Right, that's what I'm saying. Borrow or buy a ECM and swap in his PROM. That's what I did to solve the problem on my 86 some years back.

I first borrowed the ECM from a friend's 86 and swapped in my PROM. Engine instantly ran normally, so I then knew it was the ECM. So I bought one from O'Reilly's Auto Parts. BINGO!

Jake

West Point ROCKS!

 

Ok it runs better now. Still have a Lo coolant temp all the time. CTS is new as well as sender. Throwing code 15 for Lo coolant temp. Not sure what it is. Any ideas? Why is it always reading low temp

 

The 86 FSM says to clear the existing code (disconnect battery), wait 30 seconds or so and reconnect.

"If the code repeats, the problem is an open circuit 410 (yellow wire), circuit 452 (black wire), a poor connection at the ECM or a faulty ECM."

Since you just replaced the ECM, I'd first suspect a wire connection.

There's a step by step trouble shooting procedure in the FSM that I can post later (got a dinner date) if you need me to. Has to do with grounding wires.

Jake

West Point ROCKS!

 

If u could post it I'd appreciate it. No loose wires at ECM

 

I'll summarize the parts you already know.

Clear Codes, start engine and let run for minute or until SES comes on.

Engine off, ground ALDL and check what code was stored. If it's Code 15:

Engine OFF, Clear code again, disconnect sensor connector and jumper harness terminals together; start engine and run for 1 minute or until SES comes on.

Ignition on, engine STOPPED, ground diagnostic terminal and note code

Ignition ON Engine STOPPED, PROBE COOLANT SENSOR HARNESS CKT 410 (YELLOW WIRE) WITH A VOLT METER TO GROUND SHOULD BE 4-6 VOLTS

If volts are 4-6, Ing OFF, disconnect ECM C-D connector, Check CKT 452 for OPEN ckt. If ckt is NOT open, it is a faulty ECM connection or ECM

IF volts are BELOW 4 VOLTS, with Ignition OFF, Disconnect ECM C-D Connector, Check CKT 410 for OPEN ckt If ckt 410 is NOT open, it is a faulty ECM CONNECTOR OR ECM

The coolant temp sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage on CKT 410 to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore the ECM will see high signal voltage.

"As the engine warms, the sensor resistance becomes less, and the voltage drops. At normal engine operating temp the voltage will measure about 1.5 to 2.0 volts at the ECM terminal C10."

"Code 15 will set if:"

"A signal voltage indicates a coolant termperature less than -44C (-47F) for 3 seconds."

"This tests simulates a code 14. If the ECM recognizes the low signal voltage and sets a CODE 14 (fourteen), the ECM and wiring are OK."

"If code 15 repeats, the problem is an open CKT 410, 452, a poor connection at the ECM or sensor or a faulty ECM."

Also, make sure you didn't plug in the sensor backwards. I don't know if doing that will cause your problem, but it's worth checking.

Also, make sure you bought the correct sensor for your engine. A different year sensor may cause your problem.

Jake

West Point ROCKS!

 

Ok the circuit is good. No more code 15. Now it idles rough and surges. It will run fine for about a half hour when i put new plugs in. It runs rich and then fouls out the plugs (makes them black) then doesn't want to idle or run correctly.

I also do not get a coolant temperature reading on the gauge inside. It just says Lo coolant temp and never changes. I do not know what to do now. ECM is new and plugs and connections are good. Injectors are good. O2 sensor is new. Timing is set properly.

Still running rich and do not know what is going on. Please help.

 

Any help would be appreciated. I'm again stumpted and do not know where to start.

 

Anybody?

 

Have you checked the fuel reg vacuum line for gas ??

 

Also, check to see if the 15 is back, that will make it run pig rich.

 

No gas in line and no codes

 

The dash temp gauge gets its signal from the sender screwed into the passenger side cylinder head. Should be between about cylinders 4 and 6, or 6 and 8, I forgot which.

Running rich and surging makes me first suspect a vacuum leak. I'd check to be absolutely sure that all the vacuum ports are either plugged or have a vacuum hose connected to it.

