Rover EFi flapper AFM, fettling. TVR 350i

[Fed_up_Stag-owner]

Acceleration and general running improved after replacement of the throttle pot (thanks Dave and Ramon) but still some flat spots and general lethargy (the car, not me... although..), no obvious air leaks. The removeable cover to the AFM appeared to be unsullied by levering screwdrivers or similar so logical to assume that it had never been removed; removed same after some effort, pot tracks were grubby and worn but not excessively so.

Cleaned tracks and tested car, no real difference, marked up toothed wheel as per vintagemodelairplane (bed time reading for Flapperists everywhere) and turned anti-clockwise 5 teeth, flat spots cleared but still lacking that mid-range (it's all relative) although smoothly revs out up to 5.5k rpm (enough!), so improvement (but perhaps I'm working round an air leak), turned another 3 teeth anti-clockwise and lo and behold a historical mark by a previous owner appears as if by magic from behind the mounting plate for the pot tracks, no idea where the original static reference point is, but clearly can't be behind the plate. More road testing later.

Lambda probe into exhaust and logging data via laptop might be an option. Otherwise it could be off to the local dyno shop for the ritual transfer of shekels.

[DaveEFI]

Acceleration and general running improved after replacement of the throttle pot (thanks Dave and Ramon) but still some flat spots and general lethargy (the car, not me... although..), no obvious air leaks. The removeable cover to the AFM appeared to be unsullied by levering screwdrivers or similar so logical to assume that it had never been removed; removed same after some effort, pot tracks were grubby and worn but not excessively so.

Cleaned tracks and tested car, no real difference, marked up toothed wheel as per vintagemodelairplane (bed time reading for Flapperists everywhere) and turned anti-clockwise 5 teeth, flat spots cleared but still lacking that mid-range (it's all relative) although smoothly revs out up to 5.5k rpm (enough!), so improvement (but perhaps I'm working round an air leak), turned another 3 teeth anti-clockwise and lo and behold a historical mark by a previous owner appears as if by magic from behind the mounting plate for the pot tracks, no idea where the original static reference point is, but clearly can't be behind the plate. More road testing later.

Lambda probe into exhaust and logging data via laptop might be an option. Otherwise it could be off to the local dyno shop for the ritual transfer of shekels.

I fitted a Tech Edge wideband O2 sensor some time prior to the MegaSquirt. And it confirmed what I thought - my standard flapper system runs weak at near all times apart from on full throttle. But even at full throttle was leaner that the 12.6:1 normally accepted as being needed for peak power

[ChrisJC]

Have you checked fuel pressure? as that can give lean running.

Check that the fuel pressure changes with manifold vacuum too.

Chris.

[ramon alban]

Cleaned tracks and tested car, no real difference, marked up toothed wheel as per vintagemodelairplane (bed time reading for Flapperists everywhere) and turned anti-clockwise 5 teeth, flat spots cleared but still lacking that mid-range (it's all relative) although smoothly revs out up to 5.5k rpm (enough!), so improvement (but perhaps I'm working round an air leak), turned another 3 teeth anti-clockwise and lo and behold a historical mark by a previous owner appears as if by magic from behind the mounting plate for the pot tracks, no idea where the original static reference point is, but clearly can't be behind the plate. More road testing later.

Blimey, You might be surprised to learn you are the first person to come back and report they used that process. I think that normal people dont like to go there.

It was reviewed and revised ad nausium during preparation before it went to PDF and I am confident in all the stuff it contains, but I never did any fettling myself.

I cant recall, if you have a stock Rover Flapper system on your Stag, but I suspect not, so if some components are maladjusted, or you have adjustable FPR then all the normal rules become more difficult to apply and for that reason, more road test fun is on the agenda.

At least if you make careful notes of changes you'll stand a good chance of "getting there". The learning first hand is so educational?

Working around an air leak is a distinct possibility, andyou may be interested in a recent spippet. Someone had an undetectable air leak eventually traced to breached rocker cover gasket that effectively destroyed the crankcase breathing process.

Such a leak is not dissimilar to removing the oil filler cap when idling which upsets the idle performance quite noticably. Check it out, you never know?

Keep me informed

[Fed_up_Stag-owner]

Thanks for the replies,

Dave: Can you please provide more details of the sensor, which part of the exhaust system did you fit it to?

Chris: I have a fuel pressure gauge in the lock-up ... somewhere. What gives me hope is that the wound_fully_open performance is OK but the pressure clearly needs checking.

