained at 1500. Considering that the relay was a potential source of troubles I tried switching on and off. While in ON there was no increase in RPM, and when in OFF in 2-3 secs it went from 1500 to 1300, I repeated the on/off and it went down to 1100, going to 900 at third attempt. 4th and 5th attempts didn’t decrease any further.
I switched off then restarted and this time it started idling immediately at 900-1000 and there it stayed with no surging, no misfiring, etc.
Will see when it’s cold again if the pattern repeats, and if so I will try removing the relay and see if 1) it cures the symptom or 2) the switch itself acts upon idle, which implies the timer unit of the heater is involved rather than the relay.
It was when I tried to understand if actual wiring is as expected from diagrams that I discovered the front screen heater has a timer unit. This what the manual says:

“……HEATED FRONT SCREEN
The heated front screen will operate when the
switch is operated with engine running. The timer
unit, see Relays-identification, will provide a preset
time cycle of 7 112 minutes + 20%.
Switching off the ignition, or further operation of
the heated front screen switch during the cycle will
switch off the screen and cancel, reset and switch
off the timer unit……”

Anybody knows what is the correct time? It obviously cannot be 7112, nor it can be 7 or 112. It could be 7/12 and a bad scan of the page on paper....
As far as I could inspect wiring is ok but... anybody knows why the oil pressure switch feeds into the front screen timer unit (as per diagram on manual)?

Sometimes the logic behind these things is really hard to pick up…..

Many thanks

Ciao
Adri

I just googled it... the oil pressure switch is to feed the circuit only when engine is running, so that one is solved. What I couldn't find is why or how operating the switch could modify idle....

According to the D1 owners handbook, " The heated screen operates only with the engine running. After 5 minutes of continuous operation the heater switches off automatically".

Unfortunately the above doesn't help, with the 300 series D1 the multi function unit look after most of the electrical circuits, even the oil pressure switch, so if a 1990 RR has one maybe worth looking into that item.

Glad to hear it is running and that it is smoother than before.

About the fuses and relay for the heated screen, AFAIK this will have no effect on idle speed. The idle speed hang up you describe may not be a big issue, mine does it sometimes and I suspect it is due to a dirty stepper motor or you are giving the engine some throttle on start up.

For now I would suggest live with it because at least it is running. Who knows with use and a bit of time it may well settle down all on its own.

BTW the heated screen timer is 7 1/2 minutes (7m 30s).

Hi All,
Kev thanks for the info, it had to be 7 1/2, I couldn't think of any other combination. However I wonder how many times a bad quality copy/scan has misled some judgement/operation.
I have found on the diagram the connection that senses the Heated Front Screen ON and tells the ECU, which in turn is expected to slightly increase idle as it does for A/C or selecting drive on auto boxes. I tried again several times by now, and a few times idle rested at 1500, but in every occasion it was possible to take it down by repeatedly switching the HFS ON and OFF again. I know it's weird, but that's the evidence. No other interactions, if I leave it, it stays at 1500 at least 30' or (may be more, didn't try), if I use the switch it gets down to a stable 900 RPM very reproducibly. Well, at least I know I can do something to keep it under control.... )
Today I had the opportunity of a long drive and tested it in several conditions. It runs smoothly, but there is still sign of that hiccup I described earlier. Very rare and very weak, but it is definitely there. Also running at 65 to 80 Mph (different speed limits here) it sometimes cuts for 1 may be 2 seconds then it runs again smoothly. These cuts sometimes come in clusters of 3-5 sometimes it does only once and then it's back to normal.
I wonder if it could be something to do with the TPS, that I checked as carefully as I could, though I understand that with a digital Vmeter some spots could be missed. Unfortunately I haven't got an analogic Vmeter to try.
It also reminds to me the faulty torque converter I had immediately before rebuilding the whole engine, but that was fixed (replaced) and run smoothly for a while, may be 10K miles. Could that be the symptom again?

