350i misfire - the return....
Discussion
Right, as posted previously my Wedge developed a nasty misfire on the way home from the TVR-CC Millbrook day. Upon inspection the distributor was knackered with the rotor arm totally distorted causing the cap to do the "hokey cokey". A new distributor eventually sorted this and all was well for a few weeks, but then a misfire reappeared which has proven elusive to track down.
I've swapped the ignition amp on the new dissy, fitted a new coil (third one), swapped in a new set of HT leads, swapped the thermotime switch, new set of plugs, checked all engine and ancillary earths, checked all resistances on sensors (all good) and checked the wiring and connections to the AFM, ECU, power resistors, sensors etc including a good dose of pukka electrical contact cleaner (also all good). I've double and triple checked the timing and vacuum advance and I've checked and dropped the fuel pressure to 36psi. Despite this the problem persists, and it is definitely electrical.
The car starts fine, revs clean, but as it gets warmed up the misfire starts and then gets worse. It drives along quite happily then there is a cough as if it's momentarily lost all electrical power and then half a second later kicks back in and runs clean. I've ordered a brand new CTS out of curiosity, even though the resistance figures for the installed one appear okay.
I was suspecting the very old engine immobiliser however this wouldn't be affected by the engine temperature?
I'm going to drop the bloody thing off at the garage at the weekend so they can have a prod and a poke and I'm tempted to get them to rip out the immobiliser. I've only one fob anyway so if I lost it I'd be buggered.
So the things I'm left to suspect are:
Immobiliser
Dodgy pickup in the new distributor
Buggered ECU.
Are any of these three likely to give the misfire only when the engine is warmed up? Anything else I should be checking?
I will be going to the Neil Garner open day on the 26th September - but most likely in the bloody diesel BMW!
I've swapped the ignition amp on the new dissy, fitted a new coil (third one), swapped in a new set of HT leads, swapped the thermotime switch, new set of plugs, checked all engine and ancillary earths, checked all resistances on sensors (all good) and checked the wiring and connections to the AFM, ECU, power resistors, sensors etc including a good dose of pukka electrical contact cleaner (also all good). I've double and triple checked the timing and vacuum advance and I've checked and dropped the fuel pressure to 36psi. Despite this the problem persists, and it is definitely electrical.
The car starts fine, revs clean, but as it gets warmed up the misfire starts and then gets worse. It drives along quite happily then there is a cough as if it's momentarily lost all electrical power and then half a second later kicks back in and runs clean. I've ordered a brand new CTS out of curiosity, even though the resistance figures for the installed one appear okay.
I was suspecting the very old engine immobiliser however this wouldn't be affected by the engine temperature?
I'm going to drop the bloody thing off at the garage at the weekend so they can have a prod and a poke and I'm tempted to get them to rip out the immobiliser. I've only one fob anyway so if I lost it I'd be buggered.
So the things I'm left to suspect are:
Immobiliser
Dodgy pickup in the new distributor
Buggered ECU.
Are any of these three likely to give the misfire only when the engine is warmed up? Anything else I should be checking?
I will be going to the Neil Garner open day on the 26th September - but most likely in the bloody diesel BMW!
90% or early immobiliser will just take one wire form the ignition and run it via a relay in the immobiliser. all the other sensors will be twined. so re-join the cut wire, and just cut off all the join ones, and no more immobiliser, if you got a soldering iron and some heat shrink.
I need to get my Flapper ECU logger finished, to monitor ECU's while the car us running.
I need to get my Flapper ECU logger finished, to monitor ECU's while the car us running.
I take it you replaced the rotor arm. Think about premature failure of any new parts.
I had a new rotor arm on mine that only lasted a couple of thousand miles before arcing right through the insulation from the top to the dizzy spindle.
Is the spark OK at the king lead? What about each ignition lead one at a time? You will have to wait until the symptoms appear before starting this testing.
Another way of testing the HT leads is to measure the resistance - this is between 1000 and 5000 ohms depending on wire type and lead length.
I had a new rotor arm on mine that only lasted a couple of thousand miles before arcing right through the insulation from the top to the dizzy spindle.
