I installed a 93 LT1 motor in a 62 Pickup. I had a stand alone wire harness built for a 95 because I was told by the seller of the engine it was1 95. The harness has a couple of extra connectors the engine doesn't have. A computer was also re configured. The enfine starts and runs but there are two problems so far. The fans don't come on and the Idle is about 1500 rpm when the idle air control is plugged in.
How do I fix these problems?

Thanks in advance for your help, Jerry

 

well, this is gonna be complicated IMO...

first, you somehow need to verify that the harness you have is the correct harness for that ecm, engine and its sensor group.

Its ALL about the data...if the ecm is getting bad data its going to provide poor performance.

Fans: you DO know that the fans are programmed for around 228 degrees, right? they do not come on prior to that in the stock "tune". The engine depends on vehicle motion to catch fresh cooling air. The fans are really designed for stop n go traffic and a/c use.

you should then get it on a scanner and see what the ECM is seeing and then you can ID the source of the hi-idle and other issues. Do you have the fan relays? are there ANY relays missing from the system? is the a/c hookled up? the fans are part of the a/c system...perhaps thats the break in the fan thats keeping them from running.

This is why its ALWAYS good policy to take the harness and complete system from the donor vehicle. Then you know its right.

 

The Ac is not hooked up, I have the compressor and the condenser? (in front of the radiator) I had Speed Scene Wiring out of Texas build the harness and the ecm. the fans have relays. The idle is normal until I connect the power to the idle air control.

 

The AC is not hooked up yet. The fans have relays. The idle is normal until I connect the plug to the idle air control and the rpms jump to about 1500

 

The fan realys are run by the ECM It grounds one wire at each relay. Look up a pin out for your 93 ECM and make sure the wires are hooked up to the fan relays. Once you find what wires are the"trigger" wires you can ground them out to test the fan circuit. I wish I could help more but I do not have the 93 wiring schematic.

 

So what year computer are you using?
'93 or '95?

 

The ECM uses the CTS (Coolant Temperature Sensor) to determine when to turn on the fans. It sounds like yours is not connected. I believe it's mounted in the thermostat housing for your year engine.

If the ECM thinks the engine is cold it will raise the idle speed to compensate. If the CTS circuit is open the ECM will think the coolant is around -40°.

From these symptoms it's pretty obvious that there is a problem with the CTS or its connection to the ECM.

 

problem with this is that even with a FSM drawing, that is useless since this is a "custom" harness...
The basics are likely there but are the circuits that link things like the a/c high pressure switch to the harness for the ecm to see, or the CTS wired in properly.
If that a/c switch (plug-in) is present, you can jump that switch and it should turn the fans on within seconds regardless of engine temp.

Finding the grounds for the fans relays and sensors is the place to start for testing to see if the fans even work, but do keep in mind that under normal circumstances, its gonna be close to 230 before they will try to come on UNLESS the a/c high pressure switch is closed and that grounded circuit tells the fan relay to operate...

I'd do link Ch@os says....find those grounds at the relay plug ins and test the circuit. Hopefully the mfg of this harness stayed with the color codes...if so, look for a solid green wire. Sometimes green with a wht or yllw stripe.

Just out of curiousity, what did you do for harness grounding? On the C4 that harness would have about 12 wires that ground on frame or chassis bolts, even engine & trans bolts. Some are absolutely CRITICAL...especially the bunch behind the driver side cyl head...make sure those are WELL attached to a good ground...or nothing will work right. The grounds are how the ECM operates every servo and system and control under the hood. Everything. Most things have their hot wire ON all the time. The ground is the secret. like injectors...hot all the time. They cycle when the ground is alternated.

 

I don't know, the plugs are long not square. It is not the one that came with the engine. Speed Scene said he could not use the one that came with the engine with square plugs.

 

How do I test the CTS? It is hooked up.

 

I have bypassed the system and both fans run on high.

 

The new harness came with a ground wire which I connected to the transmission.

 

If you bypasses the system by grounding the trigger wires the the fan circuit is fine. You are not gettin a signal from the ECM to actuate the releys. Its time to call the guy who sold you the computer and harnes and ask him how those fans should work. there are no part #s on the ECM? With that I could help more.

Come to think of it this may work for you.

http://www.ecklerscorvette.com/corve...1984-1995.html

 

I jumped the red power wire on one relay to the small trigger wire to make both fans run on high. When I unplugged the temp sensor the engine stalled, I tried this twice and it stalled both times, Is this normal?

 

IDK what you jumped because the trigger wires are grounds. You need the pin out of your ECM and the wiring schematic fro the harness.

 

You need to get a laptop and datalog to see whats going on.

 

Do you have an ALDL connector? If so, the fans should run when you jumper pins A & B together. That's done through the ECM, so it tells you a lot about whether the problem is between the CTS and the ECM or between the ECM and the fan relays.

 

So you have the 94/95 PCM ; most commonly GM # 16188051

The PCM connector pin outs can be seen here
http://www.lt1swap.com/lt1_pcm_pinout.htm
Your custom harness should not have the wires hi-lighted in yellow

92/93
Absolutely no support for that LT1 ECM

 

I am not familiar with all the initials that every one uses. Is there a web page that explains all these? I am not a mechanic, I am a retired builder so these terms are new to me. Thanks for all your input. I did have a local GM tech come over with his computer but he couldn't seem to read anything. What is a ALDL connector? Thanks again for all your help. This project has been going on for about three years now. I am home only half a year at a time so it takes me a while to pick up where I left off.

 

Thanks for the info, I will go thru it.