OK, so, as Kev suggests, these cars do seem to learn and adapt to situations with time. Mine is peculiar though as it seems to learn to be naughty instead of trying to improve....
A major hiccup is back now.. It is almost undriveable, I was on the motorwya today and I doubted I could make it back home....
idle is ok, correct and stable RPM, no problems putting a load while idling, but the engine really misses when I accelerate, and the more I push the more it refuses to run. So I could make it back only because I was trying to drive with a very light foot and very little throttle. If I keep it steady and light it will eventually increase speed ad run reasonably, yet there will be random hesitation, sometimes just occasional, sometimes worrying (definitely not the torque converter though, it does it in every gear, any speed, any RPM...). It is more evident while running, but it is there also while resting in N.
It looks as if it was an electrical cut, not just fuel related, but I might be wrong. If I floor the pedal it will simply not revv up and will start stuttering and backfiring, no way to take it past 3k RPM.
I was thinking TPS, or fuel pressure regulator, or...what else? Could a faulty ground give this symptom as well? I could understand a faulty ground to go faulty while running due to vibrations, but with the car parked a faulty ground should be faulty all the time or no be faulty at all...or am I wrong?
I have re-chaked all the handy connectors and tried to wiggle wires while running, but to no avail.
Any ideas?

Thanks
Ciao
Adri

adri1957 said:

A major hiccup is back now.. It is almost undriveable, I was on the motorwya today and I doubted I could make it back home....
idle is ok, correct and stable RPM, no problems putting a load while idling, but the engine really misses when I accelerate, and the more I push the more it refuses to run. So I could make it back only because I was trying to drive with a very light foot and very little throttle. If I keep it steady and light it will eventually increase speed ad run reasonably, yet there will be random hesitation, sometimes just occasional, sometimes worrying (definitely not the torque converter though, it does it in every gear, any speed, any RPM...). It is more evident while running, but it is there also while resting in N.
It looks as if it was an electrical cut, not just fuel related, but I might be wrong. If I floor the pedal it will simply not revv up and will start stuttering and backfiring, no way to take it past 3k RPM.
I was thinking TPS, or fuel pressure regulator, or...what else? Could a faulty ground give this symptom as well?
Any ideas?

Click to expand...

If I was a betting man I would say you have an inlet leak. TPS is a possibility or maybe ignition amplifier. I know you have rebuilt the engine but that doesn't mean there isn't an inlet leak or even a leaky head gasket. Do a compression test and also stick a vacuum gauge on it that should give you a better idea of what is going on. Get the pattern ignition parts off and get genuine ones on.

If there is anything that could be said to be constant in this problem that would be it is intermittent. On the same run it does it only sometimes, and that can be either randomly (or what appears to be so) or only when under full throttle.
Engine can be made to revv up by applying a very light throttle. There are instances of full throttle not causing the backfiring problem though, as well as instances of cutting even with light throttle, and this seems to put some randomness on top of everything. But definitely there are also times when it runs smoothly.
Therefore I say it is an intermittent fault.

I am not a professional mechanic, and this is pretty obvious from my previous posts, but I try to identify causes based on their ability to explain symptoms. In this case I can imagine a component of a mechanisms such as distributor shaft+pickup plate/reluctor+rotor arm/cap contacts to be faulty only at given RPM, or only when strong centrifugal forces are applied (full throttle for example) and also have random fluctuations in their being faulty; or a TPS not being linear in response with some dead spots that could or could not be made evident according to the position of the throttle or the speed at which the throttle lever will operate the TPS.
But because I probably ignore most details of other situations I cannot put together randomness, RPM, full throttle and inlet or head gasket leaks. May be I am wrong here but I would be inclined in considering this type of fault to be more permanent and showing up in every condition, may be more or less intensely but always there.

