Flapper afm faulty ?

[Rockettvr]

Yes this old chestnut again....
At the fest yesterday I put the old girl in the RR and got a reasonable result (185Bhp). It also showed up a problem with the air/fuel ratio being all over he place through the rev range going lean in a few places- the top line in this graph

Thought possibly fuel starvation ( blocked filters, failing pump or faulty fuel pressure regulator ) but would have thought that would have given me a lean mix throughout the rev range or got progressively worse toward the top end as demand for fuel gets greatest - not at specific rpm(they did the run 3 times - same result ) This leads me to think that the AFM may be at fault.
Can it be tested to see if a fault exists ?
If there is a fault can it be repaired or do I just replace with another ?
Any other possible causes ?
Thanks In advance chaps
Ron

Edited by Rockettvr on Sunday 8th June 12:24

Edited by Rockettvr on Sunday 8th June 12:26

[Rockettvr]

Knew I'd seen the info I needed somewhere - http://www.vintagemodelairplane.com/pages/Rover_Te...

[Wedg1e]

Rockettvr said:

Thought possibly fuel starvation ( blocked filters, failing pump or faulty fuel pressure regulator ) but would have thought that would have given me a lean mix throughout the rev range or got progressively worse toward the top end as demand for fuel gets greatest - not at specific rpm(they did the run 3 times - same result ) This leads me to think that the AFM may be at fault.
Can it be tested to see if a fault exists ?
If there is a fault can it be repaired or do I just replace with another ?
Any other possible causes ?
Thanks In advance chaps
Ron

Does look a bit erratic but I've never seen a flat line on an RV8 yet... could be the AFM spring tension or carbon track, throttle pot, ECU calibration.
AFM can be stripped but the carbon track can be replaced without much work, although where you'd get a new spare I don't know.
If the spring tension's been monkeyed with it can be un-monkeyed but you need to know where to start - another AFM as a reference is useful.

[smash]

Ron - I've got my own spare and Stu's spare here at the mo. if you need

[Rockettvr]

smash said:

Ron - I've got my own spare and Stu's spare here at the mo. if you need

Cheers Smash. Gonna try a few tests on it during the week to see if anything obvious. I'll Let you know how I get on and if I need to borrow one to eliminate it as the cause I'll let you know.
Thanks Ron

[adam quantrill]

I tested mine recently by getting a voltmeter on the wiper wire (refer to the wiring diagram to find out which one) and push the flap in slowly. I think the voltage varies from about 3V-ish down to zero as you push, and do it slowly. If the track is shot the meter voltage will be erratic rather than changing smoothly.

Another thing worth checking is the earthing of the ECU back to the block.

[Rockettvr]

Ok- got round to testing the AFM and ........ all voltages and resistances are bang on the money ( used honest johns info on vintagemodelairplane ). It's clearly a fuel delivery problem and the fact that it occurs at specific rpm I would have put money on it being the afm. So where do I go from here ? Fuel pressure regulator? Fuel pump? Injectors ? Your Advice please

[mrzigazaga]

Hi Ron...As i understand it the mix will be slightly richer and then should lean off a bit when under load..Erratic fuelling can be contributed to a faulty fuel pump, I had this and noticed the fuel pressure having peaks and troughs of as much as 10psi!..Replaced the pump and everything seems to be ok...But check that the plug to the ECU is fully home...Even removing it and giving it a clean with some electrical contact cleaner and a light clean with some emery boards or 1200 grit...If the plug is even a mm out then you will get shyte running.

The solid state FPR can fail...I have a sytec AFPR with a pressure gauge..The malpassi ones are good as well..Mine is set to 38psi at WOT, Its good to see the fuel pressure.

Hope you sort it...


Ziga

[V8 Fettler]

Rockettvr said:

Ok- got round to testing the AFM and ........ all voltages and resistances are bang on the money ( used honest johns info on vintagemodelairplane ). It's clearly a fuel delivery problem and the fact that it occurs at specific rpm I would have put money on it being the afm. So where do I go from here ? Fuel pressure regulator? Fuel pump? Injectors ? Your Advice please

Can you monitor fuel rail pressure when driving? But probably not by running a petrol line into the cabin.

[Jack Valiant]

Ron, I would be tempted to do some simple swap outs to find this type of fault, if you have done the flapper swap with a test drive under load then put your original back on and try another known good stock 4CX ECU and re-test. In my opinion cold voltage tests are all good but a drive with a known good item is far better and helps to localise the problem rather than the scatter gun effect! Given that the power looks good for a stock 350i and the AFR is all over the place I would go to the AFM and ECU as my first stop. I assume you have made sure that there is no air leaks any where first?

Chris

[mrzigazaga]

V8 Fettler said:

Can you monitor fuel rail pressure when driving? But probably not by running a petrol line into the cabin.

Mmmm...Thanks for that..Looks like i might have found a use for the endoscope that i bought a year ago which is still in its box....

[Rockettvr]

Jack Valiant said:

Ron, I would be tempted to do some simple swap outs to find this type of fault, if you have done the flapper swap with a test drive under load then put your original back on and try another known good stock 4CX ECU and re-test. In my opinion cold voltage tests are all good but a drive with a known good item is far better and helps to localise the problem rather than the scatter gun effect! Given that the power looks good for a stock 350i and the AFR is all over the place I would go to the AFM and ECU as my first stop. I assume you have made sure that there is no air leaks any where first?

