350i misfire - the return....

[KKson]

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!

[KKson]

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:

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!

[KKson]

TVRleigh_BBWR said:

Keith sent you a mail via PH system.

Leigh, just responded. Thanks anyway.

[KKson]

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.

[KKson]

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]

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.

[KKson]

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.

[KKson]

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?

[KKson]

Hi Mark, yes misfire from early in the year was traced to a knackered coil. Replaced that and it ran without issues until Millbrook. I followed my mate in his S2 over to the Shuttleworth collection on the Saturday for 140 miles, at pretty much full revs in every gear and it ran perfectly. It was as we left Millbrook on the Sunday that it started playing up although it did splutter a bit on the second flat out run down the 1 mile straight earlier in the day.

Misfire does not occur when the engine is cold. As the engine warms up it occasionally and randomly "coughs" for a split second. It coughs more regularly the hotter the engine gets. It feels as if all power is dying and then instantly is fine again. It is very random, not rev or load related or cornering related. I could drive for a couple of miles and nothing and then a cough, and then it could be 100 yards or 2 miles before the next time.

I've checked all electrical contacts and cleaned them with pukka electrical contact cleaner. It's had a new fuel pump and pressure does not vary when engine coughs, instruments do not appear to twitch, cough is there with old and new HT leads, with old and new ignition amp, with old and new coil, with old and new CTS, thermo time, and no difference with remade section of wiring loom.

The interesting fact is that when the new PowerSpark dissy went in, all was good for about 3 weeks and then the misfire came back. As I know it's not the ignition amp then maybe it is the dissy pick up? More head scratching needed. Cheers.

[KKson]

Hi Mark, yesterday I picked up a known good ECU from a guy with a Rover 3.5V8 EFi mounted in a Stag. He's rebuilt an original Triumph engine so is putting that back in. I got the AFM and ECU off him.

Swapped the ECU tonight and I've been for a 30 minute blast down the lanes and no difference. Random cough is still there every few miles. Tomorrow night I'll swap the AFM out of curiosity.

Would the TPS potentially cause this sort of issue? If the carbon track is worn and the actual circuit is broken as the throttle moves about would this give a signal to the ECU that could result in a soplit second shutdown of power? Just a straw to clutch at? I've got a spare over with the 390SE so I could give that a try also?

[KKson]

mrzigazaga said:

Its possible but realistically its best to test the TPS across the range of operation, Not sure of the values but someone will know them.. ...If you have a spare then give it a try...Failing that i have a good working spare you could borrow.

However looking at your post from February i would have a closer look at the dizzy as the internals are probably sourced from Korea or China and most of the original parts on ours are Lucas or Bosch genuine parts which are obviously better quality which can cause an incompatibility in some cases with new inferior parts...Lets be honest here most of the components on our cars have lasted nearly 30 years...Some of the new parts that people have fitted have lasted all but 2...Some only a week!...

Just seems strange that you had a mis-fire...Changed the distributor as it was made of jelly...Mis-fire goes...Happy days....6 months or so later back to where you were 6 or so months ago....My thought finger would be pointing in that direction......Possibly......

Mark, yes agree with you. I've got the spare TPS and AFM so it's a 10 minute swap when I get in from work tomorrow, after I've dropped off the new camshaft kit to the garage for the 390SE! I've got a couple of older dissys so will pull them apart to try and get a decent spare one and I'll give it a test powered up but not installed in-situ by spinning the end drive to check the spark. If it looks like it's behaving them I'll drop it in to see if any difference.

[KKson]

Right, a positive update:

Good AFM fitted - no change still misfiring.
Good TPS fitted - also no change.

Then spent an hour dissecting three broken dissys to make one okay one. Took the good pick up from my old one, plus a three pin amp from a second and managed to bolt them in a third dissy with good bearings but blown electronics. Swapped the almost new PowerSpark dissy out with the cobbled together unit and guess what - no bloody misfire! I've thrashed it around the lanes for 30 minutes and all is good, apart from the timing being a little out. I'll take it to the office for a good run tomorrow but it certainly feels back to normal. I may well give Simon at PowerSpark a call in the morning.........

I'm now on the hunt for a GOOD original second hand unit. Anyone got one going spare?

[KKson]

Well after last nights success all hope is lost this morning. Wedge started okay, went a mile up the road and engine started continually coughing, misfiring and ran like a bag of nails. I'm hoping that it's just the cobbled together Frankenstein of the temporary distributor. I'll get a good second hand one sorted and take it from them.

[KKson]

Spoke to PowerSpark and to be honest they couldn't have been more helpful. Full set of dissy electronics and base plate FOC posted today so I should have the package Monday. You never know - by next weekend I might have two Wedges up and running! Hope I haven't spoken too soon.........

[KKson]

Thanks Adam. I've watched the fuel regulator gauge while the car is sat there occasionally "coughing" and there's not a blip on the pressure. There is absolutely not a twitch on the instruments. I have gone through the lot.

The dissy was definitely the original cause. New dissy and misfire immediately disappears. Comes back 3 weeks later. As the dissy was new I didnt think it could be the issue so changed about everything I could until last night when I swapped the dissy out again (with slightly ropey botched one) and no misfire again.

