Misfire problems
Discussion
rev-erend said:
Dave
Nice to see you on here.
Those sound like excellent suggestions.
Also - got to say your website is one of those that I have really loved reading - I've learnt a lot from it :
http://www.pumaracing.co.uk/
Well said! Nice to see you on here.
Those sound like excellent suggestions.
Also - got to say your website is one of those that I have really loved reading - I've learnt a lot from it :
http://www.pumaracing.co.uk/
BTW, just a final thought on fuel mixtures. The exhaust system can have a big impact on the pulse tuning of the inlet tract. It tends to affect carbs more than FI but if you have a crack, leak or other problem on one side of the exhaust it might help explain why one bank of the engine has darker plugs than the other.
Cracks in the manifold often manifest as a crackle on the overrun. Leaks can be found more easily with a friend holding a rag or tennis ball over the end of the tailpipe while the engine idles. If you have separate tailpipes for each bank you might find a difference in how blocking them affects the idle or stalls the engine. If there's less effect on the engine on one side when doing that it's a sure sign the gases are finding their way out somewhere else.
Dave
Cracks in the manifold often manifest as a crackle on the overrun. Leaks can be found more easily with a friend holding a rag or tennis ball over the end of the tailpipe while the engine idles. If you have separate tailpipes for each bank you might find a difference in how blocking them affects the idle or stalls the engine. If there's less effect on the engine on one side when doing that it's a sure sign the gases are finding their way out somewhere else.
Dave
Rechecked the compressions this afternoon. They ranged from 220 to 250 psi, with the highest being on number 6 cylinder.
Tried dropping the plug gap to 0.6 mm with no discernable difference.
Even removed the plugs that were recommended for wasted spark on the RV8 (NGK BR7ES) and refitted the original plugs for the car (NGK B7ECS). No difference again and when I came back from a short thrash plug 6 was black again. Will have to check the injectors somehow.
Wish I'd bought an Emerald system now as I'd be able to drive down to them and get them to sort it out.
Bit frustrating really.
Tried dropping the plug gap to 0.6 mm with no discernable difference.
Even removed the plugs that were recommended for wasted spark on the RV8 (NGK BR7ES) and refitted the original plugs for the car (NGK B7ECS). No difference again and when I came back from a short thrash plug 6 was black again. Will have to check the injectors somehow.
Wish I'd bought an Emerald system now as I'd be able to drive down to them and get them to sort it out.
Bit frustrating really.
Starting to sound like an injector that is weeping or perhaps stuck open..
What injectors are you using ?
If it's the original Lucas jobies .. I have my old ones.. or you could just swap 2 of the existing injectors - to see if the problem moves to the new location.
What injectors are you using ?
If it's the original Lucas jobies .. I have my old ones.. or you could just swap 2 of the existing injectors - to see if the problem moves to the new location.
Edited by rev-erend on Wednesday 13th August 19:37
deetes said:
Rechecked the compressions this afternoon. They ranged from 220 to 250 psi, with the highest being on number 6 cylinder.
Maybe nothing, but perhaps a clue that you've got fluid of some sort in that cylinder. Is the engine smoking significantly when you start up from cold?Compressions are awfully high assuming the gauge is accurate. I don't know what spec or CR the engine is but you don't often see much over 200 psi even on race engines and 250 is heading for diesel engine territory. Go much higher and you won't need spark plugs anymore, it'll fire itself up. At least that will solve the misfire problem 
You could conceivably get such high readings with a very high CR plus a cam that's installed far too advanced. It wouldn't want to run at high rpm though.
On pretty much any engine although you need more CR as you run longer duration cams the two factors cancel each other out in terms of cranking psi figures. A really good road engine at about 10.0 to 10.5 CR will show 200 psi on a standard type cam and as you move up to 11:1 or 12:1 on rally and race cams the cranking figures might rise a bit but not much. The later inlet valve closing more or less exactly offsets the higher CR. In fact the cranking pressure isn't a bad way to establish if you've got the right CR for the cam duration. I usually aim for about 210 to 215 psi on a race engine. I've certainly never seen anything close to 250.
You sure your misfire isn't detonation?
Dave
You could conceivably get such high readings with a very high CR plus a cam that's installed far too advanced. It wouldn't want to run at high rpm though.
On pretty much any engine although you need more CR as you run longer duration cams the two factors cancel each other out in terms of cranking psi figures. A really good road engine at about 10.0 to 10.5 CR will show 200 psi on a standard type cam and as you move up to 11:1 or 12:1 on rally and race cams the cranking figures might rise a bit but not much. The later inlet valve closing more or less exactly offsets the higher CR. In fact the cranking pressure isn't a bad way to establish if you've got the right CR for the cam duration. I usually aim for about 210 to 215 psi on a race engine. I've certainly never seen anything close to 250.
You sure your misfire isn't detonation?
Dave
Next step must be to pull the fuel rail and move #6 injector elsewhere. Remember the fuel rail is usually pressurised and need to be released.
You need to be running resistor plugs (R) or the resistor caps with the angled bit (tvr)
Not sure how the brand of ECU would help, apart from Dave Walker charging you to do what you are doing yourself right now.
You need to be running resistor plugs (R) or the resistor caps with the angled bit (tvr)
Not sure how the brand of ECU would help, apart from Dave Walker charging you to do what you are doing yourself right now.
eliot said:
You need to be running resistor plugs (R) or the resistor caps with the angled bit (tvr)
That only affects interference generation, it won't affect how the engine runs. If anything running with no resistor anything will improve the firing but you'd probably need it in a lab to see the difference.No signifacant amounts of smoke on start up.
There has been a lot of problems with pinking and I retarded the whole spark map considerably, while on the dyno, to stop it.
