Hey all, thanks for stopping by again. I'm in the process of trying to get my '92 RS with a 305 TBI running again. It sat for about a year before I started working on it again.

Initial problem (last year) was that the car overheated so much that it blew the lower radiator hose off while at idle. Decided to replace the thermostat, bolt broke off in the intake manifold. Drilled the bolt out, put a tap in, started to back it out and it broke off in the intake manifold. Intake manifold was then replaced. Along with a new thermostat, new plugs, wires, distributor cap & rotor.

Had some timing issues afterwards. Finally got everything cranked up and running, but had some cracked vacuum lines that hadn't been replaced yet resulting in the car having hard times initially cranking up and idling. It wouldn't idle unless I kept giving it gas. After about 2 minutes of keeping the motor revved around 1500-2000 RPM's, it would eventually idle and run fine. Service Engine Soon light came on after about car would idle, checked codes and got code 15, Coolant Sensor Circuit Low or Open. Started driving it short distances, everything seemed fine but it my temperature kept getting hotter than it should. At one point going down the interstate it actually maxed out on the temperature. Pulled over for 10 minutes with the fan on, waited on the temperature to come down to 220 again, cranked it up and the temperature almost instantly dropped below the first hash mark on the gauge. After it cooled, I drove it home and the car never got above 220 again. Let it sit and idle while it cycled the radiator fan on/off 4 times, working as it should.

Replaced all vacuum lines, the coolant temperature switch, radiator cap, and the coolant temperature sensor. Car would now crank up and idle fine. It would speed up the idle when cold, and slowly lower it until the car warmed up, as it should and as it did before any work was done. Let the car get up to operating temperature, then shut it off for 2 hours before driving it to work. After 1.5 miles of driving the temperature read high again, first hash mark above 220. Still getting too hot. But this time I noticed steam coming out of the defrost vent, telling me the heater core had gone bad. Never leaked into the floorboard though, it was actually dripping behind the center console.

Started to replace the heater core. I did pull the ECM down from under the dash, but did not disconnect it. Also pulled the VATS control box down from under the dash, to gain access to the heater core box. Heater core went in, and before putting the box back together and putting the dash back together, I cranked it up to check for leaks. When I turned the ignition switch on, the Service Engine Soon light began flashing rapidly. Car started up and went to fast idle, SES light still flashing rapidly. Turned it off, disconnected battery for 5 minutes thinking it may clear the codes. Hooked the battery back up and turned the car on, still have a rapidly flashing SES light. Engine seemed like it was running fine, so I let it warm up to check for leaks. It stayed at about a 1700 RPM idle the whole time, with the SES light flashing. Temp still got up above 220 before I shut it off, but this could be because of an air pocket in the coolant system since it was just drained. I pulled codes again and now I'm getting a code 51, which is Calibration Error, Mem-Cal, ECM or EEPROM Failure.

I'm not sure where I need to go from here. I still flash code 12 on the SES light when checking codes, so the ECM does seem good still. Any ideas about this latest code? Any other ideas about the overheating issue? I'm baffled at this point. Sorry for the long post (wanted to be thorough) but thank you for reading and for any input you may have!

 

1) Make sure your ECM has all connections in tight and good.
2) Is the fan running at all?
3) Not sure I understand the coolant temp circuit code, TBI cars don't send coolant information to the ECM, so I'm baffled on that one - there must be another option for that code.
4) Is the air dam in place? Directly under the radiator should be an air dam that always scrapes on speed bumps and driveways - if not get one, car HAS to have one.

You car should start and run at about 1200rpms MAX until it warms, then idle at about 750 rpms, or 5-600 in gear. Of course, these gauges are far from accurate.

Have you checked oil for water in it? Might have blown a head gasket if it got that high. Oil will look like chocolate milk if it has water in it - if so then you'll need to tackle that first.

What is base timing set at? Stock should be zero, some bump it up to maybe 4*, but no more on a stock car.