Check all the vacuum hose for leaks. Sometimes the hose(s) will dry-rot and look okay but will be brittle and will leak vacuum. These engines are very sensitive to vacuum leaks, especially downstream of the MAF.

You may have to resort to the garden hose trick to find the leak, if there is one. I tried carb sprays, unlit propane torch and spraying water in my attempt to find a pesky vacuum leak. It was not until I resorted to using the garden hose (on slow flow) directed at various areas that I found one of the injector "O" rings was leaking.

Running rich and surging tells me, too, that the engine isn't going into Closed Loop operation. Even without a scanner, there's a way to tell if it is or isn't. I have to look up the exact procedure for you, but it involves installing a paper clip or wire into the ALDL and with the engine idling watch to see how quickly the SES light is flashing.

I'll post the procedure in a few, as soon as I track it down in my 86 FSM.

It could be a bad MAF or possibly a bad TPS. I'll see what I can find that fits your symptoms.

Jake

West Point ROCKS!

 

Manual says:

Loose or leaking air duct between MAF and throttle body
Alternator output low
EGR; there should be NO EGR at idle
Inspect Vacuum lines for kinks or leaks
Ignition timing
In-line fuel filter dirty or plugged
Incorrect fuel pressure
Bad 02 sensor; contaminated

From personal experience, a failed 02 will sometimes NOT set a code. It can set a Lean Condtion code if there's a vacuum or exhaust leak. The ECM monitors the 02 voltage and from that info knows what fuel mixture to give the injectors.

The MAT, (Manifold Air Temperature) sensor is important for proper EGR operation.

"Coolant Sensor: NOTICE: Care must be taken when handling the coolant sensor. Damage to coolant sensor will affect proper operation of the fuel injection system"; that's from the FSM.

A bad TPS should set either code 21 or 22. You can check it if there is no code. You'll need to connect a digital volt meter to the center and top wires and with the engine off/igntion ON, reach over and slowly open the throttle body butterflies which watching the voltage. Voltage should smoothly increase as you open the butterflies with no sudden jumps or stall in the voltage readings.

I believe at this point, you'd be better off using a scanner since it will show which sensor is operating out of range.

Hope some of this helps,

Jake

West Point ROCKS!

 

Your fuel pressure regulator could be leaking fuel, internally. You can remove the vacuum hose and see if any gas runs out.

Jake

West Point ROCKS!

 

I suspect the engine isn't going into Closed Loop and is running on a pre-programmed map. In order for the system to go Closed Loop the following must occur:

The 02 sensor voltage must cycle above and below .450 v several times which indicates to the ECM that it is ready to give reliable feed-back. It must drop below . 350 and above .550 v repeatedly.

The Coolant temperature sensor has to be above about 104F

There's a timer built in to the system that has to run down; the time varies but if I remember correctly it's like 2 minutes or so.

Once those conditions are met, the system switches to Closed Loop and the ECM then begins accept the voltage readings from the 02.

The 02 has to be at about 600F before its voltage readings will be accepted by the ECM. That's why some guys have to go to a heated 02 after installing headers. Headers keep the 02 too cool at idle.

I'm still looking for the Closed Loop test procedure.

Jake

West Point ROCKS!

 

"Grounding the diagnostic terminal with the engine running enables the "Field Service Mode", which allows the ECM to confirm either open or closed loop operation using the 'SERVICE ENGINE SOON" light."

So it's how fast the SES light blinks. Haven't found the specific time intervals yet, but I believe when the system is in Open Loop, the light will flash FASTER than when it's in Closed Loop.

You should be able to see the difference when (and if) the system switches from Open to Closed loop.

Jake

West Point ROCKS!

 

FOUND IT. "In Open Loop the SERVICE ENGINE SOON light flashes two and one-half times per second. In "Closed Loop" the light flashes once per second. Also, in Closed Loop the light will stay OUT most of the time if the system is too lean. It will stay ON most of the time if the system is too rich."

I had it backwards, so I'll correct my post on that.

Jake

West Point ROCKS!

 

So what will this tell me?

 

It'll tell you if the system is going into Closed Loop or not. Closed Loop operation is extremely important for a properly operating engine.

Jake

West Point ROCKS!

 

Any luck yet?