Is the spark OK at the king lead? What about each ignition lead one at a time? You will have to wait until the symptoms appear before starting this testing.
Another way of testing the HT leads is to measure the resistance - this is between 1000 and 5000 ohms depending on wire type and lead length.
TVRleigh_BBWR said:
90% or early immobiliser will just take one wire form the ignition and run it via a relay in the immobiliser. all the other sensors will be twined. so re-join the cut wire, and just cut off all the join ones, and no more immobiliser, if you got a soldering iron and some heat shrink.
I need to get my Flapper ECU logger finished, to monitor ECU's while the car us running.
Thanks - it's a rats nest of wires under the dash from the immobiliser including a sensor as part of the ignition barrel, LED drilled into the steering column housing and a rather large control box. I think I'll get it professionally ripped out because:I need to get my Flapper ECU logger finished, to monitor ECU's while the car us running.
1. I have very little spare time at present,
2. I'm just a bit fed up with the bloody thing, having missed half of the summer,
3. If it doesn't start afterwards I've got someone to blame!
adam quantrill said:
I take it you replaced the rotor arm. Think about premature failure of any new parts.
I had a new rotor arm on mine that only lasted a couple of thousand miles before arcing right through the insulation from the top to the dizzy spindle.
Is the spark OK at the king lead? What about each ignition lead one at a time? You will have to wait until the symptoms appear before starting this testing.
Another way of testing the HT leads is to measure the resistance - this is between 1000 and 5000 ohms depending on wire type and lead length.
Hi Adam, I've checked the rotor arm and it's all okay. Spark at the king lead is healthy and over half an inch. I was running an older set of Bosch HT leads. Just swapped out for a brand new set of Powerspark ones with no difference whatsoever. I will check the resistance tomorrow to see how they compare though. Thanks. I had a new rotor arm on mine that only lasted a couple of thousand miles before arcing right through the insulation from the top to the dizzy spindle.
Is the spark OK at the king lead? What about each ignition lead one at a time? You will have to wait until the symptoms appear before starting this testing.
Another way of testing the HT leads is to measure the resistance - this is between 1000 and 5000 ohms depending on wire type and lead length.
Jack Valiant said:
Have you tried a test with known working ECU? I have seen quite a few cause similar symptoms when the 30 year old power transistors start failing when heated up. Just a thought test then eliminate.....
I've not got a spare ECU to play with although I'm tempted to pull the 390SE ECU just as a test around the block to see if the misfire is still there, even if the fuelling is not quite right. Is it worth trying this?
KKson said:
I've not got a spare ECU to play with although I'm tempted to pull the 390SE ECU just as a test around the block to see if the misfire is still there, even if the fuelling is not quite right. Is it worth trying this?
It's worth a shot although my guess is you'll prove how varied the fuelling can be on these ECUs 
- you may even find it won't start, or if it does it won't idle, or won't pull, none of which will help you work out what's going on...Right, 350i has been in the garage a week - new ignition section of the loom has been made, new CTS fitted, new ignition amplifier fitted, old alarm and immobiliser temporarily disconnected and...... the bloody car still misfires when it gets hot! It starts fine, revs clean and then as the temperature rises the same old "cough" returns.
I'm hoping to pick up a spare AFM and ECU to try them next. I certainly won't be going to the Neil Garner open day in a TVR this weekend.
I'll be the one in the diesel estate.
I'm hoping to pick up a spare AFM and ECU to try them next. I certainly won't be going to the Neil Garner open day in a TVR this weekend.
I'll be the one in the diesel estate.
KKson said:
adam quantrill said:
I take it you replaced the rotor arm. Think about premature failure of any new parts.
I had a new rotor arm on mine that only lasted a couple of thousand miles before arcing right through the insulation from the top to the dizzy spindle.
Hi Adam, I've checked the rotor arm and it's all okay. Spark at the king lead is healthy and over half an inch. I had a new rotor arm on mine that only lasted a couple of thousand miles before arcing right through the insulation from the top to the dizzy spindle.
