03 cobra 5.3 tt misfire

[chrisquirk187]

Ok guys Ill skip the ranting and raving about how frustrated I am and just get to the issue.

I have a brand new MMR Mod 1000 5.3l stroker. Heres the mods


MMR Street Mod 1000 4V Longblock (4V, 8 bolt, 9 to 1 Comp 14-20lbs of Boost)
Upgrade to Boss Block
Upgrade to Stroker
Upgrade to Race Bearings Rod and Main
PC001Piston Coating - Ceramic Dome, Teflon Skirt
Head Porting of Cylinder Heads (Stage 3)
Stage 3 turbo Cams 4V with Manley High Performance 4V Springs
Timing chains, lifters, Rockers, Tensioners
Mainstud kit for 4.6/5.4 Iron Block
Upgrade to Cometic Head Gaskets
MELLING High Performance Oil Pump w/Billet Gears
MMR Street/Strip Oil pan for 4.6/5.4

I then added a non-compund Hellion 64mm ball bearing billet wheel twin turbo set up that has just been rebuilt from Work Turbochargers.

The car has Lethals 1000hp return fuel system, 80lb injectors, electric water pump, SCT BA-3000 MAF, and I converted to a built 4r70w auto from TCI.

HERES THE ISSUE:

after an 800 mile break in I changed the oil and returned the car to the shop for its 18lbs of boost tune and we noticed a bad break up above 4k rpm. Datalogging showed a misfire from cylinders 3&5. This missfire is at any rpm as long as I hold the throttle steady its there.

a/f for the test is about 11.7 and volts are about 13.5. This is a well respected shop so I know the tune work is on point.

The shop and I have been troubleshooting this for 2 weeks now with no solution. Heres what we have done:

Switched all the injectors around
Switched all the coil packs around
Replaced all the power wires to zero gauge
replaced the ccrm
replaced the ecu
replaced the crankshaft position sensor
replaced the camshaft position sensor
Put in NGK BR7E at .28
Put in NGK TR6 at .32, .28, and .24
put a whole separate tune in the car
Did a smoke test for boost leaks
did a compression test
pulled the engine harness and tested each wire for breaks
did a leak down
replaced trigger wheel
and probably a few more things im forgetting about..

The only correlation between cylinders 3 and 5 are the ECU and the trigger wheel as far as I know.


PLEASE PLEASE PLEASE someone have a solution.

Thanks guys.

 

[Parts-is-Parts]

It may be far fetched, but the cam and crank sensors are magnets and can get full of metal on the ends and disrupt spark.
Try that first.

 

[chrisquirk187]

Already replaced them today

 

[TwinTurbo4vGT]

Why do you have supercharged cams on a huge turbo build like this?

 

[TwinTurbo4vGT]

Just looking at it get rid of that SCT BA 3000 they are not very good. I had one and I ended up getting rid of it due to the troubles it gave me. You really should put a PMAS HPX sensor in there.

 

[itSSlow98]

Just looking at it get rid of that SCT BA 3000 they are not very good. I had one and I ended up getting rid of it due to the troubles it gave me. You really should put a PMAS HPX sensor in there.

I run a ba3000 blow thru with no issue. I am actually friends with the tuner at Revauto and he also tuned my car. Ive seen your car on the dyno multiple times and was just asking about it the other day.

 

[chrisquirk187]

Why do you have supercharged cams on a huge turbo build like this?

Sorry I edited the post. When I received the motor I called Comp and read them the grind number on the cams to be sure what I was putting on it and they told me they were some really good custom grind turbo cams so I went with hellion instead of the whipple that was going on there originally.

I meant to go with the ba5000 but didnt have time for any fabrication at the time.. Going on 4 moths at the shop I wish I had now but the MAF wouldnt have cause this issue at low rpm

I run a ba3000 blow thru with no issue. I am actually friends with the tuner at Revauto and he also tuned my car. Ive seen your car on the dyno multiple times and was just asking about it the other day.

I think I saw your dyno.. My power curve follows your identical till it breaks up from the misfire.

 

[Turbo98]

Sorry to hear about your issue. Very nice description of what you've already done. And, man, you've done a lot so far to try to solve it.

The only thing I can think of is that harness wires can expand a bit when they get hot and breaks can occur. It might be worth replacing the harness. What year/model car is this? What ECU?

I've been through many similar bizzare issues and they can be very frusttrating. You'll get it though.

 

[01yellercobra]

Not sure if I missed it, but are you running a draw through or blow through set up for your MAF?

Misspelling brought to you by Tapatalk

 

[itSSlow98]

Blow thru

 

[chrisquirk187]

Sorry to hear about your issue. Very nice description of what you've already done. And, man, you've done a lot so far to try to solve it.

The only thing I can think of is that harness wires can expand a bit when they get hot and breaks can occur. It might be worth replacing the harness. What year/model car is this? What ECU?

I've been through many similar bizzare issues and they can be very frusttrating. You'll get it though.

It was a 2003 gt that I converted to 03 cobra so the computer and engine harness is cobra and the dash is gt. Im ready to buy a brand new engine harness at this point.

Just replaced the trigger wheel today and the old one looks fine. will know tomorrow or the next if it was an issue.

 

[SVTMang]

Blow thru

Have you checked to make sure you aren't throwing a maf performance code? This kind of setup requires specific tuning normally. Also you can try cleaning the maf sensor. Blow thru set-ups tend to accumulate moisture on the maf sensor worse.

 

[SVTMang]

Also do a boost leak test mainly right at the throttle body or anywhere after the maf sensor. Any leaks after the maf sensor can cause a misfire.

 

[chrisquirk187]

Have you checked to make sure you aren't throwing a maf performance code? This kind of setup requires specific tuning normally. Also you can try cleaning the maf sensor. Blow thru set-ups tend to accumulate moisture on the maf sensor worse.

I did remove the intake tube to pull my harness and there was a small amount of oil all around the tubing (not enough to worry the tuner) but enough to make me say wtf. I will spray some maf cleaner in there and dry it up. Thanks for the moisture info.

Also do a boost leak test mainly right at the throttle body or anywhere after the maf sensor. Any leaks after the maf sensor can cause a misfire.

We did, hooked a smoke machine up to the intake manifold and no smoke came out anywhere else except the turbo filters.

 

[01yellercobra]

Have you tried running it with the MAF unplugged?

Misspelling brought to you by Tapatalk

 

[TwinTurbo4vGT]

If your getting oil in the intake tube it sounds like the seals are bad in the turbos.

 

[chrisquirk187]

If your getting oil in the intake tube it sounds like the seals are bad in the turbos.

the turbos were just rebuilt a few weeks ago. I'm guessing some oil is will always come .through. My tuner isn't worried about the amount but to be sure i may pull a turbo..

 

[chrisquirk187]

Have you tried running it with the MAF unplugged?

Misspelling brought to you by Tapatalk

No, datalog shows a good maf

 

[itSSlow98]

the turbos were just rebuilt a few weeks ago. I'm guessing some oil is will always come .through. My tuner isn't worried about the amount but to be sure i may pull a turbo..

Your running breathers on both valve covers, if there is any oil in the intake piping id be concerned. Really doesnt have anything to do with a misfire on 3 and 5 though. Tell Adam if theres anything he can use my car for to eliminate any possible issues to give me a call.

 

[chrisquirk187]

Your running breathers on both valve covers, if there is any oil in the intake piping id be concerned. Really doesnt have anything to do with a misfire on 3 and 5 though. Tell Adam if theres anything he can use my car for to eliminate any possible issues to give me a call.

Ok, thanks alot. Ill pull the piping on the turbos and see if theres another puddle of oil