Yet another rv8 rich idle headache..
Discussion
That is typical of what all 8 plugs currently look like. I appreciate that with more than normal idling being done during driveway diagnosis that they will carbon up more than usual but after only 20 miles or so driving they start getting black on one side then end up with the entire white insulator being covered in thick black carbon with only the electrode tips remaining clean.
I know rv8s tend to dirty their plugs, not helped by being an auto which mostly mopes about at not much more than 2.5k rpm, the old engine always looked too rich even when it was spot on but I’ve definitely got a rich/carbon issue as everything is coated in black. If I hold a white tissue near the tailpipe I can see it collecting soot within 10 secs or so.
I think I posted a pic some time ago of what the piston crowns looked like after 500 miles and I was was really upset at what the inside of my lovely new engine looked like. All 8 exhaust ports were very heavily coated.
Weirdly when rebuild 1 went in it did seem to be running lean as the plugs had typical idling carbon buildup on the outer but the insulators were whiter than white except for cyl 7 which had a red tinge to it. That all soon changed after 500 miles when it went to 7 rich looking plugs and one steam cleaned from the cracked block.
I know rv8s tend to dirty their plugs, not helped by being an auto which mostly mopes about at not much more than 2.5k rpm, the old engine always looked too rich even when it was spot on but I’ve definitely got a rich/carbon issue as everything is coated in black. If I hold a white tissue near the tailpipe I can see it collecting soot within 10 secs or so.
I think I posted a pic some time ago of what the piston crowns looked like after 500 miles and I was was really upset at what the inside of my lovely new engine looked like. All 8 exhaust ports were very heavily coated.
Weirdly when rebuild 1 went in it did seem to be running lean as the plugs had typical idling carbon buildup on the outer but the insulators were whiter than white except for cyl 7 which had a red tinge to it. That all soon changed after 500 miles when it went to 7 rich looking plugs and one steam cleaned from the cracked block.
Revs sitting high at idle sounds like stepper motor/ air leak.
I’m not sure a smoke tester can replicate the suction an engine can muster so I’d still keep an open mind on it.
In the case of a friends Tvr car, juggling the inlet manifold into place must have just caught the corner of one of the lugs on the gasket bending it over. Impossible to see until manifold got removed again.
The point being it caused poor combustion on 3 and 5 through that air leak which revealed itself with a header heat test, both being colder than the rest.
Leans out fuel mix, blows out the spark and causes mis firing I assume.
As soon as the air leak was fixed the car ran well.
Has your plenum and base been sealed down with a smear of sealant. I’m sure it has.
I’m not sure a smoke tester can replicate the suction an engine can muster so I’d still keep an open mind on it.
In the case of a friends Tvr car, juggling the inlet manifold into place must have just caught the corner of one of the lugs on the gasket bending it over. Impossible to see until manifold got removed again.
The point being it caused poor combustion on 3 and 5 through that air leak which revealed itself with a header heat test, both being colder than the rest.
Leans out fuel mix, blows out the spark and causes mis firing I assume.
As soon as the air leak was fixed the car ran well.
Has your plenum and base been sealed down with a smear of sealant. I’m sure it has.
Classic Chim said:
Revs sitting high at idle sounds like stepper motor/ air leak.
Here is a story that backs this statement............Last time I cleaned the stepper I replaced the PTFE tape with a proper gasket, all good. The begining of April I took it for an MOT everything normal until I started it to take it home. The revs were higher than they should of been. Turn off engine and try again, lower revs quickly settle down to 900 RPM. At home when checking, the stepper had come loose in the housing so I put some gasket sealant on both sides of the gasket and tightened it up again.
Probably been mentioned before but over tightning the stepper can crack the housing and a bad joint where the housing is attached to the plenum plus the small flexible pipe to the fuel pressure regulator from the housing being cracked or missing can cause air leaks..
Thanks guys!
In days of old I used to seal the plenum/ trumpet base with some suitable rtv but as it’s such a cow to get it back off once it’s set I used hylomar blue this time, seems to be what most people use?
Does anyone know if the idle valve gaskets are available? There isn’t a part number for it in my parts book.
I had to spend all day in the garden today digging out conifers for a new fence so the car didn’t get looked at sadly.
I’m not holding out too much hope of the smoke machine revealing a leak I’ve missed but this misfire causing fault has to reveal itself sometime and i’m just trying to ensure I am 110% sure all external systems are fine before I take the spanners to the inner workings yet again.