2. Change the dizzy cap.
3. Replace the CTS with a 300 ohm resistor after it's hot and misfiring (cheap test).
4. Go around each cylinder one by one and remove the injector plug, and run the engine. Does the misfire convert to a miss? In which case it's cylinder-specific so you can concentrate on that one, plug, injector, valves (maybe valve sticking), etc.
Hi Keith...Thats a bummer...Before you enter into the realm of darkness..Lets rewind a minute...You changed the pick up in the dizzy right?..Have you tried it with the old ignition amp..New ones can fail...And you have got the right coil?...And there are 3 different rotor arms..Make sure anything you buy is for "EFI"...This might sound silly but did you unplug the battery terminal for a while to reset the ECU..They are sensitive to voltage changes...It will be something simples....
mrzigazaga said:
Hi Keith...Thats a bummer...Before you enter into the realm of darkness..Lets rewind a minute...You changed the pick up in the dizzy right?..Have you tried it with the old ignition amp..New ones can fail...And you have got the right coil?...And there are 3 different rotor arms..Make sure anything you buy is for "EFI"...This might sound silly but did you unplug the battery terminal for a while to reset the ECU..They are sensitive to voltage changes...It will be something simples....
Thanks Mark, I think I've pretty much checked or swapped most things. The "cough" appeared after Millbrook where the Wedge was driven with some enthusiasm. It was a very hot day. It misfired every few miles all the way home. When I had a good look at it that's when I noticed the distributor cap doing its "hokey cokey" so I assumed it was the dissy, so a new one was purchased and apart from a timing issue the problem disappeared for about 3 weeks. It then returned. Since then I tried two new coils, two new ignition amps, fitted new HT leads, had a new wiring loom (coil to distributor) made up, as it was very brittle with high resistance, new correct and functioning CTS, new thermo time switch, both alarm and immobiliser checked and temporarily disconnected. The misfire does not appear until the engine is hot and it appears to affect the full ignition system - it is not an individual cylinder. I've inspected both the rotor arm and dissy cap and both look perfect.
I'm away on business for a couple of days but on the drive over to Bedfordshire I'm picking up a spare AFM and ECU so I will fit them Thursday night. The only other thing I can think of is as you point out the distributor pick up, rather than the ignition amp.
I know how Smash must have felt after 18 months chasing the fault on the 390SE! The fault certainly feels electrical.
If the ECU and AFM swap doesn't improve things then I might borrow a dissy to try that also. If that doesn't work then hopefully the 390SE will be up and running and I'll park the 350i in the garage, give it a good kicking and it can stay there until I drum up some enthusiasm to investigate further.
Mmmm...Im just wondering...If you changed the pick up then you would of had to of used the new type ignition amp...The two pin type are unobtainable now...I know of two that have failed possibly due to being in the heat whereas they are intended to be remotely fitted away from heat, Perhaps the material they are made from is poo....
Ideally a test to the amp should confirm if its that..Not sure what they kick out when cranking?..Maybe a cold and hot test...Also i found this on a RV8 forum...
"As the injectors are driven from the ignition pulse, a misfire by the ignition amplifier will instantly drop out the injectors as well. I would suggest first checking the security of the distributor pickup wires as they move with vacuum advance. Also the air gap in the pickup. Try disconnecting the vac advance for the next test drive."
Apparently removing the vac advance is just to confirm if the movement is causing the mis-fire.
Have you also checked the connectors from the amp to the bullet connector to ECU...There is one that goes to the speedo which also communicates with the ECU...Could this be linked to the voltage drop you had last year even?....
Ideally a test to the amp should confirm if its that..Not sure what they kick out when cranking?..Maybe a cold and hot test...Also i found this on a RV8 forum...
"As the injectors are driven from the ignition pulse, a misfire by the ignition amplifier will instantly drop out the injectors as well. I would suggest first checking the security of the distributor pickup wires as they move with vacuum advance. Also the air gap in the pickup. Try disconnecting the vac advance for the next test drive."
Apparently removing the vac advance is just to confirm if the movement is causing the mis-fire.
