*********
Well we didn't really get anywhere on the fan issue today, just ran out of time. Got the tie rods changed pretty easily though, so got her aligned. The car is off to my body guy about 2 hours away tomorrow, gone for 3 weeks, and when it comes back will be black instead of white and have a fiberglass ram air hood

One question I did have is this: when you short the diagnostic connector to put the engine into diagnostic mode & the fans turn on, does the diagnostic port turn the fans on directly, or does it go through the computer? Basically we're trying to isolate if the computer isn't getting a signal out to the fan. The way I see it, if the diagnostic connector signals the computer to turn the fans on, we know the computer and all of the connections to/from the fans work. But then WTF doesn't it work?
*********

So we bought a 92 RS B4C (police package) which was supposed to have the L98 & 700R4. The car had overheating, temp gauge, and stalling issues which we figured were related to a huge wiring mess in the engine bay.

My mechanic got most of that sorted out; a lot of that wiring was to hook up the AC fan directly to the battery, some flashers on the headlights, and other stupid stuff. We replaced the cooling fan switch and temperature sending unit. Now the temp gauge reads properly (before it would swing temperatures very quickly) and we've verified the fans work by hooking power directly to them.

The big problem we have left is this: the coolant temperature sensor that reports to the computer. All the information we found says the coolant temp sensor is at the back of the motor, but there is nothing back there. After much searching, we found the sensor at the front of the motor, just below the TB I believe. The other really weird thing is there is another coolant sensor just hanging there at the back of the engine, attached to a two-wire connector that goes back into the main wiring harness. No clue why that is there at the rear, or why there isn't a sensor at the rear at all.

Why is this a problem you ask? Well there was another wire going from the main wiring harness and it was grounded to the chassis. While looking for the fan switch and other goodies, we pulled this wire and found out there were some diodes (resistors) wired in series into that wire between the harness & the ground. As soon as we pulled that wire, a CEL popped up. Pulled the codes and it was for the coolant temp sensor. So it appears whoever had this car before, wired up those diodes to prevent the CEL from tripping.

My mechanic also noticed that the engine has definitely been pulled out of the car and rebuilt. It has been to a machine shop and everything, so we don't know if this is even a 92 L98 that was supposed to come in the 92 RS B4C's. The heads appear to be steel, not aluminum, so that lends to the fact that they rebuilt this engine with non-92 parts. What's the best way to tell what kind of engine this really is? Any engine ID numbers on the bottom of the engine we can find or anything?

Any thoughts on this diode preventing a CEL from tripping about the coolant temp sensor? Why is the coolant temp sensor on the front and not on the rear? Does this indicate a particular year engine or model?

Another interesting fact is this: there is no AIR equipment in the engine bay, but the factory dual cats still have AIR tubes going to them. So whoever rebuilt this engine pulled the AIR equipment and I guess just welded the holes in the cats. The manifolds are factory, but with no AIR tubes that have been welded or anything. So they replaced the manifolds with stock manifolds sans AIR, where could they have gotten those from? I thought all 3rd gen f-body's had AIR.

And the last odd fact: there are two extra sensor connectors tied off just sitting on some of the AC tubing I believe. They would probably go to sensors on the engine itself, as the wires lay down flat and don't stick straight out the back of the connector. Also, the two sensors are connected very close to eachother, probly less than 1" of wire between the two; so whatever they are for, the two sensors would've had to have been right next to eachother we figure. Does that help figure things out any? See attachment for a picture of these random plugs.

OK one more weird thing. We can't get the cooling fans to turn on when they are supposed to. Brand new fan switch. When we short the two upper pins of the diagnostic port to force the engine into diagnostic mode, the fans are supposed to come on. We can hear the fan relay clicking and trying send power somewhere, but it ain't getting to the fans. We've switched relays, so we're pretty sure the relay isn't bad. Could be a bad ground or other wiring issue? Thoughts on that?
Also when we force the engine into diagnostic mode, it appears the idle air control valve or something over there at the intake is constantly moving or opening/closing or something. You can hear a constant mechanical noise from the intake and feel the vibration of something moving. Is that supposed to happen?

I would appreciate any and all help you guys have to give with this. We just need to get this coolant temp sensor sorted out and the car's mechanical issues should be fixed!

 

See why I said to find a car that hadn't been fooled with?

