The V8 Owners Forum -

3.5EFI with flapper AFM.

I have been trying to sort out some intermittent problems. Unstable idle when warmed up. Sometines it runs rough with a lack of power at about 3K revs.

I have fixed a leak in a breather hose, fixed a poor connection from the ignition amp to the coil. Replaced the hose between the plenum and the AFM. It has certainly improved things. Leaning the mixture off also helped.

When looking at the engine after a run yesterday I unplugged the throttle pot. Just out of curiousity. The engine continued to run so I took it for another run and I could feel no difference in performance with the pot plugged in or unplugged. This has got me confused. Something is clearly wrong.

So I took some measuremnts at the pot. Yellow to green wire is 4.12V, so within spec. Red to green is 0.22V where it should be 0.325+/- 0.025.
I will adjust this if I can get the knackered screw out.

I am beginning to think that the pot is getting power from the ECU as it should and that has a working ground, but the signal is not getting back to the ECU. This ECU is working on some sort of default setting. Possible?

Any thoughts?

Paul.

Hello Paul, Spot on! First this:

• The throttle potentiometer is connected to the spindle of the throttle butterfly. Its purpose is to advise the ECU of the driver's accelerator pedal position and its rate of change.
• When the throttle is operated, the wiper moves over the resistance to vary the voltage and the appropriate signal sent to pin 2 of the ECU. In this way throttle movement is sensed.
• The ECU detects the rate of change of the voltage across the potentiometer connections (pins 2, 3 & 18 ) and when appropriate, triggers the acceleration enrichment circuits.
• At full throttle the ECU detects the appropriate signal to provide full load fuel enrichment.
• If the throttle potentiometer is disconnected, the engine will continue to function normally with the exception that both enrichments circuit will not be activated resulting in poor acceleration and full load response..

More information on the PDF available here:

http://www.vintagemodelairplane.com/pag ... Pot01.html

You'll see therein the full test process, but it goes without saying that good connections to the ECU are vital, as you surmised, so check connectivity too.

Finally, these items go faulty any-time after 60-80,000 miles, so repair/replacement/substitution has to be done when the unit fails the recommended instability tests.

A faulty unit variously causes erratic running due to random unwanted acceleration enrichment signals (noise).

hope this help

Ramon - You have an excellent website with loads of useful information.

I'll take some more measuremts and borrow an analogue meter to see how erratic the pot is.

A couple of other things, I can't here the injectors opening at full throttle and it does smell very rich.

Thanks,

Paul.

mrcheese wrote:Ramon - You have an excellent website with loads of useful information.

I'll take some more measuremts and borrow an analogue meter to see how erratic the pot is.

A couple of other things, I can't here the injectors opening at full throttle and it does smell very rich.

Thanks,

Paul.

By far the best way to test this pot is to put 5 volts across it and look at the output on a scope while you slowly open and close it. Other more eccentric way is to wire it up as a volume control and shove audio through it. A single frequency is best.

mrcheese wrote:A couple of other things, I can't hear the injectors opening at full throttle and it does smell very rich.

OK, Paul.

Unburned petrol will/may be smelled during audible/electrical testing of the TPS and accelerator enrichment circuits.

If otherwise smelling rich along with the running problems described, you might check the spark plug condition for clues to mixture control. Wet/sooty would confirm overfuelling for some reason. A badly worn TPS is just one of several possible causes though.

Not hearing injectors at full throttle is of no consequence as there may be other ECU input circumstances at play for full load enrichment (I dont know for sure) but they must be heard on a regular pattern at the same times from a good TPS with a repeated opening of the throttle quickly as described for that test.

Once you know the result, stop, as continued repetitive testing could flood the engine, of course.

Any sort of damage to the TPS carbon track can produce a raft of different jiggery responses. It's as random a the nature of any damage.

The analog meter voltage test described in my essay is perfectly adequate to check for TPS damage. Hooking in a power supply, scope or audio signal is hardly necessary or convenient (equipment-wise) if you can see the needle of an ordinary voltmeter.