Ramon: I have no watchmaking skills so I drew the line at fettling the throttle pot. Rule number 1 with the AFM must be to mark the starting point before adjusting. It would be interesting to find out how much difference 5 teeth makes to the mixture.

I spent a couple of hours on a deserted industrial estate this afternoon with a laptop, internet connection, vintagemodelairplane pdfs and a toolbox. Sealing the AFM cover after each adjustment is a PITA; big improvement though, the bypass port adjustment screw on the AFM had been set at four turns out so additional unmetered air in the mixture, I ended up setting the thing by ear for a good pick-up, turned it down to 1.5 turns and reset the AFM to 2 teeth weaker than my starting point (who knows where the factory starting point was), much more driveable but still not perfect, then trimmed the idle screw on the plenum. Will need to analyse the mixture for further improvement though. There is obviously some history here, the box that came with the car contains 3 spare AFMs. My guess is that the AFM bypass port screw had been adjusted to overcome the incorrect signals from the worn throttle pot tracks.

Edit: I should add that my user name is probably confusing. My Stag is still in the lock-up, I bought the TVR in July 2008 to supply an engine and gearbox for the Stag, but the Wedge was too good to break, even when the gearbox went bang! Must get the Stag back on the road this year.

[ramon alban]

much more driveable but still not perfect, then trimmed the idle screw on the plenum. Will need to analyse the mixture for further improvement though. There is obviously some history here, the box that came with the car contains 3 spare AFMs. My guess is that the AFM bypass port screw had been adjusted to overcome the incorrect signals from the worn throttle pot tracks.

You need to give up trying to get it perfect with the AFM tweaking now, its prolly close enough FTTB..

The throt pot has to be repaired/replaced if faulty, but the regular flapper will run ok with it disconnected, just lacks oomph from the enrichment ccts..

there may(will) be other issues that need dealing with, why not peruse the 15 things a boy can do to make his flapper work better.

http://www.vintagemodelairplane.com/pag ... wer01.html

clean everything, ign, timing, air leaks, sensors, pressure, crud, loom connections, earths, the whole nine yards and when dun, go back to the afm and a gas analyser to finish the job.

[DaveEFI]

Thanks for the replies,

Dave: Can you please provide more details of the sensor, which part of the exhaust system did you fit it to?
[snip]

I used this one:- http://wbo2.com/2y/default.htm
with this display:- http://wbo2.com/ld02/default.htm
both the kit versions to save some money.
The sensor is a Bosch LSU 4.2

Wideband sensors need to run rather cooler than narrow band ones, so can't usually be fitted to the manifold. Mine is located in the y pipe output where the two downpipes join just after the gear box. The controller is mounted alongside the MegasSquirt both where the original ECU was sited.

[Coops]

i use this one,
http://www.vems.hu/products/round/EN/

[DaveEFI]

i use this one,
http://www.vems.hu/products/round/EN/

That doesn't appear to give a wideband output to a MegaSquirt, etc?

[Coops]

its a stand alone unit,
my vems ecu has its own O2 sensor,
i think this can be used with the vems ecu, dnb will be able to confirm or deny this.

[DaveEFI]

its a stand alone unit,
my vems ecu has its own O2 sensor,
i think this can be used with the vems ecu, dnb will be able to confirm or deny this.

Looking at their ad, it only gives a narrow band output. The Tech Edge one I'm using gives a choice - and indeed you can programme your own. So rather more than just a reader.

[Fed_up_Stag-owner]

Thanks for the replies, lots of testing at the weekend in the sunshine

Ramon, throttle pot has been replaced with one manufactured by DaveEFi, new plugs installed (old ones were Bosch four electrodes but of unknown vintage), all electrical plugs dismantled and cleaned with contact spray (not WD40). no visible air leaks (ha! That's been said before), timing to adjust and then through the rest of your list.

I think that part of the "problem" is that the engine used to out perform the tyres, suspension and brakes. Fettling has improved handling, biggest improvement was to throw away the Wanli tyres in the back (lethal in the wet and dry) and also to adjust the wheel alignment front and rear. The P6000s from the front where scrapped last weekend, lots of tread left but cracks in the sidewalls, so perhaps the rest of the car has now caught up with the engine? However, careful throttle control is required to avoid bogging down at approx 3.5k rpm, this never used to be the case, so more work needed. Fuel pressure still to check (can't find gauge, will have to buy new one).

Dave and the thev8kid: thanks for the links. I have some multi-channel voltage logging equipment, is it possible to install a Bosch LSU-4 sensor and measure voltage outputs, or does the sensor require a bespoke controller to function correctly?