Still I'm not quite there yet so fingers crossed! Tonight when I got home I had a good look at the temporary dissy and guess what - the rotor arm again looked as if it had overheated and distorted slightly. Spare rotor arm in and all good again. I'm suspicious that these new plastic rotor arms are too sensitive to heat under the bonnets of our Wedges and the good old "bakelite" style ones are way more robust.

[KKson]

adam quantrill said:

I bought and fitted ebay item 361184303635 a few months ago and they have performed well with no problems. I have put about 1200 miles on them so far I guess.

I agree the original Lucas ones would be best but they are probably all used up now.

Ha! Bought this exact set last night on line so good to hear it's still going strong. At the Neil Garner day today Racetech were there and they had all sorts of bits and pieces including OEM spec rotor arms. I bought one for £12 to see how it compares to the PowerSpark ones. It must weight twice as much and is a totally different material - similar to the old bakealite of years ago. When my new distributor internals arrive I'll refit with the OEM rotor arm for starters. Cheers.

[KKson]

Thought I'd update the situation re the 350i and it's mysterious misfire. Well the dissy is now working and the large hesitant misfire has gone and been replaced with a major continual misfire on every cylinder, once the engine is warm.

Just to summarise then, list of things checked or changed so far:

1. Distributor replaced
2. Ignition amps replaced (twice)
3. Coil replaced (twice)
4. Ignition loom around coil/distributor area remade
5. ECU swapped over with a known good one - no difference.
6. AFM swapped over with a known good one - no difference
7. CTS swapped with a brand new one - no difference
8. Thermotime switch swapped with known good one - no difference
9. All injectors were replaced in the summer as was the fuel pump and fuel regulator.
10. Full set of new spark plugs have been fitted which made no difference.
11. New set of good quality HT leads fitted - no difference.
12. Engine earth has been checked and is all okay.
13. Throttle pot sensor changed with a known good one - no difference.

Just to summarise the fault - car starts on the button, revs clean and is a happy thing until the engine gets totally warmed up. Engine then starts to misfire and hunt a little and then gets progressively worse to the point where it stalls.

As it starts and runs okay for at least 10 minutes without issue then I'm assuming it's not a mechanical problem such as camshaft/tappets etc. There are no nasty noises and oil pressure is also okay.

Fuel pressure is spot on and timing is correct. When the engine is misfiring and hunting the gauges are all steady and the fuel pressure is also steady.

When it's misfiring I've tried one at a time disconnecting the TPS, the thermotime switch and the cold start injectors and this makes no difference at all.

It's got to be something breaking down with heat. About the only thing I've not changed yet is the power resistor - would this give these symptoms? Anything else obvious I'm missing here?? Thanks.

Disgruntled Wedge owner.

[KKson]

adam quantrill said:

Keith, out of your list above, what have you swapped since changing the distributor to the latest one?

Also do you have any way of checking the CO/mixture when it's warm?

Hi Adam, I swapped the dissy this morning and all was well - until it warmed up. This afternoon I've tried again and swapped out coil, AFM and ECU. Plus checked timing, fuel pressure, plus tried disconnecting various items while it was running to see if any made a difference.

I could try ignition amp again but the one fitted was brand new 3 weeks ago.

I'm hoping to get my hands on the 390Se this week, fingers crossed, and in disgust I'm probably going to give the same garage the 350i to bloody sort out. They have CO/mixture equipment plus a load of diagnostics. It seems the summer has gone and apart from the BBWF and the TVR-CC 50th weekend the Wedge has been broken. I do so much like the idea of carbs......

[KKson]

adam quantrill said:

So from your list you still have to do again:

7. CTS swapped with a brand new one - no difference
2. Ignition amps replaced (twice)
3. Coil replaced (twice)
11. New set of good quality HT leads fitted - no difference.
13. Throttle pot sensor changed with a known good one - no difference.
8. Thermotime switch swapped with known good one - no difference

Do 7 first then work your way through the rest one by one. I have re-ordered them in what I think is the most to least likely.

At least now the misfire is consistent and once it's warm it should be a matter of minutes to swap stuff back over (apart from the HT leads).

Okay - job for the dark evenings this week. I've got a brand new CTS that I've just bought from Neil at ML Performance. Cheers.

[KKson]

Okay. I'd just like to say I think I've FOUND IT, FOUND IT, FOUND IT!

So changed the CTS, TPS, ignition amp and no difference. Car starts from cold great, revs clean, pulls like a train, go for a drive and then..... it starts to warm up and the mysterious misfire slowly creeps in, getting worse and worse as the engine bay temperature increases.

So, pulled up in the garage with it coughing and spluttering, opened the bonnet and turned all the lights off and guess what - it's like fing Blackpool illuminations! The brand new coil is lighting up like a thunderstorm and 4" of the (also brand new) king lead where it runs close to the offside rocker cover is pulsating like a fluorescent light strip. You can see 2" either side of where it gets close to the rocker cover physically and quite spectacularly buzzing away, in a very attractive shade of electric blue!

I'm guessing that as the temperature increases then so does the breakdown of the insulation qualities of the HT lead and coil. So yet another (third) coil to be ordered plus a new set of HT leads. The last two sets of HT leads were from PowerSpark, 8mm silicon jobbies. I think Mr Bosch is calling me. Anyone tried these new solid state coils rather than the old fashioned oil filled ones?