lean running condition

[MaxEnergy]

I've been fighting a missfire above 6500 to redline. The car almost cooked itself at the pig roast (appropriate name of our New England July NHIS event). I had no idea just how lean it was running until I spent the last 4 days at the Dyno trying to trouble shoot the problem. Above 6500 the car missfires and the air/fuel ratios go through the roof running in the 14-16% range with the header glowing not red but white hot almost before I can get off the gas. I have replaced the fuel pump, filter, changed the injectors (primary and secondary) with ones just back from cleaning and blueprinting, turned up and turned down the fuel pressure, changed the fuel rail, bypassed the adjustable fuel regulator(and returned to the stock one). I even ran turbo injectors (I know they are not legal but I was trying to get it to rich). I've made 1 change at a time between each dyno run and all the runs are too lean just to varying degrees. I checked for pinched or crushed lines from the tank. Unless someone has a better idea I'll verify that no injector wires are broken on the harness (maybe all this time it is only running on 3 injectors? The front header pipe does seem to glow even whiter) I'll change the MAF and even the ECU. I am seriously frustrated not to mention the hundreds of $$ on dyno runs.
I think my timing is right, at idle leading is at 5 deg after TDC and at full advance around 4000rpm is 25 deg before TDC. Any suggestions are greatly appreciated.

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Jamie Kekeisen
86 ITS RX-7 NER
92 325IS under construction

[MaxEnergy]

PS the car is an 86 rx7 with 89 motor internals ie 86-88 ECU, AFM, tps and injectors. 89 intake manifold, rotors, flywheel and conterweight.

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Jamie Kekeisen
86 ITS RX-7 NER
92 325IS under construction

[benracin]

I have an 83 rx7, so I know our engines and most other things are different, but I've been having a very similar problem. I have some crazy rich jets on now and the EGT's are still above 1700. I'm guessing that it's not really a fuel issue, but maybe it's an air leak. I think air might be getting into the mix somewhere making it lean. I don't know if your second gen has tons of crazy vacuum holes to plug but my engine does and I'm guessing the problem is around there.

[paulydee]

I experienced a similar misfire situation on my `91 but at 7500 and above. It was most prominent when the car would get dyno'd. I sent the ECU out to have the rev limiter removed and problem solved. It seems that the factory ECU cuts fuel above a certain RPM but below actual redline.

When you said larger secondaries didn't help, it leads me to believe they were being shutoff (cutoff), so regardless of injector size they are not operating.

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Paul D'Angelo
73 ITS CENDIV
Indy Region
http://www.iridiumracing.com
http://www.iridiumracing.com/headernew.jpg

[MaxEnergy]

My ecu has been modified to remove the limiter and the same ecu powered the car before I had to replace the engine due to a rotor bearing.

I suspect my secondaries are not firing I can clearly hear the primaries with a stethescope but am not sure about the secondaries as the car is very loud above 3500 when the secondaries would start firing.

Does anyone know how to test if the secondaries are getting activated?

How high could you run the car on primaries only ie when I run it on the dyno and the air/fuel goes way lean at 6400 is that about what the primaries can do by themselves?

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Jamie Kekeisen
86 ITS RX-7 NER
92 325IS under construction

[MaxEnergy]

I was thinking of installing an EGT to be able to help monitor the lean condition. Does anyone have a suggestion as to location for the sender. I have a standard 2 into 1 header. Either I monitor only 1 exhaust or I have to have 2 egts. I don't think it makes sense to have it further down the exhaust where they come together, that wouldn't be accurate temps correct. How far should I mount it from the outlet of the engine and what range of gauge should I get? Thanks

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Jamie Kekeisen
86 ITS RX-7 NER
92 325IS under construction

[BrianB]

Jamie,
If you're still having problems,give me a call during the day 413 374-1136.
Brian
#70 ITS RX-7

[MaxEnergy]

I am, will do, thanks.