It’s hard to imagine that it can be a valve/ cam issue as it has plenty enough compression and drives without major issues but the fact that the misfire has been present right through two engine builds and countless testing/ unplugging and replacing of virtually all fuel/ ignition components and inlet manifold off four times just leads me to think there’s something I’ve missed on the motor itself.
I’ll run suggested tests and check everything again as soon a poss.
In days of old I used to seal the plenum/ trumpet base with some suitable rtv but as it’s such a cow to get it back off once it’s set I used hylomar blue this time, seems to be what most people use?
Does anyone know if the idle valve gaskets are available? There isn’t a part number for it in my parts book.
I had to spend all day in the garden today digging out conifers for a new fence so the car didn’t get looked at sadly.
I’m not holding out too much hope of the smoke machine revealing a leak I’ve missed but this misfire causing fault has to reveal itself sometime and i’m just trying to ensure I am 110% sure all external systems are fine before I take the spanners to the inner workings yet again.
It’s hard to imagine that it can be a valve/ cam issue as it has plenty enough compression and drives without major issues but the fact that the misfire has been present right through two engine builds and countless testing/ unplugging and replacing of virtually all fuel/ ignition components and inlet manifold off four times just leads me to think there’s something I’ve missed on the motor itself.
I’ll run suggested tests and check everything again as soon a poss.
Any fibre washer should do or PTFE tape. There is enough travel in the stepper motor to allow for a couple of mm either way in the stepper motor position on the thread, it just needs to be air tight.
BTW, probably mentioned it already, but you can use easy start to detect leaks, if you spray around the joints and the idle changes you have found your leak. I would not use lots of it on a hot engine or if there are any sparks about however unless you want a Ken Dodd hairstyle.
BTW, probably mentioned it already, but you can use easy start to detect leaks, if you spray around the joints and the idle changes you have found your leak. I would not use lots of it on a hot engine or if there are any sparks about however unless you want a Ken Dodd hairstyle.
Edited by blitzracing on Monday 26th April 10:26
Ha!
After a year without seeing the barber I’d be in for one hell of a hair fire!
I did try using brake cleaner around the inlet manifold some time ago and couldn’t notice anything. Just for reference I sprayed just a little in front of the afm at idle and it instantly altered rpm. Will add it to the last ditch to do list along with a fire proof hair net!
I’m drowning in work this week so it may take a while before I can find more diagnosis time, will let you all know the outcome as soon as poss.
After a year without seeing the barber I’d be in for one hell of a hair fire!
I did try using brake cleaner around the inlet manifold some time ago and couldn’t notice anything. Just for reference I sprayed just a little in front of the afm at idle and it instantly altered rpm. Will add it to the last ditch to do list along with a fire proof hair net!
I’m drowning in work this week so it may take a while before I can find more diagnosis time, will let you all know the outcome as soon as poss.
Hi guys,
I managed a little time on the car tonight so i’ll begin with a review of the cheap Chinese smoke machine.
Opening the box with the usual mix of excitement and trepidation that comes from such purchases the machine seems ok and has loads of rubber bungs and attachments.
Set up above the engine, ‘on’ switch set to off, attach croc clips to battery and the machine starts right up..
Seems the wiring could be better as it’s on regardless of where the ‘on’ switch is set. Still, it producing a pretty good head of stinky burning baby oil smoke.
Final result- it produces plenty of easily visible smoke and found me two small vacuum leaks so I’ll forgive it it’s foibles!
The first leak is a teeny tiny one from the tps but not the gasket, from the actual sensor itself.. a whiff of smoke eminatinb from between the lucas stamped cap and the sensor body. I don’t want to risk breaking it so I may just carefully run some superglue around the joint.
Second leak is again not ever so big, its coming from around the back of the plenum. I can’t see where from but either the plenum/ trumpet base joint or from the idle valve housing somewhere. The housing already has a new gasket so i’ll investigate when I have time to pull the plenum off.
I managed a little time on the car tonight so i’ll begin with a review of the cheap Chinese smoke machine.
Opening the box with the usual mix of excitement and trepidation that comes from such purchases the machine seems ok and has loads of rubber bungs and attachments.
Set up above the engine, ‘on’ switch set to off, attach croc clips to battery and the machine starts right up..
