Engine Running Problem - 1989 350I
Discussion
Hi folks, I would be grateful if anyone could shed light from their experience of my recent engine running problem, it's a 1989 350I with a flapper.
It only started doing it a few days ago, it's kind of like it's hunting but does at at idle and on throttle, making smooth driving very difficult.
It's not so bad under a reasonable amount of load, but still a bit down on power.
Another strange effect is that it sounds different (quieter) on the overrun, much less popping and banging than usual.
Then, maybe temperature related as most of my journeys are within 10 miles, it will suddenly stop doing it and idle / pull smoothly and strongly, and pop and bang properly!
I'm thinking it's electrical but I can't afford to start buying every electrical part and guessing at it, but I realise internet diagnosis might lead to that.
Any advice is much appreciated.
Thanks,
Martin.
It only started doing it a few days ago, it's kind of like it's hunting but does at at idle and on throttle, making smooth driving very difficult.
It's not so bad under a reasonable amount of load, but still a bit down on power.
Another strange effect is that it sounds different (quieter) on the overrun, much less popping and banging than usual.
Then, maybe temperature related as most of my journeys are within 10 miles, it will suddenly stop doing it and idle / pull smoothly and strongly, and pop and bang properly!
I'm thinking it's electrical but I can't afford to start buying every electrical part and guessing at it, but I realise internet diagnosis might lead to that.
Any advice is much appreciated.
Thanks,
Martin.
There are some cheap things you can do first:
a) check and clean each end of every earth strap, don't forget the gearbox one.
b) EFI plugs, remove, spray with WD40, plug back in, for all sensors and the ECU multiplug
c) WD40 under the dizzy cap, on the leads etc (leave dizzy cap to evaporate a bit before starting!)
d) drive 20 miles instead!
a) check and clean each end of every earth strap, don't forget the gearbox one.
b) EFI plugs, remove, spray with WD40, plug back in, for all sensors and the ECU multiplug
c) WD40 under the dizzy cap, on the leads etc (leave dizzy cap to evaporate a bit before starting!)
d) drive 20 miles instead!
On the flapper there is an overrun valve at the back of the plenum. It could be gummed up, or the bolt holding the spring is 'relocating' itself. If it doesn't let in enough air on the overrun, the revs will stay up and could perhaps cause part of what you are experiencing. Puzzled by the problem suddenly disappearing from time to time, as it is a mechanical setup and would thus not expect this. So probably I am barking up the wrong tree....
Another philosophy: Could an airleak cause this? And with heat close (when it is a very small leak)?
Rob
Another philosophy: Could an airleak cause this? And with heat close (when it is a very small leak)?
Rob
ROOODBOY said:
Another strange effect is that it sounds different (quieter) on the overrun, much less popping and banging than usual.
it will suddenly stop doing it and idle / pull smoothly and strongly, and pop and bang properly!
I'm thinking it's electrical but I can't afford to start buying every electrical part and guessing at it, but I realise internet diagnosis might lead to that.
Last point first, every electrical component on the Efi flapper except the ECU, can be tested with simple instruments following a proper procedure and a diligent approach, so there really is no need to choose a scattergun method to component fault findin that involved loadsa money.it will suddenly stop doing it and idle / pull smoothly and strongly, and pop and bang properly!
I'm thinking it's electrical but I can't afford to start buying every electrical part and guessing at it, but I realise internet diagnosis might lead to that.
Regarding the popping and banging.
For the record, the popping and banging phenomenom was not the default condition when these engines left the showroom.
Those detonations are now happening inside the exhaust manifold and long term overrun percussion there-abouts will eventually cause colateral damage and problems to local gaskets.
After all, the explosions are supposed to occur INSIDE the cylinder head, not the exhaust system.
Because owners of RV8 Efi cars sometimes like to make loadsa noise they are inclined to adjust the overrun system to actually cause the phenomenom. Dun it meself!! Its a boy-racer thing!!
What follows assumes that you have the conventional Rover Efi overrun valve mounted on the rear of the plenum chamber - at least initially.
In your case the overun valve its either maladjusted or faulty.
Its purpose on the standard flapper is to PREVENT the phenomenom, NOT to create it.
What follows is the first part of my full scientific analysis of the phenomenom as experienced in the Rover SD1 Flapper System.
Introduction - Causes of Problems created on Overrun
- Overrun is generally understood as travelling, usually at higher speeds, often downhill, with the throttle fully shut. This exposes one of the Rover SD1 Efi System imperfections that not all the fuel injected into the inlet manifold and the plenum chamber is burned in the combustion chambers.
- Sure, under normal cruising conditions, there is no significant amount of fuel coming into the plenum because the injectors squirt directly into the inlet manifold runners just prior to the intake valves where the gasping engine is waiting to breathe in everything that is available. Even so, the injectors do not squirt in sequence with the individual induction strokes, so fuel does hang around in the inlet manifold, mixed with the air already there, until it is inducted in turn.