First off, find a new mechanic. Your's doesn't seem to know what he/she is doing and you've got a lot of work ahead of you.

Second, skip mechanics altogether and start getting up close and personal with your new project vehical. First and foremost, get on EBAY and get yourself a 1992 Camaro service manual.
eBay Motors: 1992 Camaro Passenger Side door mirror, manual, Red (item 120033083381 end time Sep-24-06 12:01:56 PDT)
eBay Motors: 1992 CHEVY CAMARO Z-28 IROC SERVICE SHOP REPAIR MANUAL (item 280029475002 end time Sep-24-06 16:42:45 PDT)
eBay Motors: 1992 Chevrolet Camaro factory Service manual repair (item 260033288736 end time Sep-26-06 10:45:45 PDT)
eBay Motors: 1992 Chevrolet Camaro Shop Service Repair Manual Book (item 300031117822 end time Sep-30-06 10:22:08 PDT)
There are four listed right now, a couple with buy it now. A fair price is about $30 for a used manual. Otherwise you can go to www.helminc.com and buy new, but you'll probably spend $50+. The manual is an invaluable resource and will save you a lot of time and money since you'll have wiring diagrams, diagnostic charts, etc that you are going to need.

Third, read the manual. Familarize yourself with it. Learn to use it. The layout takes some getting used to, but again once you learn to use the book it's the best tool at your disposal.

Ok, now onto your problems... The coolant temp sensor is on the front of the intake manifold baseplate, directly below the throttle body, next to the fuel lines to the plenum. The wires are yellow and black. This sensor sends the coolant temperature to the computer. Chances are it's not defective. If it were you'd be getting a code. The fans (it should have two of them being an L98) are controlled primarily by the computer. The computer determines when to switch the primary fan on/off based on the signal from the CTS. When the temp is over 220*F it comes on... You can bypass the CTS and the ECM from the circuit by grounding terminal F on the coolant fan relay while the key is in the run position. If the fan runs, then your relay, fan motor, and wiring from the relay to the fan is fine. At that point it's most likely ECM or CTS related. If not then it's possible the relay, or wiring is bad.
The secondary or aux fan is controlled by a switch in the passengers side head. When that switch is grounded the fan will come on, but the temp for that switch is higher yet at 238*F. You can bypass the switch by shorting the wire directly to ground.
You can also test the grounds for the fans by checking for resistence between the negative battery cable and the A terminal on the fan connectors, they're constantly grounded and there should be no resistence.
That should give you a few things to try and should point you in the right direction on the fans. Most likely you aren't getting the engine hot enough for the fans to come on, or the relays have failed since late style GM relays seem to go out frequently.

The second sensor at the back, is likely your IAT (intake air temp). It's used by the computer to aid in delivering the proper air/fuel ratios... It's popular to run a resistor in place of the sensor to trick the computer into an enrichment mode, however it's best to just leave it alone. In this case someone probably removed it from the bottom of the plenum to read cooler temps, or swapped to a different style sensor that reads air temps. If it is the IAT, you'll want to put it back to the stock configuration.

All Fbody L98's are iron head motors. Aluminum heads were Corvette only, from 87-up. 85 & 86 L98 Corvette motors were iron, with perimeter valve cover bolts. Whoever told you they should be aluminum is out of their element.

The best way to tell if it's a numbers matching engine would be to look behind the A/C compressor on the passengers side of the block. Directly in front of the cylinder head, on the block, there will be a couple sequences of numbers. One of these two sequences will contain a partial vin number. This partial vin number should match the last 6 digits of the vin number visible through the windshield. If they don't match, it's not the original block. If the block has been zero decked by a machine shop the numbers might be missing. It may take several squirts of carb cleaner and scrubbing with a brass or stainless steel scrub brush to bring out the numbers, they're very lightly stamped. You can check the casting numbers on the heads and the block also, but they won't tell you if the engine is the exact engine the car came with from the factory.

If your manifolds have no air tubes, and no plugs in the airtube holes, they aren't correct for the application. Earlier Chevy cars used similar style manifolds to the L98 but without the tubes. Some of those early manifolds don't have the O2 sensor boss drilled and tapped either. If the tubes and or plugs aren't there, then it's probable they aren't High Output manifolds.