Seems the wiring could be better as it’s on regardless of where the ‘on’ switch is set. Still, it producing a pretty good head of stinky burning baby oil smoke.
Final result- it produces plenty of easily visible smoke and found me two small vacuum leaks so I’ll forgive it it’s foibles!
The first leak is a teeny tiny one from the tps but not the gasket, from the actual sensor itself.. a whiff of smoke eminatinb from between the lucas stamped cap and the sensor body. I don’t want to risk breaking it so I may just carefully run some superglue around the joint.
Second leak is again not ever so big, its coming from around the back of the plenum. I can’t see where from but either the plenum/ trumpet base joint or from the idle valve housing somewhere. The housing already has a new gasket so i’ll investigate when I have time to pull the plenum off.
Had a little go again tonight. I didn’t have much time so I thought to expedite injector wiring worries for now I swapped the injector connectors to cylinders 4 & 6 over to see if it made any difference to cyl 4 running colder. Symptoms remain exactly the same. The engine is also cranking for too long before it fires. It always used to fire within a couple of revolutions but it’s taking more like ten revs before it fires now.
I then tried the colour tune plugs again in the same cylinders as it was dusk and I hoped I’d be able to see them easier. That worked to a degree as I could see the combustion colours better but I couldn’t see any discernible difference between the two cylinders. Both seemed to flash mostly blue with an occasional bright orange. I took a short video of it with my phone. The sparks seemed to be regular.
I wasnt able to run the car to fully warm as it seems I have a new emissions tester- my next door neighbour complaining of my fumes entering their house..
Cyl 4 spark plug smelt of fuel more than cyl 6 and maybe a red herring but was partially wet, seemed more like thin clean oil than fuel but it could just possibly be a smidge of baby oil remains from the smoke tester as it seemed to spit some out into the induction pipe yesterday. Cyl 6 spark plug just smelt like an old engine.
Shining a bright torch down the plug holes reveals a lot of black crap on the piston crowns and cyl 4 piston crown looked wet.
I’m starting to think I either need to find somewhere to park the car up for a while and take a break from it or tear the engine down yet again as I’m not sure the engine will recover from the amount of crud In the combustion chambers after so few miles but I’d rather know what needs fixing before I start any major dismantling.
I then tried the colour tune plugs again in the same cylinders as it was dusk and I hoped I’d be able to see them easier. That worked to a degree as I could see the combustion colours better but I couldn’t see any discernible difference between the two cylinders. Both seemed to flash mostly blue with an occasional bright orange. I took a short video of it with my phone. The sparks seemed to be regular.
I wasnt able to run the car to fully warm as it seems I have a new emissions tester- my next door neighbour complaining of my fumes entering their house..
Cyl 4 spark plug smelt of fuel more than cyl 6 and maybe a red herring but was partially wet, seemed more like thin clean oil than fuel but it could just possibly be a smidge of baby oil remains from the smoke tester as it seemed to spit some out into the induction pipe yesterday. Cyl 6 spark plug just smelt like an old engine.
Shining a bright torch down the plug holes reveals a lot of black crap on the piston crowns and cyl 4 piston crown looked wet.
I’m starting to think I either need to find somewhere to park the car up for a while and take a break from it or tear the engine down yet again as I’m not sure the engine will recover from the amount of crud In the combustion chambers after so few miles but I’d rather know what needs fixing before I start any major dismantling.
Topic's big now and things are easily misread or missed
Have you proved that all the injectors are ok?
Mmmm thinking back, it could be this topic that included the spray pattern test and compression test
Have witnessed engines passing a compression test yet when head/heads have been removed valves have proven to be at fault, not sure about V8 though, more straight 6 and V12
As you know, a wet plug does point to a problem on its cylinder if the HT voltage is good
Sorry that I can't help
Someone here knows though
Have you proved that all the injectors are ok?
Mmmm thinking back, it could be this topic that included the spray pattern test and compression test
Have witnessed engines passing a compression test yet when head/heads have been removed valves have proven to be at fault, not sure about V8 though, more straight 6 and V12
As you know, a wet plug does point to a problem on its cylinder if the HT voltage is good
Sorry that I can't help
Someone here knows though
Unlucky48 said:
Had a little go again tonight. I didn’t have much time so I thought to expedite injector wiring worries for now I swapped the injector connectors to cylinders 4 & 6 over to see if it made any difference to cyl 4 running colder. Symptoms remain exactly the same. The engine is also cranking for too long before it fires. It always used to fire within a couple of revolutions but it’s taking more like ten revs before it fires now.