- It’s slightly different at idle when the low velocity of intake air-flow will allow some of the atomised fuel to migrate back into the plenum area aided by the fact that the plenum experiences higher depression (vacuum) at idle so there is an obvious tendency for parlicles of unburned mixture waiting its turn in the runners below the trumpets to migrate towards the point of highest vacuum.
- Also, during cranking, fuel may be injected into the plenum from the cold start injector directly opposing the incoming stream of air. This produces a rich mixture, not all of which is ingested if, for some reason, the engine does not fire and run first poke. This leaves variable amounts of residual fuel in and around the plenum, trumpets and tunnels which, for example, can be strongly smelled when investigating a non-starting engine.
- In addition to fresh air rushing into the plenum a stream of foul air is sucked up through the crank-case ventilation system containing unburned hydrocarbons mixed in with other noxious gasses.
- The different conditions and sources of fuel combine to leave varying quantities of juice which, at average pressures experienced in the inlet area, condenses out into liquid form on the walls and surfaces of the plenum chamber and other parts of the inlet system, a normal phenomenom! These fuel residues do no harm, they just innocently exist thereabouts, until conditions change.
- Inevitably, when the engine next encounters rapid deceleration with the throttle plate(s) shut, otherwise known as Overrun, a very high vacuum occurs in all the inlet areas which encourages any liquid fuel lurking there to vaporise. Messers Boyle and Charles wrote some laws about this!
- With throttle shut, a small volume of air enters the engine via the Air Flow Meter (AFM) through the idle air gallery plus whatever sneaks past the closed throttle disc. The ECU responds accordingly by trying to inject correctly matched amounts of fuel at a level similar to the quantity at idle. Unfortunately the Overrun depression felt in the inlet manifold is much larger than that normally corrected for, by the Fuel Pressure Regulator, so the overall pressure differential across the injectors is much larger than the usual maximum of 36 psi.
- This has the effect of sucking even more fuel from the injectors than intended by the ECU, exacerbating the overall richness making it impossible for any resultant mixture ito ignite inside the combustion chambers from where it passes unburned into the exhaust manifold.
- Here, the rich unburned mixture encounters variable quantities of air, very hot gasses and piping hot metal surfaces enabling random combustion right there in the exhaust system. The result is loads of popping and banging, typically a very loud crackle, capable of generating spectacular flames from the tail pipe depending upon the state and nature of the silencers.
- Apart from the anti-social nature of the associated decibels these random detonations outside the combustion chambers create excess stress and eventual damage to any local manifold gaskets.
If you reached this end of the above introduction, still awake, you may now want to read exactly how Rover/Lucas chose to deal with the problem, their solution and how the valve might be serviced and set up to make the problem you are experiencing go away.
In which case go here
You will now have experienced the pulling together of all the information available to me in conducting my analysis and hopefully are in a position to correct any anomolies present in your set-up.
If your overrun system is not as described then it is operated by a vacuum switch cutting out the engine running signal as you will have read in the full analysis.
That being so, then your overrun "coming and going" phenomenom is probably due to a faulty vacuum switch or relay or local electrical connections.
Futher to my very first observation, you may like to review all the RV8 Efi component descriptions and test processes here
ROOODBOY said:
It only started doing it a few days ago, it's kind of like it's hunting but does at at idle and on throttle, making smooth driving very difficult.
It's not so bad under a reasonable amount of load, but still a bit down on power.
Then, maybe temperature related as most of my journeys are within 10 miles, it will suddenly stop doing it and idle / pull smoothly and strongly
This response is further to my reply on overrun symptoms.It's not so bad under a reasonable amount of load, but still a bit down on power.
Then, maybe temperature related as most of my journeys are within 10 miles, it will suddenly stop doing it and idle / pull smoothly and strongly
The cause of hunting at idle is rooted in a slightly rich mixture and normally only happens during warm up phase.
For you to experience hunting when warm and also when cruising says that you have a mixture problem that might (only might) be due to overrun valve maladjustemnt/intermittency.
If it were due to air leaks then one might expect the symptoms to be permanent as they do not normally self-mend.
That leaves two other possibilities.
- (as per Adam and Wedg1e) electrical connection problems somewhere in your Efi loom which also include the engine earths behind and below the LH rocker cover. Such problems can respond to heat changes in and around the engine bay and affecting the local connections.
- A sensor component on the blink.
Generally though, whilst the temptation is to blame the Efi system, one cant rule out a temperature affected ignition fault.
Hold up - I hear you say! I might have to test everything, when all I really want is a quick solution. Well, given the nature of intermittent problems and their causes, dont hold your breath.
Instead, why not go for full blown, low cost health check as recommended here:
good luck with sorting this problem, i have had the same on my 350i for approx 12 months went through everything that everybody mentions and the last thing was to try another ecu to see if it was the dry joint thing which it was, but by the time i had finished it had cost a lot of dosh and pushed me to the brink of getting rid. was only the buzz i got when driving it as it should be that saved the day.
honestjohntoo said:
Regarding the popping and banging.