You mentioned changing wires, sure you got the firing order right?

Car have A/C? If so, you can test to see if fan motor runs by turning on car and turning on A/C switch - that makes the fan run automatically, then you know if the fan or the fan relay is bad. Otherwise, would be fan switch in pass side head between #6 & #8 spark plug - single wire connector. If fan doesn't come on when temps get up to about 220 or so, then remove connector for the fan switch and ground it with key on - if fan runs then you know you have a bad fan switch.

Air "trapped" in the cooling system really doesn't happen that often - not as often as most people post about on here. I've had my cooling system apart well over a dozen times with parts swaps and such, and never once have I ever seen air get 'trapped' in any respect that would keep the cooling system from circulating. It's thje "catch all" answer that everyone uses but seldom is the real issue.

First thing is that ECM - something's come apart with respect to it when you had the dash apart - get that issue resolved first. I'm not sure why you even had the ECM and the VATS module out to change a heater core - it's a simple matter of going under passenger side dash at the floorboard to swap it. The ECM is not anywhere close, and neither is the VATS module. But it's done now - next time heater core goes out leave dash, VATS module, and ECM untouched, just go through pass side underdash panel.

 

Hey thanks for the reply. Here are some answers to narrow some things down:

I pushed the plugs into the ECM to make sure it was connected well before starting the car up the 2nd time after the SES light was rapidly flashing.
The fan comes on when the gauge reads 220, and will come on when turning the a/c on, like it should.
OBD1 codes aren't vague one bit
The air dam between the core support and front bumper is there. Is there another that goes behind it? I know it has had the front bumper off before.

Before any work was done the car idled as it should, right around 1200-1300 and slowin down after it warmed up. It also did this right before the heater core was replaced after all the vacuum lines had been replaced.

Oil still looks good, changed it right after I finished the intake manifold. Never has been milky and motor doesnt burn any oil or coolant. Timing is at 0 and the firing order is correct. It runs very well other than the overheating & recent SES light. The car does have a/c but there isn't any refridgerant in it, has a slow leak. Fan will come on when the a/c is turned on, and the temp switch between 6 & 8 has been replaced. Fan also comes on when temp shows 220.

I actually pulled the ECM and VATS system out because I couldn't reach the top bolt on the heater core box with them still installed. The VATS box was just sitting on top of the heater core box and not attached to anything. The wires were in the way of the bolt on top of the box. I had to pull the ECM down to fit my hand up and over the heater core box also, and had the top of the dash detached to have a little more wiggle room. I didn't unplug anything or tug on anything. I'll try pushing the plugs into the ECM a little more tomorrow when I have some more time. Thanks for the input, any other ideas?

 

the air dam hangs below the vehicle. There is a diffusor in between the front clip and radiator but you need the dam too.

 

The one sticking down vertically from the core support? Yes it's still there if that's the one we're talking about.

 

Update:
I went home on my lunch break, unplugged the ECM and took the 8 screws holding it together out. Looked inside and everything looked good, so I took out what I believe is the PROM chip? (on the raised portion of the circuit board, opposite the side where the ECM plugs into the harness) and reconnected it. Looks like it said Superchip on it, I reckon the previous owner must have put that in.
Anywho, after putting the ECM back together, I plugged it back in and turn the switch on. SES light came on and stayed on, as it should without the engine on. Cranked up the engine, SES light went away, car ran perfectly. Idled up to about 1200 until it warmed up a little then went down to the 700-800 range (manual transmission so it idles a little higher than an automatic).

Before doing all of this I checked the coolant level and added about 1/2 gallon of water, so it still wasn't completely full. Didn't have a chance to let the car get up to operating temperature but after idling for 10 minutes the guage showed on the first hash mark below 220.

Are there any tricks to getting the coolant completely full? I've just been cranking it up, letting it warm up some, then turning it off and letting it cool back down, then checking the coolant level in the radiator. Thanks again.