Chris

Hi Chris good to hear from you
Not swapped out the afm just did the static voltage and resistance tests as per honest johns website (vintagemodelairplane) as said all ok - in fact absolutely bang on the money. The voltage drop during opening the flap was smooth no peaks or troughs.
To be honest the fault is a little bit erratic - definitely worse sometimes than others, usually when cold it's at it's worse - other times it seems to disappear almost altogether.
May try to borrow the spare one smash has - at least that way I can rule the afm out as the cause for certain.
Gonna try to get down for the meet on Sunday - the run down to the bush would be a good opportunity to try it out

[mrzigazaga]

Ron...My fuel pump played up for weeks before it eventually failed...I was getting some really lean running..(White spark plug tips)...There were times when it would misfire or stall and start again whilst driving and then times it was fine...After a while it started to pop and bang on hard acceleration..Then it just failed....Ziga

[Rockettvr]

mrzigazaga said:

Ron...My fuel pump played up for weeks before it eventually failed...I was getting some really lean running..(White spark plug tips)...There were times when it would misfire or stall and start again whilst driving and then times it was fine...After a while it started to pop and bang on hard acceleration..Then it just failed....Ziga

Hi zig
Think I'll try the afm swap first. It's an easy job and it'll eliminate it from the equation. If that fails I'll look at the pump and FPR next. As Chris said I think I need to be systematic in trouble shooting - don't want to be changing too many things at once it can just cloud things if a cure isn't forthcoming.
Cheers Ron

[adam quantrill]

My money is on the FPR. As the revs build up you will get different pressure in the plenum, it will be dropping slightly as the engine pulls air through the open throttle, the air filter and along the tube. As you get the dips at similar places in the rev range it could well be the FPR not sensing the drop in pressure and allowing the rail to build up too high a pressure.

Besides I though you had already tested the AFM and it was working?

[Rockettvr]

adam quantrill said:

My money is on the FPR. As the revs build up you will get different pressure in the plenum, it will be dropping slightly as the engine pulls air through the open throttle, the air filter and along the tube. As you get the dips at similar places in the rev range it could well be the FPR not sensing the drop in pressure and allowing the rail to build up too high a pressure.

Besides I though you had already tested the AFM and it was working?

Only static voltage and resistance tests Adam. my gut feeling is that its ok but thought if i swap it out with a known good AFM and the symptoms persist it rules out a faulty AFM 100%.
My feeling is that its a supply pressure issue - so as Zig says weak/failing pump or as you say an iffy FPR but its the fact that it occurs at certain rpm which nags at me to think it maybe the AFM.
Efi is not a strong point of mine, and i'm just wondering if the TPS could be an issue if mal-adjusted or faulty? what symptoms would it cause?

[adam quantrill]

It would case no symptoms at all on the rolling road - because the test is at WOT and the TPS is on max volts.

[honestjohntoo]

Rockettvr said:

the TPS could be an issue if mal-adjusted or faulty? what symptoms would it cause?

Reworking my TPS web page explanation - apologies as needed.

Efi System response to Throttle Pot normal and fault conditions

• Ignition on, engine not running. Voltmeter connected to red/green wires.

• Providing the voltage change is slow and smooth the injectors may be heard firing or clicking just once for full load enrichment as the assembly approaches full throttle.

• If the maximum voltage measurement (4.3 V) is undesirably low (below 3.3 V) then this function might not take place and the above mentioned full load fuel enrichment is denied.

• Open the throttle RAPIDLY and the injectors fire much sooner during rotation.

• This simulated fast acceleration triggers supplementary injector firing to provide extra fuel needed as soon as possible during the period of acceleration demand.

• However, if the voltage rise is erratic even when slowly operating the throttle, it is very likely that the injectors will be heard firing randomly or in sympathy with the sharply varying voltage reading .

• This is because the erratic voltage signal fools the ECU into thinking the throttle is moving swiftly when it is not, triggering unwanted fuel enrichment under casual driving conditions resulting in a randomly unstable fuel/air mixture leading to very lumpy engine performance with gross adverse affect on fuel consumption.

• This random injection of extra fuel may not occur when the car is cruising at constant speed with the throttle not moving.

• However even casual acceleration or deceleration can cause havoc with mixture control.

• Alas, the potentiometer is prone to wear at the point where it is most used at normal driving speed so the effects on normal driving are at their most noticeable.

• The erratic voltage readings are observed more readily with an analog voltmeter.

• It is possible to prolong the life of the throttle potentiometer a couple of ways. It can also be substituted with a readily available alternative.

[Rockettvr]

Not likely to be the TPS then as I'm under fueling rather than running rich. I'm going to swap out the AFM just to be 100% that's not the cause then move on from there.
Thanks for the advice chaps
Ron

[Jack Valiant]

Ron, a few people close to you will have the AFM and 4CU good spares, so it will not take long to diagnose and cost nothing to do. Replacement of them is not difficult or costly. I gave away all my flapper based stuff when I created the monster but let me know if I can help

Chris