Built CA sudden backfire.

[Leve1One]

First of all, hello from the other side of the Atlantic Ocean and more specifically from Greece. I have been reading Nico for a long time and it is about time i contributed to the community. Unfortunately, with a problem.

I have a fully built CA18DET (i have all sorts of faith on this little engine), with specs as follows:

-Supertech forged 84.00mm pistons (.050 thou)
-ZRP Steel Connecting Rods
-Cometic MLS head gasket
-ARP bolts all aroung
-Garrett GT2860RS
-3" all the way back
-NisTune setup
-Z32 AFM
-Evo pink 560cc injectors

The car has been tuned on a dyno, worked brilliantly, pulled 338whp at 15 psi for a long time now (almost 6 months, never missed a beat). The problem is as follows: It happened all of a sudden, cold started it in the morning (previous night was ok) and it started backfiring when on high boost (more than 10 psi). AFR's look normal, only a large backfire on boost.

I have tried changing:

-Ignitor Chip
-A fresh set of coil packs
-Did a boost leak test
-Spark plugs
-Fuel pump
-Checked timing and it is as it were.

I would like your thoughts on what to look for next. Other than that, the car rides beautifully, no idle problems, no temp problems, fuel consumption is in par. If you drove it normally, you would have no idea the engine has a problem whatsoever until you went hard on it. Also, no white smokes from exhaust pipe. Only black smoke (rich) when the car misfires.

It's been almost a month i have been living with this problem and it's starting to get to me...

[r34 gtr]

Do you get any instantaneous rise or drop in AFR when it backfires?

And this problem happens every time it gets into boost?

Maybe try changing the coolant temperature sensor? They can cause funny problems when they go bad.

If the temperature has changed a lot since you tuned it, you may also try re-gapping your spark plugs to a smaller gap. You could be blowing out the spark in higher boost. Its a bit of a long shot, but it certainly won't cost you anything to try it.

[Leve1One]

I have been having some issues with the coolant sensor but not the one that controls mixture. My dash temp sensor is acting up, but it has been for a long time now. I will try swapping the one you suggested, though.

My sparks have been changed 3 times, and messed with gap a lot. Ranging from stock 1.1mm down to half 0.55mm with PFR6A's, BCPR7ES and now with the BCR8ES's...

AFR's are spot on. Outside temp also hasn't changed much, couple degrees or so. Could it be the fuel pressure regulator going/went bad?

[float_6969]

Maybe a bad ignition amplifier (igniter).

[Leve1One]

Thanks for the reply, but as you can see in the first post, it was the first thing I changed

[float_6969]

Sorry, I missed that line! It sounds like you've tried everything. This is a very rare occurrence, but you may have a bad CAS. Do you have access to a known, good CAS you could test it with?

[Leve1One]

It is indeed! I thought i should have a PhD on that engine by now but I guess it's true what they say about biting your own tongue when speaking in haste. :P As for the CAS, I sure hope i can find one. Is the CAS known to cause such an issue?

[r34 gtr]

We have seen quite a few CAS's go bad. Not the most common occurrence, but it happens more than you might think. When they go, it can cause some odd problems.

Your issue seems to be ignition-related, so lets try to cover all the bases there.

[chalander]

First, kudos for the 338 whp on 15 psi!

After looking at what you've changed out already, The CAS is the only thing I can think of that may be bad. For reference, a CAS can fail causing intermintent operations. I personally have gone through two different CASs that work but are failing.
-The first one runs fine until it gets hot, 15 mins later once operating temp is reached it would began to back fire and in the matter of 5-10 seconds it quits delivering the signal for spark thus resulting in a engine that will crank over and never start, until the CAS cools down.
-The second one which is also failing has a different symptom, it has a miss at idle and sputters under load ( as if the spark was being blown out.) however this CAS never results in killing my engine no matter how long I drive it.

So as you can see, from my personal experiences that a bad CAS may have more than one specific kind of symptom. If you can, grab a buddy's CAS and swap it out. The CAS unit, part # 2373185M10, is expensive $250-500 USD. Also I believe a ca18de CAS will work too, the CAS should have the same part #.

If you are forced to purchase a new one then you may want to check out the link at the bottom, it's a thread tht I started regarding the replacement of a CAS. I found a vendor who sold it to me for $60+$40 for shipping for a total of $100. My CAS is about two days away from being delivered to my door step, but once recieved I'll be doing a quick review so that others may use this vendor or avoid it if there s*** is wack (hopefully not).
- ca16-cas-on-a-ca18-t573909.html

Good luck in troubleshooting, keep us posted.

