MISFIRE HELP PLEASE?
Discussion
just got the car on the road, did have a misfire when i got car,but still drive some what, change lots, leads,coil ects,put another ecu from a 350i on it ,misfire gone on when just reving up,but so as you go to drive it car misfires big time will not drive at all,put old ecu back drives bit with a small misfire may be v7 any help would be great on this one, new pump.ect;s,is it something with the ecu maybe?? 
Edited by superwedge on Wednesday 8th May 00:16
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Check all the bits and pieces of your ignition, that's likely to be the culprit.
Check all the bits and pieces of your ignition, that's likely to be the culprit.
I am wondering whether the misfire could be either a connection with the ecu or the rectifier pack on the inner wing. you could also remove each individual injector wire see if it makes a difference. Checking at the injectors means you would not need to check all the wires for continuity.
Checking the engine bay in the dark normally shows up any shorts in the HT. You could also pull the plugs when you get the misfire to check condition and maybe identify the cylinder. Best of luck.
Checking the engine bay in the dark normally shows up any shorts in the HT. You could also pull the plugs when you get the misfire to check condition and maybe identify the cylinder. Best of luck.
Can go round in circles with faults like this. Check fuel pressure as a start, if only to eliminate it. Does the fault vary according to road surface (loose electrical connection)? I had poor connections to the electronic thingy on the wheel arch in the engine bay(passenger side), flapper system, a beggar to resolve, the loom was too short. Or have the engine mounts worn?!
superwedge said:
misfire gone on when just revving up, but so as you go to drive it car misfires big time will not drive at all, put old ecu back drives bit with a small misfire
Assuming you have a flapper AFM system, notwithstanding different behaviour from two ECU's, it would seem that your problem may be lack of torque at launch due to a weak mixture, the most likely cause being a rogue air leak into the plenum chamber/air rail.Whilst the ECU acceleration enrichment circuits may be working correctly in response to the fast opening throttle, the ECU cannot sustain the needed mixture competing with an uncontrollable air leak, so the engine misfires, then usually stalls and dies.
You can test for air leaks in many ways, my recommendation is:
Testing for 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. Now attach a suitable external tachometer, connected as per the manufacturer’s instructions, to a spark plug lead, the negative side of the coil 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.
• A breached rocker cover gasket allows rogue air into the breather system. With engine idling normally, remove the oil filler cap and note any significant change in engine tone/rpm indicating a leaking or damaged gasket.
• After fixing any air leaks idle speed and CO level must be reset as per the manual.
I commend its elegance to the house!
been outside on car,looking for air leaks,found this rubber pipe at back engine was very easy to move,so put some clips on it bingo, no misfire/runnnig lumpe any more revining up lovely,when to go a test drive got to the top off road,cuts out will not start,after some time starts runs a little bit now will not rev at all.do think now its too runining too weak now or too rich??
Edited by superwedge on Thursday 9th May 16:34
Edited by superwedge on Thursday 9th May 16:43
Hi Mate..I dont know a great deal as regards to the V8 but it sound's like either the timing is well out or you have an electrical issue..Coil..Dizzy..ECU..Or even a loose connection or faulty lead somewhere?..Have you checked for a healthy spark at each plug?..Could be a leak of air or a lack of fuel..Again are all injectors firing?..Might be something here...Ziga
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