Have you also checked the connectors from the amp to the bullet connector to ECU...There is one that goes to the speedo which also communicates with the ECU...Could this be linked to the voltage drop you had last year even?....
Hi Keith,
did you install a Power Spark dizzy ? I bought one some time ago and the car didn't run like it should. I replaced it with the original dizzy and everything is fine.
I had a very interesting discussion with some dutch wedge friends on the german wedge meeting. They told me to set the ignition timing to 28° before TDC at 3000 rev and it works great. Fuel pressure set to 39-40 psi.
Good luck, I hope you'll find the fault soon.
Cheers
Bernd
did you install a Power Spark dizzy ? I bought one some time ago and the car didn't run like it should. I replaced it with the original dizzy and everything is fine.
I had a very interesting discussion with some dutch wedge friends on the german wedge meeting. They told me to set the ignition timing to 28° before TDC at 3000 rev and it works great. Fuel pressure set to 39-40 psi.
Good luck, I hope you'll find the fault soon.
Cheers
Bernd
mrzigazaga said:
If you changed the pick up then you would of had to of used the new type ignition amp...The two pin type are unobtainable now.
Mark, new PowerSpark dissy did come with the newer "3 pin" ignition amp and conversion lead. 2 pin original amps are now available via a dozen sellers on ebay. I've bought a brand new 2 pin unit and also tried that on the dissy and the "cough" is exactly the same so I'm sure it's not that.I am suspicious of the actual dissy pick up. It's AFM and ECU swap first then if that fails I will source an alternative dissy to rule that out. If the problem still persists then I'm getting a little stumped?
Hi Keith...Sorry if you have said it before but i can't see it...(Forget temperature for a minute)..Does it happen at a particular rev range and does it rev passed it or is it like a wall?...How many times would it happen while driving...How long does it happen for..Is it just a blip for a second or two?...Has it ever cut out completely after this?...Does it happen on a bumpy road, Will it do it if you rev it while its stationary?...Is there any voltage drop on the instruments when it happens?.
Thing is with these mis-fires is pinpointing exactly what it does and when..I have had three totally different related mis-fires that were all quite similar...
1. HT lead breaking down.
2. Twisted CTS wires...This was temperature related.
3. Fuel pump dying....This happened over a two week period!.
I know its been said a thousand times but have you checked that all the connectors are on securely...Especially the ECU plug...Checked all the earths, Including the bunch down near the N/S suspension turret.
Once a month i wipe out the dizzy cap and check the rotor arm and clean the AFM, ECU, Thermotime and CTS plug connectors..(Male & Female)....I don't touch the injector ones as they are too brittle and i fear breaking one.
Its a long systematic process but each time you change something or clean something you need to drive it to see if its cured it, Otherwise it will disappear and no-one will ever know what it was...Which doesn't help anyone in the future with the same issue...Try to keep ya chin up mate as i know what a headunfunken it is...We will find it and you will be once again grinning like a cheshire cat....Ziga
Edited as i found this:
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Could it be the same issue?....
Thing is with these mis-fires is pinpointing exactly what it does and when..I have had three totally different related mis-fires that were all quite similar...
1. HT lead breaking down.
2. Twisted CTS wires...This was temperature related.
3. Fuel pump dying....This happened over a two week period!.
I know its been said a thousand times but have you checked that all the connectors are on securely...Especially the ECU plug...Checked all the earths, Including the bunch down near the N/S suspension turret.
Once a month i wipe out the dizzy cap and check the rotor arm and clean the AFM, ECU, Thermotime and CTS plug connectors..(Male & Female)....I don't touch the injector ones as they are too brittle and i fear breaking one.
Its a long systematic process but each time you change something or clean something you need to drive it to see if its cured it, Otherwise it will disappear and no-one will ever know what it was...Which doesn't help anyone in the future with the same issue...Try to keep ya chin up mate as i know what a headunfunken it is...We will find it and you will be once again grinning like a cheshire cat....Ziga
Edited as i found this:
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Could it be the same issue?....
Edited by mrzigazaga on Tuesday 22 September 10:03
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