[Leve1One]

Thanks for the replies and the insight. r34 gtr you are right, i need to cover all the bases ignition-wise. But i think the only thing left is to get a set of Yellow Jacket coil packs or Splitfires (does anyone know if they are worth it?). On the to-do list, probably first thing tomorrow morning is:

-Check the fuel pressure regulator
-Remove the fuel rail and make sure those injectors sit correctly and snuggly

I am having some second thoughts about the CAS, since the problem is purely boost-related and RPM-independant and I can't see any relation between the two. Of course, i will try swapping it just to see.

The AFM reads ok in idle and shows no sign of fatigue voltage-wise (NISTune says so, not me).



This is a dyno at wastegate boost. 12psi i think. 8-port head with deleted butterflies and stock exhaust manifold.

[float_6969]

If it's truely due to a weak spark issue, gapping the plugs down or turning the boost down should have fixed the issue. The fact that you've narrowed the plug gap tells me it's likely not a weak spark issue. You can try turning the boost down and see if it fixes it, but I doubt it will.

[Leve1One]

Update: I did all sorts of things today, checked the FPR, re-seated the fuel injectors, removed all the harness plugs and cleaned them, re-measured compression ratio, NO change whatsoever. Swapped all 4 coil packs for used ones, nothing changed. Same backfire under same circumstances.

What seemed to do a bit of difference, is the advance timing. It used to read 17 degrees at 850rpm, now is at 20. Backfire almost stopped (only a minor misfire is felt) BUT it knocks like a mofo. Especially in that high-boost area.

@float_6969 i forgot to mention that when i dial down the boost (stock wastegate pressure) it does not backfire. It only does it when i give it some extra boost. Boost controlling is done via an APEXi AVC-R.

Faulty CAS?

[boost_boy]

Sounds like you are maxxing-out something or hitting a fuel cut or just a programming issue. If it starts giving you grief after 15 minutes, it means your open/closed loop system is functioning just fine. Turn the boost down to 12 psi and see how she acts. Stop spending money in places you don't need to. And I highly doubt if your spark is weak.

[Leve1One]

The weird thing is that the car worked perfectly for 6 months or so, until last week. It has been tuned on a dyno and it has never skipped a beat!

At 12psi everything is peachy. No misfires, no backfires, pulls as hard as it is supposed to. All hell is breaking loose when i boost up the damn thing.

I also have an Innovate MTX-L wideband O2 sensor in the place of the stock, and i am sending the simulated narrowband output of the Innovate to the ECU. It has been like that ever since i tuned it. Closed-open loop works perfectly, so is the idle valve.

[boost_boy]

Perhaps your fuel pump is failing. Something is hitting peak faster than everything else. That backfire you speak of may not be good at all.

[Leve1One]

I already changed my fuel pump with a same -brand new- Walbro 255lph. I know it's not good, i am not doing anything to provoke it and under no circumstances am i hammering it, at least not before i find out what is wrong with it.

[boost_boy]

I don't think there is anything mechanically wrong with your engine, but I do believe your issue lies in the areas of fuel and igntion timing, which points me to your NISTUNE.

[Leve1One]

I got a feedback from a friend who suggested i may have a fried valve or a head gasket related failure... Looks remote, though. I think i will pay a visit to my tuner to do a maintenance check.

I am so out of ideas...

[boost_boy]

A failing or bad headgasket sure as heck won't cause back-firing. If you told me your engine was overheating, then I would start suspecting your headgasket. Back-fires are cause by ignition timing, fuel and/or air issue (too much or too little of one or the other or some of them) in the form of bad values entered in your engine management system.

[float_6969]

Boost_boy is in the right track here. If pulling the boost back fixes the issue, it is NOT a mechanical problem. Plain and simple. This is a tuning issue or a sensor issue. What really gets me is that advancing the timing helps. If anything retarding the timing should help. Not to sound like a broken record here, but it still sounds like a bad/failing CAS. They make the engine behave in strange ways when the fail. My guess here is that the CAS is sending the ECU an erroneous signal (probably an delayed sync). This is causing the ECU to charge the primaries on the coils too late, resulting in the effect of a weak spark. Advancing the timing could have the effect of artificially increasing the dwell and boosting the strength of the spark...with the con being detonation, which is far worse.

Put the timing back to 17° (I actually run more like 15°) and see if you can find a CAS to borrow to test with. I'll be very surprised if it doesn't fix it.

[Leve1One]

You guys are probably right. I'll do anything i can to get my hands on a working CAS to see if things get better before i actually buy one.

[float_6969]

Good luck, and PLEASE, post back here with the results. It helps other members later on down the road when we actually find the solution and post it.

[Leve1One]

Of course i will! Thanks for all the input!

