Tuning problem - breaking down when on boost

[redss]

Just chasing some advice. All ideas welcomed. I have a 427ci RHS block with ETP LS7 heads. Also running an ASE turbo kit with GT4508 turbo. Shaun's manifold, ice coil packs, and the usual other bits and pieces. The car is also running on E85. We're continuing to have a tuning issue. The car runs fine when driving normally, but as soon as we try and get the tune right on boost on the dyno it has been breaking down. Has fuel, has spark. AFR is spot on. Have tried brand new Ice coils, along with the previous Ls1 truck style coil packs which had worked ok on previous tune. Engine is making boost according to gauge and ECU read out (12psi). We've tried 3 different ECUs thinking it was an electrical 'glitch'. Added 3 new sets of plugs (6s and 8s) gapped down to 25thou. Motor is good in leak down test, valve springs are good with seat pressure fine. Thought we had found an issue with the earth from the ECU so fixed that... but no improvement. In fact, the issue seems to be getting worse. It is gradually losing more power, currently down at least 200rwhp on where the car had run previously (>700rwhp). The tuner has been scratching his head, along with everyone else we've run it past. Tech2 shows no issues either, so not tripping an error in that way.

As I said, the car runs fine in 'normal driving', but when it comes on boost it's not happy. No power and misfiring.

At this point we're about to pull the engine and start changing crank angle sensor and cam sensor. Just looking for any other ideas before we set off on that path. Any ideas welcomed... other than a hell of a lot of work we've pretty much run out of them...

Cheers

Tony

[Cobalt]

These are just a few thoughts ... Hope some of which you haven't had.

Cam angle is only really used to get the car to fire. It will run without it just doesn't know where home is so it tries both possible locations till it fires. So I doubt there is a problem there. Disconnect it and see.

Is the RPM signal erratic on boost? Crank angle may be the cause but if it runs fine low boost I doubt it.

Run high rpm low boost and see if there is still an issue I know it wont make power but you it will isolate whether this is an rpm or a boost problem

Power Supply - Try disconnecting the alternator and running a battery charger while tuning/dyno One thing that is a noise creator that is easily isolated.

Is the timing where it says it is.... Check it with a light .. I have seen crack trigger rings move / or be installed incorrectly by the manufacturer. We check then weld them... As it runs low boost fine probably not the problem but worth a check. A few degrees can make a difference.

Have you checked resistance on the power side of the coils. Had a problem with on a supercharged vy. The ignition power wires run through the plug next to the radiator on passengers side. Was going high with vibration ... replaced the plug with a deutsche and worked perfectly.

The engine isn't moving and stretching/pinching the wiring?

I have heard of issues with the ecu going to low power mode due to high reading above what it expects on certain parameters - grans/sec I think - not sure that would generate a misfire though. HPTuners is down atm so I cant check....

I have been lucky with my high hp stuff and never had those issues.

Let us know what else you try and if it helps... I'll put it in my brains rotation as I usually have my epiphanies at 2am.

I have also just recently had an issue with plug/pins where they would work and then driving - eps right hand corners would disconnect/go high resistance to loose connection. Pulled the plug and removed the suspected faulty wires - crimped the female plugs aa little and Voilà no problems. Hard to trace sometimes.. Mine was easy as it was main GMLAN that was loosing termination at the EBCM.

Hope you get it sorted.

Cheers

[macca_779]

What's your plug gap? Perhaps try closing it up a bit

[Bling Bling]

Have you checked fuel pressure and the injectors good luck, and let people know when you find the problem.

[whitels1ss]

Could your valve springs be getting soft or weak & not holding under load?

[redss]

A big thanks to everyone for their suggestions. I'll try the ones I haven't already and keep you posted.

[duke5700]

Where are the coils located? Stock loom?

[redss]

Hi. Yes stock loom stock location and no hair left haha

[V28VX37]

A completely different motor of course but I had a really tedious issue with my RB25DET, broke down on high rpm (past 4000), tried everything from coil packs to new harness to O2 sensor to specific gapping to AFM cleaning etc. etc. Ended up being a stuffed CAS, invisible to the outside but damaged on the inside. New CAS -> ran perfectly. Maybe worth checking?

Here's the full thread for some ideas: http://www.sau.com.au/forums/topic/3...t-rb25det-neo/

[redss]

Yes on the list to check thanks

[Delft Maloo]

Try running more boost and see if you get it, if not the heads may be lifting.

[zorro]

Have you any logs on the power runs?

[Toddler78]

could it be a collapsed cat?

[Tre-Cool]

I have the same issue with my ve ute at the moment, drives perfectly fine when off boost, but starts to misfire under boost, it's not plugs as ive changed them. I suspect it's either the leads or a collapsed cat. I'll probably get around to looking at it this weekend on the hoist.

[redss]

Hello There,

Has been logged. No unusual issues and it's not the cats. In the process of replacing crankshaft sensor and redoing all the wiring harness in the engine bay. Will be checking all joints.

Fingers crossed!