I then tried the colour tune plugs again in the same cylinders as it was dusk and I hoped I’d be able to see them easier. That worked to a degree as I could see the combustion colours better but I couldn’t see any discernible difference between the two cylinders. Both seemed to flash mostly blue with an occasional bright orange. I took a short video of it with my phone. The sparks seemed to be regular.
I wasnt able to run the car to fully warm as it seems I have a new emissions tester- my next door neighbour complaining of my fumes entering their house..
Cyl 4 spark plug smelt of fuel more than cyl 6 and maybe a red herring but was partially wet, seemed more like thin clean oil than fuel but it could just possibly be a smidge of baby oil remains from the smoke tester as it seemed to spit some out into the induction pipe yesterday. Cyl 6 spark plug just smelt like an old engine.
Shining a bright torch down the plug holes reveals a lot of black crap on the piston crowns and cyl 4 piston crown looked wet.
I’m starting to think I either need to find somewhere to park the car up for a while and take a break from it or tear the engine down yet again as I’m not sure the engine will recover from the amount of crud In the combustion chambers after so few miles but I’d rather know what needs fixing before I start any major dismantling.
The color tune burns sound OK, its basically bunsen blue with the odd flash of yellow- if you want to see the colour shift and the effect, run it on the green map and tweak the CO trim screw on the AFM- it should go from very pale blue when too lean, to luminous orange burn when too rich. In terms of mechanical issues you have basically only two ways for oil to get in, past the oil ring or down a valve guide. Id be pretty sure if there was a piston / oil ring problem the compression would be down on that pot, like wise with a leaky head gasket, and I cant see how valve guides could ever be that bad to cause a misfire.I then tried the colour tune plugs again in the same cylinders as it was dusk and I hoped I’d be able to see them easier. That worked to a degree as I could see the combustion colours better but I couldn’t see any discernible difference between the two cylinders. Both seemed to flash mostly blue with an occasional bright orange. I took a short video of it with my phone. The sparks seemed to be regular.
I wasnt able to run the car to fully warm as it seems I have a new emissions tester- my next door neighbour complaining of my fumes entering their house..
Cyl 4 spark plug smelt of fuel more than cyl 6 and maybe a red herring but was partially wet, seemed more like thin clean oil than fuel but it could just possibly be a smidge of baby oil remains from the smoke tester as it seemed to spit some out into the induction pipe yesterday. Cyl 6 spark plug just smelt like an old engine.
Shining a bright torch down the plug holes reveals a lot of black crap on the piston crowns and cyl 4 piston crown looked wet.
I’m starting to think I either need to find somewhere to park the car up for a while and take a break from it or tear the engine down yet again as I’m not sure the engine will recover from the amount of crud In the combustion chambers after so few miles but I’d rather know what needs fixing before I start any major dismantling.
Thanks guys.
I’m very much in agreement with you both.
I haven’t seen any definate oil problems til now. Plugs have only looked heavy carbon black and no blue smoke. I think that oil may have been just the smoke machine oil.
I did do an injector flow test previously but have since put brand new Bosch ones in and haven’t re-run the tests since.
Compression is not truly awful in any one cylinder. It does vary and is down on where I’d like it to be but I’m assuming that’s because of all the idling the engine is doing while I test things that’s slowly buggering the new rings.
There is definitely some ring blow by going on as indicated by my cheap leakdown tester (which I don’t really trust) and when I changed the oil the other week while it was fairly clean in colour it stank of combustion and not like a new engines oil should. I’ve built plenty of new smaller capacity engines, mostly multi cylinder bikes and the oil always comes out virtually like new after a few 100 miles. This oil smelt more like it had done a good few 1000 miles in an old carb’d engine.
I was surprised that the colourtune looked reasonably ok, I was expecting it to look very rich or see some obvious misfiring. I did do the test on a non cat map but I didn’t have time to adjust the afm trim as I’d already been moaned at about the fumes by then so I stopped for the evening.
The two colder cylinders and what seems to me an overall rich at idle problem are kind of at odds with each other as far as diagnosis goes. A good gas analysis might help I guess if what’s coming out the tailpipe could be measured more accurately than by nose and basic co tester.