I am making progress. Yesterday I checked for contiunity and set the voltage between the red green wires to 0.325V

My analogue meter only has a 10V scale so it is not really sensitive enough. I used a DMM in parallel with it. The analogue meter moves smoothly all the way up to 4.1V. But the minumim voltage is now 0.306V.
This did drift up slowly to 0.314V. The DMM reading was not jumping around. Then I discovered that if I put pressure on the trottle arm as if to try to close the butterfly valve even more the voltage rose to 0.337V.

I removed that pot and found that there is some movement in the shaft. Side to side a little and in and out by obout 0.5mm. If I move that shaft in or out or side to side I can get the resistance to change from a low of 70R to a high of nearly 300R. This suggests to me that the pot is shot. I can't find any way of opening it up though.

I removed a spark plug from each bank. They look normal with perhaps a small indication that they are sooting up. But it has only done about 40 miles since that problem first started.

I also found the cover on the AFM is lose. No evidence of muck or water in it and the resistance measurements check out.

I still can't hear hear the injectors opening. But thay must be as it does run.

Paul.

Paul, your variable readings at the low voltages may not be due to a faulty TPS, but just as likely, wear in the throttle linkages, shaft, butterfly and bearings, allowing the pot shaft to rotate a tad.

The variation low down, is only 5% of the total 5000 ohms easily accountable by mechanical wear which can also manifest itself as an unreliable idle speed setting. This condition is otherwise known a "Idle Speed Hang-up"

Fettle the throttle assembly to improve. See here for clues what to look for and how to improve: http://www.vintagemodelairplane.com/pag ... ing01.html

You can also test the TPS off-car by looking for smooth resistance reading too. If smooth, not erratic, throughout, these small variations may be inconsequential. An erratic fault, results in jerky running and slight to moderate overfuelling depending upon severity of damage.

Worry not, about plug colour until you can take the car for an extended run. If normal, then OK. Then let the car idle for a good while and check again, any idle overfuelling can be detected thus. Or you can measure emissions.

To open up this version of the TPS,



pick out the epoxy filler from the three cover fixing screw holes with a sharp instrument to expose the screw heads. All fully explained in the TPS essay mentioned.

Just because the engine runs does not mean the ECU is 100% OK. The fact that you cant hear the injectors clicking when the TPS is rotated fast is a problem as it implies the enrichment circuits are not working.

OR your hearing is duff. So, put a voltmeter across an injector and repeat the test, to see if the voltage flicks (to about three volts max) as the TPS is rotated fast. Analog is better and all you will see is the needle flick.

The AFM cover being loose means someone has been in there for a look-see. If the car runs well and the plug colour is acceptable, emission OK, the AFM spring may not have been disturbed.

If you read this: http://www.vintagemodelairplane.com/pag ... ter01.html you get the whole nine yards.

Ramon,

I have been reading your site and it has been given me a lot of information. I am going back to the start and making sure all is correct.
I have a feeling that a number have faults have built up over the last few years.

Getting a stable base idle has been a problem for quite a while. It does not always go low enough using the idle screw. I am going to take the plenum off and clean it. Then clean and adjust the throttle assemble. I'll then do a careful check for vacuum leaks.

I have borrowed two spare AFMs, two ECUs and a throttle pot.

Let's see what happens.

Paul.

Way to go, Paul!

Not mentioned so far, but it has to be recognised that more than 80% of Flapper Efi faults are due to air leaks into the plenum and electrical connection problems around the Efi and ignition looms. Not far behind is the problem of cleanliness, both around and within the ignition components and inside the plenum chamber.

By and large then, with the exception of the TPS and ignition amplifier, all the items making up the Flapper Efi are pretty much bulletproof and a neglected plenum chamber can cause several issues, crud in galleries, throttle butterfly seating, excess internal moving parts friction, crankcase ventilation.

It is also a precursor to uninformed adjustments being made elsewhere, such as CO mixture, ignition timing, throttle pot, AFM tinkering, throttle stops (on some cars) and fuel pressure (if adjustable) in an effort to make corrections to totally unrelated problem(s).

