strx7

I have always believed cracking plates was the result of pre-ignition, its not just detonation, but the engine trying to run backwards for a spluit second hence the loud noise/violent result

Judge Ito

check your trigger wire being used for the haltech, make sure the haltech is not bouncing/reading different maps across the board.



also Brian rotaries do not like to be to lean.. keep them happy with fuel, and away from detonation. I have broken a few plates with an un-expected lean mixture when boost spiked high

PDF

I had a stock s4 come in recently that had had a brand new engine 3000km earlier. It had blown the seals in the rear rotor for no apparent reason so I rebuilt it and while running it in the rear plate cracked as in the pics above. This is a stock engine, stock turbo with an external gate running 10psi and a Microtech. So I replaced the rear plate and worked through everything to figure out what caused the engine to fail. I replaced eveything to do fuel & ignition atleast once and re-routed the crank angle sensor wiring to no avail. 3 carefull dyno pulls later and an apex seal cracked. No warning at all. What I did notice was a miss fire every now and again which was showing up as RPM and HOME errors on the ecu. This could only be caused by RFI on the input side of the ecu.



After stripping the engine again I had another go at tuning and the missing cleared up a lot when I changed from resistor spark plugs to non-resistor. That confirmed my suspicion about the RFI. Changing leads, coils etc made no difference but the plugs did. So I went back to the resistor plugs because they werent the root of the problem, just a band aid.



After more carefull tuning it was running ok but under load it would randomly fire at the wrong time, not very often and for no reason. No matter what I did to the fuel or ignition maps its still did it. The engine would give one big bang and I could hear combustion coming back through the inlet. By this time I was at my wits end so I changed the only thing left in the car, the ecu. And what do you know it ran perfectly. I could then lean it out and advance the timing without fear of destroying the engine again.



I had earlier sent the ecu back to factory for testing and they said it was fine. It obviously was not. Although in saying that it may well work fine in another car. For some reason that particular ecu was picking up RFI from that particular car, and what an expensive way to learn. I also tried mounting the original ecu in different positions which helped some but still didn't eliminate the problem.



So my guess is you have an RFI problem. Are the plug leads suppressed? Have you tried a different ecu/spark plugs/ leads etc? Not just new parts but a different type? Also, if you are still using the factory s4/5 ignitors they may be struggling to make the numbers you are.

PDF

As Lynn said earlier if the spark cannot fire properly it has to go somewhere and this makes RFI worse. Its a chicken and egg situation, if the ignition system isn't up to scratch (e.g poor ignitiors) the spark can break down under load e.g high boost, large plug gap etc. BUT the increased resistance also increases RFI which may not be enough to make the ignition itself missfire but it may be enough to give the ecu an incorrect crank input reading causing the computer to FIRE AT THE WRONG TIME.



Its basically a process of elimination, assuming the tune is on the safe side. Good luck.

Sorry about the long story above!

Lynn E. Hanover

I note with great sadness that the plug wires are actually touching, or if not, are dressed way too close together.



Run them well away from each other. Same for the primary wires to the coils. Those wires are anttena

leading back to the brain box. Bad mojo. Triggering wires go into an aluminum tube that is grounded to the engine/chassis. Grounded shielding for the primary wires also.



Plug gaps down to .010" max.



Detonation would probably not expose the dowel to much pressure as it is after the ignition event.



More likely preignition or a cross fire.



I would only use inductive wires on MSD powered coils.



Good ground to the brain box that is also the same to the engine and chassis.



Lynn E. Hanover

Lynn E. Hanover

On further review, I note that intake air for the turbo is from inside the engine compartment where 200 degrees is not uncommon. I think I would get that air filter in the center of the grill opening at the top of the hole. The magnehilic gage says that is where the highest air pressure is located.



Lynn E. Hanover

Comitatus

http://store.summitracing.com/partdetail.a...mp;autoview=sku



These are the wires that I am using. I think I will be replacing these with a set of NGK's. Should I still stick with BUR9EQ's all around or should I step up to 10.5's?

BDC

I say stick with BUR9EQ's on street stuff then switch to 10.5's when you pump race fuel in the tank.



Something I wanted to mention that I've run into recently re: the spark plug wires. As some of you know, I've been doing alot of alcohol injection stuff on my car and have begun to wrap the RPM's out and put the motor under load of load. A couple of weeks ago (maybe three now), I noticed that I had an odd, intermittent misfire that happened under load a couple of times. It discouraged me from running the car hard anymore 'til I'd found the source. Long story short, I took the old Jacobs Race Wires I had off and stuck on a set of stock NGK plug wires. The change of wires back to the stock set cured the misfire.



I can't help but think that this is a valid point to look at. I've seen it two other times since, coincidentally enough.



Luke, on your setup, the way to troubleshoot this once you change the plug wires is to drive it around normally and turn some high RPM (not under load; perhaps in neutral in the garage) and see if there's any weird "misses". It might be difficult to notice w/ the engine being a BP, but even still it'll be evident.



B

j9fd3s

yep, ive had similar experiences with plug wires.



first time in 95, i had a gsl-se that lacked top end, i tested everything and it all checked out, but it wasnt until i replaced the racing beat wires with some $12 kragen ones, that i fixed it



ive since run into that a few times too.

BDC

I've seen this same intermittent misfire not only on these Jacobs 8.5mm race wires (that could be understandable though given what these wires are made for ) but also on the RE Amemiya wires and Magnecors, I think. It's compelling me to re-think the entire thing about aftermarket plug wires. I've already ditched the notion that you "get horsepower" by putting on these super ninja gee-whiz wires; that's a line of crap. Perhaps the OEM stuff is the best to use.



B