I have a feeling I’m going to have to pull the engine apart again, hone/re-ring it, double check all cam lobes for lifts/ timing (or fit another cam) and have a specialist double check the heads/ valves or just clean up and fit a pair of standard unmolested heads and hope.
I’m very much in agreement with you both.
I haven’t seen any definate oil problems til now. Plugs have only looked heavy carbon black and no blue smoke. I think that oil may have been just the smoke machine oil.
I did do an injector flow test previously but have since put brand new Bosch ones in and haven’t re-run the tests since.
Compression is not truly awful in any one cylinder. It does vary and is down on where I’d like it to be but I’m assuming that’s because of all the idling the engine is doing while I test things that’s slowly buggering the new rings.
There is definitely some ring blow by going on as indicated by my cheap leakdown tester (which I don’t really trust) and when I changed the oil the other week while it was fairly clean in colour it stank of combustion and not like a new engines oil should. I’ve built plenty of new smaller capacity engines, mostly multi cylinder bikes and the oil always comes out virtually like new after a few 100 miles. This oil smelt more like it had done a good few 1000 miles in an old carb’d engine.
I was surprised that the colourtune looked reasonably ok, I was expecting it to look very rich or see some obvious misfiring. I did do the test on a non cat map but I didn’t have time to adjust the afm trim as I’d already been moaned at about the fumes by then so I stopped for the evening.
The two colder cylinders and what seems to me an overall rich at idle problem are kind of at odds with each other as far as diagnosis goes. A good gas analysis might help I guess if what’s coming out the tailpipe could be measured more accurately than by nose and basic co tester.
I have a feeling I’m going to have to pull the engine apart again, hone/re-ring it, double check all cam lobes for lifts/ timing (or fit another cam) and have a specialist double check the heads/ valves or just clean up and fit a pair of standard unmolested heads and hope.
Whereabouts are you in the UK?
I have a working Crypton analyser and emissions tester so may be able to help if you are near.
As Blitz has said not many Crypton analyser are now functional but having the circuit diagrams does help to sort them out. Having owned several, the early 3 Series are not too difficult to mend the later ones packed full of computer technology are a nightmare even with the circuits.
Damp is the biggest enemy especially for the EHT units that drive the CRT display.
I have a working Crypton analyser and emissions tester so may be able to help if you are near.
As Blitz has said not many Crypton analyser are now functional but having the circuit diagrams does help to sort them out. Having owned several, the early 3 Series are not too difficult to mend the later ones packed full of computer technology are a nightmare even with the circuits.
Damp is the biggest enemy especially for the EHT units that drive the CRT display.
Unlucky48 said:
Thanks guys.
The two colder cylinders and what seems to me an overall rich at idle problem are kind of at odds with each other as far as diagnosis goes. A good gas analysis might help I guess if what’s coming out the tailpipe could be measured more accurately than by nose and basic co tester.
Really difficult as the results will always be a sum total of 4 cylinders at best if the exhausts are fed down separate pipes per side. This is not common practice as it sounds weird (like the current build TVR) , and you don't benefit from basically balancing out your back pressure available between two exhaust gas routes, so there is normally a joint box or pipe between the two sides and as a result your gas results will be a confused mixture of good bad cylinders.The two colder cylinders and what seems to me an overall rich at idle problem are kind of at odds with each other as far as diagnosis goes. A good gas analysis might help I guess if what’s coming out the tailpipe could be measured more accurately than by nose and basic co tester.
That is a bit far to travel for an emissions test! Hehe!
Thanks Mark,
very true. I honestly don’t think there is any remaining fault now with the fuel/ spark side of things as I’ve been over it all countless times now.
I think I’m going to have to trust my intuition and go with start digging into the engine looking for a mechanical fault that i’ve missed. I’ll see if I can measure valve timing on each cyl then see what’s happened to the bores/ rings as they are definitely letting by more than they should be for a new engine. If it comes to it i’ll fit a pair of cleaned up standard cyl heads and hope.
Thanks Mark,
very true. I honestly don’t think there is any remaining fault now with the fuel/ spark side of things as I’ve been over it all countless times now.
I think I’m going to have to trust my intuition and go with start digging into the engine looking for a mechanical fault that i’ve missed. I’ll see if I can measure valve timing on each cyl then see what’s happened to the bores/ rings as they are definitely letting by more than they should be for a new engine. If it comes to it i’ll fit a pair of cleaned up standard cyl heads and hope.
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