Hello Doug - thank you for the clarification that the 85 XJ has the 4.3 FI engine, not the 3.6 - so for the replacement function of a throttle potentiometer to provide a signal to the fuel ECU, you state that the AFM flap movement will provide a signal to the fuel ECU (after re-reading the posts above, I noticed that Frank mentioned something similar also) - is the flap movement of such a design that there is an electrical contact section being used as a potentiometer to provide a signal to the fuel ECU - Niels did state that the AFM flap was not stuck, so I am wondering if the is a disconnected wire from the AFM flap area - Tex Terry, II - 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe - sent 9/8/2020 2209hrs. EDT USA.
Entirely plausible that there is a wiring or connector problem at the AFM, yes.
Or perhaps an internal AFM fault?
Cheers
DD
Hello Robin - thank you for the post with the electrical and mechanical operation of the AFM - this does help with an understanding of how the system works to provide a signal to the fuel control ECU - hopefully Neils (the original poster with the 1985 XJ6) will see your post and will make a test to verify that a signal is, or is not, getting to the ECU during the flap operation - Tex Terry, II - 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe - sent 9/8/2020 2331hrs. EDT USA.
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He positively verified that the AFM flap was not stuck, Dougā¦
My problem is simply the āno engine responseā to throttle opening - without fuel added (failed AFM); the engine engine would misfire and stall on a (very) lean mixture. āNo reactionā is simply impossibleā¦
Frank
xj6 85 Sov Europe (UK/NZ)
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Itās really acts voltage divider - but a potmeter is used for the function, Texā¦
However; the throttle is controlled by the driver - but the driver has no control of the mixture; which is controlled by the ECU. Ie; the driver opens the throttle to increase air, but with no fuel increase to maintain mixture - the engine stutters and die. āNo engine reactionā is simply unfathomableā¦
frank
xj6 85 Sov Europe (UK/NZ)
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The overrun valve is mounted inside the air distribution block - which is indeed connected by hoses.
Disconnected hose(s) at the air distribution block is indeed an air leak, and must be connected up! However, it should have limited influence - and there should still be some sort of engine reaction to throttle movementsā¦
Frank
xj6 85 Sov Europe (UK/NZ)
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Iām stretching here, but what the heckā¦
I wonder if the throttle blade is actually opening when the pedal is pressed?
Has this been checked, I wonder?
Cheers
DD
āBrokenā spindle?
I would also push the AFM flap open during running but all symptoms point to a functioning AFM and a nonfunctional throttle despite the pedal moving the butterfly per Niels. And the massive air leak would still lead to a throttle response if it ran at all.
I have the Throttle body out on the table and everything is perfect and the blade move when you press the pedal
Have tested there is no leak
Yes it just keeps on idling whatever I do
Niels
Hello Niels - have you tried testing the signal volts produced by the AFM to determine if a signal is going to the fuel control ECU during the movement of the AFM flap (look back about 11 posts at the picture submitted by Robin to note the pin 7 output to the ECU) - Tex Terry, II - 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe - sent 9/9/2020 2015hrs. EDT USA.
It is a wonder, Dougā¦
He says ācontinues to idleā when pedal is pushed - which is a wee bit different from āno reactionā. While throttle butterfly is hidden; it is easy to observe AFM flap operation - just removing the air filter and look while operating the gas pedal. And for the record; I assume the 7-pin AFM connector is firmly pushed homeā¦
If there is no flap movement; no air is going through the AFM when/if throttle opens, for whatever reason. No air change and no more fuel - and no change in idle. The reason for this eludes me - the answer must be ridiculously simpleā¦
Frank
xj6 85 Sov Europe (UK/NZ)
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1 Like
I can not test anything on the AFM it is out on the table I am waiting for new gasket to the Throttle body I hope it is here before the weekend.
Niels
Hello Niels - while you have the AFM out on the test table, use an ohm meter to check for a reading between pin # 6 and pin # 7, pin # 8 and pin # 7, pin # 9 and pin # 7 - you should read changing ohms as you move the AFM flap - Tex Terry, II - 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe - sent 9/10/2020 1359hrs. EDT USA.
Hello Terry
Thank you for your interest in my problem.
I have measured the AFM and found the following:
pin #7 To pin #6 ohms changing
pin #7 to pin #8 ohms changing
pin #7 to pin #9 ohms changing
Niels
Hello Niels - just trying to help (as I have been helped by the members of JL) - since you have made this test to verify that the AFM flap should be able of giving a varying signal upon movement, try to test the AFM connector in the engine bay - utilizing the chart from the post from Robin, use a volt meter to check to see if you have the supply 12 volts present on pin # 39 [you will probably have to have the ignition key in the āonā position (position II)] - also check to see if you have a ground on pin # 6 (verify the ground on pin # 6 by using the ohm meter between pin # 6 and the engine block ground) - Tex Terry, II - 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe - sent 9/10/2020 2108hrs. EDT USA.
#6 to #8 should read 220 ohms, constant, Niels this is fixed resistor in parallel with the variable one.
#8 to #9 should read up to 400 ohms, constant. This is the variable resistorās āendpointsā with a tap-off to #7
So connections involving #7 will be variable with flap deflection - but readings between #7 and #9 is ābiasedā by the parallel fixed resistor.
There are no specs for resistances at varying flap angles - but the ECU sorts it; your AFM is likely OKā¦
Frank
xj6 85 Sov Europe (UK/NZ)
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Can a bad ECU do this?