Jeremy Himsel

I've seen this happen with a MSD box using solid core wires on the dyno. If you have solid core plug wires you may want to switch to spiral core wires and see if that solves your issue.

Here's what magnacore says abourt it....... EMI from spark plug wires can cause erroneous signals to be sent to engine management systems and other on-board electronic devices used on both racing and production vehicles in the same manner as RFI (radio frequency interference) can cause unwanted signals to be heard on a radio receiver. Engine running problems ranging from intermittent misses to a dramatic loss of power can result when engine management computers receive signals from sensors that have been altered by EMI emitted from spark plug wires. This problem is most noticeable on modern production vehicles used for commuting where virtually every function of the vehicle's drive train is managed by a computer. For many reasons, the effect of EMI on engine management computers is never predicable, and problems do become worse on production vehicles as sensors, connectors and wiring deteriorate and corrosion occurs. The problem is often exacerbated by replacing the original ignition system with a high-output system.

Josh B

Interesting - I just swapped out the Magnecor wires that were on there for these from Paragon but it looks like they are solid core as well.

http://www.paragon-products.com/Perf.../kb_09-566.htm

Maybe I should pull the stock wires off this white 951 I just picked up and try them on there...

It is strange too as I had the dyno runs where after the car was dis-connected from the induction wire it was fine. Then I filled up with E-85 and it started doing it all the time. I guess with e-85 there was more load on the injectors and maybe on the ignition system as well? Wonder what the connection is?

Tom M'Guinn

Ya know, thinking about it, when I first installed my WS I used magnacore wires and had a bogging problem. Mine happened just tooling around town. I chalked it up to faulty wires because all was great when I switched to factory wires, but now you have me wondering...

Rob

Also, what is your plug gap set at?

fast951

Josh, you may recall, but we swapped a couple of plug wires with factory ones. We just swapped the ones that were showing corrosion, may be a good idea to swap a complete set.

Rob, the software is setup to handle E85.

boerge

Had a silver rose stock that was acting normal up to a certain rpm and boost/load.
After several weeks of diagnose, the problem was one of the injectors were bad. Replaced and worked fine.

B.O

Chris White

I always find it interesting when somebody says they swapped out ‘everything’ and the problem is still there…..but they still have one constant – the wiring harness!
The wiring harnesses are one of the biggest causes of problems on these cars, regardless of how they look they are prone to internal insulation failures and the copper wire wicks moisture like no other wire I have seen. Wires that look prefect on the outside may be 95% green dust on the inside. I am sure that John can share 100’s of problems he has seen/solved that were wiring related.

Why does it not show up on the dyno? Its because the car is very stable – minimal vibrations to jostle the wires and help them to act up. Why at 4500 – 5000? That’s a little tougher – but it is just above peak torque so that is usually the most difficult range to fire a spark plug.

Now there is something interesting if I am reading the post right – it sounds like you were running on gas at the dyno and then filled it with E85 afterwards and the problem got worse. With the E85 you are flowing a lot more fuel at the same boost level and the misfire started showing up at lower boost – that would lead me to think it might be a fuel flow issue – bad injector or injector wiring. Are you using the stock injector wiring? That is the most common failure for wiring….even though I love to pick on wiring – it sounds more like a funky injector.

John – can you log the injector duty cycle from the DME to see if there is a correlation between duty cycle and the misfire?

The other test is to switch back to gas and see if the onset of the problem goes back up in the boost range.

fast951

Chris this is a brand new wiring harness!

Yes, logging injectors duty cycle vs. RPM. vs. Boost is possible (all DME parameters can be logged).

Josh, when you found the junk from the disintegrated fuel hose inside the fuel pump, didn't you replace both pump and filter? (this occurred early on, before the dyno)... Fuel pressure seems to be steady, so fuel supply to the injectors is fine.

This leaves the injectors, the +12V supply line to the injectors or the wires from DME to injectors as possible causes.

67King

Have you replaced teh knock sensor? They don't go bad often, but funky wiring in that circuit can cause ignition issues.

Josh B

Yep - I've replaced the knock sensor.

Just went out and swapped on stock wires and the car is still doing it. Part throttle is fine but WOT or almost WOT and it studders. It doesn't add knock counts though.

Tom M'Guinn

I also learned (inadvertently) that the motor runs with the wires not installed per johns instructions (since the wasted spark fires every time) but doesn't run right.

If that checks out, id try injectors and look at their resistors if any.

Josh B

How did it not run right? I thought it didn't matter? Your talking about how 1/4 and 2/3 are hooked up to the coil packs?

Tom M'Guinn

Yes, but can't remember the symptoms other than I had to change to match johns instructions. Remember wondering if the coil dwell was the same for the spark that is wasted.

Duke

I'm bumping my questions... does it stutter just once, or does it completely misfire in that specfic rpm range? Does the rpm where the stutter kicks in vary with boost level? That would be an easy check to see if it can be injector related or not IMHO.

Josh B

It is continually stuttering and since the AF goes up I lift right away. It doesn not seem to be something I can accellerate through.

I need to check and see if it moves based on boost level. I am starting to get suspicious of the injectors but wish I could find some to borrow to swap in instead of buying a new set.