So we’re working on my daughters car (Lightning), 1993 Z28 A4 3.23 gears, 134k mi. We have 2 issues with the car.

The only modification the car has is the catalytic converter was deleted.

The entire cooling system has been replaced except for the heater core.

The whole suspension has been replaced shocks, spring, control arms, tie rods, etc. front and rear.



First issue is the low speed cooling fan (driver side fan) doesn’t come on automatically. If the car idles longer than 5 min temps climb quick and just before it gets in the red the high speed fan (passenger side fan) kicks on. Both fans work and I have replaced the ect sensor in the pump. If the A/C is on both fans come on and the temp stays in the normal range. I put in a switch to turn them on manually for drive thru’s and extended idling.

I installed the switch by splitting one wire at pump temp sensor, so the switch is constantly on completing the circuit, when the switch is off it’s like disconnecting the temp sensor and kicks on both fans for extra cooling.

the second issue is that the car runs perfectly fine for 30-45 min then starts to run like it’s out of gas for 1-2 minutes. If I pump the throttle I can catch it but sometimes it dies out. It’ll start back up and run like crap. I’ll keep it running with the gas pedal then it smooths out and runs fine. And does it all over again.

I ran my fuel pressure gauge to it pressure jumps to 45 psi at key on and holds 40-45 psi depending on throttle position while engine running. I drove around with the gauge connected and pressure is stable when it starts to stall.

This car has come a long way and we’ve worked on it together. Any help is greatly appreciated, thank you.

 

Problem 1: You check the fan relays to ensure they're good?

Problem 2: Could be the beginnings of an opti issue. Possible the rotor screws in the opti are backing out causing odd behavior.

 

yes both relays are working and when temp sensor is disconnected both fans kick on.

That’s what I was thinking. I replaced the icm with a AC Delco and it didn’t help.

 

Issue #2] Is the MAP sensor connection snug? When it starts acting up does the tachometer jump around?

 

I definitely would not have a switch on the temp sensor feed to the computer. The 93 especially is sensitive to getting correct temp readings because 93s run in speed density mode. You can find a correct way to wire a fan switch on my website. http://shbox.com/1/fan_sw_diagram1.jpg

You need to use a scanner and monitor when the primary fan is commanded on, then check that the ground signal is getting to the relay.

http://shbox.com/1/4th_gen_tech2.html#cooling

 

I’ll check the map sensor and keep an eye on the tach.

Thank you for the information. I will delete the switch later today. What scanner would you recommend that would give that data? I have an innova that does obd1 but only gives dtc.


Thank you all.