I just wanted to say thanks for all the information on the board regarding tuning. I got a TON of information just lurking here, but now I am at wits end.
I'm having some trouble getting my EFI tuned. This is a 1990 Corvette.

The motor is a 427, built by Musi, specs are:

242/246 cam with 112 LSA set at 108* 66* of over lap
1.6 Comp Pro Mag bring the lift to .605
Dart Pro1 215CC heads with a clean up port
TPIS Miniram intake
1 3/4 long tube headers

The issue is that I was getting an AFR off a wideband on the passenger side which was reading lean between 2400-2800 RPMs. The ECU was trying to pull fuel out as I was gettting a lean reaing from the wideband. It made no sense.

So I decided to put it on a dyno. Put in new widebands, and try it again. Following are the results.

Why the difference between AFR on both sides?

Weak injector? Air leak? Plugs? Valve adjustment?

Anyone have any ideas? Why the difference between cyl banks?
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I went to TTP performance, worked with Matt and his guys, they were fantastic.

Here's some of the results. The RED LED AFR meter is on the passenger side, the one on the dyno screen is on the drivers side. To recap, the wideband I was using was on the passenger side, and it was reading lean. Yet the ECU was trying to pull fuel out.

You can see the passenger side is lean, and after we hit 4500 RMPs, it goes very rich. down to 10.0, which is as low as the meters will read.

Following is some pictures of the two side by side.

 

 

one way to see if it the injoctor is to swap sides, put the ones on the left on the right and see id the afr follows. Never had 2 wide bans on the same car before. that may be a good idea to check into. Who is to say my car is not the same way and I just don't know it.

Good luck finding the problem, and please keep us posted.

 

Wow, that is a really nice motor combination you have there!

A few questions here. Where is the NB sensor located?

Are you running true dual exhaust?

What side does the fuel enter the rails? driver or pass

What type of ecm are you using? Is it batch fire or sequential?

What fuel pressure?

First guess is a bad injector, but weird that it only happens at part throttle. Measure the resistance across all the injectors, one by one. It would be good to see the fuel pressure throughout the rpm range.

 

Yes, please keep us posted

 

Very good suggestions thus far, but I'm going to add one to the list

swap the sensors first and see where the trend goes

good luck with it

-jason

 

I guess it could be a bad injector that for some reason don't open and then when the voltage reaches a certain level pops open too far.

Have you pulled the plugs in that side? That should at least tell you which cylinder/s it is.

 

That is on my list of things to do today. I was in an accident and I'm working with 1.5 hands at the moment, everything takes me longer than I expected.
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Thanks, here it is going in:
In the collector of the header

Here's the exhuast, the cats are since gone. 3 inch pipes off the header:


Passenger side. I am using a Miniram and TPIS fuel rails.

Stock ECU, so batch fire.

55lbs

The injectors are new and flow matched. I have checked the pressure through the range, looks OK, but I'll do it again.
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Yep, that too is on my list of things to try. Thanks.

 

Glad you asked:

I'm thinking of going to a cooler plug, they look a little hot. These are -5 NGKs, think I'll go to -9 see how that works out.

I pulled the plugs, here's what I found, they all look about the same:

 

 

The lean side is misfiring, almost certainly. Now you need to do the detective work... Cap? wires? plugs? injectors? valve adjustment?

Edit - seeing plugs - look at the porcelain where the boot connects (not combustion side). Seems shady, got any side pics? On new plugs that are misfiring, I can often see carbon tracing along the side in that region. Wires can be checked in the dark dark dark, and look for light, aside from replace and check, and move around and check, and looking for melted sections. Injectors - one by one - disconnect, and watch the widebands - that can help find the right hole, but doesn't necessarily mean it's the injectors fault. Valve adjustment is very unlikely, but it can cause strange things when the valves can't close.

 

Cap, rotor, plugs, wires all new. I used some Accel crap and the car would barely run, I replaced it all. Wires are custom cut Taylor I made up myself. I have wire looms and AT LEAST an inch between the wires and any grounding surface for the most part.

What's the odds it's the module? This is HEI with the coil on the cap.

I can get you some pics of the porcelain, but they all look the same, new and clean.

 

Maybe try leaning it all out a bit, without applying load (take out 20%, maybe just add 20% to the value for injector flow rate), in open loop. See if it gets terrible, or perks up. 10:1 is ~47% too much at part throttle...

Also, no matter what - do the injector disconnect test. It's one of my favorite methods for pinpointing almost any problem (on 4 cylinders at least, 8 makes it a little harder to "see" the smaller differences).

 

Sorry, the 10.0 AFR was at WOT. The rest were under light load.

This is a light load condition.

 

Out of curiosity, what did you replace the ignition parts with exactly?
Dist, coil, MSD ?

 

Sounds like an air distribution problem at lower speeds.
Try reducing the TB opening to make the IAC work more or do the opposite.
Another member did abunch of testing with a SR and found his difference was mainly due to air flow at low speeds. Easy enough to adjust and see the results.
10:1 is just rich, Are the upper VE's good when not in PE?
What ECM, bin and tuning stuff are you using?

 

Standard Brand Cap and rotor, Taylor Wires, and NGK Plugs.
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It's a Mini Ram, not a Super Ram. I have to work on the tune under WOT when it goes to 10.0. That's easy enough.

My problem is at partial throttle, light load, at 2400ish RPMs, and shows up a little again at about 3700RPMs also under light load.

I am using Tuner Cat and an Ostrich.

 

I just checked all the valve adjustments on the passenger side, looks good. I'm going to switch the injectors over, see if that helps.

 

So your ECU is running closed loop using a narrow band O2 in the exhaust as well?

Have you eliminated the possibility of an exhaust leak?

 

i've seen a few thread about this over the years... never seen anyone figure it out.


good luck.

there was a guy on the innovate site with a 3rd gen that had this issue too. there's the link if you want to search for it. i don't believe he fixed it thou.

http://www.innovatemotorsports.com/forums/index.php

 

Yes and yes. I have four O2 bungs. Two in the collectors, and two I just put in for testing just slightly behind the collector.

 

So today, I checked the valve adjustment on the passenger side, looked good. No adjustments made. I also swapped the injectors from left to right.

Tomorrow I have to pick up new plugs, a few heat ranges cooler, and I'll put in the new plugs and fire it up to see what happens.

 

Minirams have been quite notorious for the split in AFR left to right at light load. All sorts of things were blamed, and messing with the IAC steps and throttle openings (min air setting) seemed to help most.
I don't know the true cause or best fix. I can imagine a few things, like fuel rail design causing strange things (crossover diameter, material stiffness, exit location).
Also, just for sanity's sake, make sure your exhaust has no leaks within several feet of the O2's. Block all things going into the intake (breathers, brake port, etc...).
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And check the intake gaskets - some have found the intake doesn't seat to the heads well at all, some blaming decked blocks, some blame the intake being machined completely wrong.

 

Great. I called TPIS this morning, and as you can expect they never heard of such thing. My block is brand new Dart SHP 400 block. I had the miniram gasket matched to the 1206 and it was put together by Musi. He checked when he did it, as I told him there were some gasket fitment issues.

 

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

 

That is so cool. What exacltly was the problem? I know you said IAC, but how was it effecting the motor at 2400? Was your problem at idle or at light idle?