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Strange Misfire On Full Boost, Full Load When Hot


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#1 GreenMini17

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Posted 23 September 2016 - 01:51 PM

1293cc A+ Series Turbo. High spec engine using SCCR box, SC drops, X-Pin diff, Omega Pistons, Steve Benross big valve head. Garrett T3 turbo. Omex 200 series ECU, Evans Waterless Coolant, 74°C thermostat, etc, etc, etc. A proper engine. Not some cobbled together ebay second hand engine.

 

Water temp is constantly good, sits at 65°C at normal driving, gets to about 85°C when driven hard on a hot day. Oil pressure sits at about 70 PSi when driven hard, 30-35 PSi at idle when hot.

 

Above engine has a weird an unexplained misfire.

 

The background: 

 

Car on the dyno would produce good power and good torque (150bhp. 150 lbs/ft.)

Engine would drop to 3 cylinders on high boost and high load (13 PSI. 4th Gear)

Using the car on the road, the problem persisted. 

After doing some research, I ditched the waterless coolant I was using and went back to using normal 50/50 mix of anti-freeze and water.

 

Using the car on the road again, misfire on high boost, high load = Gone. Excellent!

 

BUT! Using the car on a race circuit after about 2-3 laps on full chat (so high load. high boost) misfire reappears.

 

Initially I thought it could be fuel starvation. So brimmed the full tank and went back out, same thing happens after about 2-3 laps. So I do not think it can be fuel starvation. When getting back in the car on the road I can drive it "hard" and the misfire does not happen.

 

When it begins the misfire, the car pops from the exhaust, I usually get a "pop" sound out of the air filter (could possibly be the dump valve) and then it just vibrates, looses power (but not total loss of power, it will still accelerate but not very quickly). It's hard to hear it every time, but I occasionally get a mechanical "ticking" noise at the same time (sounds like a tappet-type noise?). The misfire gets worse with the more laps I do.

 

If I put my foot on the clutch and let the revs drop to about 1,000 rpm (so it's off boost and no load) for about 4/5 seconds, and release the clutch, the engine runs as normal and I can continue driving, even when doing 70/80 mph.

 

My head is telling me it must be something to do with the extra heat generated when using the car at full chat for an extended period of time (i.e on the circuit). Apart from this, I have no idea what it could be?! I don't want to go changing a heap of parts/things to no avail.

 

Any advice would be greatly appreciated. Thank you.

 



#2 nicklouse

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Posted 23 September 2016 - 01:55 PM

any pictures of the cooling system?

 

how are you flowing the water around number 4 piston?



#3 GreenMini17

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Posted 23 September 2016 - 02:20 PM

any pictures of the cooling system?

 

how are you flowing the water around number 4 piston?

 

I do yes, here: https://scontent-lhr3-1.cdninstagram.com/t51.2885-15/e15/13392835_1751810201727728_1101537857_n.jpg?ig_cache_key=MTI2NjE2NzAwNzM2MjcxODAxMQ%3D%3D.2 

 

The water flows around no 4 piston as per standard. It has not been dry decked. I do not have a heater so this has been blanked off.



#4 nicklouse

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Posted 23 September 2016 - 02:28 PM

so no flow out of that end!

 

not good.

 

I would either plumb it back into the bottom hose after passing it through a small extra rad. or plumb it into the top hose so it goes through the main rad.

 

you could just run it directly to the bottom hose which has good and bad points warms engine up fast but as there is no cooling you are hoping that the water from the main rad is being cooled enough to cool that as it mixes going back into the block.

 

lets see what the others say.



#5 GreenMini17

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Posted 23 September 2016 - 02:41 PM

so no flow out of that end!

 

not good.

 

I would either plumb it back into the bottom hose after passing it through a small extra rad. or plumb it into the top hose so it goes through the main rad.

 

you could just run it directly to the bottom hose which has good and bad points warms engine up fast but as there is no cooling you are hoping that the water from the main rad is being cooled enough to cool that as it mixes going back into the block.

 

lets see what the others say.

 

This makes a lot of sense. Thank you very much for your input! I can now see how this would cause the problem. Do you think the heat generated at no 4 cylinder would be hot enough to cause a valve to "stick" in the guide thus creating no compression and it falling on to 3 cylinders?