The two mystery harnesses are your AIR diverter valve plugs. Basically GM used solenoids to direct airflow to either the manifolds or the cats at different times. When Roger Ramjett pulled the air he left the plugs behind to swing in the breeze. If they haven't melted to a manifold yet, consider yourself lucky.

 

Thanks for all the help! I'll update tomorrow once we take another crack at this. Should be an easy fix, from the searching I've done it does look like someone wired in a resistor to put it in enrichment mode. Might explain why this pig is sucking down gas way more than it should. The rest of the stupid electrical issues are pretty much taken care of. Then the steering box & front struts, voila she's running good again! Then off to the body shop

 

Code 14 is a CTS code. 'High temperature indicated' Basically the sensors resistence is reading low, telling the computer the car is running extremely hot. It'll only pop the code under normal functioning conditions if the temp exceeds 266*F. Check for shorts in the circuit, rubbed through insulation, a pinched wire, etc. It can also be caused by a poor connection, or a broken wire inside the insulation. To troubleshoot it beyond a physical inspection will require diagnostic tools you will not likely have access to... In short, if the wires look ok, replace the sensor.

Code 43 is a knock sensor code. Basically the voltage on the knock sensor circuit was high or low for 1/2 second or longer. Check the obvious first... is the knock sensor plugged in? It's the can with a single wire, located on the passengers side of the block just above the oil pan rail, forward of the starter. If it's plugged in, check the wire. They tend to take the brunt of the elements and can rot away, also it could be burned if it came into contact with exhaust. After that, you can either follow the diagnostic chart in the manual, or just throw a new sensor in. It's about $40 at the dealership and I'd consider it good maintenence since they like to go bad with age anyway. For any sensor replacement, it's a good idea to go with GM parts. You'll spend a bit more, and you might have to wait a few days for the parts to come in, but you'll get the part that the car is supposed to have. While you're there, order a fuel filter, and a PCV valve. Both will function better then aftermarket parts, it's cheap preventive maintenance.

The fans won't function normally without the CTS functioning properly, however, you can isolate the problem substantially by bypassing the ECM altogether simply by grounding the F terminal on the fan relay.

That's a whole new group of problems. In general the SLP headers are the only ones available that supposedly clear everything and have a decent design. Having owned a set, I can honestly say they didn't impress me. The low grade stainless doesn't rust, but it doesn't stay very nice either. It tends to get spots of discoloration, etc. The 1 5/8" tubes came alarmingly close to the brake lines and the fuel tank vent line. I had to modify a spark plug socket, or purchase a modified socket from SLP for $20, simply to install the spark plugs. Also, the AIR tubes get in the way, I eventually had mine cut off and welded closed. Finally the cost is rediculous, by the time it's all said and done it's a $500+ modification for a minimal improvement. I won't even get into how SLP has discontinued nearly every part they offered for the thirdgen platform while they continue to come out with new parts for Mustangs, GTP's, GTO's, etc. Check your manifolds for casting numbers and post them here and I can tell you if they're correct or not. The pros of headers over the stock high output manifolds don't outweigh the cons.

edit: I almost forgot, the headers required plug wires with 90* boots, as where the factory wires have one or two straight boots to clear the factory manifolds.

 

Thanks again, I should know more later today

 

You probably won't find most people on here saying anything bad about a product they've bought, unless it is completely not as advertised. Most people aren't going to come on here and complain about a part they spent hard earned money on... In fact, most will do something totally insignificant and come on here to talk about how great it was and pat themselves on the back. The idea of how much a part is going to improve performance is drilled into their minds till they want to believe it was worth the trouble so bad that they don't even notice or don't want to admit that it did virtually nothing. It's the placebo effect, HUGE in the bench racing world of the internet.

My friend who I had install the headers the first time around (I didn't have time to do it myself) was so concerned about the headers heating the gas vapors or the brake fluid, or causing a fire, that he didn't want to install them. They were so close to the frame, it's surprising they didn't rub or rattle, however I did install polyurethane motor mounts at the same time.

Go with whatever you like and trust, but honestly until the car is making some real horsepower the manifolds aren't going to be a huge restriction as long as they're the correct HO manifolds.

