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Discussion Starter #1
For starters I'll let you guys now what my set-up is on my formerly NA '89 900 sport:

-LH 2.2 ECU from '86 900 turbo
-stock turbo injectors with 3.0 bar FPR
-NGK BCP 7ES plugs
-water/alcohol injection
-9000 FMIC
-Forge Motorsport BOV
-EZK ignition
-turbosmart MBC

I'm currently running about 10-12 psi boost with no knock, according to my knock LED.

A week ago I lost my automatic idle control, and the car would idle extremely low, about 250-500 rpm when warm. When it was cold I had to give it gas to keep it running. My AIC valve was not buzzing at all. There was voltage to the centre pin, but the ECU was not sending any output signals to control the opening and closing of the valve. Luckily I had a spare matching ECU, so I put it in and I had proper idle control again.

Now a new problem has risen with this new ECU. When I stomp on the throttle hard and boost rises quickly and hits about 12 psi, I get what almost feels like a fuel cut-out. Now remember my car was NA, so there is no fuel pump over-boost pressure switch. As far as I know, the LH 2.2 AMM's don't cut the fuel, like the LH 2.4 ECU's, when the motor is flowing more air than the AMM is capable of. It just feels like the fuel is cut for a split-second when this happens. It happens so fast I can't even glance at my air fuel ratio gauge to see if it is leaning out.

Any ideas of what this might be? This never happened with my previous LH 2.2 ECU, so could this new ECU be faulty?

Any advice would be great. Thanks!!
 

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could be entirely wrong here, but, maybe the problem is not the ECU but that your car is missing. might have something to do with the ignition system. just a thought

sam-
 

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Discussion Starter #3
I thought the same thing, so I pulled the plugs and put in a different set gapped to .024" and the problem still happens. This problem does not occur consistenly. Sometimes I can drive it hard and it won't stumble and other times it does. I've had a similar problem with plugs before, but when it's plugs it's a missfire that comes in softer and lasts for as long as I'm on the throttle and boost hard. I cured that problem by putting a different set of plugs in. This hestitation feels like a sudden lack of fuel or spark, that lasts only for a second. I'm leaning toward the fuel computer because this started to happen right after I swapped ECU's.

Thanks for the input!!
 

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Discussion Starter #5
Well, the wires are fairly new Niehoff silicon wires, so that shouldn't be the problem. I have had this problem before from a bad wire though. As soon as boost came on it missfired bad, and that's when I went to these Niehoff's, which cured the problem.

I'm stumped, it only happens intermintently, not at a certain engine load. I was out driving recently and it happened just cruising through town at light load. Maybe my cap and rotor are bad? I know they're old, so I'll probably replace them.

This weekend I'll try changing plug wires and swapping back to my previous ECU, eventhough it has no idle control, to see what happens.
 

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Good idea, just remember to only swap one part at a time, to make sure you find the problem...

Daniel
 
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