And on a sidenote, today was HOT (90 degrees almost) and i thought i'd beat the living s*** out of it at wastegate boost (12psi). It didn't skip a beat, and took all the beating i threw at it like a proper CA. It just wants to mess with my head, that's all.

[boost_boy]

Sounds like something is definitely peaked or electronically limited. We'll be waiting to find out what it is that's giving you drama at specific boost levels.

[Leve1One]

Hey, did you miss me? :P

I wish this post would be the solution to my problem, but it is not. However, I *think* I may be on to something.

As you may remember, the car backfired under high boost ( >17psi) and ran flawlessly at waste gate pressure, about 12psi for my 2860RS. You may also remember me reporting that when the car misfired, the AFR was approximately as tuned. A healthy, on the rich side, 11.2...

What I forgot to do, is to check my AFRs with the car working perfectly at 12psi. And I did so today, only to find out that at WOT, it reads a -not healthy at all, and by far on the rich side- 12.9-13.2...

Could the engine leaning out on high boost cause that elusive misfire? Which only raises more questions than it answers.

Why would it show near perfect AFR just before the misfire?
What could cause the leaning out after everything fuel-related is changed??

[chalander]

...it reads a -not healthy at all, and by far on the rich side- 12.9-13.2...

Could the engine leaning out on high boost cause that elusive misfire? Which only raises more questions than it answers.

Why would it show near perfect AFR just before the misfire?
What could cause the leaning out after everything fuel-related is changed??

Few things, u mention its rich at wot, well rich IMO is 10:1 or 11:1 not 12.9:1. I think you may have the scale a bit backwards. 12:1 is leaner than 11:1. So you mean that your AFR is leaner at wot at 12psi (no miss fire) vs at ur original boost pressure, 17 psi where it is running richer at 11.2:1 (miss fire present).

A wrong a/f mixture can cause a misfire but I believe only if its the a/f ratio is really lean.

A good a/f ratio before the misfire would point me in the direct of an ignition problem rather than fuel.

From what I have read you have not changed out everything fuel related.

I'm still not sure what's goin on with your rig but hopefully I've provided some insight and maybe cleared up ur misconception of "leaner" and "richer". Also I do find it interesting that changing the timing almost completely reduces the backfire

[boost_boy]

Is it a back fire or is the engine breaking with multiple "pops"? Also, monitor the operation of your BOV and make sure it's not leaking under no circumstances. As I stated before, fuel seems to be a factor and it's either at your fuel pump or your tune. Sounds like 'No fun" at all .

[float_6969]

12.9-13.2 isn't that lean under full load. That's about where max power is made on most engines. The "tuning standard" of 12.5:1 is a VERY safe (ie, too rich) mixture. Most engines don't make peak power at that AFR on gasoline and will require a leaner mixture.

The fact that it's getting really rich when it mis-fires indicates to me an ignition problem. I think you're seeing the after effects of the spark not igniting the mixture and a bunch of unburnt fuel ending up in the exhaust with the AFR going rich, although I might be remembering that backwards and it goes lean when you have a spark mis-fire, so you might do some research on that. (it's early and I haven't had all my coffee yet, LOL!)

[Leve1One]

Okay. I may have been misunderstood here. Let's talk facts though:

Fact #1 : The car has been tuned to pull 24psi with 11.2 AFR. I know it's actually quite rich, but I wanted to play it safe. And it has done so for 6 or so months, without breaking sweat, without spark plug failures.

This is a recent pull. http://www.youtube.com/watch?v=1dGPNNcVu1s

Fact #2 : It started backfiring all of a sudden when reaching boost levels > 17psi.
Fact #3 : At wastegate pressure it operates normally only the AFR dropped to 12.9-13.2 where in fact, it should be EVEN richer (since the car was tuned to run 11.2 @ 24psi).
Fact #4 : Fuel pump has been changed, no difference. Fuel pressure regulator changed, no difference. Injectors flow checked, re-cleaned, and re-seated to ensure proper seal. System pressurizes OK to > 30psi (BLT). No BOV present.

@boost_boy I think I know where you're getting at. Multiple pops would indicate a failing coil pack. Has happened to me a lot before (been through at least 8 of them in the last 4 or so years). But no, only one LARGE backfire escorted by black smoke (unburnt fuel).

[boost_boy]

What is your car's vacuum @ idle ? Actually, as far as the type of popping I was referring to, was that indicative of a fuel system being insufficent or ignition cut-out; similar to that of a rev limiter or 2-step function. I would seriously look at your tps inputs as well, especially if it's happening when your release the throttle. That type of back-fire is not from a lack of fuel, but more of too much fuel being pre-ignited. Also, go back to monitoring timing as well. This is good!