High RPM/load miss

[Spetz]

Hi everyone,

I have a track car that used a 6A12 MIVEC Mitsubishi engine.

It has a coil on plug wasted spark ignition system.

At the racetrack it sometimes misses for a few seconds at high rpm (~7,000rpm) and loses power.

It appears to be heat related (happens when it's hot).

Is that indicative of a coil plug issue?
The spark plugs are copper. They have had about 6 track days on them.

 

[MichiganMadMan]

A couple of things that cross my mind:

A miss at rated can cause hot metal and fluids to be shot out of the engine everywhere. I'd avoid running it hard at a track event until I got this issue sorted out.

Can you tease any predictability or trends out from when it's acting up? As an example, does it only happen after hard braking or turning one direction or another? When your fuel level is low, say 1/4 tank or less?
Do you have access to a scan tool? It might have stored codes that could be a lot of help in tracking down the root cause.
Are you running gasoline or E-85? From a quality source?
Can you recall when this started happening, maybe since your most recent installation of spark plugs?

When you say "it sometimes misses for a few seconds", does it come back if you upshift to the next gear or will it continue to act up?

From the info supplied, I can't determine if it's spark or fuel delivery related as both systems are impacted by temperature. Losing ignition at high RPM is annoying, but having fuel go lean can be catastrophic (ask me how I know).

 

[JLTD]

Fuel delivery is my guess. I'd check for spots/contact on the fuel line caused by being close to hot items.

 

[Spetz]

Hi guys,

It has only happened for the first time during the last track event I went to.

It'll miss a bit (slight loss of power but I can feel/hear the miss) but it only does so for a split second and then just continues fine (still at WOT in the same gear, same rpm).

It might be fuel related. It only happened a few times and power was not severely impacted which made me think only 1 cylinder is likely missing. If it were fuel related wouldn't the whole car cut out?

At some stage I was getting fuel cut out when it was low but that was much more abrupt.


Answers to above questions:
Can you tease any predictability or trends out from when it's acting up? As an example, does it only happen after hard braking or turning one direction or another? When your fuel level is low, say 1/4 tank or less?
- It happens after corners, but that is likely due to the fact that that is when I am at WOT at high rpm

Do you have access to a scan tool? It might have stored codes that could be a lot of help in tracking down the root cause.
- I do not, it is an old ECU and may not store these things in detail. I can do a fault check on it though

Are you running gasoline or E-85? From a quality source?
- Normal pump fuel (98 RON) from Shell

Can you recall when this started happening, maybe since your most recent installation of spark plugs?
- First time was the last track day. No preceding mechanical work had taken place

 

[MichiganMadMan]

Hmmm. Sounds like it's going to be a challenge.

Since it seems to not be a total power cut, it could still be a number of things. Running lean can have the same effect as losing one cylinder. There is variation in injectors and cylinders as well as combustion events from cycle to cycle, so it can seem like it's "losing one cylinder" but not always be the same one every time it cuts out.

If you can monitor any data, I'd watch for the oxygen sensor voltage (assuming it has one) to flicker, this will tell you that the problem is with fuel or spark as opposed to a mechanical issue such as a cam actuator deciding it doesn't want to play nice any more.

I'd love to know fuel pressure during this event. Peak power is also peak fuel flow demand, so you could have good fuel pressure most of the way up and then it's dropping off as you get near rated. I like to see rock-solid fuel pressure all the way up, so if it's flickering or wandering, it's time to dig into the fuel system. If you had another set of coils around or know someone who'd loan you some, I'd try that but I tend to hunt around and be as sure as I can what is causing the problem before I load up the parts cannon and fire it at the car.

 

[MichiganMadMan]

@ Spetz, any updates? Hoping it was something you could track down easily.

 

[Spetz]

No updates as of yet.
The car is only used on the track so I won't be testing for a while yet.

I am however thinking about getting the A/F looked at prior to the next track day.
There was a bit of popping from the exhaust which I know lean mixture can cause so better safe than sorry

 

[CrAlt]

I would install a widebade A/F gauge.Independent of the built in O2 and ECU.
I have one from AEM and it has removed a lot of guesswork in troubleshooting and tuning.

https://www.aemelectronics.com/prod...trollers/digital-wideband-uego-afr-gauge

 

[PandaBear]

Can you narrow down to which cylinder? If so you can swap plugs, coils, injectors, etc until you find it.