greyzone

I need some help with a weird problem:

See below for entire list of setup components. Plugs are NGK ZFR5F-11.

I put in new plugs, gapped at .32 and engine runs perfect. Turbo is at 7 PSI. After about 400 to 600 miles the gap somehow increases, and becomes .35 to .36 and the engine starts to miss and backfire. I figure this is because the spark is getting “blown out” with the bigger gap, so I put in new plugs gapped at .32 and it runs perfect...until about 400-600 miles.

Heres the question: Why is the gap INCREASING over a short period of time?

I put new plugs in again and it runs perfect until the gap increases to .35 or more, then it misses and backfires...and I put in new plugs and it runs perfect until....

Why is it doing this? What is the solution? What gap should I be able to use with this setup? Should I use different plugs? What in the hell is going on?

–96 EX Coupe 5spd
1.6L SOHC D16Y8 170WHP
–GReddy Turbo w/Blue Box
–GReddy Type S BOV
–GReedy T-31 Intercooler
–GReddy EVO Exhaust
–Gutted Oversize CAT
–NOS Fuel Pressure Reg (Boost Dep) 38 psi at idle, 54 psi full boost
–Missing Link
–AutoMeter Phantom Boost Gauge
–AutoMeter Phantom Fuel Pres. Gauge
–1 Pillar Dual Pod
–A’PEXi V-AFC
–HKS Turbo Timer
–Holly 255lph Intank Fuel Pump
–MSD SCI Ignition
–MSD Blaster 3 Coil
–MSD Pro Cap
–MSD Plug Wires
–NuForms Block Guard
–2 Mil Head Gasket
–ARP Head Studs
–NGK Plugs gap @ .32

VaporTrail

your plugs are too hot. Correct me if I'm wrong here, but the factory plugs are a 6 heat range, yes? You will want to go cooler with boost, so a 7 HR is the way to go, not the hotter 5 as you listed. The hotter plug can cause detonation, which can destroy the spark plug, hell even your whole motor. Try a 7 HR and see if that doesn't fix your problem

greyzone

Hey Magic,

How do you like your MSD BTM?? Im gonna be getting that soon, heard its great thing to have.

My plug wires are MSD and fairly new, so I dont think its them...I just went to a plug TWO STEPS colder, put it in last night, we'll see how it works.

Your erosion of electrodes? Try NGK ZFR7F-11...my opinion Autolite is trash, like someone told me, "if you wanna be cheap with your car, use Autolite" so there ya have it...

DocF

Last time I checked there is no such thing as an NOS boost dependent FMU, 38-54 psi difference is no due to boost but the difference from idle vac to 0 vac. If you are running the stock injectors you are not getting enough fuel into that motor, which is probably why you are overheating those plugs and getting gap spread. 54 psi is not nearly enough pressure for anything more than 4 psi of boost. I ran stock heat range plugs on my car for the entire time I had the turbo and never had a single problem.

greyzone

Okay, so answer this...on the dyno from 4000 rpm to 7000 and under full boost (up to 7 psi) the car is actually running slightly on the rich side...????

DocF

How are you determining your a/f on the dyno and on the street? You should be running way rich, not slightly rich. What I am telling you is not my opinion it is a fact.. there is a reason why people run a vortech 12:1 fmu that drives the fp up to 100+psi at the same boost levels you are running at 54 psi. Perhaps an EGT gauge would help here.

greyzone

The NOS FPR I have is identical to the Vortech 10:1 FMU, I was going to replace the NOS with the Vortech unit until I found out they do the exact same thing...that was according to a tech at Vortech AND at GReddy...and I got the NOS unit cause my shop said they liked it better than the GReddy FMU that comes with the Turbo (I still have that one)...

I agree an EGT gauge would be good, but I think I'm gonna get the GReddy Air/Fuel gauge first (340.00 list) although its pretty damn expensive I think its a good investment,and more acurate than the EGT gauge.

What is a good dyno reading for a/f on the dyno?

I want to do whatever is right, man, you know how many different ideas people have?

Hard to know whos advice to follow. Is there anyplace on web where this stuff is in writting???? That would be nice.


[Modified by greyzone, 12:42 AM 6/18/2001]