nahasapeemapetalon

iTrader: (9)

Just a brief history.

Car
408 Turbo
E85
Versafueler
Bosch 120lb
backfire started last summer at the track. Was using N20 on top of 10-14psi. Backfired at the top of 2nd/beggining of 3rd. It shuts off the car immediately.


Ever since i have had backfire problems. At the same track day the tranny started slipping, i think thats completely separate, tranny is now fixed and shifts perfect. I did have some issues with my injectors plugging up last year.
Backfire seems to occur mostly in 3rd gear after being in the throttle for a long time, seems to be around same rpm range 5700-6000rpm.

THe attached log show the a/f ratio taking a dump down right before the backfire, we recently adjusted tune so the a/f is good and the backfire is still there.

Any ideas would help!!!!!

We are going to start by swapping, coils, wires, and packs.
After that im not sure what to check.

Not easy to find injector or injector driver problems.
After that....valvesprings, valves etc...

Car runs great other than this, feels good in boost up to backfire.

Boost is usually 10-15psi when this happens.

Eagle02

iTrader: (20)

Post your tune file too.

Looking at the scan, I'd guess its going lean. You're commanding only 12.12AFR, should be more in the mid to POSSIBLY high 11s, tops IMO.

Old Geezer

iTrader: (3)

E85 @ 12+ AFR???
Fuel psi being logged?? [I can't see the log].
Correct amt of fuel being added w/ N2O?

nahasapeemapetalon

iTrader: (9)

It uses the richer of the VE table values or the commanded afr, car is in the mid to low 11 a/f's.

We changed valvesprings and spark plugs and it went away as far as i can tell!!!
We had a theory it could be the valve springs. They were PRC .650" lift springs that had 35k+ miles on them.

More testing to come.

Old Geezer

iTrader: (3)

E85 stoic is near 9.6....
Check the crank end play. Just found a similar problem. Crank was running away from the sensor, causing problems.

MontecarloDrag

iTrader: (3)

Use lambda instead AFR

nahasapeemapetalon

iTrader: (9)

Fail.

Still having issues. High boost it backfires. Yet at 10lbs it was fine up to top of 3rd gear.

Car has been having part throttle missing issues. Seems to clear up with WOT.

This is getting old. Tried different coils and wires, still there.

b4cz2896

Alternator maybe? what's the battery voltage doing?

nahasapeemapetalon

iTrader: (9)

Voltage has been crap since battery was put in the back. Does ok when engine isnt 5 billion degrees. I am going to start digging into it again, i needed a break. Think cam, crank, or tps sensor could be funky? Doesnt really show up much on scan but maybe could be malfunctioning. Ill double check that wiring didnt get melted or something either i guess....

Hemi2Slo

Friend of mine just had similar problem with an N/A 416, I had a thread on it actually. Car pulled great up till about 5800, then backfire and die. Had some rough running part throttle issues also. Wound up being crank sensor. Had to go through 3 of them before getting a good one. Gap has to be correct also, .040 I believe. Somebody correct me if I'm wrong on that.

KRAZY K 2000 TA

iTrader: (5)

A wot AFR on e83 should be 8.3 min on naturally aspirated and probably about 7.8 on boost.

KRAZY K 2000 TA

iTrader: (5)

E85 I mean

nahasapeemapetalon

iTrader: (9)

Hmm thanks for the input on crank sensor.

nahasapeemapetalon

iTrader: (9)

Swapped in a used cam sensor, didnt improve situation with part throttle missing. Havent bothered with WOT with high boost till its running better

Onto the next items......

Alvin

iTrader: (2)

I've seen this on a couple different occasions. Most of the time its the battery lenaing back on hard accel causing it to short against the frame. Since you moved yours check to make sure nothing can short. No loose batteries, no chafted wires, etc.

The last car we had it happen on drove us nuts to find. On a hunch they checked crank end play. Long story short the converter was ballooning pushing the crank forward which ate the thrust bearing. It would backfire when the crank was pushed away from the crank reluctor.

Orangecoupe

iTrader: (1)

His wide band is calibrated for pump gas.

so stoichiometric ratio on pump gas is 14.7*.76 lambda = 11.2

stoich on e85 is 9.76*.76 lambda = 7.37

So his commanded stoich ratio on e85 is 7.37

Old Geezer

iTrader: (3)

volt drop on the entire charging/ starting system. Check the + and - sides.
What size wiring is used?
NE "bolt on" batt terminals in use?
Check all ground points for drop.

Old Geezer

iTrader: (3)

that the E-85 is actually 85%.
I'm seeing info that's being derived using a fuel comp tester, [Summit], that tells a much different story. Some of it is at/near 70%...

I'd think that these differences would be a good reason to test the fuel B4 assuming a particular afr is good to go..Yes/no???

http://www.summitracing.com/parts/QFT-36-E85/

Orangecoupe

iTrader: (1)

I did test the e85 in the area yesterday. Before I head to the track and it was e85 not e70.

I am in the same town as the OP.

nahasapeemapetalon

iTrader: (9)

Think thats what it is.

Ding ding ding. Long story short, was out romping on the car a few months ago and had a bad backfire, oil pressure was at zero. Went up some when i reved it. Dropped the oil and was full of bearing material...

Took a few months off, needed a break.

Took out the motor yesterday and found..... (post pics later)

Main bearings were shot, THRUST BEARING was worn down quite a bit and the crank was rubbing on the block.

It seems that was the backfire issue, crank walking from sensor. Not sure what caused this yet but id guess my crank and block are shot. Going to have them looked at over the next few weeks.

Have a whopping 12k miles on the engine.

The backfiring started about 1/2 track one day with 12-14lbs and a 100shot towards the top of 2nd gear.

Kinda sucks, was hoping to quit the spending all the time. Now have to think about what to do....

Thanks for your input guys.