 

OK, here's what we've found thus far:

• There is no place in the block for a knock sensor. We will be verifying this for sure when we're under the car replacing the steering gear box, but it definitely isn't anywhere near the proper location. Thus it looks like the people who rebuilt the engine used a different block; what blocks didn't come with knock sensors? The ones that came in trucks maybe?
• The black wire was definitely tricking the computer into thinking the knock sensor was there. We've put it back for now, did a better wiring job of it.
• Temp gauge is working properly now, thanks to new temp sending unit.
• Replaced fan switch, didn't fix the fans. Relays are fine. Isolated problem to some burned out wiring at a harness which I believe runs power from the battery to the fan relay. The wires are really burned up and falling apart, so we're just going to pull that harness and re-wire it manually. Not sure if it is a fusible link or what, but my guy will be able to figure it out once we tear the thing apart. Any easy way to just get a new harness? Once we repair this wiring, fans should work.
• The sensor hanging free at the back of the engine compartment was the IAT sensor. Pulled the top of the intake off, screwed it in, so that should be good to go (sensor appeared to be new, threads were still coated).
• No other clues to what engine is in there yet. We'll be getting any casting numbers possible. Where on the manifolds should I look for those numbers? We're assuming it is a 350, just based on the power behind it, but is there a more concrete way to verify that? We'll see what numbers we can find I suppose...

Since there's no knock sensor on the block, any reason to worry? Obviously I'm going to use 93 Octane only, and it isn't going to be raced or anything; just a weekend cruiser.

Other than that, the engine is in good shape.

 

1) The KNock sensor is usually located on the RH (PASSENGER) side and its stuffed into the block where the Block drain plug used to be. At least thats where I have found a few.

2) Exhaust manifolds are easibly swapped and if the engine is not original then chances are they re-used the Manifolds.

3) Do as Drew stated, look behind the AC compressor on the engine and there is a Hog with numbers stamped into it.

Good luck

John

 

Thanks for the tips, I'll be working on it again in a little while.

Are there any 350 blocks they could've used to rebuild this that didn't have a knock sensor?

 

All blocks have holes for the knock sensor.

 

Every single 350 small block did? Even if it wasn't designed for a 3rd gen? I heard some of the 350 truck motors at the time didn't...

EDIT Assuming this block is a 350, which I can only assume at this point...

 

Like stated before, you can use the Coolant drain plug in the bottom/side of the block...

My 1967 Buick Riviera has a place to put a knock sensor. IF by some off chance the drain plug is a different size than a knock sensor you can go to Home Depot and get a BRASS fitting to screw it into. They use a standard US pipe thread...

JOhn

 

Every small block ever did. Those were coolant drain holes for decades before someone though to stick a knock sensor in one.

 

OK guys, here's an update:

• Got the steering box in, much easier than figured.
• Still didn't re-wire the radiator fan harness, that's first thing in the morning.
• Same for the oil sending unit, first thing in the morning.
• Found some numbers on the block:
  • On the block: 638
  • Aluminum plate on block: 1101962A (probly put there by the person who rebuilt it)
  • Motor mount: 14039436; From what I'm reading, this is the mount needed to put a big block in a 3rd gen?
  • Exhaust manifold number might be 14094068, hard to make out

Also of note is that I finally noticed the stock exhaust manifolds do have AIR fittings, but they're sticking straight out perpendicular from the manifold instead of more angled upwards like I've seen on the stock f-body manifolds.

I just saw where to look for the engine displacement and casting numbers. Whenever I get the car home from my mechanic's, I'll get some degreaser, a tooth brush, and a mirror & start hunting for that casting number.

She's almost running right...

EDIT My buddy also mentioned he saw that the fuel pump "boss" (Not sure what he meant by that...) is running off the camshaft and there is a "5" beside the mechanical fuel pump housing. If that helps any...

 

The 638 is the L98 block.The 1101962A is the date and rebuilders code IE. November 1st 1996 the 2a is the code that identifies the rebuilder for GM.

 

I've read that 638 can still refer to a 305. I'm not expecting it to be (Who would rebuild a 350 and put a 305 in?), but I'll be looking for further confirmation on that today/tomorrow.

Thanks for the explanation. Any way to look up who rebuilder 2a is?

 

Chances are its a 350, IF you take an SD car and remove the block only to replace it with a smaller engine you will need to change the EPROM, and the fuel injectors... Much more money and work than putting in another 350.

John

 

Here's a link to the casting numbers. The 638 block is 350 only.