 

Anyone else with idea's?



#6 Turbo Phil

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Posted 23 September 2016 - 04:24 PM

That's exactly what I was thinking. Possibly a valve just nipping up a little when it gets hot. I would definately use the heater take off on the end of the head, then back into the bottom hose as suggested. This should promote better flow around number 4.

Phil.

#7 nicklouse

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Posted 23 September 2016 - 04:33 PM

Another thought.

Is 50/50 the right mix? Sounds high to me.

Aldo what coolant?

Also have a look at done water wetter additive.

And yes it is known about poor flow without using that outlet. Vizard wrote about it many years ago.

As I mentioned above there are a few thoughts about how to then plumb it in.

Either way have a look at DSN Retrosport foe some nice alloy take offs and connectors.

#8 GreenMini17

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Posted 23 September 2016 - 07:20 PM

That's exactly what I was thinking. Possibly a valve just nipping up a little when it gets hot. I would definately use the heater take off on the end of the head, then back into the bottom hose as suggested. This should promote better flow around number 4.

Phil.


Thanks for your input Phil, much appreciated. Would you plumb it back into the bottom or too hose though? And via a small rad or not?

Thanks.

#9 GreenMini17

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Posted 23 September 2016 - 07:25 PM

Another thought.

Is 50/50 the right mix? Sounds high to me.

Aldo what coolant?

Also have a look at done water wetter additive.

And yes it is known about poor flow without using that outlet. Vizard wrote about it many years ago.

As I mentioned above there are a few thoughts about how to then plumb it in.

Either way have a look at DSN Retrosport foe some nice alloy take offs and connectors.

I don't know whether the 50/50 mix is correct but i've always used that theory and its never caused a problem. Im not sure what brand of anti freeze i am using but its the 10 year pink stuff.
I know of water wetter but I havent had great experiences in the past with it. Plus, the coolant temp is fine.
Indeed DSN make some lovely stuff, im sure i will be purchasing some things from them!!
Thanks again for your help.

#10 nicklouse

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Posted 23 September 2016 - 07:48 PM

Yes coolant temp can well be fine where you are reading it but incorrect mixture of anti freeze thickens the surface "strength" of the liquid and does not allow the heat to be transmitted from the metal to the water.

This is why the correct mix should be used. Incorrect mix and flow can easily lead to hot spots.

Water wetter is good at breaking the surface tension down so you get good heat transfer.

There are also issues with some anti freezes that react with some materials in the engine such as Brass. So please check it is suitable.

#11 GreenMini17

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Posted 23 September 2016 - 10:26 PM

Yes coolant temp can well be fine where you are reading it but incorrect mixture of anti freeze thickens the surface "strength" of the liquid and does not allow the heat to be transmitted from the metal to the water.

This is why the correct mix should be used. Incorrect mix and flow can easily lead to hot spots.

Water wetter is good at breaking the surface tension down so you get good heat transfer.

There are also issues with some anti freezes that react with some materials in the engine such as Brass. So please check it is suitable.

I was not aware of this so thank you for bringing it to my attention!
I may add a bottle of water wetter to the system after rearranging my plumbing just to be sure.
What ratio mix would you recommend?

#12 MIGLIACARS

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Posted 04 October 2016 - 08:02 AM

Do the plugs look the same when it has been misfiring!!!



#13 Turbo Nick

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Posted 07 October 2016 - 12:28 PM

Is there a wideband fitted? Sounds like fuelling to me personally.

 

Still on a std tank? I've had the gauze on the end of the pickup inside the tank cause me issues before and had to remove it. After a few 4th gear pulls the car would lean out and lose power as the fuel couldn't get out of the tank quick enough.



#14 MIGLIACARS

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Posted 07 October 2016 - 07:22 PM

Is there a wideband fitted? Sounds like fuelling to me personally.

 

Still on a std tank? I've had the gauze on the end of the pickup inside the tank cause me issues before and had to remove it. After a few 4th gear pulls the car would lean out and lose power as the fuel couldn't get out of the tank quick enough.

Interesting  never thought of that as ive ever really had experience on full race cars,   minis!!!! you think you know it all then something comes up and stumps you!!!






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