flapper type lucas air flow meter !
Discussion
pk500 said:
It run rough I put the emission machine on and it was running 0.03 and wouldn't adjust so I took the top off to cheat it but can only get it up to 0.95 which I feel is far to lean especially when cold
I'm assuming your running rough came before any adjustments to the AFM? If so, running rough is not the most likely indicator of a faulty AFM. Air leaks (and electrical connection issues) are a much more common cause!It's not normal to measure emissions (CO) when cold and then make radical conclusions from the resultant reading. You are right, a rich mixture when cold would be heavily poluted but there is no common data with which one could compare those results. Why would there be? Running an engine cold is only a transitionary phase to running hot, when measurements are normally taken.
One of the features of the Standard 3.5 flapper Efi is that they run on the lean side at idle and at cruise, perhaps your flapper variant is similar? Your expectations could be affected by that.
A loss of CO adjustment may be due to a blocked bypass airway in the AFM or simply a sticky flap or a small piece of debris, thereabouts.
If you have not seen them before, and if you are adjusting the AFM innards in hope, it may help to study this and this
Edited by honestjohntoo on Tuesday 8th January 20:31
pk500 said:
cant see any air leaks ! couldn`t adjust mixture by the allen key !
Visual inspection is a cursory method of finding air leaks into the plenum chamber. Spraying around the hoses/gasket joint with Plusgas or WD40 can be a little more successful. The best method is this:Dynamic Testing for RV8 Efi Air Leaks
• If during the process of fault finding its is established that all the ignition, fuel and sensor components are working correctly but engine performance is still not up to standard, then obviously there remains a fault as yet undiscovered.
• With so many pipe connections to the plenum affecting what happens at the inlet manifold there is a high probability of rogue air leaks into the system.
• The following mode of diagnosing the location of any air leaks will also prove if the extra air valve and the air-con anti-stall valve (if fitted) are working correctly
• Run the engine until it attains normal working temperature and “try” to set the idle speed to somewhere near its normal level.
(nb: If the idle speed adjust screw has no effect the idle air gallery may be blocked or the throttle plate is held partially open negating idle screw effect. Generally the plenum has to be removed to ream out the gallery).
• Attach a suitable external tachometer, connected as per the manufacturer’s instructions, to a spark plug lead, coil negative or an injector, as appropriate, and stop the engine.
• Begin by disconnecting the vacuum pipe (‘A’ in fig.1) to the fuel pressure regulator and suck on the open pipe to check the integrity of the regulator and the pipe. If the vacuum generated by sucking does not hold, check the pipe. If the vacuum still won’t hold, the regulator is definitely faulty. This test can also be performed using a vacuum pump working at no more than 15 inches of mercury.
• Thoroughly check the inlet hose(s) between the air flow meter and the throttle butterfly housing to ensure the laminations have not separated, there are no holes in the hose(s) and the hose clips are secure.
• Restart the engine and allow it to come up to operating temperature again. Reset the idle speed with the help of the external tachometer to an easily remembered level (say 800 rpm) and make a note for future reference. Stop the engine.
Fig.1. Plenum Air Connections
• Disconnect all air/vacuum related systems joined to the plenum which can affect performance and seal off all the inlets marked X with patches of self-adhesive tape (badge tape is good) as follows:
1 Disconnect the brake servo, and seal the union connection at the plenum
2 Disconnect the pipe to the ventilation system reservoir and seal the port
3 Disconnect the extra air valve “U” shaped hose and seal the port
4 Disconnect the air rail hose from the pipe next to the throttle and seal the port
5 Disconnect the breather from its pipe near the throttle pot and seal the port
6 If fitted, disconnect the air-con valve hose from its stub pipe and seal the port
7 Disconnect the air supply to the overrun valve and seal the input to the valve
8 If fitted, disconnect the vacuum pipe to the automatic transmission and seal the port.
• With the exception of the pressure regulator connection, all the air/vacuum connections at the plenum have now been sealed off, as illustrated in Fig.1.
• Start the engine (if necessary depress the throttle to raise the engine rpm), run it to attain normal operating temperature then allow it to idle. Check and record the idle speed, and compare with that recorded earlier.
• If there is no change in idle speed, this proves that all the disconnected systems are sound as far as air leaks are concerned. On the other hand if the engine speed has altered significantly (say 100 rpm or more), this indicates one or more of those systems is faulty and must be found by a process of elimination.
• Air leaking into the vacuum connections or blockage of a permanent air feed into the inlet system can cause the engine speed to increase or decrease by as much as 200 rpm or as little as 10 rpm if, for example, the crankcase ventilation oil separator is blocked.
• Faults which cause small changes in idle speed are often overlooked or are erroneously rectified by readjustment of the idle screw. Over time these minor faults can build up and interact so they should not be disregarded when they can be detected and analysed by the following tests.
