Any of you guys having this problem? I have a TPIS MiniRam intake with a Gen 6 DFI. Car was tuned with a wideband O2 and its right on the money, but the further away I go from the TB the fatter the plugs are reading, cylinders 1-4 are reading really clean, 5 & 6 are alittle rich and number 8 cyl the worst. Is it maybe the way the intake is designed? Has anyone come across this problem? I’ve heard about accels variable injector controller, but I don’t think they make them anymore, I feel that would fix my problem. Is there something I can do to adjust my injectors individually? Resisters or something like that in the DIY section?
Thanks
Tony

 

Tony - If it makes you feel any better I have the exact problem. This is typical of a MiniRam intake. The VIC is the answer for a Gen 6 but a sequential system is the answer. I'm pretty sure this is an issue at idle and very light throttle. I'm going to try running a hotter plug in cylinders 7 and 8.

 

It's a known problem that's due to the design of the idle air routing. Or lack of it in a MR. And the plenum design.

Note-BLM is basically a fuel trim.
>128 means adding fuel & < 128 means removing fuel.
128 = approximately 14.7 afr as seen by the NB o2 sensor.

https://www.thirdgen.org/forums/diy-...plit-blms.html
https://www.thirdgen.org/forums/diy-...ram-split.html

 

Thanks for the reply, I was thinking that the intake design might be part of it, especially the back two runners that are up against the back wall. Funny you should mention the hotter plugs, I just did that on Monday, I’m running AC/Delco FR3LS plugs gapped at .045, since the worst cylinder was #8, I switched that one with a FR5LS plug gapped the same. I’ll pull the plug out tomorrow and see if there is a difference.
I’ve been driving the car lately a lot, back and forth to work, around town mostly, idling it around in traffic not really getting it over 40mph. Probably not the best thing to be doing with the car since its kinda on the wild side, a pretty healthy solid roller cam & 12.8:1 compression, that’s also why I went with the colder plugs.

Z69...
Hmm, after reading all those posts,,,I now understand whats going on! Makes a lot of sense! I can relate to the LT1 intake with the air passages and where they enter into each runner.
I guess now after reading up on it, the VIC will not correct the problem, it seems however, depending on your application it could be an issue or not with the plugs sooting up, as long as your cruising up above 2000rpm. My setup, since my car is really a street racer, as long as I’m not doing a lot of traffic driving I’ll be ok, I was trying to keep my plugs looking perfect, oh well.
My thoughts about mod’ing a carb intake with injector bungs and a TB elbow like a super vic jr or strip dom intake will most likely have the same issue, but I am curious about what difference in power they will make.
Thanks for the posts!!

 

Since the split blm s are occurring with the mini ram would it be fair to assume that it would occur with the lt1 manifold? Or is this a design flaw in the miniram since the ports are larger vs the lt1??

Rabi C.

 

It'll occur with the LT1 manifold if your throttle body bypasses the IAC port in the throttle body flange. It's an inherent characteristic of the log style plenums. Only, GM had the wherewithal to fix it by adding the IAC port and TPIS doesn't.

I had to essentially duplicate what GM did, but externally rather than cast into the manifold, in order to defeat the problem. My split BLMs are completely gone.

 

Don't mean to hijak your thread krazedz,

but ULTM8Z,

Just a quick lesson for me ... is the reason why the iac fixes this problem is because as the incoming air passes over the coolant flow it warms the air and inherently the warm air rises and is capable of making it to the rear. With cold air it drops and has a tendency to get sucked into the 1-4 cylinders at a greater rate and the available air is exponentially less the further back you go to 5-6-7-8 the cylinders?

Sorry I just wanted to make sure I had the right thought process.

Thanks again,

Rabi C.

 

Actually, the temperature of the air doesn't really play into it. Rather what's happening is that (if the IAC passages are bypassed) the air enters the main plenum and is basically hogged by the front cylinders. On a batch fire system where the same amount of fuel is distributed to each cylinder, the front cylinders can get lean whereas the rears get rich.

The way the IAC passages help is to distribute idle air equally to each cylinder. Rather than have all the cylinders battle it out for their share of the air, with the IAC passages each cylinder has an equal shot at getting the correct amount of air.

 

Thanks ULTM8Z,

I found your post where you plumed in those air passages a while back. Seems like this concept is efficient at distributing air evenly. I will have to consider this for my mini. Great work and thanks again for your explanation.


Rabi C.

Ps you wouldnt happen to have a working link to that post?

 

https://www.thirdgen.org/forums/diy-...ram-split.html

This one should work...

 

Ulitmate - Do you think you would get the same result by tapping into the bottom of the plenum (not individual runners) installing a plug and run a line to the side of the throttle body? See pic of my motor here.www.geocities.com/dzperf It's the yellow plug on the side of the throttle body.

 

I think this is a problem with all log plenums. If you run a cam sensor and go full sequential, some controllers (like the FAST XFI) can give you individual fuel trim so customize the fuel delivery for each cylinder: i.e. lean up the rear cylinders and fatten the fronts for optimum burn.

I'm nowhere close to getting to that state of tune yet where I can take advantage of that, yet though. What about you guys?

 

I'm doubtful that anything short of individual runner porting will cut it. Though, you could give it a shot and see...