Shielded cable from VR to ECU.
Even thought about sticking the coil and dizzy back into operation to see if the problem continues. Not sure how easy that would be, or even if it's possible with the MS configured for wasted spark.
Anyway, booked the car into a local tuner, tomorrow, to see if he can suss it out.
There has been a lot of problems with pinking and I retarded the whole spark map considerably, while on the dyno, to stop it.
Shielded cable from VR to ECU.
Even thought about sticking the coil and dizzy back into operation to see if the problem continues. Not sure how easy that would be, or even if it's possible with the MS configured for wasted spark.
Anyway, booked the car into a local tuner, tomorrow, to see if he can suss it out.
Taking it to a rolling road won't solve everything, or anything, if there are internal engine problems you need to fix first. You need to do the compression tests again with a different gauge and if they're still high check the cam timing. If that's a couple of teeth advanced you'll waste a lot of money on the rollers and have to do it all again. It might help if you say what spec the engine is so we can estimate what it ought to be showing.
Not surprising it's pinking if those cranking readings are correct. For the sake of 20 quid I advise anyone with a decent engine to get their own gauge so they can do repeatable tests whenever they need to and not be at the mercy of variations in other people's equipment.
Dave
Not surprising it's pinking if those cranking readings are correct. For the sake of 20 quid I advise anyone with a decent engine to get their own gauge so they can do repeatable tests whenever they need to and not be at the mercy of variations in other people's equipment.
Dave
Dave,
It's not going on a dyno. The guy I'm taking it to is just an old school engine tuner, he's been working on hot motors around the NE of Scotland since I first started driving. The first car I took to him was a Mk1 Escort RS1600. He's going to have a look around the engine etc and see if he can spot anything.
I'll mention some of the suggestions put forward by everyone.
Allan
It's not going on a dyno. The guy I'm taking it to is just an old school engine tuner, he's been working on hot motors around the NE of Scotland since I first started driving. The first car I took to him was a Mk1 Escort RS1600. He's going to have a look around the engine etc and see if he can spot anything.
I'll mention some of the suggestions put forward by everyone.
Allan
Daveuk9xx said:
Jim King perhaps? If so remember me to him while you're there. I gave him a hand with a crossflow with wasted spark ignition he was having some problems trying to decipher the strobe readings on last time I was up.
Dave
Nope, it was Ricky Gauld, a Hillman Imp man back in the good old days. Although I've heard of Jim.Dave
Anyway went to his garage today and spent a couple of hrs tinkering and checking. The consensus is that number 6 injector is probably leaking or dribbling, as previously mentioned by a few of the replies on this subject. So I'll have to get them out for a butchers.
The local auto eltrical mob, Taylor's, can ultrasonically clean the and pressure test the injectors, but they can't test the spray pattern. Don't know if that's a big deal or not.
On the subject of injectors, can hotwire injectors fit flapper manifolds as I believe there's a bit more scope for tuning in the future with these? I'd also be able to get rid of the resitor pack.
Edited by deetes on Friday 15th August 16:57
The hotwire setup has the injectors fitted directly into the fuel rail, flapper I believe uses as short fuel hose to connect them. In that case they're unlikely to be interchangeable unless you take the fuel rail as well. If they have scope to produce more power that would seem to imply a different (greater) flow rate which would mean adjusting the fuel map or playing some other trick to get the fuelling right.
By the way it's fairly easy to check the flow rate and pattern yourself if you have a spare pump and pressure regulator, you just need to be cautious about allowing the resulting atomised fuel/air mixture to get near any electrical equipment that could produce a spark.
By the way it's fairly easy to check the flow rate and pattern yourself if you have a spare pump and pressure regulator, you just need to be cautious about allowing the resulting atomised fuel/air mixture to get near any electrical equipment that could produce a spark.
Edited by GreenV8S on Friday 15th August 17:13
The plot thickens.
Went to start the car, yesterday, to go for a little run, lo and behold, it was extremely reluctant to start. When it eventualy did start it would momentarily cut out every now and again. While looking around for the culprit of this problem I waggled the connector for the injector resistor pack, ex flapper, and this caused a similar cut out.
What next??(see below)
Gave up on the idea of going for a run in the TVR and went in the everyday motor instead.
Today I decided to whip out the injectors. Took off the plenum and there was a small pool of oil at the back of the trumpet base. I'm assuming it's come from the breather hose attached to the RH rocker cover. I had the plenum off during the winter and didn't notice this and because of the problems it's hardly run at all. I distinctly remember removing the oil filler cap, during some of my previous investigations, to check if there was a lot of blow by and found next to none. So I'm puzzled.
Now I've got a misfiring car that doesn't want to start and is also blowing oil out of the breather.
I'm back to work next Wednesday, for two weeks, so that'll probably be that until I come back.
Went to start the car, yesterday, to go for a little run, lo and behold, it was extremely reluctant to start. When it eventualy did start it would momentarily cut out every now and again. While looking around for the culprit of this problem I waggled the connector for the injector resistor pack, ex flapper, and this caused a similar cut out.
What next??(see below)
Gave up on the idea of going for a run in the TVR and went in the everyday motor instead.
Today I decided to whip out the injectors. Took off the plenum and there was a small pool of oil at the back of the trumpet base. I'm assuming it's come from the breather hose attached to the RH rocker cover. I had the plenum off during the winter and didn't notice this and because of the problems it's hardly run at all. I distinctly remember removing the oil filler cap, during some of my previous investigations, to check if there was a lot of blow by and found next to none. So I'm puzzled.
Now I've got a misfiring car that doesn't want to start and is also blowing oil out of the breather.
I'm back to work next Wednesday, for two weeks, so that'll probably be that until I come back.
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