Running Rich in Cylinder 4 only when past 25 lbs of boost, Any Ideas?

[scottr126]

So I was having my car tuned this past saturday and discovered a interesting problem. Ill first give a quick rundown of the car:

-AEM EMS
-2.1L 6 Bolt
-2G Head
-Jun Cams
-Supertech Valves and Dual Springs
-1600cc Injectors
-AMS VSR Intake Manifold
-42R Turbo Kit
-Auto

Basically when making runs at 20 lbs of boost the car will make 400hp and the plugs will come out clean. We then raised the boost up towards 30 lbs and made about 650hp but when we pulled the spark plugs out to make sure everything was good 1,2,3 were perfect but 4 was black. It did not look like oil but more like soot so it has to be rich.

At first we thought ok, the injector must be messed up so we swapped a brand new one in and sure enough, same deal. We also checked the wiring to that injector and it also checked out ok.

We are guessing it is something in the valvetrain but before I start tearing things apart I wanted to see if anyone has dealt with a similar issue.

 

[ekanddsm]

Looks like you found a the flow limit of that intake manifold.

 

[scottr126]

Looks like you found a the flow limit of that intake manifold.

Wouldnt I be running rich in all of the cylinders then?

I doubt thats the issue, I made over 900 crank hp last year with the same manifold. The only thing that changed this year is the engine.

 

[1992awdlaser]

Could be part of the ignition not firinng the plug strong enough also. Could be blowing out the spark some. If it is not the ignition and not the injector it is most likely in the valvetrain.

 

[scottr126]

I was thinking it could be a ignition issue also but I am using MSD coils and 1+4 are on the same coil. And 1 is running perfect, its just 4 that goes rich.

Could be part of the ignition not firinng the plug strong enough also. Could be blowing out the spark some. If it is not the ignition and not the injector it is most likely in the valvetrain.

 

[wishihadatalon]

I was thinking it could be a ignition issue also but I am using MSD coils and 1+4 are on the same coil. And 1 is running perfect, its just 4 that goes rich.

Have you measured the resistance on the plug wires? It could be starting to fail or just not able to keep up like the other ones.

 

[scottr126]

Yah I checked the resistance and it came out to about 108, i checked #3 and it was like 100 which made sense since #4 is a longer wire.

Have you measured the resistance on the plug wires? It could be starting to fail or just not able to keep up like the other ones.

 

[wishihadatalon]

Yah I checked the resistance and it came out to about 108, i checked #3 and it was like 100 which made sense since #4 is a longer wire.

hmm sounds like you have pretty much ruled out anything but something mechanical. Good luck, I can't wait to see the mirage in action

 

[slowgsr]

What is the temperature of the EGT's in that cylinder compared to the others?

 

[scottr126]

I dont have any sort of EGT monitoring setup but we used a infrared temp gun and the 4th cylinder was atleast 100 degrees hotter then the rest at about 2" away from the head at the Exhaust manifold.

What is the temperature of the EGT's in that cylinder compared to the others?

 

[wite96gs]

I would check for a misformed rocker, short valve stem, or shoddy port work on the head itself. It sounds to me like the air flow on #4 isn't up to par with the rest of the cylinders.

Just my .02, good luck with that.

 

[turboglenn]

I would check for a misformed rocker, short valve stem, or shoddy port work on the head itself. It sounds to me like the air flow on #4 isn't up to par with the rest of the cylinders.

Just my .02, good luck with that.

Yea, you might have reached the limits of how well it will equally distribute air to the cylinders. #4 being closest to the TB by design on a stock mani usually results in that cylinder getting the least air (that's why EGT probes are usually on #1 because it gets teh most/runs leanest). But being an aftermarket intake you think they'd designed it better than that (but who knows??)

Are you pikcing up any misfires under the higher boost?

If you are in sequential mode you may check to see that the trims on the injectors are equal ( i think the AEM has that feature). Also might want to log the duty cycle of all 4 cylinders/injectors... i know you can, i just forget how...the AEM log software has always given me fits at getting teh data i want, halt teh time i get a blank log with only RPM in it

 

[scottsee]

I don't mean to under play the issue here, but runner # 4 on the intake is going to run leaner then any of the others becasue of flow design. Even on a SMIM the hardest part of the design is trying to eliminate extra lean situations in upper rpm bands.

 

[ilikespeeding]

Injector seal maybe?

 

[diambo4life]

Did you attempt to switch the coil/plug wire around to completely isolate the ignition being the problem?

 

[ilikespeeding]

not to get off subject, but you have 500 whp and you run 12s? WTF?