MorTec, Inc. Chevy Smallblock V-8 Casting Numbers List

 

OK guys, big update here:

• Fixed the wiring harness to the fan and the fans now turn on when you put the engine into diagnostic mode. However, the fans do not turn on under normal operation. The secondary fan will turn on with the AC, but the primary fan does not turn on under any circumstances.
• We pulled the fan switch and grounded the wire, the fan still did not come on. As a recap, we replaced the fan switch, the coolant temp sensor, and the temp sending unit.
• Looking at the wiring diagram in my Haynes, it looked like the only possible other problem is the ECM itself. Went to Adv Auto, picked up a reman ECM, and I just swapped it out. Engine got almost into the red zone, fans did not turn on. Put engine into diagnostic mode again just for kicks, fans turned on.

PLEASE HELP!! So dang frustrating I'm out of ideas here....

 

WHat we know:
1) the fan works through the ECM when in diagnostic mode.
2) The fan does not come on under Hot conditions.
3) The fan apparently operates and therefore there should not be a problem with the relay or the fan, or the ECM as it does send a signal and the wire is connected...

that leaves us with... the temp sensor, I remember you saying you had a problem earlier with that.

WHAT is the reported temp from the ECM? If it is not accurate then its the sensor or the wire going to the ecm from the sensor. or the power to the sensor.

I suspect a faulty sensor, I had one go bad and it was basically stuck at 200° the car would not idle when cold, as it warmed up the idle would bounce up and down irratically and then level off as it got up to normal running temp.

Do you know the reported H2O temp at the ECM?

You may also conisder that the Cal-Pack is damaged or the program is gorked up. IF by some off chance the Fan-On condition within the BIN is screwy then it will make your fans turn on at the wrong temp. I have mine set at 205°F but stock was 220°F...

Is the gauge on the IP correctly reading, or is the sensor for the gauge sending faulty information or is it the wrong sending unit.

IIRC -
The Left head has the gage sensor
the Right head has a switch for the secondary fan to kick on (Right
the ECM controlls the Primary Fan (Left)
The ECM's temp sensor is below the Throttle body
the ECM's Manifold temperature sensor is located under the Plenum
The AC circuit can control the Secondary fan via direct wire OR through the ECM, TPI cars were generally through the ECM... kind of.

There are several stock possiblities with the AC Fan,
1) it can be controlled directly by the heater control in the dash,
2) it can be turned on VIA the ECM when AC is reporting a pressure above a set number determined by a sensor on the back of the compressor
3) It can be turned on diectly by a pressure switch on the back of the AC.

The 87 LG4 cars were controlled through the switch in the Dash.
The TPI cars I am not positive how they are controlled I suspect via pressure switch that woud report when the AC was on...


Good luck

John

 

Do not know any reported temperatures. My guy's scan tool doesn't have a card for the 92's.

We replaced the coolant temperature sensor with a new one, but bad ones are a possibility.

Is that the only sensor that could cause this in this case?

 

90 & 91 LB9 or L98s ECMs are the same as 92, If he has another year try one of those...

John

 

His last card is for '90 GM cars, but last time we tried it it did not work. He said he'll try it again since we replaced the computer. Also picked up another coolant temp sensor to swap out. Gonna do all this tomorrow along with the tie rods & wheel bearings, which I found out were bad when I went to get it aligned

Any other ideas please keep them coming...

 

Well we didn't really get anywhere on the fan issue today, just ran out of time. Got the tie rods changed pretty easily though, so got her aligned. The car is off to my body guy about 2 hours away tomorrow, gone for 3 weeks, and when it comes back will be black instead of white and have a fiberglass ram air hood

One question I did have is this: when you short the diagnostic connector to put the engine into diagnostic mode & the fans turn on, does the diagnostic port turn the fans on directly, or does it go through the computer? Basically we're trying to isolate if the computer isn't getting a signal out to the fan. The way I see it, if the diagnostic connector signals the computer to turn the fans on, we know the computer and all of the connections to/from the fans work. But then WTF doesn't it work?

 

The diagnostic port A-B is basically your grounding out the port either A or B is a ground IIRC.

Since the Diagnostic port does several things:
1) it runs the fan(s)
2) it reports to the SES light DTC's (Detected Trouble codes)
3) I believe it it also runs the Fuel pump...

I would think that since it does all of that it should be going thru the ECM

JOhn