1979-1993 & 94 Conv [Subscribe to Daily Digest] |
If you hit the overboost cut off, you will experience a dramatic and sudden drop in power caused by the fuel pump shutting off. aka face in windshield.
Depending on year, this is triggered by a simple pressure switch under the driver's side dash or by the ECU. If you have an earlier LH 2.2 ECU, you have the switch that can be bypassed or adjusted. The later LH 2.4 ECU's shut the fuel pump when the Air Mass Meter senses too much air and sends a signal to ECU. Only fix here is to go to a chipped ECU or install 30lb injectors and put a resistor into the orange AMM wire to trick the computer.
Regardless, your description sounds more like normal knock sensor intrusion. Insufficient fuel octane, too warm a fuel charge, advanced timing, and lean mixture can all cause the knock sensor to cut boost momentarily. The turbo then spools up again.
Just for kicks, throw a bottle of octane boost in and see if you get more boost before.
If that works and you want to reduce knock sensor intrusion without having to use booster, you should first set your base boost, do a basic tune up and inspect that no one has disabled the pressure transducer under the dash, by pulling the hose off and plugging it(unlikely). There is a good saabnet bb faq on setting base boost. All you need is a cheap calibrated boost gauge, a vacuum tee and some hose so that you can have the gauge in your cabin when test driving.
There is also a chance that the stutter is caused by plug gaps that are too wide, incorrect plugs, a bad distributor rotor, bad distributor vacuum/pressure module or incorrect timing.
Plugs should be NGK bcpo7es or 7ev and the gap should be 0.024".
OEM rotor is also important since there should be 1000 ohms restance between the rotor tip and center contact. El cheapo rotors typically have zero ohms resistance between tip and rotor...not good for high boost.
Distributor timing module should hold vacuum when you suck on its hose. Timing should be 16 degrees BTDC. If you can't get good fuel, you can retard timing to 15 or so, but off boost performance suffers very slightly.
All sorts of tweaking for the APC box is possible and may have been done to your car, explaining mid red boost. Engine can safely take 2x OEM boost but trans pinion bearings can't take the high torque, so max boost must be used judiciously.
posted by 208.208.152...
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