• So if idle speed changed, record the readings at this and each subsequent stage as they are required for ongoing comparison to pinpoint which of the disconnected pipes or components is at fault during the remainder of the tests:
o No.1. Unseal and reconnect the brake servo pipe. Restart the engine and compare with the idle speed just recorded. If it has changed a fault lies in the brake servo hose, the non return valves (Normally, there are two on Efi cars!) or the brake servo itself which must be investigated and resolved.
o No.2. If fitted, set air-con controls to “on” then unseal and reconnect the pipe to the ventilation system vacuum reservoir. Restart the engine and measure the idle speed. Any change from the previous figure indicates an air leak into the vacuum control system. To isolate a fault, first move the controls to “off” and recheck the idle speed. If still affected the fault is in the vacuum reservoir or connecting pipes. If the idle speed is restored the fault lays in the vacuum distribution unit, one of its associated vacuum servo units that operate the flaps or their associated pipes. Investigate and resolve.
o No.3. Unseal and reconnect the extra air valve hose at the plenum. Restart the engine and check if there is a change in the idle speed. Assuming that the “U” shaped hose itself is sound, and remember, the inlet hose is open at the throttle end, any change indicates that air is leaking through the extra air valve mechanism into the plenum and therefore the fault lies in the extra air valve itself. If when the hose is reconnected there is no change in the engine speed then the extra air valve is proved to be sound with respect to air leaks.
o No.7. Unseal the input pipe to the overrun valve and restart the engine. If the idle speed is unchanged the valve is not leaking. If the idle speed changes there is a fault in the valve that must be corrected. A common cause is debris between the valve head and the valve disc preventing it from closing properly.
o Nos. 4 & 6. Unseal and reconnect both the air-con air valve connection at the plenum (if fitted) and the air hose at the throttle butterfly. Restart the engine and measure the idle speed. If no change is detected this proves that the air hoses and the air-con air valve are sound. If the idle speed has changed, air is entering the plenum either through a faulty air conditioning air valve or the associated pipes. Investigate and resolve.
o No. 5. Unseal and reconnect the crankcase breather pipe and check the idle speed. Any change in engine speed indicates a possible air leak in or around the oil separator or the pipe itself which can be easily checked by visual inspection. However, the crankcase ventilation system is complex and interactive with several seals and gaskets which should be carefully inspected if problems are indicated. It may be that there is a problem with the engine itself regarding how much gas is able to bypass badly worn pistons into the crankcase and subsequently affect the idle speed. If such a condition exists then chasing non existent air leaks will be a fruitless exercise.
o No. 8. Unseal and reconnect the vacuum control pipe to the automatic transmission modulator valve (if fitted). Restart the engine and check the idle speed. Any change will indicate a leak in the rubber connecting elbows at each end of the metal pipe or the transmission modulator valve itself. If the modulator valve is faulty then manifold vacuum is able to suck transmission fluid into the plenum where it enters the engine and burns with a dense white smoke. Such a fault would surely have been previously observed?
• Having checked all the connections and components mentioned there remain a number of other ways in which rogue air can enter the system. It can leak past the plenum/trumpet housing joint, the trumpet housing/inlet manifold joint, the cold start injector seal, any of the injector seals or even the inlet manifold gasket.
• The plenum to trumpet housing joint is particularly vulnerable to poor sealing because the metal to metal face is only 1/4” wide over an aggregate length of 30”.
• To check for leaks in any of these inaccessible areas, restart the engine and squirt very thin oil, WD40 or Plus-Gas around the mentioned joints and gasket locations in turn. Any ingress of fluid into the manifold can usually be heard or seen.
• Repeat the test around all the injectors to ensure each has an airtight seal. Fluid gaining access to the inlet manifold may also be indicated by a change in engine rpm and/or by changing colour of the exhaust gasses.
• If leaks are found they might be temporarily sealed using a brand of Damp Start Lacquer (i.e. Holts). Use it when an area to be sealed is dry and free of grease. Sprayed from an aerosol around the suspect area of leakage, it forms a plastic latex film which can seal the most inaccessible of leaks into the air inlet system.
• This type of sealant should be only used when the engine is switched off as during application, it gives off a flammable propellant. Bear in mind that such a cause temporarily cured by this method would still need to be permanently corrected.
• After fixing any air leaks idle speed and CO level must be reset as per the manual.
pk500 said:
the car has sat under a tree for several years so could be something stuck will pull it back off when i get 5 min`s spare, cant see any air leaks ! couldn`t adjust mixture by the allen key ! would like to try another one !
Indeed, I'd be concerned after all that time that the flap pivot bearings were corroded and sticking, preventing the flap from closing fully. That would give the ECU a higher than expected voltage for the idle airflow, leading it to run rich and bu99ering up your idle CO reading. Pull off the air hose from the AFM, insert fingers and see if the flap can be swung freely but smoothly with a constant amount of resistance. While you're in there.. check for dead spiders, webs, leaves and any other debris that could be blocking the bypass air channel.Also allow for the fact that the fault(s) may have been there before the car was parked, the AFM could already have been swapped and/ or fannied about with.
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