For the same reasons I tend to be skeptical on the problem of non original components (pattern vs EOM), which doesn’t mean that I believe that every part will do.
I know V8 are said to be very fuzzy about non original ignition parts, but in fact V8 are just engines and cannot be fuzzy or not fuzzy. If there are bad quality components that doesn’t depend on their being original OEM or not. There are good quality parts even if not OEM and if they fulfill the physical or electrical requirements they should go and do their work even if just pattern and not EOM. The problem here is more on not having been able to say in the past in what precisely pattern parts are wrong or not adequate, contributing to build up the fuzzyness theory of V8 engines. In other words, what are the differences between pattern and OEM components that one should look at to understand which is good and which is not? May be starting from new they are all good and pattern ones only go more quickly, or it may be that some tolerances are not observed. For example, how relevant would a difference in length of 0,3 mm (or more) be on a rotor arm? Would the longer one be also the better or the other way around? I have both OEM and pattern rotor arms and measured the sizes, but won’t tell which is which, see if we have a theory to explain why one should be better than another and then see if that fits with the observations and only after this conclude if pattern are the bad ones and OEM the good ones. How critical is the alignment of contacts in the dizzy cap? How far can one go out of a perfect circle and still work properly, given that none of them (even OEM) will ever be aligned on a perfect circle with the technology used to build them up? Could it be possible that arm+cap go together as far as arm length and circle radius of the contacts are concerned, so that may be it is the mixing of pattern and OEM parts a bad idea rather than fitting pattern parts in itself? Why is the allowed play in dizzy shaft not mentioned anywhere on manuals? I can hardly imagine it is just not relevant, but how would that interfere with the above mentioned arm length and cap radius?
These are just my very personal ideas and I am not saying that past experience is not important. I am only trying to put together what I observe with the way I “know” it works, and see if it makes any sense. If it doesn’t either I don’t know how it works (more than likely…), or I am using the wrong observations to draw conclusions.

Compression tests are costly (at least to me), and to my knowledge I have no symptoms of gasket leaks. Engine starts in may be 2-3 seconds, has power, oil pressure light goes off even before engine starts, no coolant consumption, no overheating. What else suggests there is a gasket leak?
Could an inlet leak be intermittent or related to throttle opening?

Clearly you no longer want or need my help. Hope it works out.

Kev,
The reason why I raised those questions is just the opposite: I think it would help a lot discussing those points, and I honestly think they are reasonable points as well. Each of us has a personal approach to solve problems, and comparing approaches is generally better than taking something for granted.
I also would like to stress the point that this attitude of mine does not mean not trusting someone else's opinion or skills but rather the opposite. If I don't trust someone I generally don ask for discussing ideas. So your help (and everybody's help) has been and will always be greatly appreciated, but it is only form questions (and answers) that we build more knowledge.
Thanks
Ciao
Adri

Adri,

I have been abusing my RRC for years and I know what does and doesn't work. If you search you'll find many will agree only genuine ignition parts will do, I don't know why exactly but pattern parts just don't do the job and can cause a variety of odd running problems.

A compression test is not difficult or expensive. You just need to buy a compression gauge, they cost peanuts and as long as you know how to do a compression test then there is no problem but you can then gain a better understanding of the condition of your engine. The same is true using a vacuum gauge - again very cheap to buy and easy to use but very useful in diagnostic work.

I disagree what you say about head gasket or inlet gasket leaks. The Rover V8 is incredibly tolerant and will run even with duff gaskets, I know this to be true because I have run mine around with failed head gaskets and it wasn't until it was really bad that the engine started to cough and splutter to the point that it was clearly in need of attention.

So, as I have already suggested, do vacuum and compression tests and if possible put genuine distributor cap and rotor arm on it. Once you have done that and hopefully gathered some data we can hopefully pinpoint your running problem.

classic kev said:

A compression test is not difficult or expensive. You just need to buy a compression gauge, they cost peanuts and as long as you know how to do a compression test then there is no problem but you can then gain a better understanding of the condition of your engine. The same is true using a vacuum gauge - again very cheap to buy and easy to use but very useful in diagnostic work.....

Click to expand...

Ok then I would greatly appreciate if you could please point me to suited gauges, just to have an example of what I'll be looking for, thanks.

Just as an update, and to stress the intermittent aspect, yesterday it did run really awfully, on top of the hiccup at some point cylinder 5 stopped firing almost completely. Checked plug, lead, everything OK. I also found a faulty wire on the coolant sensor but I can't tell if I ripped it off while checking TPS or else, however I fixed it this morning. Misfiring had gone by the time I started it again, and all 8 were back together, and it retained only a moderate hiccup under throttle opening. Then it rested a few hours (in the sunshine so didn't cool that much). When I started it again the hiccup was also gone and up to now it run "perfect". Just couldn't believe it, though I am sure it will be back soon....

Just a quick thought, I had a similar idling issue with my 3.9 and it turned out (after a lot of swearing and complaining, whinging, more swearing and many many parts replacement) to be the oil breather pipe not having the restrictor in it causing the effects of an air leak.

I've skimmed read your posts and didn't spot a check on that issue so maybe worth a check?