[ramon alban]

careful throttle control is required to avoid bogging down at approx 3.5k rpm, this never used to be the case, so more work needed. Fuel pressure still to check (can't find gauge, will have to buy new one).

As you say still things to do, but have you considered a run out with the car, get it to bog down and stop, to immediately check condition/colour of one spark plug from each bank. Youll get some immediate idea of whats going on, methinks. Weak, Rich or Normal.

Probably turn out to be something really simple, but "out of left field", two more considerations that could cause your "bog down" symptoms.

Cam Wear and Ignition Breakdown at speed or due to heat.

==========================================

For a cool worn cam diagnostic process without recourse to kryptonite or dismantling the engine try this:

To Detect a Badly Worn Cam Lobe on an RV8

# set up a an accurate rev counter on the engine.

# some multimeters and strobe timing systems can be used for accurate rpm measurement.

# get the engine warm and set the idle speed to something easy to measure (say 800 rpm).

# using suitably insulated grips/pliers, remove one spark plug lead at a time from the distributor (or spark plug), and observe the drop in idle speed for each cylinder.

# note down the results for No's 1 thro 8.

# removing the plug lead from a normally functioning cylinder would cause a drop in rpm of approximately 250 rpm (to about 550 rpm).

# removing the plug lead from a cylinder with a badly worn cam would cause a drop in rpm of approximately 100 rpm (to about 700 rpm).

# intermediate results might indicate partial wear on the camshaft or possibly a spark plug/lead malfunction.

# (such possible plug/lead causes can be eliminated by substitution)

# detection of approximately 250 rpm drop in idle speed not due to spark plug/lead issues now warrants a visual inspection of the cam function.

# removal of a rocker cover will confirm any faulty valve lifting issues (on Efi models, this is only possible on the R/H bank without removing the plenum).

# further symptoms of probable cam wear are as follows:

o idling seems to be OK but raising the engine speed to 2000 rpm induces significant jerking/vibration as if a plug lead is removed, which then partly diminishes at higher rpm.

o general loss of all round performance - not easy to detect subjectively over long periods of time.

o the spark plug on a cam-affected cylinder will be fouled with oil/carbon deposits.

Please feel free to critique, comment and improve upon this process and let me have any considered corrections as you deem appropriate.

==========================================

Could it be an ignition issue? Probably not, but heck, you can never be sure, so try this simple, surefire method to identify an intermittent ignition problem:

Guaranteed Foolproof Intermittent Ignition Fault Finder.

Rig up two 4/5 watt 12 volt bulbs (or better still, 2V, 15mA LED's + 680 ohm resistors) on test leads into the cabin and connect one between coil +ve and earth and the other to coil -ve and earth. Mark the bulbs POS and NEG. Beware cables dont foul hot/moving parts.

Start the engine and observe:

POS sensing the ignition input voltage is permanantly on,

AND

NEG sensing the pulsed voltage across the Ignition Amplifier flickers in sympathy with engine rpm, or is dimly lit (LED's flicker better).

Now drive the car and have a helper note what happens when the engine misbehaves.

If POS and NEG go out together there is an open circuit interruption of the 12 v feed such as a faulty wire/ignition switch,

OR

A short on the same circuit due to burned insulation.

If NEG comes full on the Ignition Amplifier (due to excess internal heat) or its associated wiring/earth has failed in open circuit mode,

OR

The pulsed input (ie Hall Effect or Reluctor) to the amplifier from the dizzy has failed or the associated wiring is faulty/shorting to earth,

OR

The Coil has failed in a short circuit mode (unlikely cos it would surely kill the amplifier methinks?)

If NEG goes out the Ignition Amplifier has temporarily failed in short circuit mode due to excess internal heat,

OR

the local wiring is shorting to earth,

OR

The coil has failed in open circuit mode due to insulation breakdown or internal heat

If POS stays lit and NEG show signs of flickering instabilitynot sympathetic with engine rpm, then the Ignition Amplifier or its connections are on the blink..

Again, - Please comment on errors/omissions.

[Fed_up_Stag-owner]

Thanks Ramon, lots to work on from your last post. I must admit that I've been out driving rather than fettling (feeble excuse); the acceleration appears to be smoother but perhaps I'm "working around" the flat spot with throttle control. Historical misfire on tight corners (which is where this problem/opportunity started) is cleared, and what a great engine for sitting behind in a convertible out in the sunshine.

[Teesdale_landrover]

good post, is it ok to quote that stuff ramon?