I have been struggling with a bad hiccup in my car for the past few weeks. It only happens at higher rpm's and high boost. The air fuels are great on the car, but it will hiccup, air fuel will drop to 8.75 and the boost will spike to 26 psi. I am leaning towards something spark related, maybe the spark isn't jumping the gap. Plugs were gapped at .030, but after taking them out, the gap was closer to .035. #8 ngk's with an msd 7al-3 ignition with a hvc coil. If I could send it to someone I would appreciate it! Thanks!

Anthony

 

This is just a wild guess but a problem in the wiring. Both the 02 and MAP are probably using the same 5v wire? Check that wire from ECU on out and also the grounds. Maybe a wire is rubbing somewhere??

 

Very well could be. I will go over all my wiring and make sure all connections are tight. I don't think the xfi shares the same 5v for map and o2 sensor, but I will make sure to check. Thanks for replying man, I appreciate it, I will let you know how it turns out.

Anthony

 

when I was carberated I had some issues kind of like that and it was RF signal causing the problem. Completely intermittent and hard to diagnose.

Drove me Freakin crazy

 

Well i checked my wiring and all is good. I am now getting a surging idle from the car, that happened literally overnight. I was getting the "AMP" light come on in my dash. I removed the alternator and the white wire was loose, i fixed it and I put it back on (200 amp alt.) and now the amp light isn't on, but the idle started surging like crazy, charging volts at 900-1k rpm idle is 13.4-13.5. The only thing i can possibly think of what is causing this is some kind of electrical noise. I have the plug wires run right by the alternator wires. The plug wires are run down from the distributor and behind the alternator/along the block to the plugs. The XFI box is mounted inside the car on the passenger side trans tunnel, and the ignition box is mounted behind the drivers seat, wires are run on opposite sides of the car.

The only thing i can even come up with is that after the alternator fix, it is finally feeding the car with more volts/amps that weren't there before, and maybe i ran the alternator wires closer to plug wires than i though, is this logical thinking or should i be looking somewhere else?

The one thing i noticed is that i can get the car to idle W/O the IAC valve steadily, and as soon as i plug the IAC back in, the idle goes crazy. I changed the IAC valve and nothing changed. Can electrical noise cause the IAC to freak, or is there a driver in the XFI that can go bad? The car literally idled fine before the alternator reinstall.

I checked A/F on the car and the VE numbers have remained the same, A/F hasn't changed, just the idle freaks out.

Other things i have checked ~ Removed the intake to check for blown intake gaskets (none found), checked elbow gaskets and they were fine, BOV o-ring and it was fine, throttle body shaft for excessive shaft play/cracks and none found, and IAC gasket and it was fine.

Could this issue be RF signal like you suggested bad69bird?

Thanks for any help!

Anthony

 

I never found the actual souce of my Rf signal problem.

I just seperated the wires and I ran them only across eachother where I could.

I also got rid of my two step rev limiter at the same time(too many changes at once) the problem went away so I never connected the 2 step again for fear of having issues again durring the season.

I have now gone to Gen 7 DFI and I am just getting up and running.

Rf signal if I rember correctly usually shows up at certain RPM's somewhere in the 4800 RPM range and possiblky other areas That might help you decide if its RF related.

As far as IAC goes I have read on here that you need to open the trottle blades to a pont where the IAC is in the middle of its range so maybe check that too.

 

Thanks a lot man! I didn't know what was causing my problem, so i changed the intake gaskets. After I changed the gaskets I remembered that I ran the alternator charging wires a different way and they were much closer to the plug wires as I have the plug wires run down along the front of the block and under the headers. I moved the wires to where they were originally. Being that I changed the gaskets along with the wires I don't know what the actual culprit was, but I am leaning toward the alternator wires as the intake gaskets looked perfect. Thanks a lot for the help sir, I do appreciate it!

Anthony

 

The wires that don't like RF noise are the cam sync and the crank trigger.

If you suspect rf problems connect a scope to it and watch both of them at the same time on the screen.
RF noise can cause the cam sync to restart the firing sequence when you don't want it to.
Make sure that the shielded cable on both are grounded.
FAST grounds them at the sensor end.
Electrical techs I know both said that grounding at the ECU end is better.
Not both.

Double check that the plug wires are seated in the dist cap good and that the rotor and carbon contact in the cap are good.
Any arcing will throw out RF noise like a welder.

 

X2

 

Awesome guys, i am going over everything. I will check my grounds as well. Appreciate the input!

Anthony

 

Check the resistance on the coil. Should be fairly close to .016 ohms on the primary side and about 30 ohms on the secondary side. We fought a problem that sounds similar to yours, the car would be pulling the miss and puff a little black out one side or the other, then continue on. Fought it for two and a half years, nitrous'd and turbo'd. We were pulling into the burnout box one night and the car just died. Ohm'd the coil, found it was dead. Replaced it and we never have had another misfire. If you think about it, high boost is going to cause higher cylinder pressure which inturn is going to be harder on the coil. I still can't explain the boost spike though...Evan

 

Evan, thanks for the suggestion. The coil is a better part of 6-7 years old, could very well be it, I just got a gift card for summit and I will use it on that.

My best explanation for the boost spike, is that when the motor cuts out, it drips a solid 1k rpm, and the boost backs up in the intake tract. I will change the coil out and let you know what happens! Thanks!

Anthony