For the record, the popping and banging phenomenom was not the default condition when these engines left the showroom.
Yes that's the case for SDi's but remember that the 350i has a different exhaust system with tubular manifolds, and a bigger bore exhaust. More room for popping and banging if air gets in ;^)For the record, the popping and banging phenomenom was not the default condition when these engines left the showroom.
As for the state of tune, it's quite possible that TVR adjusted the air meter and/or ECU to make it a bit richer, we ought to get a baseline for this so we know what the differences are.
Today I removed and thoroughly cleaned the engine earths, coil terminals, most of the EFI wiring and the over-run valve, but then needed to get other stuff done.
Anyway, drove to the supermarket and still lumpy and horrible.
Came out of the supermarket and it ran perfectly for the rest of the afternoon...
I'll try and get round to looking at a few more things tomorrow.
Anyway, drove to the supermarket and still lumpy and horrible.
Came out of the supermarket and it ran perfectly for the rest of the afternoon...
I'll try and get round to looking at a few more things tomorrow.
adam quantrill said:
Yes that's the case for SDi's but remember that the 350i has a different exhaust system with tubular manifolds, and a bigger bore exhaust. More room for popping and banging if air gets in
Hello Adam, Maybe? "Air getting in" is not the issue, to my way of thinking, tho', and in any case one would reasonably assume that most zorst systems are not leaking. Fuel getting out is what induces the explosions.I dont see how tubulars would make any difference to the factuality that detonations in the exhaust system are wholly due to unburned fuel getting there because it cannot ignite in the combustion chamber.
As mentioned in the analysis, small amounts of air, hydrogen and oxygen in the form of water and loads of CO, plus super hot surfaces all co-habit in the manifold, enough in combination to allow any expelled fuel to ignite, thereabouts.
And the reason for the expelled fuel is the grossly rich mixture caused by the multiple conditions explained in the analysis mentioned, that simply will not combust where its supposed to.
Sure, a tubular exhaust will behave differently, being larger than the standard SD1 version.
Having said that, my Twin Plenum has been modified to tubulars and I can eliminate the popping and banging by adjusting the overrun valve to let in the correct amount of metered air so that all the detonations take place where intended.
Indeed for several years I had it adjusted for the undesirable effect, but eventually I tired of the racket and the propensity for damage - after I realised the truth.
I would concede, however that perhaps TVR tuned their engines to be noisy as described, considering their target buying public.
If that was true, however it would seem odd that they overlooked the potential for collateral damage.
The was an interesting by product of tuning the overrun valve for maximim noise however.
By doing so the air flow meter did not open its flap on overrun and the ECU did not respond by adding some extra fuel to make a more combustible overrun mixture, the end result being - IMPROVED economy.
One could observe the effect directly by monitoring the "INST MPG" on the trip computer. Probably the only example of a boy racer doing something positive for the environment.
Chuck the fuel shutoff-on-overrun vacuum switch into the mix then.
TVR never fitted it as far as I know but plenty of cars got the ex-Rover wiring loom that includes the wiring for it (two white wires with Lucar connectors just in front of the bulkhead).
Two possible reasons have been suggested to me: firstly, the SD1 was touted as an executive car and snap, crackle and pop on overrun was deemed unseemly, so the vac switch turns the fuel off to mask the fault.
The other possibility is that it was originally intended to give the Range Rover greater engine braking (eg for descending hills whilst towing) by not fuelling at all on over-run.
If it's the former it would suggest that Rover themselves couldn't get the SD1's fuelling correct...
TVR never fitted it as far as I know but plenty of cars got the ex-Rover wiring loom that includes the wiring for it (two white wires with Lucar connectors just in front of the bulkhead).
Two possible reasons have been suggested to me: firstly, the SD1 was touted as an executive car and snap, crackle and pop on overrun was deemed unseemly, so the vac switch turns the fuel off to mask the fault.
The other possibility is that it was originally intended to give the Range Rover greater engine braking (eg for descending hills whilst towing) by not fuelling at all on over-run.
If it's the former it would suggest that Rover themselves couldn't get the SD1's fuelling correct...
Wedg1e said:
Two possible reasons have been suggested to me: firstly, the SD1 was touted as an executive car and snap, crackle and pop on overrun was deemed unseemly, so the vac switch turns the fuel off to mask the fault.
The other possibility is that it was originally intended to give the Range Rover greater engine braking (eg for descending hills whilst towing) by not fuelling at all on over-run.
Neither, according to this extract from Efi tech training manual is was emission and economy.The other possibility is that it was originally intended to give the Range Rover greater engine braking (eg for descending hills whilst towing) by not fuelling at all on over-run.
I've toyed with the idea of retrofitting this, and its so simple that no replacement loom would be required, just a few small additions to the regular Flapper loom.
Gassing Station | Wedges | Top of Page | What's New | My Stuff