Some owners even resort to removing things to make the system go better, . Oops!

The eventual combination of maladjustments and actual faults is quite a tough ask, so going back to basics is best all round. Remember, all the components bar the ECU can be tested with simple equipment.

The alternative process of buying and fitting expensive new components in a random scattergun approach is rarely ever succesful and never uncovers those air leak and connection problems until after the wallet is empty.

"Look after your Plenum and your Plenum will look after you!"

with apologies to Trigger's Broom in "Only Fools and Horses".

I think it is fixed and it was, as suspected, more than one problem. It is a Land Rover after all!

I took off the plenum and trumpet base and cleaned them all up. There was quite a lot of muck inside. A bit of a surprise as a rebuilt engine went is 5 years ago and I cleaned all the parts up then.

I found a lose hose clip from the fuel rail to the 9th injector. I have been getting an occasional waft of petrol fumes from the engine bay.

The movement of the throttle pedal is now very smooth as I cleaned and lubricated the mechanism.

The replacement throttle pot went on as well as the spare AFM. When started the exhaust smelt normal and much less rich.

With the engine not running and the ignition on I could still not hear the injectors firing when opening the throttle. So I put on the spare ECU and that fixed it.

I took it for a test drive and it is going great. I'll put in the the old throttle pot at some point as I need to know if the AFM or the pot is faulty.

Thanks for your help.

Paul.

The TPS makes no difference at low/medium steady throttle - the engine will run without one. What it does do is control the acceleration enrichment at any speed and mixture at wide openings.

mrcheese wrote:I think it is fixed and it was, as suspected, more than one problem.

Well done Paul,

You are right, a combination of possible component faults, air leaks, cleanliness, maintenance and likely maladjustment.

# Maybe ECU because the acceleration ccts were not working, but then maybe not an ECU fault - see note.

# Perhaps, but not proven, the throttle pot, but with the ECU enrichment ccts not wkg for some reason, perhaps not.

Note: I say "for some reason", because changing the ECU may also have enlivened a dodgy multiplug connector fault. You'll recall, this was one of your suspicions in your opening post - connectivity.

# Maybe the AFM because after replacing it, you got an improved mixture and less smell. Lets be clear tho', there was also the possibility of uninformed tampering with the AFM because the cover was off. So the AFM could be perfectly OK, just maladjusted. Mind you resetting it correctly is a minefield.

# Definitely the air leaks in the breather pipe and inlet hose that you found at the GetGo.

# Finally the dirty plenum and throttle mechanism smoothness are not actual system/component faults, more, simply conditions related to age, wear and perhaps a degree of neglect.

# You are right to be surprised at how much filth you found internally after only five years, but when an engine is maladjusted and running too rich, as you found, so then are the crankcase gasses also rich, and its from the crankcase that all that grime originates.

# Strangely then, you may find, when rechecking the suspicious components, that the faults on your motor were mainly down to air leaks, connectivity and cleanliness.

# Not an unfamiliar scenario because typically 80% of Flapper Efi breakdowns are due to precisely those reasons as mentioned in the thread.

# In summary, you may well ask, So What? All the above is irrelevant, because the engine is now OK, the faults are gone and who cares about post-mortem analysis anyway? Forget it and move on!

# Well, your particular situation and resolution, as described in this thread, demonstrates that the fault finding process works fine for any home enthusiast prepared to take the time to read up on the system, think about the symptoms and follow a logical test process.

As I say, Well done!

Thanks Ramon.

The big connector to the ECU was removed and re-connected lots of times to see if that was an issue. Plus electrical contact cleaner was added. I even put the old ECU back on and the injectors did not fire again.

I will put on the old TPS to see what happens.

I will open up the old ECU to look for dry joints.

I have to say that it has been fun and educational working through the problems. I have learned a lot.

I should have added that the tiny breather on the LH rocker was blocked.

The timing chain has probably stretched after five years so I'll check the timing.

Once again, thanks.

Paul.