A serious problem

[8upZR1]

I have a serious problem with my 90. People who have read this forum know how F'd my car is. If anyone has any ideas I would love for you to share them with me. The car starts, but does not idle. If you just hold the rpms above 1000 it runs roughly. Throttle response is absolutely miserable. As I accelerate from a stop the car has not enough torque to get going. I have to stab at the clutch a little to get the car moving. Once moving it feels alright from 1500 rpm till about 2200 rpm. Then it feels like it has hit a brick wall, I press the throttle all the way down at this point and the car slowly accelerates with much effort. Once I hit about 3000 rpm the car comes alive and runs smoothly, throttle response is great, and the acceleration is excellent, but then at around 5,000 rpm the party is over, and by 5500 rpm the motor feels like I have hit a 2 step rev limit. I get deeper into the gas and the motor just starts popping and wont go past 5500 rpm.

I have no fault codes, everything looks good. Most sensors and components dealing with engine/injection have been recently replaced. I have been swapping between factory and haibec chips. Not that much difference. One notable thing was that the factory chip would sometimes let the car idle with the A/C off at 900 rpm, very steady. Then I would turn on the A/C and the rpms would crash.

When I first got the car I remember that it would run like total crap, just like it does now, but only very intermittently. Maybe once every couple of days for a few minutes. Back then I noticed that it seemed to never do it when the car was hot but it would do it when cold. Now it is just constant. Turning the full engine power key off makes no difference.

For a while I had a short runner intake on the car and I thought that was contributing to the torque/throttle response problem so I swapped to a factory unit. It helped a tiny bit but while I could feel some improvement I could also feel this underlying problem.

Today I was playiong with the car and at one point I hopped in and started the car and it felt awesome. I pulled it out of the driveway and it felt great, but then I noticed the SES light was blinking at me. I then realized I still had the pins connected on the ALDL to get the trouble codes. I didn't know if driving the car with the pins jumped was bad so I pulled the paper clip and it ran like crap again. Can I drive the car with the pins jumped? Can I hurt something by doing this? If anyone has suggestions I would be greatful.

[Belsy]

Try basics to see: pull & clean IAC, I use ethyr which drys fast and blows hard. Clean throttle plates, run w/ no filter briefly, may be starving for air?? Could Cats be clogged?? Could there be an exhaust restriction?? Vacuum hoses OK?? All hoses on?? These thing usually won't throw codes!! Good luck=D>

[8upZR1]

No cats, filters good, cleaned the IAC yesterday. ?????? is all I can do.

[Jagdpanzer]

How does the fuel rail pressure look during all this?

[A26B]

I'm a little confused with the "short runner intake." What exactly is that?

Your problem, being intermittent and worsening, sounds to me like an electrical issue. Loose connection, bad ground(s) or open/short in the harness. Part of it sound like it's restricted to closed loop except that once you reach 5000rpm it craps out again. If it were O2 sensors, you should have a code, same as with any other sensor.

I'm leaning towards a bent pin on the ignition module (easy to do) or bad ground(s). If you could data log, you might be able to chase it down.

If you have acess to another known good ECM, I would suggest trying that too.

[8upZR1]

The fuel pressure is constant at around 40 psi and then when I give it throttle it goes up to the 50's maybe low 60's. At WOT with the haibec chip my A/F meter says rich, with the GM chip it is closer to stoich, but still on the rich side. The problem is no longer intermittent, now it is a full time affair. I have tried swapping ecu's, no luck. I was thinking that maybe it is the wiring harness or a pin connection. As of yet I have found none. In the past I have looked at the igntion module to ECU connection but everything looks good and all wires are sending good signals as far as I can tell. I plan on checking this connection carefully tomorrow. Maybe I will find something.

[8upZR1]

The short runner intake was made for me by a friend of mine. It uses a factory plenum and the runner sections are cut away from either side. Then new flanges were cut from 1.5'' aluminum on a water jet and given proper 3/4'' radius inlets. These were then port matched to the injector housings. The roof of the factory plenum was extended outward a few inches beyond the injector housings. Then a new floor was made and it was all welded up with stand pipes in place where the bolt holes need to be. The new plenum covers most of the coolant lines on the side of the motor. This intake is fairly radical for a street ZR1 with 350CID. Maybe when I go to the strip one day I will put it back on. It would probably do wonders for a 415. The runner length of the plenum becomes a straight 1.5'' with no turns and the plenum volume nearly doubles. If anyoine is interested maybe something could be arranged. I have some pics of pre assembled parts. Once I get my camera back I will take some pics of the final intake and post them. One bad thing though is that a factory intake is required for butchery. Or perhaps a 2nd gen model could have a fabricated plenum. Who Knows.

[A26B]

I would like to see some pictures. SOunds really interesting...

[guinnessdood]

Sounds a whole lot like a DIS module problem. Swap in a spare if you have one...if not...Marc Haibeck can loan you one.

[tomtom72]

I'm just a hack but I think if you can drive the car with a scanner plugged into the data port....what's the difference if just the pins are jumped?...I would think to the EEC system there is no difference. How would the system know if a scanner was attached or if the pins were just jumped?

JMHO
Tom